Sed15 -

Engineering History and Heritage Structures – Viewpoints and Approaches Structural Engineering Documents

The present Structural Engineering Document (SED) is a compilation of contributions devoted to the vast topic of history of structural engineering as well as interventions on heritage structures and structures of high cultural values. Various, sometimes opposed, viewpoints and approaches are expressed and presented. The rather heterogeneous and controversial nature of the content of this SED shall stimulate lively discussions within the structural engineering community who needs to increase the awareness of historical and cultural aspects of structures and structural engineering. Current structural engineering methods and practice are only at the very beginning of effective engineering, really integrating historical and cultural aspects in the assessment of existing structures and in intervention projects to adapt or modify structures of cultural values for future demands. Knowing the past is indispensable for modern structural engineering !

15

Engineering History and Heritage Structures – Viewpoints and Approaches

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Structural Engineering Documents

15 Engineering History and Heritage Structures – Viewpoints and Approaches Eberhard Pelke Eugen Brühwiler

International Association for Bridge and Structural Engineering (IABSE)

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About the Authors

Structural Engineering Documents Objective:

Eberhard Pelke earned his civil engineer diploma from Darmstadt University. He is Head of the Department of Bridge Engineering at Hessen Mobil Road and Traffic Management in Wiesbaden, Germany. He is a Fellow of IABSE and was from 2013-17 Chair of IABSE WG9 Construction History.

To provide in-depth information to practicing stuctural engineers in reports of high scientific and technical standards on a wide range of structural engineering topics.

IABSE Bulletin Board: H.Subbarao, (Chair), D. Laefer, (Vice Chair), M. Bakhoum, C. Bob, M.W. Braestrup, N.P. Hoej, H.H. Snijder, R.von Wölfel, R. Mor, M.G. Bruschi, I. Payá-Zaforteza, S. Kite, M. Garlock.

Topics:

Eugen Brühwiler is professor of structural engineering at the EPFL—Swiss Federal Institute of Technology in Lausanne, Switzerland. His activities include modern methods to examine and enhance structures of high cultural value. He is a Fellow of IABSE and was from 2013-17 Vice-Chair of IABSE WG9 Construction History.

The International Association for Bridge and Structural Engineering (IABSE) operates on a worldwide basis, with interests of all type of structures, in all materials. Its members represent structural engineers, employed in design, academe, construction, regulation and renewal. IABSE organises conferences and publishes the quarterly journal Structural Engineering International (SEI), as well as reports and monographs, including the SED series, and presents annual awards for achievements in structural engineering. With a membership of some 4,000 individuals in more than 100 countries, IABSE is the international organisation for structural engineering.

Publisher:

With Contributions From: E. Pelke, T.F. Peters, M. Traykova, R. Vergoossen. A. Bögle, W. Lorenz, E. Brühwiler, N. Janberg, J. Romo, B. Addis, M.J. Beiersdorf, J. Steiner, E. Vianen, R. Spaan, J.F. Duntemann, B.R. Greve, A. Traykov, D. Partov, N. Winterbottom, B. Heres, T. Chardakova, D. Wendland, P. van Bogaert, R. Barthel, J. Tutsch, J. Jordan, C. Weber, A. Kostka, M. Fischer, G. Eisele, J. Seiler, V. Wetzk, Y. Rammer, B. Espion, L. Clarke, M. Bartzsch, K. Geißler, D. Gasparini, W. Vermes, J. Voermans, R. May, Y. Yang, B. Chen, S. Nakamura.

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The International Association for Bridge and Structural Engineering (IABSE) was founded as a non-profit scientific association in 1929. Today it has more than 300 members iQ over 0 countries.IABSE’s mission is to promote the exchange of knowledge and to advance the practice of structural engineering worldwide. IABSE organizes conferences and publishes the quarterly journal Structural Engineering International, as well as conference reports and other monographs, including the SED series. IABSE also presents annual awards for achievements in structural engineering.

For further Information: IABSE c/o ETH Zürich CH-8049 Zürich, Switzerland Phone: Int. + 41-44-633 2647 Fax: Int. + 41-44-633 1241 E-mail: [email protected] Web: www.iabse.org

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Copyright © 2017 by International Association for Bridge and Structural Engineering All rights reserved. No part of this book may be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the publisher. ISBN 978-3-85748-154-3 Publisher: IABSE c/o ETH Zürich CH-8049 Zürich, Switzerland Phone: Fax: E-mail: Web:

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Int. + 41-44-633 2647 Int. + 41-44-633 1241 [email protected] www.iabse.org

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Preface

Foreword The roots of modern construction historiography reach back to the 19th century when for example in France the engineer Auguste Choisy (1841–1909) began to explicitly analyze the construction of historic buildings and to place them in the center of construction history.1 In the last third of the 20th century, such approaches followed systematically and in an increasingly professional way. A long arch spans from the works like those by Jacques Heyman (1925) who interpreted ancient techniques and theories related to vaults by means of modern structural engineering approaches,2 to the historic–theoretical research and publications like those by KarlEugen Kurrer (1952).3 In the meantime, several chairs and professorships in construction history were created and there is an impressive variety of conferences and publications. Every three years since 2003, the scientific community gathers at the International Congress on Construction History (ICCH). There is no doubt that construction history has established and consolidated internationally as an independent discipline. Actually, what is construction history? Professor Werner Lorenz, member of the IABSE WG9 Construction History, defines construction history as follows: Structural engineering is the entity of the practices and products of conceptual design, dimensioning and construction of technical structures and components in the process of the constructional designing of the environment. Construction history describes and interprets these practices and products in their historic sequence. For that purpose, construction history interrogates the products of construction and all associated written and pictorial sources. Both the historic construction research and the methods of static-constructive and scientific engineering analyses belong to the methodical cornerstones. Construction history involves architects, monument conservators, historians and engineers in a transdisciplinary approach to fulfill scientific, cultural, didactic and also structural engineering tasks and requirements.4

PREFACE

IABSE WG9 Construction History has the general objective to promote this new science and to demonstrate its importance for structural engineers. The three main objectives of the WG on construction history are to: • • •

increase awareness among structural engineers of historical and cultural aspects of structures and structural engineering; illustrate and propagate the social and technical achievements of civil engineering; improve methods and practice in structural engineering by showing ways for systematic and targeted integration of historical and cultural aspects in intervention projects to adapt or modify structures of cultural value for future demands.

IABSE WG9 focuses on the role of construction history in the structural engineering practice and is thus intentionally complementary to the classical construction history as understood by the ICCH Community. The main concern of WG9 is thus to implement construction history in the daily work of structural engineers and to demonstrate the importance of cultural values as a basic design parameter when interventions on existing structures are required. The present Structural Engineering Document (SED) is structured accordingly. It shall be understood as an introduction into construction history and how to consider the cultural values of structures in intervention projects. Although this SED is addressed primarily to IABSE structural engineers, it may also be useful for nonengineers. This SED begins with the Editorial written by one of the “deans” of construction history: Tom F. Peters. Personal statements by several WG9 members testify a surprising variety of ways how the access to construction history was found and how it influenced professional activities. In the next chapter, Nicolas Janberg provides a worldwide survey on the activities and contacts in the domain of construction history. In the following, the papers by Max Johann Beiersdorf and Josef Steiner are contributions similar to essays on the aspects of construction history. Twenty-five case studies on rehabilitation and modification of structures form the core material of this SED. Every case study outlines on a maximum of four pages the cultural values of the structure and highlights the appropriate measures for its respectful preservation. References and contact data of the author serve the reader to obtain detailed information. The case studies obviously range from ancient to modern structures and from medium to high cultural values, comprising various types of structures. Requirements of cultural heritage shall be taken as inspiration (and no longer as “hindering constraint”) for better intervention projects on existing structures. Construction history and cultural values of structures have yet to be understood as basic structural engineering disciplines. With the present SED, the IABSE WG Construction History intends to make a significant contribution to modern structural engineering and to provide access to construction history for practicing structural engineers.

References [1] Choisy A. L’art de bâtir chez les Romains Ducher: Paris, 1873. [2] Heyman J. Coulomb’s Memoir on Statics: An Essay in the History of Civil Engineering Cambridge University Press: Cambridge, 1972.

REFERENCES

[3] Kurrer K-E. The History of the Theory of Structures Ernst & Sohn: Berlin, 2008. [4] Kurrer K-E. Aufgaben der Bautechnikgeschichte. https://gesellschaft.bautechnikgeschichte. org/was-ist-bautechnikgeschichte/ Download 01.01.2017. Eberhard Pelke, Chairman of IABSE Working Group 9 Construction History August, 2017

Table of Contents

1

2

3

4

History as Educator and as an Aid to Understanding Structural Engineering; T.F. Peters

1

Personal Statements by Members of IABSE WG9 Construction History: What is Construction History and Why is It Significant for Structural Engineers?

7

Eberhard Pelke Marina Traykova Rob Vergoossen Annette Bögle Werner Lorenz Eugen Brühwiler Nicolas Janberg Jose Romo Ignacio Paya-Zaforteza Bill Addis References

7 8 9 10 11 12 13 15 15 16 19

Engineering History and Heritage Structures around the World—A Survey; N. Janberg

21

Introduction Survey Current Situation of Construction History around the World Overall Evaluation and Summary References

21 21 22 38 39

(Re)constructing History—How Building Archaeology Can Profit from the Knowledge of Engineering; M.J. Beiersdorf

41

Introduction Undulating Mud Brick Walls in Pharaonic Egypt Engineering Science Studies Building Archaeology and Construction History—A Fruitful Cooperation References

41 42 44 44 45

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The Many Footprints Left by Martin Bachmann in Pergamon; J. Steiner

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Dedication Building Z on Pergamon’s Acropolis Hill Repair and Conversion of the Southern Rotunda Next to the Red Hall Assembly of a Monumental Supporting Figure Next to the Red Hall Maintenance of Retaining Walls on the Acropolis Hill Anastylosis of a Palaestra Corner in the Gymnasium Final Remarks References

47 47 49 51 51 52 53 53

Buildings

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The Building A of Radio Kootwijk—A Concrete Building from 1920, Ready for the Future; E. Vianen, R. Spaan

55

Marina City—The History and Restoration of an Iconic Facade; J.F. Duntemann, B.R.Greve

61

Rehabilitation of the Complex Reinforced Concrete Shell Roof Structure of an Industrial Building; A. Traykov

67

Maintenance and Strengthening of the Timber Roof Elements in the Church of St. Dimitar; M. Traykova, D. Partov

71

6.5

Brighton Pier, UK—Innovation in Renovation; N. Winterbottom

77

6.6

Early Iron Structures at the Hermitage in St. Petersburg—Unique Testimonies to Construction History and the Associated Preservation Problems; B.Heres

83

Maintenance and Strengthening of the Cross-Shaped Barracks Building; M. Traykova, T. Chardakova

89

Analytical and Experimental Studies on the Technology of Late-Gothic Vault Construction; D. Wendland

95

6 6.1

6.2

6.3

6.4

6.7

6.8

6.9

Frost Damage and Restoration of Limestone Domes and Spheres in a Heritage Building; P.V. Bogaert

101

The Gothic Tower of Freiburg Minster, Germany: Analysis and Repair; R. Barthel, J. Tutsch, J. Jordan

107

The Municipal Public Bath at Strasbourg (1905–1908): A Cultural Heritage in Reinforced Concrete; C. Weber, A. Kostka

113

6.12

History and Rehabilitation of Reinforced Brick Ceiling; M. Fischer

119

6.13

Reconstruction of the Neues Museum in Berlin; G. Eisele, J. Seiler

125

6.10

6.11

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7

Bridges

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The Necessity for Construction History to Assess Historic Bridge Bearings; V. Wetzk

131

7.2

Refurbishing of the Nibelungen Bridge in Worms, Germany; E. Pelke

137

7.3

Early Prestressed Steel–Concrete Composite Continuous Bridges in Belgium; Y. Rammer, B. Espion

143

7.4

Making Rennie’s 1796 Lune Aqueduct Watertight Again; L. Clarke

149

7.5

Restoration of Robert Maillart’s Reinforced Concrete Bridges in Switzerland; E. Brühwiler

155

Examination of Two Riveted Railway Bridges over the River Rhine; E. Brühwiler

161

7.7

The Rendsburg High Bridge across the Kiel Canal; M. Bartzsch, K. Geissler

167

7.8

Steel Viaduct Refurbishment Inspired by the Original Structure and Its History—The Best Solution with Regard to Structural, Economical and Heritage Requirements; W. Lorenz

173

The Main Avenue Bridge, Cleveland, Ohio, USA; D.A. Gasparini, W. Vermes

179

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Renovation of a Historic Railway Lift Bridge; J. Voermans, J. Reusink

185

7.11

An (Almost) Extinct Engineering Heritage Asset—The Case of the Reichsautobahn Bridges; R. May

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Construction Technology of Chinese Woven Timber Arch Bridges; Y. Yang, B. Chen, S.Nakamura

197

7.1

7.6

7.9

7.12

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1 Chapter

1 History as Educator and as an Aid to Understanding Structural Engineering

Tom F. Peters, Professor emeritus, Lehigh University, Bethlehem, Pennsylvania, USA The following position papers present many valid aspects of construction history. Eugen Brühwiler discusses the sheer intellectual fascination of historical material, so different from ours today, and the inspiration that this can generate. Rob Vergoosen sees historical arguments as a way to convince young engineers that computer programs are tools and not engineering design at all. Eberhard Pelke points out that history proves that mathematical methods are also only tools. He also mentions the inspiration that exemplary professional biographies can exert. Marina Traykova discusses the importance of historical structures to the definition of national culture, and Brühwiler ties their importance to professional culture. And the many interesting case studies of built structures that have been presented at IABSE meetings and symposia over the years illustrate these and further aspects and particularly their usefulness for informed structural evaluation as relevant for the purpose of restoration or adaptation. I would like to expand a little on the interest in historical understanding and its impact on engineering thought and especially on education that both Brühwiler and Werner Lorenz raise. Understanding is abstract and at first sight, it seems to have little to do with the daily concerns of practitioners, but understanding has the ability to change and to expand professional culture in very concrete ways. I will try to demonstrate through examples how that which we might tend to dismiss as being mere impractical philosophy is actually quite down-to-earth. Understanding, as opposed to a simple accumulation of facts and methods that usually counts as professional knowledge, is deeper and it directly impacts our thinking and approach to everyday problems. Memory is one of the characteristics that make us human, and history is the concretization of memory. It situates us in our world, also in our professional world of engineering, and as JeanClaude Badoux succinctly wrote and I quoted in the preface to IABSE the first 80 years, “no history, no memory, no future”. Engineers are the professionals who create the future structure of our world, and in order to do that, they not only learn from theory, but also from experience, from mistakes and from successes. That is the value of case studies, which are historical by their very nature because they deal with completed design and building processes and thus with the

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past. However, we need to acknowledge that when we look back, nothing is absolute: we see what I call a relative reality. We see facts and their relationships from a constantly changing standpoint. Werner Lorenz touches on this issue in his contribution. I compare this to a walk along a riverbank. Looking at the opposite shore, we perceive a landscape with trees large in the foreground hiding what appear to be smaller ones farther back. As we continue along the bank and around bends in the river, our standpoint changes and the relationships between the trees change: what appeared to loom large previously, recedes and becomes small, and what was in the background now grows and moves to the fore. The objects are the same we saw before, but they now stand in different relationships to one another and to us. The trees are our facts, and they remain the same, but they can look quite different from another viewpoint. When we hike in the Alps, the mountain we know so well looks unrecognizable from a different standpoint and yet it is a stable, concrete fact—as long as we disregard the time factor. In reality, only change is constant. And so it is with case studies, whether of objects or of personal careers in engineering: our standpoint and our questions change, and with them so do our answers. What was interesting and valuable a few decades ago is now no longer so, and what did not exist before is now important. We must realize this in our daily practice when we evaluate a building for demolition, rehabilitation or restoration. It is a delicate balance we tread when we decide which are important examples of our past. In structural terms, we find ourselves intellectually in unstable equilibrium. There is no absolute “right” and “wrong”, it all depends on our criteria and viewpoint. This destabilizes our understanding. We lose our bearings in the world, and engineers always choose stability over manifestations of instability. We want “real stuff”, concrete and immutable facts to hold on to, something solid—but our world is not like that. Intellectuality, like physical instability, makes us move. The role of historical study in education is to force us to leave our intellectual “comfort zone” and to make our standpoint more flexible. Even the body of knowledge known as statics and strength of materials depends on our viewpoint. The facts are there, but the methods we construct on selected facts depend on the criteria we choose and the relationships we impose upon them. Flexibility is what makes a good theoretician, designer or builder. It gives us the ability to react to changing situations. When presenting the symbolical millionth book to my former university’s library, Galileo’s 1638 Discorsi e Dimostrazioni Matematiche Intorno a Due Nuove Scienze, the then president, a civil engineer, said of Galileo’s depiction of a cantilever, that the author had made a mistake in depicting the stresses AB in the cantilever as being constant throughout the cross- section (Fig. 1). “Even a man as great as Galileo, the founder of modern physics was not immune to mistakes”, he told us. The president had missed the point. In fact, Galileo had made one of the great discoveries of his age: he had realized that the force E is external and visible, while the resultant stress AB is internal and invisible—and he depicted this graphically, showing the two to be causally related. Far from being simple in his assumptions, Galileo was a genius and had moved our understanding of structure forward in that one diagram! The facts of the diagram are incontestable: the distribution of stress is wrong by our modern understandingi, but the impact of

i

This is one interpretation of what Galileo may have meant; other interpretations are also possible.

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Fig. 1: Galileo’s depiction of a cantilever

his realization, the “truth”, is another. So “truth” depends on our viewpoint. Had that president studied the history of his field, he might have realized that this diagram was not a demonstration of fallibility, but a manifestation of the value of structural history to engineering education. So, in my view, the IABSE History WG needs to concern itself not only with intellectual delight or with information that we can use to solve immediate problems, but it should also teach us how to step back, to reconsider, and to formulate our problems, and to ponder not only what, but also how we learn. When talking about this need to engineering educators, the invariable answer is: “Of course this is important, but our time to educate engineers is short and the curriculum is so overloaded that we have no possibility to include it.” Is this really so? Do we need to fill students’ heads with ever more facts and methods that often become obsolete before they enter practice, or should we rather teach them how to think, how to search out the relevant facts for themselves, how to put these facts into context in different ways, how to formulate questions, how to react flexibly to changing situations, how to gain an overview and gain distance to the immediate “correct”, economic, technical solution? All creativity, whether in engineering or in any other field, only occurs when one begins to “think outside the box”. History can help to see over the edge of the “box” that defines and indeed confines our logic. Historical awareness therefore helps us to search for alternatives to unthinkingly accepted solutions. Is that not the way to the future? To illustrate how to step back and question our basic logic, let us compare two bridges from two different epochs: Hans Ulrich Grubenmann’s Rhine Bridge of 1757 in Schaffhausen (Fig. 2) and Julius Natterer’s Neckar Bridge of 1976 in Stuttgart (Fig. 3).

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(a)

(b)

Fig. 2: Hans Ulrich Grubenmann’s Rhine Bridge in Schaffhausen (a) overall view, (b) detailed view Both are trussed wooden structures and have two spans of the same size and the same sharp bend between them. Both were built for virtually the same load: the first for a fully loaded 18th-century wagon and the second for a modern pedestrian load. The results look very different and the first seems structurally redundant and illogical from our standpoint. But despite the differences between modern and ancient material and connection technology, they are similar and both logical. When we understand that in the pre-statics era Grubenmann designed by overlaying one known simple system that worked with another to extend span and increase loadbearing capacity, we can easily read his structure as an overlaid configuration of king posts, queen posts and slanted struts. It now looks less confused, because we understand Grubenmann’s logic. And we can see what a gifted constructor he was when we notice how his overlaid configuration also formed a series of superimposed arches, the longest one carrying through from one abutment to the other over the middle pier. This pier had remained from the washed-away predecessor bridge, and the client insisted that he reuse it. Grubenmann distrusted its stability, and in order to relieve it as much as he could, he incorporated that 110 m long arch into his continuous beam. Of course, looking at it from a classical standpoint, we “know” that the top of a continuous beam works in tension over the intermediate pier and presume, perhaps correctly, that Grubenmann did not know this. But we have forgotten an even more relevant fact that Grubenmann as a gifted practitioner knew very well: in a stick structure, we can guide tension and compression in any way we wish through a structure!

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(a)

(b)

Fig. 3: Julius Natterer’s Neckar Bridge in Stuttgart (a) overall view (b) detailed view Now we see the true value of the historical standpoint: it allows us to shift our logic to understand a different form of equally correct logic that preceded our modern, model-based viewpoint, and we step back from what we unquestioningly call the “truth” and into Grubenmann’s “truth” that bases on entirely different criteria. We can use this insight to question our own logic. It destabilizes our thought processes and makes us realize that our logic does not create an absolute, but a relative reality. This allows us to create new structures. That is what construction history can teach us, and its value to our profession is evident.

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7 Chapter

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Personal Statements by Members of IABSE WG9 Construction History: What is Construction History and Why is It Significant for Structural Engineers?

Eberhard Pelke In 1995, my administration sent me to the “Deutsches Straßenmuseum” (German Road Museum). I was to help as a “bridge builder” in setting up the “Bridge and Structural Engineering” part of the exhibition. There, I met the great engineer Klaus Stiglat. He took my by the hand and taught me, as a practicing engineer, to see not just the here and now of the technical rules and standards but also the past work of the engineers on whose shoulder we rest. Together we developed the “History of Bridges – the Age of the Engineers” section of the exhibition. Sixteen large-sized boards displayed the development of bridge building starting in ancient times using the four basic bridge types—girder, arch, suspension and cable-stayed bridge. The task was to elaborate and personify the milestones of bridge building. What was the critical development step, who was the key engineer in defining the structure—indeed, a question of stance—informing a society critical of technology about the work of construction engineers via their work and personality. That was the beginning, purely practical without scientific superstructure and the call for creating discipline. I am very grateful to Klaus Stiglat, not only for an introduction to construction history but also for the questioning of and applying the same in everyday engineering. Even today, to me construction history is not an academic exercise that documents and archives the past, brought to a scientific community with a presentation at an international congress, but rather a tool for everyday engineering with which to understand structures, to evaluate and protect them, and to improve them in accordance with their load-bearing behavior. Or, to detect defects that may result in demolition. Yes, that is the run of things. A structure and the personality of the engineer are mutually dependent. Engineers do not necessarily arrive at the same optimum. Designing trusses is a process of rational physical criteria and the subjective perception of the engineer. He brought construction critique, a topic in construction history, back into the limelight. He taught me about that too. And above all, it is important to him to retrieve the lifework of great engineers from the anonymity of the information society. His many interviews as Chief Editor of the magazine “Beton- und Stahlbetonbau” (Concrete and Reinforced Concrete Construction) and his book “Bauingenieure und ihr Werk” (Construction Engineers and Their Works) document construction history brought to life as a primary source. Together with Karl-Eugen Kurrer, we recalled the lifework of Helmut Homberg (1909–1990) to the memory of younger construction engineers. Just in time, before

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the last sources of the genial yet uncomfortable engineer are found down the usual track of a throwaway society. And what emerged: a work exhibition of the construction of major bridges, which is perhaps more meaningful than some engineer who published diligently and was sent into retirement with academic honor. Homberg’s last bridge, the cable-stayed QE II Bridge near London, was opened for traffic after his death (1991): “Working with him was hell, but the result was compensation for everything”, said Hugh Knox in an obituary. Construction history brought Karl-Eugen Kurrer who was for long time the link and “Mother of the company” of the handful of German construction historians. After lengthy, German discussions, we now have an organization, the “Gesellschaft für Bautechnikgeschichte” (Society for Construction History) chaired by Werner Lorenz. At last! But what would the history of German construction be without Karl-Eugen? I am his foster child too. He took me to Madrid to the first International Congress on Construction History. He took care of the knowledge regarding the scientific requirements and creation of discipline in construction history. Through him, I was able to build up my international network. I built my five contributions to the International Congress on Construction History on his scientific basis. Karl-Eugen always had an open door for his authors, for his construction historians. He listened, made contributions, argued, agreed or expressed reservations. He was a disciple and true follower of Fritz von Emperger. Hour-long telephone calls drafted new theories and essays for his steel construction. Construction history brought to life! As a practicing engineer, I regret that I have no time for great theories—I would have liked to have had the time to spin a yarn to the end in a structured manner! Klaus Stiglat and Karl-Eugen Kurrer stand for my understanding of a lived and practically orientated construction history.

Short Bio Eberhard Pelke obtained his civil engineering degree from the University of Darmstadt. Since 1990, he is with Hessen Mobil—Road and Traffic Management, and since 2001 Head of the Department of Bridge Engineering, in Wiesbaden, Germany. He is a Fellow of IABSE and Chair of IABSE WG9 Construction History. He is also a member of the German Society of Construction History (Gesellschaft für Bautechnikgeschichte).

Marina Traykova The cultural and historical heritage is the most important of a nation’s wealth and a major factor in the accreditation of national identity. Historical buildings and facilities represent one of the most important parts of historical heritage. Preservation of these buildings and facilities for the future generations is a way of sustainable development and also an act of culture. The historical buildings and facilities can be viewed as a work of art representing its time period. The general concept of construction history relates to the safeguard, recognition and continuation of cultural and historic traditions in national construction practices for the public interest of the society. All these construction practices represent the culture and the techniques of time along with sentiment, intent and conscience of its designer, artist or craftsman. The recognition and the comprehension of construction history influence the selection of the method, policy and degree of intervention, and preservation methodology and techniques.

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9

The most sensitive aspect of construction history is the structural preservation because of the decisive role of the structure in the global behavior of buildings and facilities. Usually the structural preservation is related to the solution of the problem “safety versus authentic structure”. There is no generally applicable answer and the solution should be based on specific conditions. Finally, the most important is to make a decision which will permit to preserve, to rehabilitate or to reconstruct the original structure. This decision will enable prolonging the life of the buildings and facilities and will give the future generation an opportunity to learn the history and should be considered as a continuity of history. Construction history is important for structural engineers and IABSE because of the possibilities to: • increase professional knowledge and experience; • make the connection with history and the national traditions; • learn about the old structures, construction materials and techniques, and their application in actual situations; • inspire new design solutions; • provide continuity of history; • provide sustainable adaptation and reuse of historical buildings and facilities; • revive urban areas; • maintain traditional standards; • exchange good construction practices.

Short Bio Marina Doncheva Traykova, PhD, is a Full Professor at the University of Architecture, Civil Engineering and Geodesy in Sofia, Bulgaria. Her main research activities include rehabilitation and strengthening of existing buildings, construction history, preservation of heritage buildings and sustainable design. She is a member of IABSE (Working Groups Construction History and Earthquake Resistant Buildings), fib and the Chamber of Engineers in Investment Design, Bulgaria.

Rob Vergoossen As a structural bridge engineer with an expertise in existing structures, I am fascinated by the history of construction. Today, we are faced with a large existing bridge stock which is overloaded by the current immense traffic. Fortunately, our bridges are well engineered by our predecessors. With the knowledge, materials and codes of their times, they did a great job. It is our job to preserve these bridges and make the best out of them. Our young(er) structural engineers have to be taught the engineering of these structures without the use of computers. With this way of thinking, residual capacity in a lot of existing structures can be found. Therefore, structures that are functionally sufficient can be conserved and strengthening can be avoided or minimized. Society can then profit the most, as costs and hindrance of traffic are minimal. It is important that we teach our structural engineers the basics of ancient materials, codes and structures. Recent (new) codes are not meant for structural assessments, as they are a result of the materials and

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knowledge of today. Therefore, there is a need for more flexibility and expert opinions in assessing an existing structure.

Short Bio Rob Vergoossen got his master’s in structural engineering at Delft University of Technology in 1999. From the start of his career, Rob has worked on existing structures and has been involved in the drafting of assessment guidelines in the Netherlands for existing structures. Since 2015, he is a part-time PhD student at Delft University of Technology in this field. Since 2010, he is an expert in concrete structures at the engineering company Royal Haskoning DHV. At IABSE, he has contributed as a member of various committees and has authored several papers.

Annette Bögle History of design of structures is in my opinion an essential part of construction history and in my practice as a university professor a basic element for teaching creativity and conceptual design in structural engineering. Regarding today’s built environment and future developments, conceptual design needs to be a core approach in any academic curriculum to guarantee an education in sustainability. In many actual building projects like wide span roofs, high-rise buildings or bridges, an increasing rationalized planning of special engineering structures can be noticed, whereas the distinct boundary conditions are often neglected. The results are seldom satisfying from a technical, aesthetical and social point of view. For this, among other things, the engineers are responsible themselves. This is due to the fact that during the last decades, civil and structural engineers have focused unilaterally on the rational–analytic aspect of their area of responsibility and have therefore lost sight of their real and original area of activity, which arises in a mixture of logical and empirical knowledge. As construction history points out the dependencies of the boundary conditions and the influence of the designer’s personality, it is predestinated to mirror the requirements of a holistic design. Therefore, it is now becoming an essential element in teaching. First, the clear and self-evident advantage of construction history is that in history, the boundary conditions of conceptual design—focusing on the dependencies of form, structure, material and construction—become obvious. Depending on time, knowledge and capabilities of the building society, only specific structural solutions can arise. Vice versa, historic structures become only readable if these boundary conditions can be studied. Therewith, a deep understanding of the different, complex and time-depending boundary conditions arises. It becomes obvious that at a different time, in a different situation and with different people, the resulting structures are different too. This enables one main aim of studying and teaching history of design of structures: the transfer of the knowledge of the uniqueness and time dependency of boundary conditions into the actual discussion of the design of engineering structures. Examples like the Pantheon enable us to realize that not everything was or is buildable: while it was possible to incorporate a whole sphere into this building, this ideal/spiritual perfection is not visible from the outside. In history, the technical boundary conditions of what was possible were often quite limited. Certainly, the advancing socio-political enlightenment and the progress in science and technology allow the preference of certain aspects. However, construction history shows us how compro-

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mises had to be made, and how the knowledge and the values of the building society determine how the interdependency of form and structure is expressed. Second, construction history can even go a step further; it can also show the passion and the intension of the personalities behind the designs. Particularly if a new technology or material arose, the designers and builders explored with courage and creativity the limits of the technically feasible. All major developments in structural engineering can serve as examples for this. If we accept the personal influence of the designer on the development of a structure, it is most logical also to realize the cultural influence. This is also one of the reasons for different design approaches, visible in different structural styles or in different calculation and dimensioning approaches. With the knowledge of the boundary conditions, the dependencies between form and structure and the influence of the designer’s personality, our young engineers are enabled to develop their own holistic approach in their designs. Construction history enfolds engineer’s creativity; this enables new, innovative engineering solutions for actual engineering challenges.

Short Bio Annette Bögle is a professor of structural engineering and Director of the Chair for Design and Analysis of Structures at the HafenCity University in Hamburg, Germany.

Werner Lorenz Construction history is a new scientific discipline just in the process of establishing itself, characterized by transcending traditional academic demarcations: it is history of construction, history of technology, history of science, yet it does not fit either of these categories. “A construction represents and occupies a sort of boundary between the world of nature and the artificial world of culture”.1 If we refer to this elegant definition, the role of construction history is no more or less than to provide an explanation of the action of producing this hinge, in fact construction in all its facets—thinking/planning, designing, abstracting, modeling, calculating and measuring, specifying, financing, manufacturing, building, maintaining, reinforcing, destroying, disposing—in all its cross-linkages, interdependencies, and processes of interchange, right up to the use of practical applications and technology. Constructing is a multi-faceted activity: It is this process of construction in its entirety that constitutes construction history. Construction history tries to understand the way human beings have approached building. There are three main areas of investigation: 1. People: “There is no other history than that of people” (Lucien Febvre): Because any branch of history is an examination, first and foremost, of people, and because the act of constructing is deeply human and subjective, the first area of investigation of construction history is people—master builders, engineers, researchers/academics, entrepreneurs/industrialists, respectable artisans as well as brilliant mavericks, etc. 2. Institutions and networks: A second area of investigation is provided by the networks people form and in which they act, structures in which and between which construction happens, structures which influence civil engineering and which are influenced by civil engineering:

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companies, associations, universities/colleges, national and municipal administrations, last but not least the military sector. 3. Constructions: The third area encapsulates the sum total of the products of construction, be they designs, theories or regulatory systems; and of course, and first and foremost, buildings, the constructions themselves. History is interpretation—or it is not history: Construction history is not an exact science; it is something between engineering sciences and humanities. Thus, construction history is always—and especially in the IABSE context—endangered by the temptation to develop it into the strategic narrative of the mighty stream rushing towards one’s own position. The methodical imperative resulting from that is the obligation to refuse any legitimation, which perceives the present only as the future of history and distorts history to justify what is. The most exclusive commitment of construction history is to thwart this temptation by ignoring the term “progress”, by disguising our common views, by approaching all history with deep humility. History has to be read anew, again and again, as effects of different practices of construction, as side by side, hardly consecutively. It has to be acknowledged first of all as a strange world with enigmatic activities and practices, as the surprising, the unpredictable. What is the significance of construction history for structural engineers and the IABSE? Of course, the solution to the problems of today cannot be found in another epoch. The justification of current practice does not rely on the past—but the past does recover its genealogy. Construction history read as such, is nothing but an analysis and critique of the present: It is an enrichment for today’s construction practice, which welcomes challenges, courageously questions current practices, and which develops optimal ways of managing and using materials. On a more practical level, there is no need to stress that nowadays the field of handling with still existing buildings, the field of reconstruction and rehabilitation, is one of the largest parts of building activities. But an intelligent and appropriate intervention in existing structures is hardly imaginable without knowledge of the history of construction. It is a necessary condition for every present-day builder or designer who is concerned with our built heritage, be it in measuring and monitoring or restoring and reinforcing. Whether one works with the old or new, in both cases one needs history. All of a sudden it appears as a practical discipline—and as one of the basic sciences of civil engineering (for a more detailed investigation see Ref. [2]).

Short Bio Werner Lorenz graduated in 1980 in structural engineering at the TU Berlin. In 1992, he passed his doctorate with a thesis about the early history of building with iron and steel in Berlin and Potsdam. In 1993, he was appointed to the newly created chair of construction history at the BTU Cottbus where he is active until now. In 1996, he founded his own consulting office for structural engineering and assessment, which is specialized in the field of structural rehabilitation of historic buildings and bridges.

Eugen Brühwiler 25 Years ago when examining the fatigue life of riveted steel railway bridges, one evening, I found myself in the archives of the Swiss Federal Railways discovering construction plans,

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notes, photographs and other documents from the 19th century: blue-colored rivet heads on construction plans, black and white photographs from the construction era and treatises on bridge design methods. I started “whispering” with Ritter, Tetmajer, Culmann and Gubser. This adventure triggered my interest and fascination for history of bridge construction and the question: where do structures come from? Although I had no education in history of construction during my engineering studies at ETH Zurich, I quickly realized how indispensable information from the time when structures were designed and built is when dealing with existing structures of any age. Construction history deals with history as a basic scientific discipline to study the past of civil engineering construction and its achievements. Construction history relates to the memory and discovery of engineering methods and technology by collecting, organizing, presenting and interpreting information about structural engineering and construction. Construction history also deals with construction in a broad sense. It is about the fundamental value and importance of understanding the design and construction of existing structures and their related contexts for the examination of their today’s performance in view of future use. Therefore, construction history is • a basic scientific discipline consisting of rich data to identify and evaluate cultural values inherent to existing structures and structural engineering; • an indispensable basis for the examination of the performance of existing structures and the design of interventions to rehabilitate, strengthen, and modify them for modern use and demands, while respecting and integrating cultural values; • about understanding the past to build the future, a rich source of inspiration, providing an indispensable basis for the design of new structures. Consequently, construction history is a basic scientific discipline that all structural engineers should master. It has to become a fundamental course in any curriculum to educate structural engineers. Most importantly, construction history enhances the general “culture” of structural engineers, providing them the license to exchange with other professionals, like architects, on equal grounds.

Short Bio Eugen Brühwiler is a professor of structural engineering at the EPFL—Swiss Federal Institute of Technology in Lausanne, Switzerland, since 1995. His teaching and research activities include modern methods of examination of existing structures and the use of ultra-high performance fiber reinforced cement-based composites (UHPFRC) for strengthening of structures. He is involved in the examination and restoration of bridges and buildings of high cultural value.

Nicolas Janberg Construction History Can Change Your Life: My first foray into construction history was Prof. David Billington’s class “Structures and the Urban Environment” which I took as sophomore at Princeton University. While the class is meant to introduce the concept of structural art to engineering and nonengineering students alike, it also provides an overview of structural and

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construction history in Europe and the United States beginning with the industrial revolution through the works of some very important engineers: Robert Maillart, Gustave Eiffel, Othmar Ammann, Felix Candela, John Roebling and Christian Menn, The way Billington taught the class changes the way one views the world, as virtually every student of the class will attest to. I continued studying in the architecture and engineering program at the university, taking classes in art history and architecture along with the typical structural engineering courses. At the time, architects were required to learn about the history of their art and profession while engineering students had the choice. To me it seems like a fundamental difference. Architects learn from what has been built before in whatever way they choose—often as inspiration for their own designs or as a reference to what is considered good design—while so many engineers end up not even knowing whose works could inspire them. My academic career continued as a combination of structural engineering and construction history. As a senior, I wrote a bachelor thesis on the historical development of Paris-La Défense. As a graduate student, I chose to remain at Princeton with Billington as my advisor. I was a teaching assistant in his class for two years in a row. My master’s thesis explored the evolution of the modern cable-stayed bridge in Germany and France. I returned to Germany with two degrees in civil engineering and started working as a bridge engineer at a typical German engineering office doing detailed design for bridges. When I started, some colleagues were working on Germany’s longest arch bridge project—the Wilde Gera Viaduct. One of my colleagues—just as fresh out of school as myself—was proud to explain to me how innovative it supposedly was to use cable-stays to cantilever the arch without using falsework. I quickly burst his bubble by telling him that Eiffel had already done this on his bridges. Granted, Eiffel’s bridges were made of iron while the Wilde Gera crossing was made of concrete, but he could have known about this had he been taught construction history. As editor of Structurae, I have continued to keep up with current developments in construction as much as I have with historic structures. Through this work, I have read about many inspiring and innovative engineers who have changed the profession in ways no one thought possible. I have also been lucky to have met some of the ones who are doing it right now. One thing they seem to have in common is how aware they are not only of the other contemporary designers and their work but also of their predecessors, often citing them as inspiration. You could argue that knowing about the past, in fact that knowledge of construction history—as well as a critical appreciation of structural aesthetics—actually gives them a competitive advantage. I find it paradoxical and sad that a profession that relies so much on what previous generations have learned by condensing that knowledge into codes that every practicing structural engineer must adhere to has actually lost its past and seems to find no practical reason to teach it to the next generation. It makes me wonder how different the world could look if every bridge designer had been shown the works of Maillart or Menn during their studies, had learned to appreciate aesthetics and critique their own and other people’s works in order to make them better.

Short Bio Nicolas Janberg got his bachelor and masters of science degrees in engineering (civil engineering) at Princeton University and worked as a practicing bridge design engineer. He created “Structurae”, the International Database and Gallery of Structures.

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Jose Romo In my view, a good background in construction history is essential for a contemporary structural engineer. I think it is not possible to fully understand our present-day work without a deep knowledge of the evolution of the structural science and its technical application throughout history. We need to know from where we come, and who were our predecessors and their challenges, mistakes and achievements. A structure is one of the most perfect elements created by humankind; a bridge is one of the best examples of human creation where science, technique, aesthetic judgment, culture, economic, politics and social organization of a historical period crystalize in a single object. We can understand better previous societies by studying the culture of construction of a single historical period; furthermore, the knowledge of construction history enriches enormously the culture of anyone interested in structural engineering. It is obvious that this knowledge is also a fundamental intellectual tool when an engineer has to make an intervention in an existing structure. It is crucial to know the structural properties of the materials used, how the connections among elements were conceived and are working, and even, which were the codes and loads in the time of designing and therefore expectations we may have regarding its current structural behavior. As a bridge designer, I have to emphasize the importance of the deep understanding of our discipline and any other cultural knowledge, in the crucial moment of the conceptual design of a contemporary structure. This is normally an individual act where the insight of the engineer plays a fundamental role, and where the past is usually a tremendous source of inspiration. In many occasions, today’s creativity just emerges when an old structure is revisited using modern-day materials, resources or tools. Without knowing and learning from the past, that enrichment would be lost and as a consequence the possibilities of progressing could be dramatically limited. I think it is our duty to promote construction history as a way to preserve the legacy we have received. I strongly believe that construction history will help the progress, development and improvement of structural engineering and therefore will benefit the society we serve.

Short Bio Jose Romo got his civil engineering education from the Polytechnic University of Madrid in Spain. Since 1987 he is with FHECOR Ingenieros Consultores, S.A., now CEO of FHECOR. He is also a professor of reinforced and prestressed concrete at the Polytechnic University of Madrid.

Ignacio Paya-Zaforteza The terms that dominated the courses I took as a civil engineering student were “bending moments”, “concrete”, “Young’s modulus”, and similar others. Other words such as “society”, “art”, “conceptual design”, “history”… were missing. Was this a right approach to learn engineering? I think it was not. Structures are multidimensional and as such should be taught and learned. Prof. Billington stated long time ago in his book “The Tower and The Bridge. The New Art of Structural Engineering” that structures have a scientific dimension (related to their

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efficiency), a social dimension (related to their cost) and a symbolic dimension (related to their elegance). In addition, structures also have a value which is not only financial but also symbolic. The study of construction history provides an amazing way of learning about the multidimensional character of structures. The word “learning” involves looking not only at the best examples from the past, but also looking at examples which were not so good. If we do so, we will foster the virtues of our profession, we will not repeat mistakes from the past and we will promote a more critical profession and citizenship. Many other reasons support the necessity of construction history. A very important reason to me is the enjoyment that it produces the discovery of how our predecessors were able to design, build and create a legacy that provokes admiration, respect, and passion for the work of the engineer. This enjoyment increases exponentially when the structure is visited and seen as a reflection of the society that built it. This is a wonderful experience that can be shared with family, friends, students and colleagues. So, please join the club and become a construction history lover!

Short Bio Ignacio Paya-Zaforteza is an associate professor at the Universitat Politècnica de Valéncia (UPV), Spain. His main areas of interest are structural art, construction history, structural fire engineering and the education of the engineer. He has worked at the UPV, at Princeton University and at the TU Berlin. He has carried out extensive research on the works of the Spanish engineer Eduardo Torroja and on the links among structural engineering, art, society and architecture.

Bill Addis What use is construction history?i In his presidential talk to the Newcomen Society for the Study of the History of Engineering and Technology, in 1945, the eminent construction historian Stanley Baines Hamilton proposed six reasons why engineers should study history: 1. The detective interest of tracing knowledge to its source. 2. The opportunity of sharing a disinterested companionship with others who are following kindred lines, as a member of such a body as our Society [The Newcomen Society]. 3. The broadening of interest in engineering from the purely technical to a humane and liberal field of study. 4. The light which the study of invention and discovery can throw on the working of the human mind. 5. The genuinely recreative form of relaxation which history provides. 6. The contribution which the history of technology can make to the understanding of history in general.4 This opinion as to why people should study the history of construction, or rather the history of civil and structural engineering, reflects the background of the author (a research engineer) and i

This essay is a reduced version of an editorial published in Ref. [3].

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the time when it was put forward. Things have moved on and there seem nowadays to be six main views that various people have put forward regarding the possible uses for construction history, apart from its inherent interest. The first is that construction history has no direct use. It is a branch of a wider academic discipline of history and thus sits among the humanities. It aims to discover and record what happened in the past, and to explain this in the context of the contemporary states of technology, economics and society. A second view is that construction history is a cousin of the disciplines of history and philosophy of science and history of technology. It thus belongs to the broad spectrum of studies called “the history of ideas” and seeks to understand the knowledge and understanding in its field, and to discover the nature and mechanisms of progress in the field. In doing so, it identifies the main personalities and organizations involved in the discipline, and the part they played in contributing to progress within the discipline. A third view is held by many engineers who believe that, by studying engineering failures in the past, engineers can further their understanding of the behavior of structure and materials and improve their skill as engineers. Today, this process is sometime called “forensic engineering” and has been practiced for at least two centuries, and probably very much longer. It has undoubtedly been of extraordinary importance in certain cases; the collapse of Robert Stephenson’s cast and wrought iron girder bridge in 1847 across the river Dee in Chester is often mentioned in the many papers and books that have studied bridge failures. The most useful outcome of this accident was the report that was published by the Royal Commission which inquired into the cause of the accident.[5]However, while extremely interesting, it is not easy to see how engineering today would be able to prevent a “similar collapse” since virtually none of the circumstances of 1847 are relevant today. Similarly with the collapse of the Tacoma Narrows bridge in 1940 due to wind-induced oscillations. In the investigations that followed the collapse, it was discovered by the researchers (in the USA) that the Brighton chain pier had collapsed in 1836 (already well-known history in the UK) and this fact has been used to claim the potential benefits for engineers to study history. However, as with the Dee Bridge, this is perhaps making a claim with the benefit of hindsight. In fact, the collapse of the Tacoma Narrows bridge could not have been prevented even if its design engineers had been familiar with every known details of the Brighton Chain bridge collapse—put simply, the Tacoma Bridge collapse was largely a result of over-enthusiastic “value engineering” by the contractor who sought to save money.6 Taking a more positive view of historical events, many engineers also argue that a knowledge of engineering successes in the past can be a source of ideas that can be applied when designing buildings and structures today—at the very least by avoiding “reinventing the wheel” and, at best, increasing engineers’ knowledge of precedent beyond their own direct experience. This “method”, if it can be called that, is now widely practiced in university courses that focus on design, in construction and other engineering disciplines, under the heading of “precedent studies”. However, the benefit of this method is largely that the examples provide lecturers with concrete examples to illustrate the important principles of engineering design. This is not the same as studying the history of engineering. Another view taken by many engineers is that studying the historical engineering structures of the past and the engineers who created them is an essential part of developing a self-esteem for the profession, identifying role models to inspire young

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engineers and to make nonengineers aware of the engineers’ contribution to society. It is almost inconceivable that architectural history would not play an important part in the formation of an architect, or music history in the formation of a musician—both to understand what has already been done and to identify role models.ii Finally, perhaps the most direct use of construction history is linked to extending the life of existing structures—whether conservation, rehabilitation, refurbishment or “retrofitting”. When approaching such work, a series of key investigations need to be undertaken to determine: • the design and construction of the original structure; • the subsequent history of modifications, repairs and previous conservation and refurbishments; • the current state of the existing load-bearing structure and the likely cause of any cracking or other structural damage and an estimate of its remaining life; • the current state of the materials in the existing structure and an estimate of their remaining life. Together, these can be taken as a detailed construction history of the structure. Compiling such construction history of a building, bridge or other structure will reveal construction details of the original structure as well as any subsequent repair, alterations or conservation it has undergone during its life. Such information is virtually essential to assess the current condition of the structure and its materials, and to devise appropriate interventions which respect and conserve what remains when extending the life of an existing structure. Based on this knowledge, good conservation and refurbishment of existing structures can be achieved by selecting and applying appropriate repair, remediation, strengthening, and protection techniques. It is in this area, perhaps, that the future development of the discipline of construction history may prove most effective and fruitful. It is worth noting that the Construction History Society in Britain and its journal Construction History are unique in treating the discipline exclusively as a branch of history, placing it firmly in the humanities rather than the applied sciences. As it says on its website, “Construction History is the study of the development of the building industry”. Construction history societies and congresses based in other countries incorporate both the historical purpose construction history and the many ways in which it is linked to extending the life of existing structures including conservation, refurbishment and “retrofitting”. The limited scope which the Construction History Society embraces is partly explained by the fact that there are over a hundred societies in Britain which deal with building conservation and architectural heritage, and many of these have their own journals. Also, the Institution of Civil Engineers in London addresses engineering aspects of extending the life of existing structures via its website and the journal Engineering History and Heritage. In summary, there are three main types of interest in construction history: • as an independent academic discipline in the humanities, with limited application to the modern built environment; • as means to enhancing the engineering professions, both technically and in their standing; • as an essential part of the process of extending the life of existing structures and conserving our built environment.

ii

Nevertheless, it seems that the historical content of architectural degrees is, indeed, being reduced in many courses.

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Clearly, there is no single preferred or correct use for construction history, and a single study or piece of research into the subject may partly fulfill any or all of the uses listed above. Nevertheless, recognizing that there are different reasons for studying the subject, and that there are different uses to which the results of such study may be put, can help researchers and authors give their work a considered focus. When applying for research funding, academics would do well to remember that funding bodies are increasingly inclined to seek benefits coming out of funded research. The precise nature of these benefits should be the concern of us all. Above all, perhaps, we need to develop a robust defense against the oft-quoted sentiment expressed by Hegel in his lectures on the philosophy of history in the 1820s: What experience and history teach is this—that peoples and governments never have learned anything from history or acted on principles deduced from it.[7]

Short Bio Bill Addis is author of many publications on building engineering history including “Building: 3000 years of Design, Engineering and Construction”. He worked for 17 years at Reading University and 15 years with consulting engineer Buro Happold. Recently, he was visiting professor at Tor Vergata University in Rome, University of Innsbruck, University of San Sebastian and the ETH in Zürich. Bill is Chairman of the Editorial Advisory Panel for Engineering History and Heritage published by the Institution of Civil Engineers, for whom he has recently developed the Conservation Information Resource for Civil Engineers (CIRCE), an information resource for conservation engineers.

References [1] Musso SF. ‘Construction history’ and ‘Construction of histories’. University education and the future of construction history. In Proceedings of the First International Congress on Construction History, Madrid, Huerta S (ed), 3 vol., 2003; 1509–-1517. [2] Lorenz W. From stories to history, from history to histories: What can construction history do? Constr. History J. 2006; 21: 25–36. [3] Addis B, Schlimme H. Editorial: The uses of construction history. J. Constr. History 2016; 31(2). [4] Hamilton SB. Why engineers should study history. Trans. Newcomen Soc. 1945; 25: 1–10. [5] Walker Captain Simmons RE. Report to the Commissioners of Railways, on the Fatal Accident on the 24th day of May 1847, by the Falling of the Bridge over the River Dee. Available online at http://victoria.cdlr.strath.ac.uk/display.php?page=1&id=SGAV (Consulted 20/8/2016). [6] Addis W. Design revolutions in the history of tension structures. Struct. Eng. Rev. 1994; 6(1): 1–10. [7] GWF H. The Philosophy of History (Trans. J. Sibree) Batoche Books: Kitchener, Ontario, 2001; 19 Available online at http://socserv2.socsci.mcmaster.ca/~econ/ugcm/3ll3/hegel/ history.pdf (Consulted on 20/8/2016). “Was die Erfahrung aber und die Geschichte lehren, ist dieses, daß Völker und Regierungen niemals etwas aus der Geschichte gelernt und nach Lehren, die aus derselben zu ziehen gewesen wären, gehandelt haben.” Georg Wilhelm Friedrich Hegel (1770–-1831). Vorlesungen über die Philosophie der Geschichte (1st ed 1837). Available online at http://gutenberg.spiegel.de/buch/-1657/1 (Consulted on 20/8/2016).

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3 Engineering History and Heritage Structures around the World—A Survey

Nicolas Janberg, Struct. Eng., Berlin, Germany

Introduction The idea of this chapter is to provide a quick overview of the state of construction history around the world. The focus is primarily on the world of structural and civil engineering, of course, but in some cases, goes beyond into the realms of architecture where architectural history may overlap. Much more detailed descriptions of the state of construction history as an interdepartmental academic discipline are available in other publications.i One of the tools used to determine the state of construction for this chapter was through an online surveyii of IABSE members which provided several responses but which are hardly representative of the overall state. Definitions of construction history also may vary by country so that the responses did not necessarily yield a single and strongly coherent picture. The results of the survey will be described in this overview as they were given. As the number of responses was rather small, the survey results are augmented with knowledge from the IABSE Working Group 9 and additional research and sources wherever necessary and available.

Survey In late 2014 and early 2015, IABSE’s Working Group 9 Construction History conducted an online survey amongst members of the organization to obtain an overview of the state of i

Additional and much more detailed sources on the state of construction history in Europe are found in Ref. [1]. An updated and expanded version of the above is entitled “L’histoire de la construction, Un méridien européen / Construction History, A European Meridian” and was published online as a work in progress in 2015 at http://www. histoireconstruction.fr/rapport2015/. It is scheduled for final publication in 2017 by Éditions Garnier. Several civil engineering heritage country profiles were published in Ref. [2] on Spain and Germany (February 2016), Japan and Wales (May 2016), Albania and Scotland (August 2016), Ireland (November 2016), Canada (February 2017), and England (May 2017). ii The survey is still available online at https://docs.google.com/forms/d/e/1FAIpQLSfMPJCdSz1ZJJP-xJP-izuZugOke o1aZFDtnuCaBuhhRL3fIQ/viewform.

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construction history is in the members’ countries. Initially, the chairs of the national committees of IABSE were asked to personally fill out the survey or ask someone in their group to do so. Due to the small number of responses, a request was then sent out to the entire IABSE e-mail newsletter list. This chapter evaluates the responses from the survey.

Survey Questions The survey included a total of 19 questions and was divided into three sections. The first section asked for information on the person answering the questions. The second and largest section contained the pertinent questions regarding construction history and engineering education, while the third section concluded the survey with questions aimed at establishing the current situation of engineering practice in the member’s country. The complete list of the 19 survey questions, explanatory notes to the questions and possible and expected responses is provided in Table 1.

Survey Responses A total of 21 responses to the online survey were collected. The first responses were recorded on 4 November 2014, while the last member to fill out the form did so on 24 February 2015. None of the responses were anonymous, and many of the responses contained answers to all questions. Some questions did not require an answer if the previous response was negative. Figure 1 summarizes the number and types of responses per survey question. Positive responses were counted as such if the answer was “yes” and negative ones where a “no” or “do not know” was given. Conditional responses included answers such as “yes, but…” and neutral responses were those where free text was required or other responses were possible. Countries Represented in the Survey The 21 responses were from Austria, Belgium, Brazil, Bulgaria, Canada, the Czech Republic, Finland, France (three responses), India, Liechtenstein, Mexico, the Netherlands (three responses), Portugal, Spain, Switzerland (two responses) and the United Kingdom. Due to the duplications in the responses, the survey represents a total of 16 countries mostly from Europe and the Americas.

Current Situation of Construction History around the World Instead of simply reporting the results for each question posed by country, the following will summarize the responses received by groups of questions surrounding a specific issue in construction history. Also, the responses will be augmented by information available to the working group through research done in contexts not directly related to IABSE and its construction history working group as well as personal knowledge available through past activities in forums dealing with construction history.

CURRENT SITUATION OF CONSTRUCTION HISTORY AROUND THE WORLD

No.

Question Additional notes explaining the question

1. 1.1 1.2 1.3

Please tell us about yourself What is your name and affiliation? Could you please provide us with your e-mail address? Please name the country for which you are responding to this survey: If your responses are specific to a region in your country, please include this as well. Institutions Dealing with Construction History Do Technical Universities offer courses dealing with the history of construction? If so, please specify If you answered “yes” to the above question, please specify Examples: Master degrees in construction history, building preservation, etc. Is Construction History taught as part of the education of civil and structural engineers at the bachelor or master level? In the education of civil and structural engineering at the bachelor or master level, are there any courses dealing with existing structures? For example dealing with the assessment, examination, improvement, or monitoring of existing structures. Is there a list of Cultural Heritage structures established by a governmental agency in your country? This can include buildings, bridges, public works, monuments, etc. If yes, does this list include engineering structures? If engineering structures are included, what kind of structures are on the list?

2. 2.1 2.2

2.3

2.4

2.5

2.6 2.7

2.8

2.9

Are engineering structures included as part of ensembles like transportation (road, rail, pedestrian/cycle paths) infrastructure, energy production infrastructure, etc.? Are there awards in structural engineering relating to existing structures?

2.10 Are there associations dealing with Construction History? If yes, please name them and list the URL of the website Table 1: Continued

23

Allowed answers

free Text free Text free Text

Yes / No free Text

Yes, in a dedicated course / Yes, as part of other courses / No, not at all. Yes, in a dedicated course / Yes, as part of other courses / No, not at all

Yes / No

Yes / No Bridges / Tunnels / Buildings / Dams, dykes, etc. / Other (please specify) Yes / No / Don’t know

Yes, there awards dedicated to existing structures / Yes, but as part of other awards / No free Text

24 No.

Question Additional notes explaining the question 2.11 Are there museums or galleries related to civil structures in your country?

CHAPTER 3. A SURVEY

Allowed answers Yes, there are museums or galleries dedicated to the subject / Yes, but as part of a larger or more general collection / Yes, there are travelling exhibits / No, not that I know of

2.12 If there are museums or galleries, please name them: free Text List the URL of the website if available 2.13 Are there exhibitions on structural engineers? Yes/No 2.14 Please name examples of exhibits held in the past or cur- free Text rently ongoing: List the URL of the website if available 3. Current situation of engineering practice in your country 3.1 Please name the 5 most eminent structural/civil engineers free Text of your country: If known, please add e.g. year of birth and a significant structure designed by this person 3.2 Can you name notable projects involving existing strucfree Text tures in your country? E.g. regarding the re-use, strengthening, alteration/modification (extension, addition, upgrading, widening) of existing structures. If available, please name an Internet site or article with more information on the project. Table 1: List of all survey questions

Construction History in Engineering Education Questions 2.1 through 2.3 of the survey tried to evaluate if the topic of construction history played any part in the education of structural engineers. As construction history is not an established academic discipline at this point in time, there are no degree programs at the graduate nor at the undergraduate level specifically for the history of construction. There are, however, degrees dealing with the rehabilitation of existing or historic structures, where historical aspects are of importance. Generally, if engineering students come into contact with the history of their profession, it is usually by historical summaries as part of other classes, if an educator chooses to outline the development of concrete as a construction material in a module on concrete construction.iii In countries like Austria,iv iii This was confirmed by survey responses from Belgium (Free University of Brussels), Brazil (University of São Paulo), the Czech Republic, Mexico, the Netherlands, Portugal, Spain, and the United Kingdom. iv At the Vienna University of Technology, the master of architecture program at the Institute of History of Art, Building Archaeology and Restoration offers special modules related to the history of construction.

25

CURRENT SITUATION OF CONSTRUCTION HISTORY AROUND THE WORLD

Number and types of responses per survey question

Number of responses (maximum 21)

20

15

10

5

0

1.1

1.2

1.3

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9 2.10 2.11 2.12 2.13 2.14 3.1

3.2

Question number Neutral

Positive

Conditional

Negative

Fig. 1: Numbers and types of responses per question Bulgaria,v or Germany, it is often the case that architects actually obtain engineering degrees so that technical universities have schools or faculties of architecture. At least theoretically they can offer opportunities to engineering students for taking classes in the history of art and architecture otherwise intended for architecture degrees. However, engineering students rarely are able to take advantage of these opportunities. A rare example of a combined curriculum for engineering and architecture is the program in “Architecture & Engineering”vi offered by Princeton University’s Department of Civil and Environmental Engineering. The program was directed by Prof. David P. Billington from 1990 until 2008 and is overseen today by Prof. Maria Garlock. The curriculum includes a module entitled “Structures and the Urban Environment”, which covers the history of structures from the beginning of the industrial revolution to today with an emphasis on “structural art” as originally defined by Prof. Billington. The class is required for students in the program but also satisfies laboratory and science requirements for nonengineering students so that it is open to all. Students in the architecture and engineering program are also required to take classes on the history of architecture through the Department of Art History, as well as design studios and other classes offered by the School of Architecture in order to obtain a Bachelor of Science in Engineering. The program does not continue at the

v At the University of Architecture, Civil Engineering and Geodesy, there are modules dealing with the history of architecture or construction such as “History of Bulgarian Architecture”; “History of Modern Architecture”; “History of Renaissance Architecture”; “History of Medieval Architecture”; “History of Ancient Architecture”. For master degree students in structural engineering, there is a special module entitled “Diagnostic, Rehabilitation and Strengthening of buildings”, which also includes a basic outline in Construction History. vi https://www.princeton.edu/cee/undergraduate/program-tracks/architecture-and-engineer/ (visited on 29 March 2016).

26

CHAPTER 3. A SURVEY

graduate level, however. The concepts from this program have been transferred to other universities in the United States. In France, construction history is more at home in architecture than in engineering institutions as the former teach architectural history but the latter do not. The Ecole des Ponts ParisTech (Marne-la-Vallée), formerly called the Ecole Nationale des Ponts et Chaussées, offers a combined degree for “ingénieur-architecte” in cooperation with the Ecole d’architecture de la ville & des territoires (Marne-la-Vallée) where a module on the history of construction is included.vii The module is taught at the architecture school, however. Until only very recently, Brandenburg Technical University at Cottbus and Senftenberg (Germany) was the only technical university in German-speaking countries with a full professorship in the history of construction technology (“Bautechnikgeschichte”). The chair has been held by Prof. Dr.-Ing. Werner Lorenz since 1993 and includes the conservation of structures (“Tragwerkserhaltung”) since 2001. Prof. Lorenz offers various bachelor-level modules on the history of structural analysis, and construction technology as well as modules dealing with the various aspects involved in assessing existing structures. In 2016, Prof. Dr. Stefan M. Holzer was appointed to a full professorship of building research and construction history within the architecture department of the ETH Zürich (Switzerland)viii, though, neither the ETH Zürich nor the École Polytechnique Fédérale de Lausanne (EPFL) in Lausanne currently teach dedicated modules on the history of construction. At the master level, the EPFL offers a module on the “Aesthetics of civil structures” (CIVIL-476) ix taught by Eugen Brühwiler which includes historical examples of works by famous engineers. At the TU Delft in the Netherlands, to receive a master’s degree in building engineering, the module CIE4202 “Architectural History of Buildings” is mandatory for all students.x It emphasizes the period from 1840 to 1970 and discusses the reuse of existing buildings.xi Historical aspects are also included in other modules. According to the survey responses, there are master-level classes on construction history being taught in Portugal. The same applies to Spain. However, no specific examples were provided. As reported in “Construction History in the United Kingdom” (2015) by Bill Addis and James W.P. Campbell,xii the academic teaching of construction history—especially in engineering—is still not widely established despite much research and many publications from enthusiasts pursuing this specific interest alongside their regular professional life or during retirement.

Existing Structures Given the rising number of interventions necessary on existing and historic structures either for assessment, preservation, rehabilitation, strengthening or modification, this has become an vii

Ecole des Ponts ParisTech Web site (http://www.enpc.fr/sites/default/files/files/DE/GCC/Cursus-gcc-archi_2012-2013. pdf) as of 8 September 2015. viii https://www.ethz.ch/en/news-and-events/eth-news/news/2016/03/ten-professors-appointed-at-ETH-Zurich.html (“Ten professors appointed at ETH Zürich”, published on 11 March 2016). ix Course book available on the EPFL Web site at http://edu.epfl.ch/coursebook/en/aesthetics-of-civil-structures-CIVIL476?cb_cycle=bama_cyclemaster&cb_section=gc (as of 29 July 2017). x http://studiegids.tudelft.nl/a101_displayCourse.do?course_id=32441 (viewed on 29 July 2017). xi http://studiegids.tudelft.nl/a101_displayCourse.do?course_id=12914&SIS_SwitchLang=en (viewed on 29 July 2017). xii Chapter published in Ref. [3], work in progress, was available online at http://www.histoireconstruction.fr/rap port2015/ and is scheduled to be published by Éditions Garnier in 2017.

CURRENT SITUATION OF CONSTRUCTION HISTORY AROUND THE WORLD

27

increasing part of the portfolio not only for architects but for civil/structural engineers as well. The tasks often necessitate knowledge of historical construction materials, codes, methods, etc. and thus is the most practical way for practicing engineers to come into contact with construction history. The survey therefore asked questions about how existing structures are being taught to engineering students (Question 2.4) on one hand, but also how this is recognized by a more general public through awards (Question 2.9) and by general knowledge (Question 3.3). Existing Structures in University Education The need for the specialized knowledge necessary to deal with interventions on existing structures seems to have been recognized by academic institutions in many parts of the world. The following examples were reported by the survey: • Austria: The Faculty of Civil Engineering at Vienna University of Technology offers a module on “Maintenance and restoration of buildings”. • France: the Conservatoire National des Arts et Métiers (CNAM), a technical school for engineers, offers a module originally entitled “Connaissance du bâti ancient techniques de rehabilitation” and now called “Ecoréhabilitation”xiii dealing with construction techniques for structures built before 1948. • Germany: – At Brandenburg Technical University (Cottbus-Senftenberg), there is a chair of “Entwerfen, Bauen im Bestand” dealing entirely with the design and execution of interventions in existing structures, though it is located within the Institute of Architecture and not civil engineering.xiv – The Institut für Bauwerkserhaltung und Tragwerk (founded in 2003) at the Technische Universität Braunschweig offers two modules on “Bauen im Bestand”xv for a specialization in building preservation at the master level for civil engineering students. • Switzerland: At the master level, the EPFL offers two modules on existing structures (CIVIL-436 and -437),xvi both taught by Eugen Brühwiler. • The United Kingdom: The following institutions offer postgraduate courses on building conservationxvii: – Cambridge University—MSt Building History – Bath University—MSc Conservation of Historic Buildings – University College London—MA in Cultural Heritage Structures xiii CNAM Web site (http://formation.cnam.fr/rechercher-par-discipline/ecorehabilitation-207844.kjsp), visited on 8 September 2015 and 29 July 2017. xiv See department Web site at https://www.b-tu.de/fg-bauen-im-bestand/ (in German only, viewed on 29 July 2017). xv https://www.bauwerkserhaltung.tu-braunschweig.de/index.php/menu-lehre-de/mastervertiefung-bauwerkserh altung/bauen-im-bestand and https://www.bauwerkserhaltung.tu-braunschweig.de/index.php/menu-lehre-de/ mastervertiefung-bauwerkserhaltung/bauen-im-bestand-ii (in German, viewed on 29 July 2017). xvi Course books available on the EPFL Web site at http://edu.epfl.ch/coursebook/en/existing-structures-basis-CIVIL-436 and http://edu.epfl.ch/coursebook/en/existing-structures-selected-topics-CIVIL-437 (as of 29 July 2017). xvii Further courses may be found at https://www.postgraduatesearch.com/pgs/search?course=building-conservation (URL verified on 29 July 2017).

28

CHAPTER 3. A SURVEY

– – – –

Oxford Brookes—MSc in Historic Conservation University of Edinburgh—Architectural History & Theory University of Central Lancashire—MSc Building Conservation & Regeneration Bartlett School of Architecture—MPhil/PhD Architectural History & Regeneration

Without naming specific examples, dedicated modules were reported also from Belgium, Mexico, Portugal and Spain, while the topic is included in other classes in countries like Finland or the Netherlands. Existing Structures in the Public Eye/Awareness Interventions on existing structures—especially when they are part of the local cultural heritage—can often be contentious. Thus, special awards for these kinds of projects also show the importance that is attributed to them by a more general public. The responses to Question 2.9 on these special awards showed that there are dedicated awards in Brazil, Bulgaria, France, Mexico, the Netherlands, Portugal, Spain and the United Kingdom. In countries like Austria, Canada, the Czech Republic and Switzerland, these interventions are generally recognized through more general awards. Belgium, Finland, India and Liechtenstein do not seem to have any awards. In Germany, there are architectural awards for interventions on existing and heritage structures xviii but no major dedicated engineering awards. The latter are recognized generally through established awards. In March 2016, the German Bridge Award (Deutscher Brückenbaupreis) in the category for road and rail bridges was awarded to the rehabilitation project for the Kocher Viaduct.xix An honorable mention was given to the rehabilitation of the Mettlach Suspension Bridge at the 2015 Ulrich Finsterwalder Structural Engineering Awardxx (Ulrich Finsterwalder Ingenieurbaupreis), while the 2013 edition gave a mention to the rehabilitation of Hamburg central station. The newly created German Structural Engineering Award (Deutscher Ingenieurbaupreis) was awarded for the first time in 2016, and projects involving existing structures are explicitly allowed to compete.xxi The survey’s Question 3.2 asked to name some specific and notable examples of projects involving existing structures. The following were named, though the following list is not to be viewed as comprehensive of the respective country’s achievements: ▫ Austria – Gasometer Wien (www. Gasometer.at) – Kabelwerk Wien (www.kabelwerk.at) – Ankerbrotwerke Wien (www.loftcity.at) – Museumsquartier in den ehem. Hofstallungen (www.mqw.at) – Burg Perchtoldsdorf (www.burgperchtoldsdorf.at) xviii

Examples: BDA Preis Bayern 2016 “Bauen im Bestand Denkmal” (http://www.bda-preis-bayern.de/nominierungen/ bauen-im-bestand-denkmal.html retrieved on 7 April 2016) or “Respekt und Perspektive“Bauen im Bestand Preis 2014, awarded by db Deutsche Bauzeitung (http://www.db-bauzeitung.de/aktuell/db-veranstaltungen/respekt-und-perspek tive-bauen-im-bestand-preis-2014/ retreived on 7 April 2016). xix http://www.brueckenbaupreis.de/preis-2016/preistraeger-2016/ retrieved on 7 April 2016. xx http://www.ernst-und-sohn.de/ulrich-finsterwalder-ingenieurbaupreis?tab=tab252#rs retrieved on 7 April 2016. xxi http://www.bbr.bund.de/BBR/DE/WettbewerbeAusschreibungen/Deutcher_Ing_baupreis/Ingenieurbaupreis_node. html retrieved on 7 April 2016.

CURRENT SITUATION OF CONSTRUCTION HISTORY AROUND THE WORLD

29

▫ Belgium – Widening the masonry railway viaduct over the Pede valleyxxii ▫ Bulgaria – National Museum Complex (Sofia) – Building of the museum of Sofia’s history (Sofia) – Museum of the contemporary art (Sofia) – Trade center “Star Gallery” (Plovdiv) – Hotel “Ventura” (Varna) – Ethnographical Museum (Cross-shaped barracks in Vidin) – Early Christian Basilica of Joan (Sandanski) ▫ Canada – Rehabilitation of Lions Gate Suspension Bridge (replacement of the entire suspended structure). Designed by Buckland & Taylor – Rehabilitation of York Boulevard High Level Bridge. Designed by Delcan (now Parsons) – Rehabilitation of the Thousand Islands Bridges. Designed by Delcan/Parsons ▫ The Czech Republic – Reconstruction of the hall Masaryk railway station in Praguexxiii ▫ Liechtenstein – Rehabilitation of the headrace tunnels for the Samina power plant ▫ Mexico – Rehabilitation of the Mexico City Cathedral – Rehabilitation of the Old Temple of San Agustin in Mexico City – Rehabilitation of the Old School of Medicine in Mexico City ▫ The Netherlands – De Meelfabriek (http://www.demeelfabriek.nl/) – De Hef Bridge (http://dehef.nl/) – ‘Van Nelle’ Building, Rotterdam – Rehabilitation of Muider ridge across Amsterdam-Rhine-canal ▫ Switzerland – Strengthening of the Chillon Viaducts (2.1 km) – Restoration of several bridges by Robert Maillart – Railway bridges over the Rhine at Waldshut and Eglisau: upgrading of two riveted bridge structures from the 19th century

xxii

See also Ref. [4]. http://www.konstrukce.cz/clanek/prestavba-nosne-konstrukce-dvorany-masarykova-nadrazi-v-praze/ retrieved on 7 April 2016.

xxiii

30

CHAPTER 3. A SURVEY

– Widening of the Sierre tunnels – Raising of Nant de Drance dam ▫ The United Kingdom – Saint Pancras Station, London – Bankside Power Station conversion to Tate Modern art museum, London – Liverpool docks buildings conversion to museums and commercial buildings – Spitalfields Market, London – Salt’s Mill near Bradford converted into an art gallery, commercial workshop space, bookshop and restaurant Many other projects were submitted; however, these were projects of new and recent structures and not interventions on existing structures. They were therefore omitted from the above listing.

Cultural Heritage Four questions of the survey (2.5 through 2.8) tried to establish whether works of civil and structural engineering are recognized as part of the structural heritage in their respective countries. In all countries covered by the survey, there exist governmental agencies which list structures (built environment) as part of their cultural heritage and it can be safely assumed that most countries do. However, the other questions tried to determine if and to what degree works of structural engineering are included on these lists and thus considered worthy of preservation and protection. While all responses confirmed that engineering structures are included in the lists, the types of structures included in the cultural heritage vary greatly. Buildings are evidently listed in all the countries surveyed but the responses (due to the nature of question) do not differentiate whether these buildings are listed for the architectural merit or because of structural aspects (Table 2). In addition to the survey it should be noted that cultural heritage lists in Spain do include bridges and most likely other types of engineering structures as the database of the Spanish Ministry of Education, Culture and Sports lists 138 entries for the keyword “puente” and 29 for “acueducto”.xxiv Germany also lists engineering and industrial heritage structures such as bridges, factories, etc. In addition to the government listings, the Federal Chamber of Engineers (Bundesingenieurkammer) has been naming their own historic engineering monuments (“Historische Wahrzeichen der Ingenieurbaukunst”), listing a total of 18 structures since 2007.xxv The American Society of Civil Engineers (ASCE) has also created a list of over 200 historic civil engineering landmarks both nationally and internationally.xxvi These include Hoover Dam, the Boston Subway and the Brooklyn Bridge (all United States), as well as the Eddystone Lighthouse (UK), Hagia Sophia (Turkey) and Salginatobel Bridge (Switzerland).

Museums and Exhibits Through museums and exhibits, awareness of the topics relevant to the history of construction for the general public can be increased, and survey Questions 2.11 through 2.14 were intended xxiv

Searches performed on 29 July 2017 via http://www.educacion.es/bienes/buscarBienesInmuebles.do. http://wahrzeichen.ingenieurbaukunst.de/ as retrieved on 7 April 2016. xxvi http://www.asce.org/landmarks/ as retrieved on 7 April 2016. xxv

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CURRENT SITUATION OF CONSTRUCTION HISTORY AROUND THE WORLD

Country Austria Belgium Brazil Bulgaria Canada The Czech Republic Finland France India Liechtenstein Mexico The Netherlands

Types of structures listed Bridges, tunnels, buildings Bridges, buildings Buildings Bridges, buildings, clock towers, residential towers, industrial facilities, mills Bridges, buildings Bridges, buildings

Buildings, stadiums Bridges, tunnels, buildings, dams, dykes, etc., light-houses Buildings, caves, forts, monasteries, temples, monuments Bridges, buildings Monuments, churches, monasteries, public works Bridges, buildings, dams, dykes, etc., fortifications, shipyards, locks, sluices, weirs Portugal Bridges, buildings Spain Buildings Switzerland Bridges, tunnels, buildings, dams, dykes, etc., retaining walls, galleries, roads, railways The United Bridges, canals, aqueducts, tunnels, docks, buildings, Kingdom fortifications, dams, dykes, etc. Table 2: Types of listed engineering structures per country

Ensembles Yes No No No N/a Yes No Yes Yes No Yes Yes Yes No Yes Yes

to determine this for each country. Not counting individual structures which have been converted into a museum and display their own history, there are currently no museums dedicated to the general history of construction or civil/structural engineering. The Museum of Public Works in Paris (“Musée national des Travaux publics”), which was located at 1, avenue d’Iéna in Paris, is the only museum that could be classified as such a dedicated museum.xxvii From 1939 to 1955, it showcased around 400 models of bridges, roads, dams, locks, ports, etc. in a didactic and pedagogic exhibit. The museum eventually had to close because of low visitor numbers.xxviii However, there are still a number of museums in the surveyed countries which have museums with a more general focus that in part cover topics related to the history of construction or architecture. These include but are not necessarily limited to: ▫ Austria – Ziegelmuseum Wien – Technisches Museum Wien (www.technischesmuseum.at) – WienMuseum (www.wienmuseum.at) – ArchitekturzentrumWien (www.azw.at) xxvii xxviii

http://www.planete-tp.com/article.php3?id_article=1146 (retrieved on 10 September 2015). https://fr.wikipedia.org/wiki/Mus%C3%A9e_national_des_Travaux_publics (retrieved on 8 April 2016).

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CHAPTER 3. A SURVEY

▫ Bulgaria – Museum of Bulgarian Architecture, Sofia – Ethnographical Museum, Gabrovo ▫ France – Cité de l’architecture et du patrimoine, Paris (www.citechaillot.fr) – Musée des arts et métiers, Paris (www.arts-et-metiers.net) – Pavillon de l’Arsenal, Paris (pavillon-arsenal.com) ▫ Germany – Deutsches Museum, Munich (www.deutsches-museum.de) – Deutsches Architekturmuseum, Frankfurt (www.dam-online.de) – Deutsches Straßenmuseum, Germersheim ▫ The Netherlands – Historical forts: The Dutch Waterline (www.hollandsewaterlinie.nl) – North Sea Flood of 1953: Watersnoodmuseum (www.watersnoodmuseum.nl) – Pumping Stations: ◦ Ir. D.F. Woudagemaal (www.woudagemaal.nl) ◦ Museum De Cruquius (www.museumdecruquius.nl) – Fortifications: Kazemattenmuseum (www.kazemattenmuseum.nl) – Industrial Heritage: Hoogovensmuseum (www.hoogovensmuseum.nl) – Dredging: Nationaal Baggermuseum (www.baggermuseum.nl) ▫ Portugal – Museu de Lisboa, Lisbon (www.museudelisboa.pt) – Museu Nacional Ferroviário, Entroncamento (www.fmnf.pt) ▫ Switzerland – Swiss Science Center Technorama, Winterthur (www.technorama.ch) ▫ The United Kingdom – Science Museum (www.sciencemuseum.org.uk) – British Museum – Building Centre – Museum of London – Transport Museum – Kirkaldy Museum Southwark – Menai Heritage Museum – Ironbridge Gorge Museums – SS Great Britain – Brunel Centre – Waterways Museum

CURRENT SITUATION OF CONSTRUCTION HISTORY AROUND THE WORLD

33

– Fakenham Museum of Gas & Local History – Amberley Chalk Pits Museum – Weald and Downland Museum (www.wealddown.co.uk) Aside from permanent exhibits in the aforementioned museums, there are also temporary/travelling exhibits (held at the above or in other locations) on the topics related to construction history or on the works of individual structural engineers in the above and other countries. A few examples are: ▫ Belgium – 2011: “Bruxelles, sur le traces des ingénieurs bâtisseurs”,xxix held at the CIVA, invited to explore the city of Brussels through the works of civil engineers. ▫ France – 1997: “L’art de l’ingénieur”, held at the Centre Pompidou in Paris from June to September, was a landmark exhibit showcasing some of the models of the former Musée national des Travaux Publics as well as recent achievements in bridge and structural engineering around the world. The catalogue was a seminal “dictionary” of terms, engineers and structures. – 2013–2014: “Auguste Perret – Huit chefs d’œuvre! /?”, held incidentally in the building which he designed for the former Musée National des Travaux Publics, the Palais d’Iéna. It showcased eight works of this French architect who was seminal in concrete construction (www.exposiƟonperret.fr). ▫ Germany – 2009: “Fritz Leonhardt: Die Kunst des Konstruierens”, travelling exhibit on the famous German engineer. – 2011: “Félix CandelaKünstler der Konstruktion”, exhibit at the TU Berlin, translated from a Spanish exhibit (see below) and a set of lectures on shell structures. Also travelled to Munich. – At the Deutsches Technikmuseum Berlin, a lecture series entitled “Praktiken und Potenziale von Bautechnikgeschichte” (practices and potentials of the history of construction technology) is held every year and co-sponsored by the VDI working group on construction technology as well as the BTU Cottbus-Senftenberg.xxx ▫ Italy – 2010: “Pier Luigi Nervi – Architettura coma Sfida”, exhibit held in Venice and several other cities across Italy, accompanied by a catalogue. ▫ Spain – 2010: “Félix Candela: La Conquista de la Esbeltez”, exhibition in Madrid on thin concrete shells by Candela, repeated 2013 in Segovia. xxix

A description of the catalogue is available at http://www.ulb.ac.be/wserv2_oratio/oratio?f_context=unibooks¬ei d=606&style=&f_type=view&data-file=bib1 (retrieved on 8 April 2016). xxx The schedule is available at https://www.b-tu.de/fg-bautechnikgeschichte/wissenstransfer/vortragsreihe.

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CHAPTER 3. A SURVEY

– 2014–2015: the Spanish group of IABSE is co-organized an exhibit at the Palacio de Cibeles (Madrid) on contemporary structural engineering (1964–2014) in Spain.xxxi ▫ Switzerland – The Gesellschaft für Ingenieurbaukunst regularly organized special exhibits about individual engineers, offices, companies or topics.xxxii In the past events, the society has held or sponsored exhibitions on Robert Maillart, Heinz Isler, Christian Menn, Alexandre Sarrasin, concrete structures, timber structures, railway bridges, hydraulic structures and tunnels. ▫ The United Kingdom – “Unseen Hands – 100 Years of Structural Engineering”, Victoria & Albert Museum. – The Institution of Civil Engineers has held exhibitions on Telford, Brunel, Rennie, Bazalgette, Ove Arup, etc. ▫ United States – The Princeton University Art Museum has held exhibits based on research done by Prof. David P. Billington, his successors and students: ◦ 1972—Bridges & Sculpture ◦ 1974—The Eads Bridge ◦ 1976—The Bridges of Robert Maillart ◦ 1978—The Bridges of Christian Menn (exhibit travelled in USA, Canada) ◦ 1980—Heinz Isler – Structural Artist (exhibit travelled in USA, Japan) ◦ 2003—The Art of Structural Design: A Swiss Legacy ◦ 2008–2009—Felix Candela: Engineer, Builder and Structural Artist ◦ 2011—Fazlur Khan – Structural Artist of Urban Building Forms (hƩp://khan. princeton.edu/) ◦ 2013—Evolution of German Shells. Efficiency in Form (hƩp://shells.princeton. edu/) ◦ 2015—The Art of Spanish Bridge Design including a module entitled “CEE463: A Social and Multi-Dimensional Exploration of Structures” (hƩp://spanishbridges. princeton.edu/) International Congresses Every three years since 2003, researchers and academics from all affected academic disciplines gather to meet at an international congress with hundreds of presentations published in the respective congress proceedings:

xxxi

Website of the exhibition available at http://www.centrocentro.org/centro/exposicion_ficha/95 (retrieved on 14 September 2015). xxxii The society’s exhibition archive provides a full list at http://www.ingbaukunst.ch/de/veranstaltungen/archiv/ (retrieved on 10 September 2015) as well as exhibition catalogues. http://www.ingbaukunst.ch/de/publikationen/ buecher-zu-ausstellungen/ (retrieved on 8 April 2016).

CURRENT SITUATION OF CONSTRUCTION HISTORY AROUND THE WORLD

35

2003—Madrid, Spain 2006—Cambridge, the United Kingdom 2009—Cottbus, Germany 2012—Paris, France 2015—Chicago, USA 2018—to be held in Brussels, Belgium There are also national congresses held in Spain, France, Germany, Portugal, the United Kingdom and the United States.

Associations and Societies Question 2.10 of the survey asked about associations in each country which are either specific for the discipline of history of construction or related aspects. The following provides a grouped listing of the societies provided by the survey responses augmented with knowledge available to the IABSE working group. Construction History Societies Most of the respondents actually were not able to name the societies dedicated to construction history in their respective countries. The current list of construction history societies follows in the order of the year of foundation. (a) The Construction History Society (the United Kingdom) The Construction History Society (CHS) is the central focus for those interested in the subject of construction history in the UK. It was founded in 1982 and was the first such society in the world, by a margin of around ten years. The CHS now has a UK membership of around 250 and a further 200 or so members worldwide. The first issue of the Construction History, the Journal of the CHS, journal was published in 1985. This has been published annually and since 2013, twice yearly. In 2012, it was renamed Construction History, the International Journal of the CHS. The CHS hosted the Second International Congress on Construction History at Queens’ College, Cambridge in 2006. Website: hƩp://www.construcƟonhistory.co.uk/ (b) Sociedad Española de Historia de la Construcción (Spain) Founded in 1996, this Spanish society for the history of construction is the second-oldest such association worldwide. It holds regular national congresses and was responsible for holding the First International Congress on Construction History in Madrid in 2003. Website: hƩp://www.sedhc.es/ (c) Associazione Edoardo Benvenuto (Italy) Founded in 1999, the society was formed to foster research on the science and art of building in their historical development. Website: hƩp://www.associazionebenvenuto.org/ (d) The Construction History Society of America (USA) Founded in 2007 as a branch of the UK society, it organizes national meetings and congresses. It also hosted the Fifth International Congress on Construction History in Chicago in 2015. Website: hƩp://www.construcƟonhistorysociety.org/

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(e) Association francophone d’histoire de la construction (French-speaking countries) The society was founded in 2010 and hosted the fourth international congress held in Paris in 2012. While headquartered in France, it also covers other francophone countries such as Belgium and Switzerland. Website: hƩp://www.histoireconstrucƟon.fr/ (f) Gesellschaft für Bautechnikgeschichtexxxiii (German-speaking countries) Founded in Berlin in 2013, this society also uses language instead of national boundaries to define its membership. It offers researchers and academics from Germany, Austria, Switzerland, and other countries regular forums for cooperation and exchange of ideas, methods and research. One of the explicit goals of the society is to establish the history of construction technology as an academic discipline. Website: hƩp://gesellschaŌ.bautechnikgeschichte.org/ (g) Sociedade Portuguesa de Estudos de História de Construção (Portugal) SPEHC was founded in 2014 and fosters research and academic exchange on the topic in Portugal. Website: hƩp://www.spehc.pt/ Other Organizations The following are additional associations, societies, government departments and other organizations that deal with aspects related to construction history such as preservation of cultural heritage, have a vested interested in the topic, or foster the appreciation and awareness of structural engineers and their work both historically and contemporaneously. ▫ Austria – Bundesdenkmalamt, Austrian Federal Monuments Office (www.bda.at) ▫ Bulgaria – National Institute of Immovable Cultural Heritage (www.ninkn.bg) – Bulgarian National Committee of ICOMOS (icomos-bg.org) ▫ Canada – Ministry of Citizenship and Culture (Ontario) ▫ Finland – National Board of Antiquities (www.nba.fi) ▫ France – Association pour la Connaissance des Travaux Publics (ASCO-TP) (www.planete-tp. com) – Association Eugène Freyssinet (efreyssinet-association.com) – Association des Descendants de Gustave Eiffel (www.gustaveeiffel.com) ▫ Germany – Bundesingenieurkammer (bingk.de) – docomomo Deutschland (www.docomomo.de)

xxxiii

The name of the society translates as “Society for the History of Construction Technology”. One of the reasons for this choice was that a possible German translation for “Construction History” would be “Baugeschichte” but this term is already established in architecture and would correspond to “architectural history” elsewhere.

CURRENT SITUATION OF CONSTRUCTION HISTORY AROUND THE WORLD

▫

▫ ▫ ▫

▫

37

– Ingenieur Baukunst e.V. (www.ingenieur-baukunst.de) – Koldewey-Gesellschaft (www.koldewey-gesellschaft.de) The Netherlands – Locks and Dams: Stichting Historische Sluizen en Stuwen Nederland (www.sluizenenstuwen.nl) – Royal Netherlands Society of Engineers: Department of the History of Technologyxxxiv – Cultural Heritage Agency of the Netherlands (culturalheritageagency.nl and cultureelerfgoed.nl) – Bridges: Nederlandse Bruggenstichting (www.bruggenstichting.nl) – Water Towers: Nederlandse Watertoren Stichting (www.watertorens.nl) – Pumping Stations: De Nederlandse Gemalen Stichting (www.gemalen.nl) – Stichting Bouwhistorie Nederland (www.bouwhistorie.nl) Portugal – Ordem dos Engenheiros Switzerland – Gesellschaft für Ingenieurbaukunst (www.ingbaukunst.ch) The United Kingdom – Association of British Transport & Engineering Museums (ABTEM) (www.abtem. co.uk) – IStructE History Group (www.istructe.org) – Construction History Society (www.constructionhistory.co.uk) – Institution of Civil Engineers (www.ice.org.uk) ◦ ICE Panel for Historical Engineering Works (PHEW) – Newcomen Society (www.newcomen.com) – Association for Industrial Archaeology (www.industrial-archaeology.org) – The Twentieth Century Society (www.c20society.org.uk) – Victorian Society (www.victoriansociety.org.uk) – Georgian Group (www.georgiangroup.org.uk) – Society for the Protection of Ancient Buildings (www.spab.org.uk) – International Committee for the Conservation of Industrial Heritage, UK. United States – Society for the History of Technology (www.historyoftechnology.org)

Activities in Professional Associations Related activities within professional associations including IABSE but outside of this working group should also be noted and mentioned even if they were not part of the survey. xxxiv

The department’s website is https://afdelingen.kivi.nl/geschiedenisdertechniek/PAG000002476/Home.htmlCultural.

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IABSE itself published another SED (no. 12) in 2010, entitled “Case Studies of Rehabilitation, Repair, Retrofitting, and Strengthening of Structures”. Although these examples focus primarily on the details of the repair and strengthening methods, construction history is also a part. The fixed format of the contributions allows for the addition of further examples at a later date in the online version. The fib (International Federation for Structural Concrete, www.fib-international. org) was reorganized in 2015, which resulted in the creation of Commission 3 “Existing Concrete Structures”, currently chaired by Stuart Matthews. The fib Model Code 2010 includes a chapter “Conservation of Structures”, and the planned Model Code 2020 is envisaged to deal extensively with existing structures. Moreover, a task group “History of Concrete” which is chaired by Manfred Curbach as part of Commission 1 “Concrete Structures” is working on a publication.

Overall Evaluation and Summary In order to provide a full overview of the status of construction history around the world—or at least IABSE member countries—the number of responses to the survey sent out by the working group were unfortunately too small. Thus, the overview was augmented where sensible with information available to the working group through other sources. While the questions did not always solicit the intended types of responses, the most obvious conclusion is that there is still quite a way to go to establish construction history and obtain recognition as a field or discipline of academic study. While some countries like the United Kingdom, Spain, Germany, France, Switzerland and the United States have already achieved much in terms of research in the field, by hosting international congresses on the topic, there is still much work ahead to establish the field firmly at universities as is the stated the goal of the society for German-speaking historians. In most countries, however, construction history is not established at all. In fact, the lack of survey responses may point to a general lack of interest by structural engineers in the history of their own profession and its achievements. It unfortunately also indicates that most engineers do not see construction history as relevant to their daily work. Part of the problem may be that construction history is an interdisciplinary field which involves historians, art historians, architects, archaeologists, economists and engineers and often requires knowledge or research not limited to a single field. While art and architecture history has been established for much longer, engineers most often still only show interest in their own profession’s history only once retired as the relevance to current practice is often ignored or misunderstood. However, at least in some countries this seems to be changing. Only recently for example, the Institution of Civil Engineers in the United Kingdom created the Conservation Information Resource for Civil Engineers (CIRCE).xxxv This is a purely online resource intended to help practicing engineers with work on existing structures as this increasingly becomes a part of the portfolio of structural engineers. With major interventions on existing structures becoming ever more common, it is likely that through continued education programs, practicing engineers can be made aware how knowledge of historic construction materials and processes in design and building can benefit the design and planning of those interventions.

xxxv CIRCE is available online freely to everyone at https://www.ice.org.uk/disciplines-and-resources/best-practice/ conservation-resources-for-civil-engineers.

REFERENCES

39

References [1] Becchi A, Corradi M, Foce F, Pedemonte O (eds), Construction History Research Perspectives in Europe (ISBN 88–88,479–11-2), Kim Williams Books: 2004 (available in open access at http://www.kimwilliamsbooks.com/titles/out-of-print-books/97-constructionhistory.html). [2] Proceedings of the Institution of Civil Engineers – Engineering History and Heritage (ISSN 1757–9430). [3] “L’histoire de la construction, Un méridien européen / Construction History, A European Meridian” 2015. [4] Schotte K, Stael D, Nagy W, de Pauw B, De Backer H, Van Bogaert Ph. Structural Assessment of the Integrated Steel Fly-overs Widening the Historic Multiple-arch Concrete Viaduct over the Pede Valley. IABSE Report, vol. 99. 2013; 276–277.

41 Chapter

4 (Re)constructing History—How Building Archaeology Can Profit from the Knowledge of Engineering

Max Johann Beiersdorf, Chair of Construction History and Structural Preservation, BTU Cottbus-Senftenberg, Cottbus, Germany

Introduction When, in 1924, Armin von Gerkan, a German architect with many years of experience in archaeological excavations, first spoke of “building archaeology” as an independent scientific discipline, he placed it on a level with archaeology and its associated sciences (Ref. [1], 9). However, with a lack of institutional structures in Germany, the budding building archaeologist was forced to teach himself and gain the necessary qualifications for his further career through practical activities (Fig. 1). According to von Gerkan, being an architect in itself involves “familiarity with materials and design, the verifiable feeling for structural relationships and an understanding of working practices – even those of previous ages” (Ref. [1], 10). With no training opportunities or structures in the early 20th century, von Gerkan called for a clearer demarcation from other disciplines through the institutionalization of this subject. As early as 1926, von Gerkan’s efforts led to the foundation of the Koldewey Society, the “association of archaeological architects”, which campaigned for the training of young architects in the field of building archaeology in Germany and for participation in heritage conservation issues. Although the training situation for building archaeologists has changed noticeably over the intervening years and is now a separate field of study in Germany, the demands placed on graduates of this subject have changed little. Only the professional field that feeds the discipline of building archaeology now covers a much wider area owing to the master course of study, as offered by several German universities and polytechnics. Whereas in the past building archaeology was exclusively the province of architects, studies in Germany now attract graduates from archaeology, art history, restoration, geography and history in equal numbers, likewise construction engineering and other disciplines with appropriate background knowledge and, last but not least, landscape and interior architects. In other words, building archaeology courses now have a wide appeal and are characterized by greater polyvalence. Opening up this professional field to arts and engineering graduates brings with it enormous advantages because it does justice to the

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modern idea of an interdisciplinary scientific landscape. The current situation for building archaeology leads to heated debates among experts, with the shortcomings in training at the construction history chairs of German universities and the job prospects for young professionals attracting particular criticism2. This situation appears to contradict the fact that building archaeology has always seen itself as an auxiliary science and subdiscipline, which in conjunction with subjects from engineering science and the humanities has the potential to enhance projects involving widely differing issues. A project investigating undulating mud brick walls in Egypt will serve as an example to show the extent to which building archaeology can profit from the knowledge and methods of construction history.

Undulating Mud Brick Walls in Pharaonic Egypt Fig. 1: Student surveying the Castor and Pollux temple in Rome. © Sir John Soane’s Museum, London

The undulating mud brick walls of ancient Egypt date from times between the fourth century BC and the years of Roman rule. They were built to protect the country’s most important temples, and their constructional features and enormous dimensions make them an exception among ancient mud brick wall construction (Fig. 2). They differ from conventional mud brick walls in that they have sections with concave and convex brick courses and do not employ any mortar within the walls, except the outer facade.

Fig.2: The undulating enclosure wall of the Amun-Re precinct in the Karnak Temple Complex

UNDULATING MUD BRICK WALLS IN PHARAONIC EGYPT

43

Auguste Choisy (1841–1909), a French engineer and historian of architecture, was one of the first to attempt an explanation for the undulating appearance of the walls. He ruled out that the wavy shape of the walls is the result of brickwork settlings due to a weak or wet subsoil. Instead, Choisy suggested that it prevented the panels from shifting. In his opinion, the organization of a construction site could be crucially optimized by this technique (Ref. [3], 34–37). During the years 1907–1909, Walter Honroth investigated the undulating enclosure wall of the Temple of Chnum in Elephantine and proposed, according to Choisys idea, that the concave segments were raised up first and followed by the convex segments in a second step (Ref. [4], 39–42). Structural assessment of the undulating design has been a major theme of research from the late 19th to the middle of the 20th century. This changed from 1962, when Paul Barguet established his doctrine that the characteristic undulating form is an allusion to the primeval ocean Nun, the origin of all life (Ref. [5], 32). In a more recent scientific article, Egyptologist Rosanna Pirelli asked whether the design of the enclosures had technical reasons or rather mythology being the source for their appearance, concluding that the walls gain no structural benefits from this technique (Ref. [6], 77). So, according to Pirelli, the reason behind the wavy form is seen as purely symbolic. Henceforth, there have been two camps: one seeing the design of these walls as serving structural functions and the other, following Barguet, favoring a mythological reading. Contrasting with this, however, a dissertation at the Chair of Construction History and Structural Preservation, BTU Cottbus-Senftenberg (W. Lorenz), postulates a primarily constructional explanation. The work focuses on two main aspects. First, there is to be an investigation of the extent to which the characteristic undulating form of the walls can be explained by the process of their construction. Although omitting the mortar inside the walls certainly speeded up the work, at the same time, however, it weakened the masonry bond. The thesis put forward is that this disadvantage was supposed to be compensated for by forming concave and convex segments7. During construction, the concave segments (type 1) were very likely built shortly before the convex segments (type 2) for structural reasons. Owing to the fact that neither cranes nor scaffolds were used during construction, the materials had to be distributed via ramps. Ideally, the wall segments themselves would have served as ramps, and so the wall was built out of these, piled up, as it were (Fig. 3). The second focus of the study is the structural analysis of a finished undulating wall. The individual bricks of a concave segment slide toward the middle, and so shearing apart of the segments corners is prevented. On the other hand, the convex segments exert pressure on the adjacent concave segments (Fig. 4). This stress state probably lent the walls greater stability despite the lack of mortar.

Fig.3: Potential reconstruction of an undulating mud brick wall built in stages

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CHAPTER 4. (RE)CONSTRUCTING HISTORY

Engineering Science Studies In order to verify the main theses, two in-depth studies are proposed. First, a master thesis in conjunction with the Chair of Statics and Dynamics, BTU Cottbus-SenftenType 1 concave berg, will investigate to what extent the idea of a state of prestress Type 2 resulting from the construction convex process can be confirmed by more Type 1 accurate finite element modeling concave (FEM). This method of computation will enable the sliding behavFig.4: Flow of forces within the concave and convex seg- ior of the mud bricks assembled without mortar to be determined ments of an undulating mud brick wall based on known material parameters. The results can be analyzed by comparing them with calculations for conventionally built mud brick walls employing mortar and horizontal courses. A series of investigations will be carried out together with the Research and Materials-Testing Institute (FMPA) at BTU Cottbus-Senftenberg in order to determine the material parameters required. Especially interesting for the later calculations is the determination of the friction coefficients, the deformation behavior of the mud bricks, the compressive strength, the flexural tensile strength and the modulus of elasticity. The parameters derived will permit a calculation of the stress state in the undulating walls which is much more accurate than can be obtained from literature. The options available to the materials-testing institute and in FEM go beyond those that building archaeology examinations of a structure can achieve and considerably enhance the significance of any statements regarding the possible structural advantages of the undulating walls.

Building Archaeology and Construction History—A Fruitful Cooperation The study of a single undulating mud brick wall purely from the point of view of building archaeology criteria is undoubtedly worthwhile. But combining this with the techniques of construction history, engineering science and archaeology brings about promising synergy effects and, in the end, new findings. In light of this development, the construction history takes on a special role: tracing and understanding design, the process of designing forms the heart of this discipline and, at the same time, the common ground with building archaeology (Fig. 5). Construction history can provide important momentum when it comes to questions regarding not only the constructional nature of a structure, but rather its durability and renewability, also the procurement, processing and use of building materials as well as questions regarding social consequences and the interdependencies of a structure or the conditions under which those structures were built.

45

REFERENCES

• Models of structural behaviour and load paths • Studies of the construction process

• Measuring and documentation • Identification of building phases • Reconstrution Building archaelology

Archaeology • • • •

Prospecting, surveying Excavation Age determination Material analysis

Construction history

Engineering

• Structural analysis • Materials-testing • Ground investigation

Fig.5: Contributions of the disciplines involved in the project and their mutual interactions Seen in the light of increasing specialization, construction history can exploit the full potential of classical studies through an interdisciplinary dialogue with building archaeology and its associated disciplines. This interdisciplinary approach is in no way alien to building archaeology; in fact, it is its quintessential feature. At best, the dialogue with construction history allows it to do justice to Armin von Gerkan’s description once again: developing a scientifically sound feeling for structural relationships and the working practices of previous ages.

References [1] [2]

[3] [4] [5] [6]

[7]

Gerkan A v, & Boehringer E. Von antiker Architektur und Topographie: Gesammelte Aufsätze Kohlhammer: Stuttgart, 1959. Wulf-Rheidt U. Zur Lage der Bauforschung an den Universitäten in Deutschland: Vortrag, gehalten auf Anfrage des Deutschen Archäologen-Verbandes e.V. am 15. Juli 2002 in Greifswald. Accessed 24 March 2016, 2002. hƩp://www.koldewey-gesellschaŌ.de/de/ bauforschung/ulrike-wulf-rheidt.html. Choisy A. L’art de batir chez les egyptiens Rouveyre: Paris, 1904. Honroth W, Rubensohn O, & Zucker F. Bericht über die Ausgrabungen auf Elephantine in den Jahren 1906–1908. ZÄS 1909; 46: 14–61. Barguet P. Le temple d’Amon-Re à Karnak: Essai d’exégèse. Recherches d’archéologie, de philologie et d’histoire 21 Institut francais d’archéologie orientale: Le Caire, 1962. Pirelli R. Once more on Undulating Walls in Ancient Egypt: Mythological Reasons or Technical Requirements? In Egyptological Studies for Claudio Barocas, Pirelli R (ed) Napoli, 1999; 55–95. Beiersdorf MJ. Undulating mud brick walls in ancient pharaonic Egypt. In Proceedings of the Fifth International Congress on Construction History: Chicago 3rd–7th June 2015, Friedman D (ed), vol. 1, 3 vols The Construction History Society of America: Raleigh, NC, 2015; 171–179.

47 Chapter

5 The Many Footprints Left by Martin Bachmann in Pergamon

Josef Steiner, Struct. Eng., Ingenieurgruppe Bauen (until 2012), Mannheim, Germany. Corresponding member of DAI (German Archaeological Institute).

Dedication The architect and architectural researcher Dr.-Ing. Martin Bachmann, since 2006 second director of the german archaeological institute (DAI) in Istanbul, participated in many of the DAI’s archaeological sites in Turkey. Last July, Martin Bachmann died unexpectedly. This article is dedicated to him, to his achievements, and to the many visible traces left by him, particularly in Pergamon.

Building Z on Pergamon’s Acropolis Hill Since 1926, the year the Istanbul Department was founded, Pergamon has been one of the DAI’s largest and most significant excavation sites. In addition to the archaeological excavations and the careful safeguarding of antique buildings in danger of collapse, the institute’s tasks include long-term protective measures for valuable finds, as well as restorations projects that aim to offer visitors at least an impression of the original feel of an antique building. One such project that has been widely discussed among experts is the reconstruction, completed in 1996, of parts of the Sanctuary of Trajan. Situated on the acropolis hill in Pergamon, the sanctuary is visible from a great distance. The project leader at this time Klaus Nohlen reports in Ref. [1]. With Ref. [2], Wolfgang Radt published a comprehensive work on the history, the buildings and the excavators of Pergamon. At the beginning of the 1990s, during excavations to investigate antique housing construction on the acropolis hill, remains were also uncovered of a large, twostory peristyle house. In the north section of the building, excavations revealed very impressive colorful mosaic floors from the time of the Roman Empire, as well as Hellenistic stucco on a hill-facing wall. It was immediately obvious that these extraordinary finds must be protected and presented to visitors in an appealing way. This led to Martin Bachmann’s first large footprint in Pergamon: the new Building Z. Together with Andreas Schwarting, he showed that it was

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CHAPTER 5. THE MANY FOOTPRINTS LEFT BY MARTIN BACHMANN IN PERGAMON

Fig. 1: Building Z in 2004 on the acropolis hill (Courtesy: J. Steiner)

Fig. 3: Well-protected mosaic flooring in Building Z (Courtesy: J. Steiner)

Fig. 2: The impressive interior of Building Z (Courtesy: A. Schwarting)

Fig. 4: Plan of the Red Hall on the large Roman terrace (Courtesy: DAI)

possible not only to be an architectural researcher, but also to develop a relevant, eye-catching concept of modern protective structure and museum architecture (Figs. 1 and 2). On the antique foundations, a clear building structure was created that not only meets “functional and conservation requirements”,3 but also offers visitors a highly impressive feel for the space as they are guided through the rooms on walkways to view the rescued works of art. The walls were mostly constructed from antique stone material; the steel girders of the lightweight roof construction and the slat-like façade elements were manufactured by a local metal worker. The building, inaugurated in 2004, has a similarly dominating position halfway up the acropolis hill as its antique predecessor. An extensive publication documenting the history of Building Z and its valuable artworks was completed by Wolfgang Radt and Martin Bachmann just a few months ago.4 It was during the planning for Building Z that I met Martin Bachmann. Over the last 14  years, this initial contact developed into a cooperation between architect/architectural researcher and civil engineer that was characterized by great mutual understanding. The following is a brief look at some of our joint projects (Figs. 3 and 4).

REPAIR AND CONVERSION OF THE SOUTHERN ROTUNDA NEXT TO THE RED HALL

49

Fig. 5: The area around the Red Hall (Courtesy: DAI)

Repair and Conversion of the Southern Rotunda Next to the Red Hall The original construction on the acropolis hill comes from Pergamon’s Hellenistic heyday in the second century BC. In the Roman period, the focus of construction moved to the flat area at the foot of the acropolis hill. An impressive urban focal point is provided by the Red Hall, constructed as a temple complex by Emperor Hadrian in the second century AD on a 275 m by 90 m terrace designed for the purpose. The main building, an imposing construction unique in Asia Minor, with 2 m thick walls made of small tiles, was first a temple, then a Christian church in Byzantine times, and later became part of the town with houses and an olive factory in the south courtyard. The Red Hall is flanked by two rotundas, with substructures below and topped by half domes. After contemporary construction was discontinued in the 1930s, the DAI was allowed to use the southern rotunda as a depot for finds. At the beginning of the 21st century, comprehensive damage documentation by the DAI led to the introduction of a maintenance project by director of excavations Felix Pirson (Figs. 5 and 6). Fig. 6: Steel construction for the new ceiling above the Roman vaulting (Courtesy: M. Bachmann)

The aim was to repair the damage and to later use the southern rotunda for displaying large and middle-sized finds. The project lead was Martin Bachmann. I met with him on site in December

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2005 to discuss the next steps toward solving the problem. The damage to the antique substructure ceiling in the rotunda was serious. This ceiling consists of mushroom-shaped rounded vaulting with a central pillar and a generatrix in the shape of a quarter-circle. The vaulting is made mainly of Roman concrete, is extremely delicate at its upper outside edge with a thickness of only 180  mm, and rests horizontally on the ring-shaped, 2  m thick surrounding wall. About a third of this thin outside area of the vaulting had collapsed, due to Fig. 7: Completed new ceiling in the south- the weight of heavy finds. We soon agreed that the use of modern methods, for example gunned ern rotunda (Courtesy: M. Bachmann) concrete, would not appropriate for an antique element. In addition, the aim at antique excavations is always to use simple building methods, to deploy local craftsmen and to keep costs, for example for special building techniques, at a minimum. My proposal to leave the antique ceiling in its current state, only stabilizing its damaged edge while creating a new level with a 300 mm space in between, met with general agreement. In 2006, a new depot was created in the crossvaulted substructure adjoining the rotunda to the south, where the many finds could be stored. The Fig. 8: Rotunda following restoration at uprights and beams of the supporting structure the time of the work on the large support- with a mono-pitched roof are also elements of the heavy-duty shelving in the interior, and for ing figure (Courtesy: J. Steiner) the façade, Martin Bachmann again turned to the slatted construction used at Building Z, which is clearly visible from the Red Hall. Once the surface of the mushroom vaulting had been cleaned, the new ceiling in the rotunda was constructed in summer 2007. Constructed to handle a live load of 10 kN/m2, the ceiling consists of a central foundation, a steel construction set on it consisting of six steel profiles arranged in a star formation and resting on ledges in the surrounding wall, and of cross profiles to shorten the ceiling span. Bonded anchors were welded on to lost shuttering made of steel sheets. Then it was reinforced and the power-trowelled concrete slab was cast on to it. The ceiling is edged by sheet metal around its perimeter with a gap of 50 mm from the antique wall, such that it might give the impression of a floating plate, as the six supporting beams in the surrounding wall are not immediately obvious. An opening has been left in the damaged part of the antique vaulting that allows visitors to view or walk round the lower floor with its ring-shaped antique vaulting (Figs. 7 and 8). The next job was to repair the damaged exterior wall facing the courtyard, and the dome over the rotunda. The wide crack in the wall and its direct continuation in the dome had occurred because where the ring-shaped antique wall straightened at the point of transition to the courtyard, the thickness of the wall was reduced by about 50%, thus creating a predetermined breaking point in the supporting structure. At the thinnest point in the supporting structure, therefore, a single

MAINTENANCE OF RETAINING WALLS ON THE ACROPOLIS HILL

51

wide crack appeared early on. The same can be seen in the northern rotunda, which is used as a mosque. We agreed that this ancient crack did not present a danger to the dome and that there was no need for any complicated repair work. The surface of the dome was cleared of a thick layer of soil and protected with lead sheeting. For more details, see Ref. [5]. In the last few years, we also worked to close the gaps in the cross-vaulting of the substructure under the terrace, which adjoins the rotunda.

Assembly of a Monumental Supporting Figure Next to the Red Hall The courtyards between the Red Hall and the two rotundas were originally partially covered by angled or U-shaped roofing. On the courtyard side, the architraves under the beams of the roof construction did not rest on pillars, as would normally be the case, but instead on monumental supporting figures in the form of human figures of white marble with arms and heads in dark marble. The discovery of well-preserved fragments led to the decision to reassemble a supporting figure for which a large part of the original material was still in existence. This reassembled figure would give visitors an idea of the size of such a sculpture and of the enormous space under the former roof and the impressive sight of the Red Hall. To guarantee the structural stability of the 8 m high supporting figure in the face of wind and earthquakes, the individual components—in spite of their great weight—had to be well connected to each other. To do this, we used threaded stainless steel rods and composite mortar. The supporting figure was completed in 2013 and is an additional attraction for tourists on the Red Hall terrace, who all too often are hustled past the Red Hall and straight to the acropolis hill by their tour operators. The particularly generous support for the Red Hall project that was provided by the Studiosus Foundation needs to be mentioned at this juncture. The anchoring material for the assembly of the supporting figure was provided by Fischer company (Figs. 9 and 10).

Maintenance of Retaining Walls on the Acropolis Hill

Fig. 9: The supporting figure on completion (Courtesy: M. Bachmann)

In view of the settlement of the Acropolis Hill, it was necessary to divide the area into terraces that were realized by erecting retaining walls. These walls, approximately 1–1.5 m thick and up to 8 m high, are built using multiple leaf masonry. Using standard geotechnical procedures, their stability can be verified only with unrealistically high soil friction angles and cohesion values. Due to their heavy self-weight, many of them have withstood

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CHAPTER 5. THE MANY FOOTPRINTS LEFT BY MARTIN BACHMANN IN PERGAMON

the horizontal pressure of the soil for many centuries, to which they are subjected even when the cohesion and friction values are high. But several of the walls have collapsed, and from time to time partial collapses still occur today, whether due to a change in soil pressure, or due to the effects of water from the slopes, or a combination of both. Below Building Z on a large terrace is the upper Gymnasium, the site of the final large project initiated by Martin Bachmann. The damage to the retaining walls there showed that very few header bricks had been provided between the two outer masonry leaves. For walls with this kind of masonry, however, these header bricks are of great importance, because they increase considerably the stability and thus the collapse load. As the craftsmen repaired the damaged areas, we consistently ensured that header bricks were added. The multiple leaf masonry in walls that looked unsafe but had not yet collapsed were Fig. 10: Restoration of the annular retain- also linked by drilling into them and adding steel ing walls between the Odeon and Building rods that were cemented in. This improved their Z (Courtesy: J. Steiner) stability. We decided—not only for financial reasons—to forego the use of soil clamps or other civil engineering techniques such as prestressed ground anchors. What is more, in preparation for such measures it would first be necessary to perform comprehensive geotechnical investigations to determine the geotechnical characteristics of the soil behind the walls.

Anastylosis of a Palaestra Corner in the Gymnasium

Fig. 11: 3D model of the planned reconstruction of a corner of the Palaestra (Courtesy: DAI)

The large area of the upper terrace of the Gymnasium lies about halfway up the acropolis hill, but hardly attracts any visitors. To redress this imbalance, the Pergamon excavation decided in 2012 to initiate an ambitious project. The main focus of the project is the reconstruction of the northwest corner of the Palaestra directly in front of the Odeon. The idea is to exemplify the development in height of this former hall-like peripheral development from the Roman period. A basic foundation for such a reconstruction is the existence of a minimum of 70–75% of the original antique structural components. Figure 11 shows a computer-developed model of the reconstructed Palaestra corner made of existing antique and supplementary structural components. The completed Palaestra corner will be 12 m high (Fig. 12).

REFERENCES

53

The building site equipment includes a gantry crane that can carry loads of 10 ton. Due to the difficulty in accessing the building site by transport vehicles, the weight of the individual parts of the crane had to be limited to 100  kg. A reliable metal worker in Bergama made the components and assembled the crane in autumn 2014. With the lifting of the 8 ton corner pillar with a heart-shaped cross-section, it has already passed its first test. Due to its excellent stability, this pillar is the main supporting element of the strucFig. 12: Gantry crane for the reconstruction of the ture. However, for the final proof of Palaestra corner (Courtesy: J. Steiner) stability, a structural and dynamic analysis is required, using a suitable spatial framework program. This is currently being completed under the supervision of Prof. Gerhard Eisele at Potsdam University in the form of a master’s thesis. This project was close to Martin Bachmann’s heart. He fought for it to be realized, as a member of the DAI committee, following the fundamental conservation requirements. Financial support for the project is provided by the Studiosus Foundation, but additional external funding will be required to complete the project. With the tragic death of Martin Bachmann, the project may have lost its leader and its impetus, but Felix Pirson, the director of the Istanbul Department of the DAI, and all those involved intend to continue the work as Martin Bachmann would have done, and complete the project as planned.

Final Remarks The footprints left by Martin Bachmann in Pergamon have become a broad path. He was involved in particular in preserving the historic wooden houses in Istanbul, and when he talked about his research in Oenoanda, you almost had the impression that he was making the stones talk. Martin Bachmann was an excellent advocate of practice-based architectural research, had comprehensive knowledge of the construction of antique buildings, and favored pragmatic decisions. Architectural research and the DAI have lost one of their best people.

References [1] Nohlen K. The partial re-erection of the Temple of Trajan at Pergamon in Turkey. Convers. Manag. Archaeolog.. Sites 1999; 3(1&2): 91–102. [2] Radt W. Pergamon: Geschichte und Bauten einer antiken Metropole, Radt W, Bachmann M (eds) Wissenschaftliche Buchgesellschaft: Darmstadt, Special Edition 2011. [3] Bachmann M, & Schwarting A. Pergamon Bau Z, Schutzbau über römischen Mosaiken Universitätsverlag Eckhard Richter & Co.: Dresden, 2005.

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CHAPTER 5. THE MANY FOOTPRINTS LEFT BY MARTIN BACHMANN IN PERGAMON

[4] Radt W, & Bachmann M. Bau Z in Pergamon, Architektur und Wanddekor Verlag de Gruyter, 2016. [5] Bachmann M, & Steiner J. Erhalt und Instandsetzung mit einfachen Mitteln: Der südliche Rundturm der Roten Halle in Pergamon. Die Bautechnik; 90(9): 593–601.

55 Chapter

6.1 The Building A of Radio Kootwijk—A Concrete Building from 1920, Ready for the Future

Erik Vianen, Struct. Eng., Phd; Vianen Bouwadvies bv, Nuenen, The Netherlands Ron Spaan, Struct. Eng., Spaan Erfgoedadvies, Doetichem, The Netherlands

Historical Context The buildings of Radio Kootwijk were developed to establish independent contact with overseas foreign countries by the Dutch Government. During World War I, it became clear that independent contact was important. Therefore, in 1918 it was decided to build this facility in a remote location in the Netherlands, away from any existing cities. Since its construction, Radio Kootwijk has been at the center of radio communication for over 75 years (Fig. 1).

Architectural Design After the decision by the Dutch Government in June 1918, Maria Julius Luthmann was appointed as the architect for the buildings and surrounding area. The young architect designed the buildings in coproduction with Gesellschaft für drahtlose Telegraphie Telefunken. The ground plan of the broadcasting building was prescribed by the technical installation. Besides the ground plan, the need for fire resistance was an important aspect considered in the design of the building. The new building material, reinforced concrete, was chosen for the construction. Luthmann designed the Kootwijk broadcasting building keeping in mind a previous broadcasting building, the Nauen project and used more reinforced concrete in the design (Figs. 2 and 3).

Structural Design Dr. ir. Jan C. Emmen, who had graduated with specialization in reinforced concrete in 1915, was the structural engineer for this project. During the design of the broadcasting building, Jan Emmen had to incorporate the requirements of the Telefunken, which heavily influenced the final design. These requirements were:

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CHAPTER 6.1. THE BUILDING A OF RADIO KOOTWIJK

Fig. 1: Exterior of Building A in 2015

Fig. 2: Ground plan, 1920

Fig. 3: Cross-section of Building A, 1920

1. The roof structure should not be above 14.50+P, and the maximum height of the trusses would be 13.50 m. 2. The inner mold should be a large open area within which a 15 ton crane with a 20 m span could be operated. 3. The reinforcement at the top of the structure should meet the minimum requirements. With these requirements in mind, Jan Emmen designed the concrete structure of the broadcasting building. The structure was divided into four sections, using vertical dilation joints in the building from the top until the foundation. This created four separate structures: a tower with rooms at the front, a broadcasting hall (two sections) and a rear façade with additional areas. The building with the separated structures is able to minimize the effects of shrinkage and temperature differences.

The Tower The concrete structure of the tower is an open structure with the columns at the corners of the tower as the carriers. The dimensions of these columns turned out to be large because of the stability forces. The arch structures of the roof form a combined structure with the columns. During the first test period with the Telefunken installation, the reinforcement of the concrete experienced high electric induction. To prevent further influence of high temperature on the reinforcement, copper plates were used in the room to create a Faraday cage.

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USE IN 21-CENTURY

Broadcasting Hall The concrete structure of the broadcasting hall was built with three-hinge frames. The design calculations turned out to be laborious for Jan Emmen, as he did them all manually. To simplify the work, he calculated only the symmetric loads for the reinforcement of the frames. To support the perpendicular frames, the support beams of the roof were used (Fig. 4).

The Rear Façade The concrete structure of the rear façade is formed with columns that are clamped to the foundation, detached from the broadFig. 4: Interior of broadcasting hall in 2012 casting hall structure. This creates the flexibility for the temperature differences in the broadcasting hall structure. The supporting areas are simple concrete structures.

Realization Realization of the building started on 16 June 1920 by Braat Delft and Internationale Gewapend Betonbouw I.G.B. Breda. As the building was located in a remote undeveloped area, temporary access (rail)roads were provided for delivering equipment and material. Temporary housing was also necessary. Local sand and gravel were used in the concrete structure. During a short period of preparation, work was started on the foundation. After completion of the basement, plans for the underground cable network were changed; therefore, the basement was filled with sand. One year after the first concrete casting (9 August 1920), Building A was ready (16 August 1921). The exterior of Building A has a characteristic look by virtue of the chiseling of the concrete structure’s surface. By chiseling the concrete surface, it was possible to hide the wooden boards used in the structure. The chiseling however created the possibility of developing hairline cracks in the building. To avoid corrosion of the reinforcement, a 35 mm concrete cover was realized. An additional effect of this uneven surface was the growth of moss and algae. The final concrete surface would stand for a long period of time, till a rebuilding during 1958–1961. The three years of remodeling gave Radio Kootwijk a modern look. The construction company used concrete spraying equipment, which sprayed 20 mm of concrete on all exterior walls. The old concrete casting lines and hammered surface were thus replaced by a sleeker look with fine-grained surface.

Use in 21-Century On 31 December 1998, use of the building came to a formal end. In the period till 2010, different studies for new uses were carried out. The building has now become a national monument, which makes putting it to new use difficult, considering its value as a monument. Between

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2011—2013, restoration of the tiled floor was conducted, and also an elevator for disabled people within the existing structure was constructed. The elevator is located close to the foundation of a tower column, and the lift pit is connected to this foundation. After an investigation of the concrete structure of the building, it was concluded that the concrete, created almost 95 years ago, is still in very good condition. In spite of the limited experience and knowledge of reinforced concrete during the building period, the structure is still in good condition and the building capable of standing for a long period of future use.

The Intervention Concept After 85 years of service with the KPN, Koninklijke PTT Nederland (Royal Dutch telecommunication company), in 2004 Building A was transferred to the DLG Dienst Landelijk Gebied (Service Rural Areas). The DLG maintained this building for five years until 10 December 2009, when Staatsbosbeheer (Federal Forestry Services) took over ownership and management. Staatsbosbeheer and three other government authorities—the RCE, Rijksdienst voor Cultureel Erfgoed (Federal Service Cultural Heritage), the province of Gelderland and the community of Apeldoorn—confirmed their intention to realize the restoration following the Fig. 5: View over the area in 2016 (courtesy: Jan principles of cultural heritage as described van Dalen) in the document “Hallo Bandung…, Hier Radio Kootwijk” (Fig. 5). At the moment, both internal and external work has been done for Building A and its two annexes. The external work concerned the replacement of the roof and the cleaning and repairing of the crystal cement granite outer wall. The internal work includes restoration of the tile flooring in the radio hall, repainting the colors of the walls back to the original and installing an elevator to provide disabled people access to the radio hall. Additionally, several other rooms were restored and optimized for new use as well. The restoration process is being coordinated by R. Spaan. A long period of investigation and realization were done under his supervision, with support from architect Jan van den Burg. Analysis for implementing the elevator and required modifications to the reinforced structure were done by E. Vianen. Building A is now ready for its new future and visits can be planned or arranged. Also, events like concerts, symposia and exhibitions take place and have found a great platform in the radio building.

Into the Future The buildings, created almost a century ago, stand tall and can still be used for a long time without any serious modifications. During the use of the buildings, there have been many external influences, which include demolitions during World War II. Despite the limited knowledge of

REFERENCES

Fig. 6: Interior in 2015

59 the designers about reinforced concrete structures, this building will stand the test of time in future. Therefore, it is a great tribute to the structural engineer Emmen. With the recently executed restoration, the building is now equipped for future long-term use. By changing the surrounding area into a public domain, the building is also more accessible. Therefore, the former closed character is over. The building is open on special days for the public; on other days, the building is in use for concerts, symposia and exhibitions (Fig. 6).

References [1]

Spits P. Radio Kootwijk, monument in gewapend beton, ISBN 978-90-75365-92-4 Aneas: ‘s-Hertogenbosch, 2008. [2] Emmen IJ. De werken in gewapend beton voor het station voor draadloze telegrafie op het Kootwijksche Zand. De Ingenieur 1923; 12: 213–237. [3] van der Pluijm C. Radio Kootwijk. Biografie van een zendstation en een dorp in het hart van de Veluwe BDUMedia: Barneveld, 2014 ISBN 9789087882167.

61 Chapter

6.2 Marina City—The History and Restoration of an Iconic Facade

John F. Duntemann, Senior Principal; Brian R. Greve, Associate Principal; Wiss, Janney, Elstner Associates, Inc., Northbrook, Illinois, USA

Introduction The twin towers of Marina City were the tallest reinforced concrete buildings in the world when they were completed in 1962. The design and construction of Marina City was an important milestone during the evolution of concrete high-rise construction during the mid-20th century, and the unique modern design served as a model for mixed-use developments that is still employed today. The construction of the towers utilized innovative design and construction techniques. Significant concrete deterioration was identified on the facade in the 1990s, and repairing these conditions on a high-rise building in a dense urban setting presented unique challenges. This paper reviews the history of the design, construction and restoration of these iconic towers.1

Design Marina City in Chicago was designed by Bertrand Goldberg Associates. The twin high-rise towers are part of a mixed-use complex that consists of five distinct structures including the towers, a 10-story office building and a theater building. Described as “the City within the City”, the complex originally included residences on the upper portion of the towers, a parking garage on the lower floors of the towers, an office building, a marina, a theatre, an ice skating rink, a bowling alley, restaurants and retail space. While common today, this mixed use of residential, office and retail with parking was an innovative concept in urban planning when Marina City was built. Figures 1 and 2 are ground-level views of the Marina City complex and towers, circa 1964–1965 and today. The towers are 63 stories tall (178  m) and were the tallest reinforced

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concrete buildings in the world when they were completed. Each tower has three plaza levels that connect the buildings, 19 parking levels with 896 parking spaces, and 40 residential levels that contain 896 apartment units. The circular design utilizes an innovative structural center core surrounded by two concentric rings of columns and 16 radial floor beams extend from the core to the exterior columns, and curved cantilevered balconies extend out from each column.

Construction Construction of the towers began in 1960 and was completed between 1963 and 1964. The tower foundations consist of reinforced concrete caissons drilled to a depth of 35  m. Three concentric rings of caissons were used to support the core wall, inner columns and outer columns. The concrete core is supported on a central ring of eight caissons, and the core was cast utilizing a high-strength conFig. 1: View of Marina City circa 1964–1965 crete mix design that provided sufficient strength in 24 h to support continued concrete placement above.2 The core construction advanced much faster than the floors as shown in Figs. 3 and 4. The innovative construction utilized curved fiberglass forms, which were continuously reused to increase the speed and ease of assembly. The formwork, reinforcing steel and concrete placement were completed in one day on each floor. The work crews alternated between each tower to pour a new floor every two days. Figures 5 and 6 show the floor construction in progress. Concrete was delivered to the site by trucks and lifted by tower crane to each floor level. A specially designed electric conveyor belt system was used to distribute the concrete on each floor.2 In addition, lightweight concrete was utilized for the beams and floors.

Evolution of Concrete High-Rise Design The first concrete high-rise building constructed in the United States was the Ingalls Building in Cincinnati, Ohio. The Ingalls Building was completed in 1903 and was 15 stories tall. However, following the construction of the Ingalls Building, many high-rise buildings were constructed using steel, and few concrete buildings exceeding 20 stories were constructed until approximately 1960. The Marina City towers were the tallest reinforced concrete buildings in the world when they were completed in 1962, and their construction renewed interest in using reinforced concrete for high-rises. The use of concrete for tall buildings was initially

EVOLUTION OF CONCRETE HIGH-RISE DESIGN

63 limited due to challenges related to the delivery and placement of the concrete. The concrete used for the Ingalls Building was mixed on-site. The ready-mix industry began using revolving-drum mixer trucks in the 1930s, which significantly improved concrete delivery by avoiding remixing of the concrete once it arrived on-site. Trucking technology continued to improve and the ready-mix industry expanded significantly in the 1940s and 1950s in the United States. However, placement of large quantities of concrete remained a challenge until mobile hydraulic pumps were developed in the 1960s, and the technology continued to improve.3

Fig. 2: View of the towers in 2015

Fig. 3: Concrete core construction

As the delivery and placement methods improved, concrete material options also advanced. The use of lightweight concrete was particularly attractive for use in high-rise building construction. The additional material cost of lightweight concrete is partially offset by the reduced weight and related cost savings for the columns and foundation. The development of high-strength concrete also allowed for smaller column sizes in high-rise buildings, which increased the usable floor space. As the concrete delivery, placement and materials improved, structural engineers developed a variety of structural systems to utilize concrete in high-rise construction. The Ingalls Building utilized a beam-column frame system with a two-way floor slab system. Shear walls were introduced in 1940 and typically utilized a center core wall to resist lateral loads. A combined system called a shear wall-frame interaction system was a significant development in the design of tall concrete buildings. This system utilizes a combination of a central core or shear walls with the beam-column or slab-column framing in the building.3 The circular center core of Marina City serves as a shear wall and was designed to resist seventy percent of the lateral load. Following the completion of Marina City

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Fig. 4: Shoring of the concrete floor slabs in 1962, continued innovation resulted in the construction of many concrete highrises. Fazlur Khan of SOM developed the framed tube structural system in the 1960s. The tube structure utilizes the three-dimensional framework of the entire building to resist lateral loads. The development of these structural systems was a key component that facilitated the design of tall concrete structures. The DeWittChestnut Apartment building in Chicago was completed in 1965. This building is the first known building engineered by Fig. 5: Floor slab construction Khan as a structural tube. Khan went on to develop additional variations of the tube concept including the tube-in-tube system. The Brunswick Building in Chicago was completed in 1965 and has a tube-in-tube system consisting of a framed tube with an internal shear wall. Water Tower Place in Chicago was completed in 1975 with a height of 262 m. The structure consists of a reinforced peripheral framed tube with interior steel columns. The One Magnificent Mile building in Chicago was completed in 1983 and was one of the last buildings engineered by Khan. This building utilized a concrete bundled tube system, similar to the steel system used for the Sears Tower.3 The mass of a reinforced concrete structure is a significant advantage in high-rise building construction due to its increased stiffness and vibration damping characteristics. The increased stiffness and damping help reduce building motion to make building movement less perceptible to the occupants. Concrete is still the material of choice for many tall, slender towers.

FACADE DETERIORATION AND RESTORATION

65

Facade Deterioration and Restoration Significant concrete deterioration was identified on the facade of the Marina City towers in the early 1990s. An investigation revealed that the concrete had a high chloride content, which contributed to the corrosion of the reinforcing steel which, in turn, caused cracking, delamination and spalling of the concrete. The source of the chloride was from the chemical admixtures used to achieve high-early strength and accelerate construction. Major concrete repairs were performed on the facade and balconies at that time, and in some cases, extensive full-depth concrete repairs were required as shown in Fig. 7. The demolition and repair work Fig. 6: Placement of concrete floors was performed using suspended scaffolding. The repair areas were sandblasted prior to concrete placement to clean the reinforcing steel, remove surface contamination and roughen the concrete surface. The reinforcing steel was coated with an epoxy paint to inhibit future corrosion, and supplemental reinforcement was installed where required to anchor the repair areas. Polymer-modified concrete was utilized for the repair areas. The advantages of polymer-modified concrete include low permeability, good bond to prepared concrete surfaces and increased Fig. 7: Extensive concrete repair on balcony slab durability. The polymer-modified concrete was mixed on-site and placed in formwork installed on the building facade. Following the completion of the concrete repairs, waterproofing membranes were applied to a portion of the balconies and an architectural coating was reapplied to the facade to reduce the moisture content of the concrete, thereby reducing the ongoing corrosion of the embedded reinforcement. The facade repair project presented many challenges including suspended scaffolding (swing stage) access and difficult debris control. The commercial property below including the restaurant, hotel, theater and parking garage were open for business throughout the repair project. Extensive canopy protection was required to permit the continuous use of the commercial property below as shown in Fig. 8. Several additional facade repair projects have been performed since the initial repair project was completed in 1991; however, the amount of concrete

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repairs required has been significantly reduced. The concrete repair work and application of waterproof coatings has significantly reduced the rate of concrete deterioration and the amount of repairs required, thereby preserving this important architectural and structural engineering landmark.

Conclusions The high-rise towers of Marina City are iconic structures that represent an innovaFig. 8: Canopy protection at the base of the towers tive and durable architectural and structural design. The efficiency of concrete repairs and application of waterproof coatings have preserved the structure and extended the useful life of these iconic buildings.

References [1] Duntemann J, Greve BR. Marina City—The history and restoration of an iconic façade. Proceedings, IABSE Conference—Structural Engineering: Providing Solutions to Global Challenges, 23–25 September 2015, Geneva, Switzerland, 2015; 482–483. [2] Marjanovic I, & Ruedi Ray K. Marina City—Bertrand Goldberg’s Urban Vision Princeton Architectural Press: New York, 2010. [3] Ali M. Evolution of concrete skyscrapers: from Ingalls to Jin Mao. Electron. J. Struct. Eng. 2001, 2001; 1(1): 2–14.

67 Chapter

6.3 Rehabilitation of the Complex Reinforced Concrete Shell Roof Structure of an Industrial Building

Alexander Traykov, Struct. Eng., and Prof., University of Architecture, Civil Engineering and Geodesy, Sofia, Bulgaria

Brief Description of the Presented Case Including Project Aims and Challenges This case study presents the investigation and design of the rehabilitation of a storage structure for the cement industry and in particular of its roof. The storage was designed and constructed within a two-year period between 1956 and 1958 as part of a cement plant in the northern part of Bulgaria. The storage is approximately 500 m long and is divided into seven separate structures (indicated as blocks in the following text) by expansion joints (Figs 1 and 2). The main structure is a single-span frame in transverse direction and multiple-span frames in longitudinal direction. The structural span width in transverse direction is 33 m, and the span width in longitudinal direction is generally 6 m. The roof structures of three of the storage blocks are steel trusses with a cover made of trapezoidal steel sheets. The roof of the other blocks is a reinforced concrete (RC) shell structure. The RC shells span 33 m in transverse workshop direction and 6 m in the longitudinal direction. The shell structure is thin, elegant and unique for Bulgaria. It represents efficient implementation of the theoretical advantages of shell structures. The shell is divided by means of RC arch ribs supported by steel elements (two channels of 180 mm) for resisting the tension in transverse direction at each column position. The shell is additionally divided by secondary beams/ribs in the longitudinal direction in order to increase the stiffness and to minimize the shell thickness. These beams are considered as the final transverse rib of the shell. The storage has been operational for decades without need for additional maintenance during the long period of use. Material corrosion and structural damages caused mainly by crane operation have deteriorated its condition and have raised a reasonable question about the structural safety and reliable behavior of the structure. A team led by the author of the present study carried out an extensive investigation of the storage structure. It included visual observation, laboratory testing of the materials both on site and on samples, and computer modeling of the entire structure and its parts. Calculations and design checks were carried out according to the

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Fig. 1: General view of the building

Fig. 2: Sections of the roof present-day codes that are valid in Bulgaria. Even so, the roof structure theoretically displayed perfect behavior. That behavior contrasts sharply to the real condition of the roof. The designers team considered two options—to replace the RC shell roof by means of steel trusses or to preserve the original roof structure. The owner chose to preserve the original structure. An investigation that involved collecting specific details for rehabilitation of the main elements—shell, joints and beams—was carried out. The design was adequate and followed the main principles of sustainable engineering and construction, preserving a structure of historical value, obtaining economic advantages and protecting the environment.

Influence of CH Analysis Results on the Project during the Assessment Phase and in the Design of the Intervention If the importance of construction history (CH) must be considered in the decision of intervention procedures, the period of construction of the particular structure as well as the main ideas behind the use of the structure’s type must be taken into account. A comprehensive review

CHOICE OF STRENGTHENING METHOD

69

of the theory, modeling, construction and use of various types of shell structures is presented in Ref. [1]. The application of a particular type of shell structure built of specific material is considered as a result of complex influence of historical, social, scientific, technological and economic factors. Different aspects of the construction history of roof shell structures are studied in Refs. [2–4]. Different aspects of the modeling, calculations and investigation, including academic, of specific shell types are presented in Refs. [5,6]. There are also a number of studies on the rehabilitation of concrete shell structures—see for example Refs. [7–10], some of them with a lot of references to other works.

Project-specific Experiences and Lessons Learned As discussed in Ref. [3], the construction of thin shell concrete structures ended abruptly at the end of the 1970s. One reason was the higher cost in comparison with other structural systems. The other reason was the theoretical uncertainties about the structural behavior of the shells. However, computational methods and the efficient development of software allow engineers to model the structural behavior of shell structures in a very realistic way, including the material and geometrical nonlinearities. Those developments, as well as the developments in concrete technology and innovations in relation to its materials, have given new life to the idea of constructing new shell structures and rehabilitating existing concrete shell structures. The most important lesson learned is that it is possible to extend significantly the life of concrete shell roofs taking advantage of their perfect static behavior. That could be achieved by means of using materials and construction methods that comply with the original idea of their design.

Choice of Strengthening Method Significant efforts were devoted to study the construction period of the roof, its structural type and construction material (Fig. 3). Plenty of information was collected in order to choose the most appropriate techniques for strengthening. Different options were considered, including the replacement of the original RC shell structure by means of steel frames roof. Innovative methods, some of which are presented in Refs. [7, 8], were studied as well. In those works, the application of innovative strengthening method using textile RC is described. The method consists of applying three layers of finegrained concrete and textile carbon fabric, adhering to a rough, sandblasted concrete surface. However, strengthening by using any kind of fiber-reinforced plastic (FRP) fabric was not approved because of the large area that is necessary to be rehabilitated and the greater requirements during the construction. Considerations about the maintenance included the risk of any damages to the structure as well, for instance the provision of waterproofing on top of the structure. Fig. 3: The roof from inside the building

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Computer modeling of the entire storage building and a separate model for the roof alone were created by means of SAP2000 software. The results reveal the amazing behavior of the roof. The bending moments in the shell structure are practically zero for vertical loading due to selfweight, dust and snow. The above considerations led to the choice of a most “classic” method for reinforcement, which appeared most suitable for the project. A layer of small-size aggregate concrete with a single rebar mesh on a cleaned and rough surface was applied. Anchoring of the reinforcement mesh to the shell ribs was used for better connection. As a result of the structural investigation and design, a unique structure has been preserved. It combines theoretical achievements realized in a clear and simple structural form. Post the rehabilitation, the storage will be in use for a long period.

References [1] Rutten HS. Forty years of theory, design and construction of thin cells. Heron 1986; 31(1). [2] Booth LG. The design and construction of timber hyperbolic paraboloid shell roofs in Britain; 1957–1975. Constr. History 1997; 13. [3] Peerdeman B. Analysis of thin concrete shells revisited: opportunities due to innovations in materials and analysis methods. Master’s Thesis Report, Delft University of Technology, Faculty of Civil Engineering and Geosciences, Delft, 2008. [4] Ochsendorf J. Engineering analysis for construction history: opportunities and perils. Keynote Lecture, Proceedings of the Second International Congress on Construction History, Cambridge, UK, 2006. [5] Williams Portal N, Lundgren K, Walter AM, Frederiksen JO, Thrane LN. Numerical modelling of textile reinforced concrete. Proceedings of the VIII International Conference on Fracture Mechanics of Concrete and Concrete Structures, FraMCoS-8, Spain, 2013. [6] Galant JAL . Cylindrical thin concrete shells. Master of Science Thesis, KTH, Stockholm, Sweden, 2009. [7] Ortlepp R, Weiland S, & Curbach M. Rehabilitation and strengthening of hypar concrete shell by textile reinforced concrete. In Excellence in Concrete Construction through Innovation, Limbachiya MC, Kew HY (eds) Taylor and Francis Group: London, 2009 ISBN 978-0-415-47592-1. [8] Weiland S, Ortlepp R, Hauptenbuchner B, Curbach M. Textile reinforced concrete for flexural strengthening of RC-structures—part 2: application on a concrete shell. Special Publication, DOI: 10.14359/20149, 2008. [9] Brühwiler E, Denarie E. Rehabilitation of concrete structures using ultra-high performance fibre reinforced concrete. UHPC-2008: The Second International Symposium of Ultra High Performance Concrete, Kassel, Germany, 2008. [10] Meleka NN, Safan MA, Bashandy AA, & Abd-Elrazek AS. Rehabilitation of elliptical parabolic reinforced concrete shells with openings. Asian J. Civil Eng. (BHRC) 2013; 14(6).

71 Chapter

6.4 Maintenance and Strengthening of the Timber Roof Elements in the Church of St. Dimitar

Marina Traykova, Prof., PhD, Struct. Eng., University of Architecture, Civil Engineering and Geodesy, Sofia, Bulgaria Doncho Partov, Prof., PhD, Struct. Eng., University of Structural Engineering and Architecture, Sofia, Bulgaria

Brief Description of the Presented Case, Including Project Aims and Challenges Saint Dimitar is a Bulgarian Renaissance church (Fig. 1). It is located in the eastern part of Kuystendil city. It was built between 1864 and 1866 through the initiative of the Kuystendilbased teacher Dimitar Stoyanov-Dimitry and carries the name of Saint Dimitar, Miracle worker of Solun (Thessaloniki). The creator of most of the icons in the church was the famous Samokov-born artist Ivan Dospevski, a representative of the Samokov Art School. The church is a three-nave pseudo basilica. The funding for the construction and decoration of the temple was provided by wealthy citizens, craftsmen, teachers and religious representatives. In 1865, the second school was founded. The initiator and main teacher was Dimitar Stoyanov-Dimitry. Most of the buildings constructed until the beginning of the 20th century in Bulgaria are made of masonry, mainly stone masonry (exterior and some interior walls), and timber elements (floors, roofs, ceilings, interior and some exterior walls). According to Ref. [1], if properly connected, these elements promote good global behavior: the masonry walls support the floor beams and roof trusses, which act as horizontal braces, inducing a more uniform distribution of stiffness and loading throughout the structure. This type of structure is disseminated all over the country and represents one of the most applied structures of Bulgarian heritage buildings, justifying the increasing interest in its preservation as a memory of culture and identity. Unfortunately, most of these structures are seriously damaged and abandoned, requiring urgent interventions.2 In this field, and particularly for old timber structures, many authors, respecting the International charts and ICOMOS,1 recommend techniques using traditional materials such as wood and steel. These techniques, consisting of the addition of timber elements and steel plates, have been applied in the rehabilitation of old buildings with very good results.3 One example is the strengthening of

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Fig. 1: Current view (courtesy: authors) the old timber roof structure of the church St. Dimitar (Kyustendil city, Bulgaria) through techniques using traditional materials, which will be presented in this paper. The church is rectangular in plan, and some of the typical sections are presented in Fig. 2. The roof structure is made entirely of timber elements. Inside, two rows of timber columns, passing through the arch of the roof structure and reaching the inclined beams of the roof of the building, are constructed. On the columns at the level of the floor and above the level of the roof, ceiling beams and longitudinal beams are situated, respectively, bearing the weight of other parts of the roof structure. At the level above the stone walls, two unoccupied galleries with timber floor beams are located. At one end, floor beams are supported by the stone walls (Fig. 2). The inner end of the beams is based on the main longitudinal beam, which in turn is supported on timber columns. Above this level, the timber columns continue (Fig. 2). Above the galleries, columns are united using one purlin, which lies on them at the distances marked on digital axes. The purlins rest on columns by means of a pillow-like bearing. The slope of the roof (32°) is formed with inclined ribs that lie at the lower end on the stone walls. Usually, the main goal for a structural engineer is to improve the load capacity of specific elements, but in the case of timber structures, moisture is one of the most important influential factors for all the physical–mechanical properties of wood, and it creates favorable growing conditions for agents responsible for wood degradations. Wood is highly susceptible to the attack of biological agents (fungi and insects). In analyzing this aspect, it is important to realize that if fungi attacks are linked to the moisture content of the wood, insects can attack in any conditions. According to Ref. [4], the stability of the existing roof timber structure of the church is commonly studied using the general methodology of structural mechanics, the theory of timber structures, the theory of materials applied to the wood and the technology of the timber constructions. The most common causes of failure of timber structural systems are inadequacy of configuration (geometry of the structure, sizing of the members, kind of connection of the members, bracing, etc.) in relation to the both static and dynamic actions, in addition to slenderness, instability, defects of the wood laid in place, severe biotic damages, accidental factors and splits. The strength properties considered in the design of timber elements are related to the bending moment, tensile, compressive and shear forces. Other strength properties, like torsion, creep or fatigue resistance, are less important but may also be analyzed.2 According to Ref. [1], the need for interventions on timber structures is usually related to the existence of damages or alterations of use, increasing the loads. Consequently, in order to ensure safety and simultaneous proper

BRIEF DESCRIPTION OF THE PRESENTED CASE, INCLUDING PROJECT AIMS AND CHALLENGES 73

Fig. 2: Typical cross-sections of the church (design project drawings, 2015) performance of the structure, it is necessary to intervene with regard to the damage of structural elements through rehabilitation. The decision about the type of interventions should be taken only after a rigorous and careful survey of the structure.3 According to the results obtained in the survey and the circumstances of each situation, the intervention for a particular element or structure can take two different paths: rehabilitation or substitution. The rehabilitation of timber structures can be performed using different techniques. When choosing the techniques and materials to be used, there are, among others, two criteria linked to heritage protection that should be respected: compatibility and reversibility. There are many different ways of using traditional rehabilitation techniques in old timber structures, namely (a) the fixation of timber pieces or thin steel plates, with varied configurations,

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to the sides of the element; (b) the introduction of thin steel plates in the interior of the element; (c) the installation of steel belts around the element; and (d) the installation of new structural elements (timber or steel) parallel to the existing elements. Laboratory investigations are usually undertaken to increase knowledge of the efficiency of these techniques and to provide useful information to the designers about the suitability of each technique.1 The use of timber elements in the rehabilitation of old timber structures is a very common solution. On the other hand, Fig. 3: 3D model of the structure solutions with steel elements are commonly used in interventions for old timber structures, particularly for timber floors, leading to an increase in strength and stiffness. Timber structures show a very complicated deformational behavior, mainly because of the viscoelasticity property of wood, due to the nature of the material and the longitudinal position of the fibers.4 Total strengthening of beams can be achieved with or without increasing their transversal dimensions. To change the cross section, new elements of wood or metal are added above, below or laterally to the existing members. When retaining the initial beam dimensions, strengthening involves the insertion of steel profiles, which have a lower height than the actual beam.3 In the considered case study, the rehabilitation of the timber beam supports was performed through fixation with a steel triangle and steel bolts. Anchorage of purlins to the outside wall was recommended using steel plates and steel bolts. Strengthening of the damaged structural element with steel is also achieved using steel plates and steel bolts.3 After the rehabilitation of the supports and the removal of the heavy load from the roof surface, the existing deflections of the purlins were reduced through a system of struts. It was also necessary to partially substitute the damaged elements using prosthesis, with the fixed connection between the new and the existing part of the timber elements using M16 threaded rods and screws.3 Numerical analysis of the timber roof of the church shows the potential of three-dimensional computer modeling and simulation of the building structure. However, how the science of engineering and advanced computer modeling, including finite element method, can be used to increase the understanding of a whole structure is demonstrated, along with how to apply this method for the analysis of historical building structures (Fig. 3).

Influence of Construction History Analysis Results on the Project in the Assessment Phase and in the Design of the Intervention The construction history analysis in this case requires the rehabilitation of the existing building for future use (as a church) while retaining the original structure. The purposes of the project, after the assessment of the structure, are to replace, to rehabilitate or to strengthen the damaged elements with minimal changes to the original position and view.

REFERENCES

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Project-specific Experiences and Lessons Learned 1. This article demonstrated that the failure of the timber structures is very peculiar. The full understanding of the different types of failures of an existing structural system can greatly help to interpret the real behavior. This is the reason the three-dimensional (3D) model is preferred to perform global analysis.5 2. This structure is typical for National Heritage Buildings and is related to the specific peculiarities of the local construction traditions. It is very important to preserve the original structure as evidence of the construction tradition of the region and to continue the history of the place. Special interest in preservation represents the icons in the church. Their high value is related to one of the famous art schools in Bulgaria, the Samokov Art School.

Conclusions The original timber structures represent a very significant part of the historical buildings in Bulgaria. Research on their behavior is the only way to provide the best design details for rehabilitation and strengthening.

References [1] Drdácký M. Historic roofs and timber frames, state of the art studies. Proceedings of the ARCCHIP Work, vol. 4, Prague, 2006; 313–531. [2] Straka, B., Novotný, M., Krupicová, J., Šmak, M., Vejpustek, Z. Konstrukce šikmých střech Grada Publishing: Praha, 2013. [3] Mönck W. Schäden in Holz-Konstruktionen, Analyse and Behebung DDR: Berlin, 1987. [4] Vinař J, & Kufner V. Historické Krovy, Konstrukce a Statika Grada Publishing, 2004. [5] Petkov M. Numerical Model of the Church (Software “TOWER”), 2015.

77 Chapter

6.5 Brighton Pier, UK—Innovation in Renovationi

Nigel Winterbottom, CEng, MICE. Senior Structural Engineer, PM Group, Whiteley, Fareham, UK

Brighton’s Piers The Victorian piers remaining around the coast of the UK are iconic structures that represent more than just the skill of the engineers that built them. After the technical and commercial challenges of originally building the piers, they have often become an integral part of the local community and history. Within harsh marine environments, piers will always require maintenance to contribute to their safety, and managing these costs can be fundamental to the survival of the pier. Today’s engineers play a vital role in helping to sustain these structures. The 537 m long Brighton Palace Pier (now just known as Brighton Pier) was opened in 1899. Designed by Richard St George Moore, the pier also featured cast iron screw piles. It has undergone many changes and events during its life. In 1940, a section was removed as a precaution against enemy invasion in the war. In 1973, during demolition of the landing stage, a barge collided with the pier head, and significant damage was caused. In 1995, a large, piled extension to the pier head was undertaken. The owner, to his credit, has demonstrated a responsible approach to planned maintenance of the pier structure, realizing that this is necessary to ensure viable long-term business on the pier (Fig. 1). Repair work was funded entirely by the private owner and received no public or charitable funding.

The Boat Deck The central Victorian core still retains its cast iron piles and columns, although the bracing and most of the deck structure has been replaced. In the 1930s, an area known as the “boat deck” was added, approximately 35  m by 15  m on plan. A single-story building was added over

i

This essay is based on a paper published in Engineering History and Heritage, which should be consulted for full details in Ref. [1].

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this area, probably around the same time. The 36 columns of the boat deck were rolled steel joists. In the west–east direction, the column-to-beam connections were haunched for stability, whereas in the north–south direction, the frame had cross bracing. At some stage, strengthening of the columns had been undertaken, with plates welded between the flanges to form closed rectangular sections. The area immediately under the pier deck Fig. 1: Brighton Pier; 537 m long (supported by the beams) was in use as a workshop and beer store, accessible by a steel stair to a walkway. A survey of the condition had identified ongoing corrosion of the boat deck steelwork along with missing bracing and poor state of the concrete slab of the workshop. The workshop also had a history of damage from wave impact. One of the piles had been potentially identified as broken at the sea-bed level by a dive survey. The structure of the building above was in a generally good condition. An innovative solution was required to replace piles and substructure while keeping the pier and entertainment buildings above open during the restoration. This was achieved by devising a means of working on existing structural elements under the pier deck.

Concept Design A concept was established to replace the existing boat deck structure while maintaining the use of the building above. To keep the existing building supported, use of the existing structure underneath, rather than any temporary structure, appeared sensible. Although its condition was poor, the existing structure did not show any immediate signs of distress and was considered sufficiently robust in the short term. However, the existing structure itself, particularly given the relatively closely spaced columns, was a significant obstruction to many forms of access and construction. Piling through the roof of the building was not favored as this would require a large-reach marine plant with attendant weather risk as well as disruption to the building use. Piling from within the building would also be far too disruptive. Rather than seeing the existing boat deck structure as an obstruction, a decision was made to view it as an asset. Could it be used to support a temporary working platform under the pier deck? The initial reaction was “Yes”. The structure was already supporting a workshop and beer store (in addition to the building). If these were removed and replaced by a temporary working platform, this would not represent significant additional load. With the Victorian columns at a diameter of 300 mm and the 1990s pier head extension columns at a diameter of 600  mm, this gave a good idea of the likely diameter of new piles and columns. The rotary method that seemed obvious was the Victorian solution of a “screw” pile. The column above could then be fabricated in short sections (to suit the headroom) and spliced together under the pier. To complete the concept design, the columns would be cross-braced, and a grillage of steel beams would be used to support the deck and building above. Finally, the temporary platform and remaining original boat deck structure would then be removed (Fig. 2).

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CONCEPT DESIGN (a) +12.86 mCD

MHWS +6.5 mCD

Horatio’s bar Existing concrete floor

Timber decking and joists on steel support beams

Existing walkway

1990s steel pile MLWN Bed level +2.0 mCD –2.5 mCD typical

Victorian cast iron piles

1930s piles

1990s pier head extension

Original Victorian pier head

1930s boat deck extension

Horatio’s bar

(b)

Temporary working platform

+12.86 mCD

MHWS +6.5 mCD

Bed level –2.5 mCD typical

MLWN +2.0 mCD

400 dia columns in sections

New works (c)

Steel support framework on new columns

Horatio’s bar +12.86 mCD

MHWS +6.5 mCD MLWN Bed level +2.0 mCD –2.5 mCD typical

Abrasion protection jacket to columns

Fig. 2: Construction sequence: (a) existing section; (b) new helical piles; (c) construction complete

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Survey and Investigation Works The client had no record drawings for the boat deck structure or building above. Lack of safe access and the complexity of the existing steelwork meant that conventional surveying techniques were very limited. A decision was therefore made to use a three-dimensional (3D) laser scanning technique. The scanner was placed on a conventional tripod in several positions around and under the structure. The scanner generates a “point cloud” of information, each point being a point on the structure with known 3D coordinates. The information from each location was stitched together to form a cloud for the whole structure. This was then postprocessed to form a 3D computer model of the structure. This process enabled geometry to be determined even in areas where physical access was not possible.

Tender Design Loading: For the ground floor of the existing building, an imposed loading of 5 kN/m2 was used (the same as the pier deck is generally designed for). Current and wave loading was based on a 400 mm diameter column, with an additional allowance of 50 mm for marine growth. As the design life was 50 years, the design allowed for the sea level rise over this period. Nonbreaking and breaking wave loads on the columns were calculated using Morison’s equation as the basis. The total nominal breaking wave load on one column was calculated as 117 kN. Over the 14 m height of the column, the peak load of 11 kN/m occurred at 2 m below the top. The breaking wave load was applied to the first (seaward) row of piles, and the nonbreaking wave load was conservatively applied to the other rows. Analysis: An elastic 3D frame analysis was used to determine load effects in the columns, piles and bracing members. One model was established with column fixity assumed at bed level in order to generate bed-level loads for the subsequent geotechnical pile design. A second model had pile fixity assumed at a depth of 46 pile diameters below the bed, in addition to an allowance of 0.5 m for scour. This model was used to determine load effects for the structural design of the columns, piles and bracing members, as well as to check global deflections. Member design: Although a pile design for tender was prepared, the final design would be the responsibility of the contractor. The contractor would also be permitted to submit alternative tender designs. The tender design was based on a steel helical or “screw” pile. The maximum working load in compression was 1285 kN, with a coexistent moment of 145kNm at bed level. The geotechnical design considered the bearing capacity of the helices or skin friction capacity based on a cylinder equal in diameter to the helix diameter. Seventeen existing building columns that required resupporting had been identified. The columns supported relatively large areas of concrete roof slab. Typical nominal dead loads were in the range of 200–300 kN, and this was similar for imposed loads. Two generic cases required resupporting. The first was where existing building columns were supported by the top of boat deck columns. In this case, short lengths of twin new transfer beams would be welded to the sides of the boat deck columns and would be supported between the new longitudinal beams. In the second case, the existing building columns were supported by existing boat deck beams. Here, the concept was to span a new transfer beam under and between the new longitudinal beams and provide a packing member between the transfer beam and the existing boat deck beam. Both concepts involved retention and reuse

PROGRAM AND BUDGET

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of local parts of the old structure. These areas had been inspected to the extent possible, although it was recognized that full inspection would not be possible until the works commenced. Approvals by statutory bodies: The pier is a grade II* listed building, and listed building consent was required for the project in accordance with the Planning (Listed Buildings and Conservation Areas) Act 1990 (1990) https://www.legislation.gov.uk/ukpga/1990/9/contents (chapter 9). Heritage issues were discussed, and it was highlighted that it was important to protect the pier from degradation, that similar materials would be used and that the form of the new construction was similar to the original Victorian construction. It was highlighted that the use of the temporary platform, use of prefabricated elements and, in particular, the use of a rotary pile installation method all minimized the risks to the marine environment. For the formal process, the client employed a specialist consultant to deal with communication with the council and with English Heritage. The specialist’s report highlighted that the boat deck structure did not possess particular architectural or artistic interest and was supported by a designer’s technical report describing the proposed works and what demolition work was required. The technical report made extensive use of rendered images from the 3D model to help describe the project and show it from various viewpoints. The application was successfully approved with no conditions.

Construction The contractor established a site compound on the pier. Physical access and weight restrictions along the pier had been highlighted in the tender documents. The contractor also negotiated with the local council for a small storage area on the forecourt area of the pier. Deliveries and removal of materials were generally made out of opening hours of the pier. However, during quieter periods and in agreement with the client, limited access was allowed during opening hours. The temporary platform was installed using roped access techniques. The platform comprised a grillage of steel beams supported by a lower level of existing boat deck beams. The platform had steel open-mesh flooring, and similar flooring from the original walkway was reused to form edge protection. The platform was designed for an imposed load of 2.5 kN/m2 and a plant load of 45 kN plus a 20 kN weight of pile (held by the plant) in any single bay. The contractor’s alternative pile design was a bored composite pile. Like the helical pile, this not only had the advantage of rotary installation but also offered further benefits. Without the helices, significantly less torque was required, leading to more confidence in installation with a smaller rig. Combined with a more conventional design basis and a higher factor of safety, it was also considered acceptable to remove the need for a preliminary pile, thus further reducing costs. Following the installation of the transverse and longitudinal beams, steel wedges were used on top of the longitudinal beams to resupport existing floor beams. For resupport of the existing building columns, local blast cleaning, inspection and measurement were carried out. Deflection was monitored through dial gauges, and all the work was successfully carried out, with only a few millimeters of settlement typically occurring, well within the limits set.

Program and Budget The original program was for 36 weeks. The final duration was 42 weeks, and completion was scheduled for 1 October 2012. Two of the additional weeks were attributed to poor weather. However, if the work had been carried out from marine vessels, longer weather delays would

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have almost certainly resulted. The additional four weeks were due to complexities in pitching and boring early piles, changes in the jacking sequences due to unknown corroded steel and changes for the retention of the temporary platform. However, the innovative concept of working under the pier ensured that the increase in duration did not significantly affect the client’s business. In terms of budget, cost increases were balanced against cost reduction associated with not removing the temporary platform, and the final cost of £26 million was only 1% over the original contract sum.

Conclusion With a need to maintain and protect the heritage value of ageing piers in a harsh marine environment, engineers need to find appropriate solutions. This project has demonstrated the use of several innovative design and construction techniques. The use of laser scanning, temporary working platform, sectional bored composite piles and fabric abrasion jackets all contributed to the success of the project and meeting the client’s key requirement of keeping the building beyond fully operational.

Reference [1] Winterbottom N. Brighton Pier, UK—innovation in renovation. Proc. Inst. Civil Eng., Eng. History Heritage 2014; 167(EH2): 100–110.

83 Chapter

6.6 Early Iron Structures at the Hermitage in St. Petersburg—Unique Testimonies to Construction History and the Associated Preservation Problems Bernhard Heres, Chair of Construction History and Structural Preservation, BTU Cottbus-Senftenberg, Cottbus, Germany

Introduction The State Hermitage Museum in St. Petersburg is one of the world’s most important museums of fine art. It is housed in a former tsarist palace complex, the buildings of which, with their baroque and classical façades, are key landmarks in the city (Fig. 1). Less well known, however, is the fact that these buildings offer a unique tour of one of the most exciting chapters in the history of construction—the emergence of building with iron in the first half of the 19th century. The exhibits—in this case hidden from the public—are the many surviving iron structures supporting the floors and roofs. These date from the years 1838 to 1851, and their existence can be wholly put down to the devastating fire at the Winter Palace in December 1837. Fire-resistant

Fig. 1: The State Hermitage buildings (from left to right): the Large or Old Hermitage (1771– 1787) with the New Hermitage (1839–1851) behind, the Small Hermitage (1764–1775) and the Winter Palace (1754–1762) (courtesy Sinjaver)

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forms of construction were therefore chosen for the immediate rebuilding of the palace. That meant using iron for the roofs and most of the suspended floors, especially those with long spans. This decision was then also applied to the building works carried out in the following years throughout the palace complex, for example, during the conversion of the Small Hermitage (1842 and 1850s), for building the New Hermitage (iron structures 1843–1844) and during the conversion of the Old Hermitage (1850s). The result, in terms of numbers and variations, is a unique collection of early examples of European construction with iron. Since 2002, BTU Cottbus and Karlsruhe Institute of Technology have been compiling a systematic inventory of the items and analyzing them with respect to their significance for the history of construction and various levels of context in a joint research project.1,2 This research was given particular practical relevance by the full refurbishment of the roof structure to the Winter Palace, which was carried out at the same time.

Rebuilding the Winter Palace—A Chance for Experiments in Building with Iron Every conceivable means was employed to rebuild the Winter Palace as fast as possible after the fire, and the fabrication and erection of the iron structures for this prestigious project were largely completed within a year. Immediately after the fire, the building commission responsible appointed Matthew Clark, the head of the state-owned Alexandrovsky Works in St. Petersburg, to carry out the design and construction of prototypes for the roof and floor structures (for information on Clark, see Ref.  [3]). Following successful loading tests in the spring, fabrication and erection work was conducted in stages up to the autumn of 1838. The beam types Clark developed for rebuildFig. 2: Elliptical beams from 1838, section and ing the Winter Palace were described by elevation both Clark himself and contemporary writers as significant innovations, not just for Russian iron construction (see Ref. [4]). Even from a modern viewpoint, these solutions are impressive in various ways. The great number of “elliptical beams” built into floors spanning up to 15 m represents perhaps the first large-scale use of such lightweight solid-web beams in building (Fig. 2). Made up of roof sheeting and angles riveted together, their structural efficiency—the ratio of self-weight to load-bearing capacity—is similar to today’s I-sections. With the help of detailed models, finite element method (FEM) has been used to verify their loadcarrying capacity for the new loads of modern museum operations.5 The beams spanning almost 20 m, designed by Clark for the ceilings over the halls, are still in place today. This represents an imposing example of the “doubling” of load-bearing structures, very common at that time, which can be regarded as a way of finding or securing a suitable solution (Fig. 3). With a lightly cambered top chord made up of iron flats strapped together and a chain as a bottom chord, the result is a fish-belly-like girder with threaded bars to retain the

“WATCHING” THE EMERGENCE OF EARLY BUILDING WITH IRON

85

form. In addition, an arch rises from springing points near the walls to support the top chord at mid-span. The incredible amount of work needed for the fabrication and erection of this multicomponent, overall almost 2  m deep, structural system can probably only be explained by the enormous importance of this construction project. Different systems consisting of trussed rafters and truss-like girders made up from these were developed to suit the various spans of the roof structures. With no purlins, these were closely spaced to carry the roof battens and Fig. 3: View of the hybrid suspended floor struc- roof covering (Fig. 4). The girder designs ture from 1838 are very similar to the Polonceau (or Fink) system, which was developed at the same time, and are also used over the large halls and enfilades of rooms. Contrasting with that, at transitions and along the edges of the building with its many irregularities, there are parts of the load-bearing structure where it is obvious that improvisation on site prevailed, where the details also deviate from the standard solutions. Instead of the outwardly modern pinned and bolted connections that are already common, the load-bearing members here were joined together by, in some cases, Fig. 4: Typical Winter Palace roof structure— the very simplest of clamped and push-fit Throne Hall, 1838–1842 connections—a clear reference to examples from timber buildings and the very early examples of construction with iron, specifically in Russia. Thus, the Winter Palace building site represented a great opportunity for experimentation, with designers and fabricators devising what seemed to be the best answers in each case in light of the conflicting interests of tradition, innovation and transfer.

“Watching” the Emergence of Early Building with Iron The designers of the load-bearing structures for the Winter Palace were treading new ground in many ways. It is, therefore, hardly surprisingly that defects or damage appeared in some cases. One part of the research work involved analyzing archive materials, chiefly the findings on site. This revealed, for instance, various corrections and additions, particularly to the roof structures, which were implemented not long after erection. The reasons for this were severe deformations of the rafters as early as the first winter (1838–1839, see Fig. 5). It is therefore possible to trace how the fabricators tried to solve the associated problem of insufficient buckling strength of the rafters step by step. Two strategies can be seen here: the arrangement of additional or

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Add. bracing 1842

Bracing 1838

more effective lateral bracing and the stepby-step development of cross-sections less prone to buckling, either assembled from various semifinished products or in the form of the first T-sections rolled in Russia. Both strategies were combined in exemplary fashion in 1842 in the form of the roof structure, modified by several new components, re-erected over the Throne Room in the Winter Palace (Figs. 4 and 5).

Further examples allow us to “watch” the development process of the structure and the details of building with iron. For instance, comparing just the form of the roof trusses of the various fabricators shows that they were already close to the Polonceau system that emerged around 1840 in France and then later in Germany. However, closer analysis reveals small, yet very distinctive, differences that indicate a triangulated truss system, pointing more to intuition than intention. Evidence for this can be found in, on the one hand, the differences in the arrangements of the members and, on the other, a critical detail: the continuous bottom chord, fabricated in one piece with a relatively large cross-section and complicated connections to the struts. The trussing of round bars and gusset plates so typical of Polonceau trusses did not appear until the final phase of construction (Fig. 6).

Fig. 5: Roof structure of Throne Hall: rafter with typical lateral deflections and lateral braces 1838–1842

The collection of iron load-bearing structures in the buildings of the St. Petersburg palace complex is a good example of the main stages in construction with iron in the 1830s and 1840s— from the early “exploratory” phase right up to the establishment of this form of construction. The chance to be able to trace the development of important elements in design language specific to structural steelwork in the second half of the 19th century here in one place is what gives this collection its special value. In addition, many findings of the survey, for example, the numerous stamps of the foundries that supplied the sections, indicate the significance of Russian iron production and fabrication in the Ural Mountains since the beginning of the 18th century. What emerged out of this situation were numerous iron load-bearing structures that constitute one of the effective lines of tradition here.6

Fig. 6: Evolution of trussing details (from left to right): Clark, 1838 (Winter Palace); Nobel, 1844 (New Hermitage); Baird, 1851 (Old Hermitage)

THE DIFFICULTIES OF PRESERVING DELICATE HISTORIC LOAD-BEARING STRUCTURES

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The Difficulties of Preserving Delicate Historic Load-bearing Structures The risk of buckling in the rafter sections and the resulting deformation problems were the reasons for extensive rebuilding work in many areas of the roof of the Winter Palace as early as the 1880s. Many different upgrading strategies were used, ranging from leaving the original members intact to complete replacement, depending on the specific situation. Since then, almost all the load-bearing structures, with their flaws, have fulfilled their function up to the present day. The reason for the latest full refurbishment was the need to replace the existing roof covering—a single layer of sheet metal with a number of disadvantages. The new, much heavier roof covering called for structural calculations. The outcome of these, based on conventional modeling assumptions and design methods, called for widespread strengthening. The initial proposals would have reshaped the existing structure almost completely and at the same time resulted in the loss of considerable historic material. Following a heritage protection report, during the construction phase, the two contractors appointed to do the work modified the solutions that had been originally envisaged for the roof areas for which they were responsible, but loss of historic material was still unavoidable. In accordance with the two concepts implemented, almost all the load-bearing members above the rafters were removed—precisely those many different bracing elements that were especially important features of the successive improvements to the lateral bracing Fig. 7: Rafters strengthened with large angle sec- back in the 19th century. One of the two tions both sides contractors strengthened the rafters with large angle sections on both sides and thus avoided welding the historic iron material (Fig. 7). The other contractor strengthened the rafters by welding small steel flats to the top surface of each rafter and reused some of the old roof battens, and therefore, the modifications remained much closer to the look of the original (Fig. 8). These conversion works reveal the specific difficulties when dealing with early iron structures. Their particular weaknesses— for example, the often delicate members, Fig. 8: Rafters strengthened with small steel flats like the rafters in this case—represent real (painted red) welded to the top surface of each challenges when it comes to preservation and further use. rafter (Throne Hall, see Figs. 4 and 5)

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References [1] Lorenz W, Fedorov S. Die Eisenkonstruktionen in den Gebäuden der Staatlichen Eremitage St. Petersburg – Historische Bauforschung mit ingenieurwissenschaftlichen Schwerpunkt. In Bericht über die 47. Tagung für Ausgrabungswissenschaft und Bauforschung, 16. bis 20. Mai 2012 in Trier, Koldewey-Gesellschaft, Stuttgart, 2014, Bachmann M, et al. (eds), 2014; 255–258. [2] Lorenz W, & Heres B. Eiserne Eremitage. Bauen mit Eisen in Russland der ersten Hälfte des 19. Jahrhunderts Ernst&Sohn: Berlin, 2017 (in preparation). [3] Fedorov S. Matthew Clark and the origins of Russian structural engineering 1810–40s: an introductory biography. Constr. History, J. Constr. History Soc. 1992; 8. [4] Fedorov S. Rebuilding St. Petersburg’s Winter Palace in the context of Early European steel structures 1838–1850s contemporary sources and documents. In Nuts & Bolts of Construction History, Carvais R, et al. (eds), Proceedings of Fourth International Congress on Construction History, 3–7 July 2012, Picard, Paris, vol. 3, 2012; 203–214. [5] Häßler D. The ‘Elliptical Beams’ in the Winter Palace in St. Petersburg – Structural assessment of a lightweight structure. In Proceedings of Eighth International Conference on Structural Analysis of Historical Constructions, Jasienko J (ed), Wroclaw, 15–18 October 2012, vol. 3, 2012; 262–272 (based on a master thesis at BTU Cottbus). [6] Lorenz W, Heres B. The Demidov Ironworks in Nevyansk (Ural Mountains) – iron structures in building from the first half of the 18th century. In Proceedings of Fifth International Congress on Construction History, Bowen B, Friedman D, Leslie T, Ochsendorf J (eds) , Chicago, 3–7 June 2015, Construction History Society of America, Chicago, 2015, vol. 2, 2015; 505–517.

89 Chapter

6.7 Maintenance and Strengthening of the Cross-Shaped Barracks Building

Marina Traykova, Prof., PhD; Tanya Chardakova, Assistant Prof., PhD; University of Architecture, Civil Engineering and Geodesy, Sofia Bulgaria

Brief Description of the Presented Case Including Project Aims and Challenges The Cross-Shaped Barracks building is a cultural monument and one of the 100 National tourist attractions in Bulgaria. It is situated in Vidin, which is a Bulgarian city on the Danube River. The building was constructed in 1801 by local ruler Osman Pazvantoglu for the deployment of the Ottoman troops (Fig. 1). The designers, if there were any, are unknown. After the liberation of Bulgaria from the Ottoman Empire, the building was used as a court and barracks of Bulgarian troops. The building is famous for its specific cross shape in plan (Fig. 2). The building structure is of brick and stone masonry (Fig. 3). The foundations are constructed as dry stone masonry. The roof and the floors are timber structures. The building had not been maintained properly, and a settlement of the south section corner had occurred due to moistness of the soil and caused substantial cracking of the walls. Moisture was observed in all the walls up to 1 m above the ground, which had caused damage to the external plaster as well as several cracks in the internal walls. The building is situated in a region of grade 7 seismic activity according to the Bulgarian seismic code. The project aimed to rehabilitate the existing structure and adapt the building to an ethnographic museum for the region. Before the rehabilitation of the walls, the masonry was processed using polymer materials to act against the moisture and in order to fill in the cracks. The strengthening itself was designed to be carried out by means of steel elements to be anchored to the walls and sequentially sprayed with concrete (Fig. 4a). The chosen design solution provided for the best possible preservation of the architectural authenticity.

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(a)

(b)

Fig. 1: Final view: (a) exterior and (b) interior

Fig. 2: Layout of the building (structural design project drawings, 2010) A design solution where the foundations are strengthened by a new reinforced concrete (RC) structure of waterproof concrete was adopted (Fig. 4b). This included adding an air channel around the building in order to provide for proper insulation and aeration of the foundations.

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PROJECT-SPECIFIC EXPERIENCES AND LESSONS LEARNED

Fig. 3: Typical cross-section of the structure (design project) (a)

(b)

Fig. 4: Strengthening (a) of the brick masonry with sprayed concrete and (b) of the foundations When construction activities began, serious new cracks were found in some of the masonry walls. An additional RC wall in the building with a new foundation was designed for rehabilitation of the damaged masonry walls (Fig. 5).

Influence of CH Analysis Results on the Project in the Assessment Phase and in the Design of the Intervention The design solution and the techniques for rehabilitation were decided according to the results from the construction history (CH) analysis of the building: special research on the history of the region and the construction traditions. The aim was to preserve the original architecture and structure.[3] Hence, only the most crucial interventions were undertaken, and seismic strengthening was considered too invasive. Additionally, the chosen structural interventions were preferred because of economical considerations.

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Fig. 5: Strengthening of the brick masonry with additional RC wall (design project of the authors, 2012)

Project-Specific Experiences and Lessons Learned The specific experience from this project and lessons learned can be summarized as the following: 1. Adaptation of old buildings is the best solution for reviving a region and creating the original atmosphere. The adaptation of existing buildings ensures the best sustainable approach. 2. Preservation, rehabilitation and strengthening of existing structures require the application of corresponding remedial measures. The final choice should be made according to the following: condition of the building, compatibility with the original structure, avoidance of historical forgery and transparency of the interventions. 3. Selection of the best design solution for historical buildings requires a very rational and scientific approach, starting with a study of structural integrity and determination of the causes of deterioration. 4. Sometimes, innovative technologies for retrofitting demonstrate that those solutions are not suitable in all cases. Technical and economical reasons can guide the final solution for retrofitting.

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Conclusions The adaptation of the early 19th-century building of the Cross-Shaped Barracks in Vidin for an ethnographic museum is a positive example of the proper adaptive reuse of monumental structures. This, along with improper or rather lack in maintenance of this fine piece of historic architecture, led to the need for strengthening of the building. In order to preserve its original appearance while assuring its continued safe use, some inconspicuous strengthening interventions were undertaken. The aim was to stop the active process of foundation movement due to excessive moisture and the subsequent cracking of the masonry walls. The presented case study again shows that heritage buildings are an important link between the present time and history. They reflect the social, cultural and economic experiences of the past. The protection of heritage buildings is however related to many structural problems. The majority of historical buildings were built essentially following empirical rules and usually were not specially designed for both gravity and lateral actions. At the same time, the authenticity should be necessarily preserved for the future generations. The described design solution confirms that decision making for the type and range of interventions is very important and is usually specific to the different cases.

References [1] BDS EN 1998-3: Design of Structures for Earthquake Resistance. Assessment and retrofitting of buildings. [2] Ordinance “РД- 02-20-2 for design of buildings and facilities in seismic areas”, 27.01.2012 (Current Bulgarian Code). [3] Traykova M , Chardakova T. Research on the seismic behavior and the retrofitting of the buildings from the Bulgarian Cultural Heritage. Proceedings of the Sixth International Congress “Science and Technology for the Safeguard of Cultural Heritage in the Mediterranean Basin”, Athens, Greece, 22–25 October 2013, 2013.

95 Chapter

6.8 Analytical and Experimental Studies on the Technology of Late-Gothic Vault Constructioni

David Wendland, Chair of Christian Art in Late Antiquity and the Middle Ages, Technische Universität Dresden, Dresden, Germany

Introduction This paper outlines how analytical and experimental studies in construction history have led to a fuller understanding of the construction of “cell vaults”, which has enabled restoration of such vaults to be undertaken with greater confidence. According to common belief, cell vaults were invented around l470 for the construction of the Albrechtsburg, the new palace of the princes of Saxony at Meissen (Germany). These vaults that sometimes have stone ribs but in many cases only have sharp groins are characterized by their folded surface with ridges between the groins (Fig. 1), creating ceilings with subtle patterns of light and shadow. The construction material (apart from few exceptions) is brick masonry. Their design corresponds to that of late-Gothic net vaults, but the pattern of their groins and arches is often much more complex than that of conventional rib vaults. Cell vaults rapidly became popular first in Saxony and then spread all over central-eastern Europe, including BoheFig. 1: Cell vault in the second floor of the Albre- mia, Poland, the Baltic, Prussia and even chtsburg at Meissen (Germany). The folded sur- beyond. During more or less a century, face of such vaults are built with brick masonry hundreds of them were built in palaces, (Courtesy: D. Wendland) town houses, convents and churches.

i

This paper is a reduced version of ‘Research on “cell vaults”: analytic and experimental studies on the technology of late-Gothic vault construction’ published in Ref. [1].

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We learn nothing about how these vaults were built from sources and contemporary records, just as little why they were introduced and why they became so popular in such a vast area. We do not even know what these vaults were called—the names we use are of modern origin. Therefore, it is necessary to search for other ways in order to find out how the cell vaults were, or might have been, actually built five centuries ago.

Construction Principles of Late-Gothic Cell Vaults Experimental Archaeology Correlated with Detailed Surveys and Analyses of the Archaeological Evidence In order to formulate hypotheses on the construction process that is not otherwise documented, its reproduction according to the method of experimental archaeology is the most promising. In the current research on the construction of cell vaults”, experiments were carried out that were closely linked with detailed surveys of original vaults—particularly one vault where the masonry texture was visible in large portions. The curves, surfaces and single courses in the masonry texture were the subjects of three-dimensional (3D) surveys and geometric analyses that were carried out by means of a software tool for reverse geometric engineering. Using these analyses, the construction process could be characterized; principle statements on the temporary auxiliary structures needed for the building could be made; and construction principles based on the archaeological evidence could be formulated. The methodology of such analyses has been developed in earlier research by the author.2,3 By putting these hypotheses into practice in experiments carried out in full scale, they could be evaluated and refined, and the practical experiments could generate new observations about the vault.

Analyzing the Construction Principles of Cell Vaults From the geometric features of the curves, surface form and masonry texture, it is possible to learn about the building process and the principle features of the centering system. First, the geometry of the groins shows that, during construction, these must have been supported by single centering arches and not by a continuous formwork. Their curves can be described in simple geometric terms, in contrast to the shape of the vault surfaces. All arches describe circle segments in vertical planes with discontinuities at the intersection points, which also provide some indication of the whole system of centering arches. Such a layout of the arches is also common in the contemporary rib vaults, and it corresponds to what we know about the geometric design of late-Gothic vaults.4,5 The ridges or inward-folded groins, in contrast, describe curves with a complex geometry: the 3D curves demonstrate variations in the direction and radius of curvature, in addition to the abrupt changes of direction. From this, we can conclude that they were not guided by centering but resulted spontaneously in the process of the construction of the vault surfaces, which therefore must have taken place free-handed. The analysis of the masonry texture proves that the analyzed vault was actually built free-handed. This is on one hand clear from the spatial position of the masonry courses, which, over great portions, are inscribed in tilted planes that are parallel—a typical feature of the masonry texture of vaults built without formwork (Fig. 2).

CONSTRUCTION PRINCIPLES OF LATE-GOTHIC CELL VAULTS

Fig. 2: Model simulation showing that the angle of the courses at the groin (V-shaped connection in front) is not determined a priori but depends on the development of the curves of the formeret arches (in the back) (Courtesy: D. Wendland)

97

Fig. 3: The exposed masonry texture of the analyzed vaults shows the continuity of the courses over large portions across the discontinuities of the vault surfaces. This does not conform to modern masonry rules and contradicts the current description models but turned out to be very practical in the experiments (Courtesy: D. Wendland)

Finally, the masonry texture in these folds is fundamentally different from Ungewitter’s description because, in spite of what in modern terms we would claim to be a regular bond pattern, the courses usually run continuously across them (Fig. 3).

Experimental Reconstruction of Late-Gothic Cell Vaults The experiments were carried out in collaboration with an academy of historical craftsmanship, reproducing two vaults in full scale with bricks and mortar according to the original. The used bricks have the same large format as the original and are produced in the traditional manner—their porosity is of benefit for free-handed vaulting, and they can be easily cut to shape with an axe. The mortar has been reproduced according to the analysis of the original mortar. In these experiments, the hypotheses of the construction principles as developed from the surveys turned out to be practicable, confirming the observations made above. The geometric problems in the masonry texture due to Fig. 4: Experimental reconstruction of the anathe curvature of the vault surface have lyzed late-Gothic cell vault where the hypotheses occurred in the experiments in the same on the construction principles and building promanner as observed in the analyzed vault cess could be verified and refined (Courtesy: A. (Fig. 4). Gosch)

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The continuity of the masonry texture over large portions, which we could observe and which we believe to be a principle of late-Gothic vault masonry, was even surprisingly easy to reproduce in practice, just by slightly bending the beds and sometimes cutting the corners of the bricks. The axe to cut bricks is needed very often in the process (once more contradicting Ungewitter’s theory), but the traditional bricks are cut easily as they are rather soft and not brittle. The main difficulty for everybody was to pull apart the modern rules of bond pattern. These rules, although considered “historical” or “traditional”, have been formulated only in the course of the 19th century and are not relevant to earlier historical periods. As already pointed out, from the archaeological evidence, the construction principles that were used by the masons of the late-Gothic vaults could be characterized and, in the experiments, could be demonstrated to be very practical in execution. In reality, these principles also make much sense because a very good coherence throughout the masonry is obtained with the continuous texture. This can be illustrated by the fact that cell vaults built in the 19th century with modern criteria often show cracks that almost never occur in the original late-Gothic vaults. In conclusion, we can now describe the difference between late-Gothic and modern construction rules, and we are capable of reproducing late-Gothic vault masonry with high fidelity.

Conclusions In the presented study, a methodology of analyzing historical construction is proposed, which enables the formulation of statements on construction processes and design criteria in historical structures that lack documentation. This can be relevant to conservation or restoration by providing better knowledge of complex structures, as well as in basic research on construction history. The improved knowledge of the construction principles and details illuminates the original construction principles of late-Gothic vault construction, which has been perceived through the optics of modern interpretation as established in the 19th century until now. Finally, through the collaboration with an academy of historical craftsmanship, this knowledge is disseminated to the technicians and craftsmen operating in the practice of restoration.

Acknowledgements The research on cell vaults has been carried out within the research project “Form, Konstruktions- und Entwurfsprinzipien von spätgotischen Zellengewölben—‘reverse engineering’ und experimentelle Archäologie”, B. Klein, D. Wendland, Technische Universität Dresden (Germany), funded by the Deutsche Forschungsgemeinschaft since 2009.

References [1] Jasienko J (Ed.). Structural Analysis of Historical Constructions DWE: Wrocław, 2012. [2] Wendland D. Traditional vault construction without formwork: Masonry pattern and vault shape in the historical technical literature and in experimental studies. Int. J. Archit. Herit.: Conservation Anal. Restoration 2007; l(4): 3ll–365. [3] Wendland D. Lassaulx und der Gewölbebau mit selbsttragenden Mauerschichten. Neumittelalterliche Architektur um 1825–1848 Imhof: Petersberg, 2008.

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[4] Müller W, & Quien N. Virtuelle Steinmetzkunst der österreichischen und böhmisch- sächsischen Spätgotik: Die Gewölbeentwürfe des Codex Miniatus 3 der Österreichischen Nationalbibliothek in Wien. Imhof: Petersberg, 2004. [5] Wendland D. Zum Bau figurierter Gewölbe – eine Anleitung im Werkmeisterbuch des Rodrigo Gil de Hontañón. In Werkmeister der Spätgotik: Personen, Amt und Image, Bürger S, Klein B, Schröck K (eds) WB: Darmstadt, 2010; 244–272.

101 Chapter

6.9 Frost Damage and Restoration of Limestone Domes and Spheres in a Heritage Building

Philippe Van Bogaert, Prof., PhD; Ghent University, Ghent, Belgium

Introduction Domes and spheres have been used extensively in heritage buildings during baroque and rococo periods as well as in 19th-century buildings. Used as ornaments and as coverings and roofs, these curved elements add to the monumental character of imposing buildings, which are presently considered a part of the cultural heritage. The number of historic buildings containing domes and spheres is impressive and includes some of the world’s most famous structures. Most of these ornaments and coverings are made of limestone because of its excellent quality and durability. However, because limestone is a sedimentary rock, consisting mainly of calcium carbonate, it may deteriorate due to acid rain and frost. The latter introduces cracking, allowing water ingress and subsequent further cracking. Depending on the crack width, further moisture ingress is fostered, and cracks grow. In the present paper, this progressive effect is being assessed by numerical simulation. Obviously, all types of limestone blocks and ornaments are prone to degradation due to frost. However, a brief survey of various degradations shows that curved shapes are more vulnerable. The reason for this is yet to be found. The ratio of exposed surface to volume of a sphere is not significantly different from the value for an equivalent cube. However, if rainfall is considered from a single direction, for instance, vertical, the relative exposure ratio of spheres is three times larger than that of cubes. This might give some indication of the larger degradation of curved surfaces.

Southern Pressure House, Antwerp The Southern Pressure House, in Antwerp, consists mainly of two long buildings, the first of which contains the machine room and the steam hall and parallel storage depots for coal and oil.1 The boiler room and the warehouses are separated by a corridor that opens to a courtyard. The second building houses offices, homes for personnel, a repair workshop and a forgery house. Of all these, the imposing unit containing the accumulators for water pressure (Fig. 1) is the most valuable. This is mainly a brickwork building decorated with limestone façade blocks,

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which were intended to enhance the view as the city particularly wished to improve the appearance of the neighborhood.

Figure 1 Southern Pressure House: front view

The front view of the building clearly shows the two vertical parts containing the water accumulators. The entrance door and ground level appear rather massive; the twin columns are richly decorated, suggesting the cylindrical accumulators inside, and the narrow openings underline the vertical orientation of the building. Both towers are covered by domes carved from single limestone blocks. An individual dome is shown in Fig. 2. The domes are supported by white sandstone cylindrical masonry. The total height of the structure reaches 24.5 m. Figure 2 also shows some of the heavy cornices, column capitals and decorating spheres. The highly decorated industrial building was highly appreciated in the second half of 19th century and displays the wealth and prosperity of the port of Antwerp in industrial times. The style of this building may appear to be excessively heavy, but the exterior form clearly shows the particular purpose of the building. In addition, the domes entirely correspond to the inside equipment.

Although the installation was decommissioned in 1977, the whole complex was listed as protected heritage in 1979. About 20 years back, a complete restoration was undertaken, and the buildings became a center for performing arts. This lasted until five years ago when the theatre company ceased to exist. Since then, events are being organized in the 4000  m2 building with its seven rooms, except for the front Figure 2 Top of the vertical part with the dome unit (Fig. 1) which remains unused. The activities include seminars, smaller concerts, receptions, discussions and workshops, as well as art studios. During the inspection of the heritage building in January 2012, several limestone ornaments and blocks were found to be heavily cracked. In addition, during the 1985 restoration, inferior products were used at some locations. After some of the limestone debris fell, a second inspection was organized in December 2012. As both inspections were conducted in winter, it was hoped that frost was at maximum and recent degradation would be detected. Cracks reached

SIMULATION OF DOME CRACKING

Fig. 3: Degradation of the dome

103 a width of 10 mm, and some parts needed immediate removal as there was a threat of debris falling on to the footpath below. The inspections also showed that some parts of the structure were already missing. These findings have urged the owners to apply for necessary funding for a restoration program and to install safety measures in order to avoid endangering passers-by below the building. However, the largest concern applies to the domes as these also suffer from cracking. Figure 3 shows a detail of the cracked state of the domes. It is clearly seen that the limestone surface is eroded in horizontal layers. This seems to be characteristic of domes and spheres.

Simulation of Dome Cracking The domes are relatively small and consist of hemispheres with an inner radius 1.22 m and an outer radius 1.40 m, the thickness being 0.18 m. The base of the dome consists of a flat ring with an outer radius of 1.63 m, thus providing a larger support and stiffening the dome. The idea was to constitute a model of volume elements and to introduce cracking as soon as tensile stresses exceed the tensile strength of the limestone. The tensile strength value of 5.67 MPa is considered rather low, far below the average compression strength of 140 MPa or a characteristic value of 126 MPa. This type of approximation allows reasonable assessment of the influence of cracks on dome resistance. In further steps, nonlinear material characteristics may be considered, although it is believed this will not consistently modify the results. The approach consists of introducing cracks into the model, assuming subsequent water ingress and allowing the effect of frost. The latter will start the progressive effect, the issue being how far this process may continue and eventually lead to the destruction of the dome. Modeling of the effects of frost proved to be delicate. A first approach considers that an initial crack is completely filled with water. As the water freezes, its volume increases by 9%, thus causing an internal pressure in the crack. This internal pressure needs to be applied to the crack surface. The main issue is to identify the magnitude of the pressure. This, and other approaches based on the Washburn equation,2 all disregard the actual process of freezing in natural stone. The latter has been researched more extensively in Ref. [3]. Although the research is considered to be idealized, it enumerates the various phenomena involved during freezing. The model is based on the importance of the flow of water toward the solidification front of ice, as well as on the existence of thin films separating the ice and the surrounding stone, as mentioned earlier. The thickness of these films varies from 15 to 30 Å. These films also exert an attractive force on the pore water and a disjoining pressure that pushes the ice and the stone apart, which is the pressure we are seeking. The fastest damage growth rate occurs in the range from −4 to −15°C. In Ref. [3], the case of a spherical cavity has been studied using the Gibbs–Duhem equation to describe the change from liquid to solid state, the van der Waals interactions and the Clau-

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Fig. 4: Cracking of the dome wall

Stress (MPa)

sius–Clapeyron equation. The porosity of the stone has been taken into account, and three 4 στ examples have been worked out. It appears 3 σχ that dense rock-like granite can certainly 2 crack due to freezing water as the pressure 1 rises up to 25  atm or 2.533  MPa. However, crack depth (mm) 0 in the case of sandstone, in a spherical cavity, 90 110 130 150 –10 10 30 50 70 –1 pressure would rise to 12  atm or 1.22  MPa, –2 and this value also corresponds to limestone. –3 In porous stone, the main pressure rise is due to the pre-melting stage when the ice is very Fig. 5: Evolution of stresses with crack depth close to the stone. The flow then reverses, and the water flows toward the solidification front. This explains why the pressure rises sufficiently to cause cracking only in the case of very impermeable rock. Consequently, the research in Ref. [3] has been adopted for the present simulations. The pressure in a spherical cavity is most probably higher than that in a longitudinal crack, which has a larger surface area in contact with air. Consequently, an internal pressure of 1.22 MPa has been applied to a crack on the outer surface of the dome. This crack runs along a quarter of the circumference of the dome, its depth being increased stepwise. Looking at a crosssection of the dome, the local meridian stresses can be found as shown in Fig. 4 for crack depths of 1/20, ¼ and ½ of the dome thickness. 5

The former cracks have been assumed to exist before water ingress and freezing. The stresses shown in Fig. 4 may either cause excessive tensile stress at the crack tip or may crush the crack opening at the surface. In addition, the crack may be widened due to internal pressure. In all of these cases, the crack will increase until these quantities decrease below a critical level. The diagram in Fig. 5 summarizes the tensile and compression stresses as a function of the crack depth. The upper blue line shows the tensile stresses, which in all cases is below the tensile strength of 5.67 MPa. This simply implies that the cracks will not increase due to frost, and there is no progressive deterioration. This also applies to the compression stress, which is two to three times lower than the tensile stress. According to these results, water ingress and subsequent frost cannot be responsible for damage to the domes. In addition, the evolution of crack width with the depth has been summarized in the graph in Fig. 6. This illustration also shows that the crack width is moderate. Hence, the model has indicated that cracking of the limestone

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CONCLUSIONS

0.3 0.25

crack width (mm)

0.2 0.15 0.1 0.05 0 –10

crack depth (mm) 10

30

50

70

90

110

130

150

Fig. 6: Evolution of crack width with depth

Fig. 7: Developed crack

ornaments is probably not due to freezing of water in the cracks. Calculations were continued until 80% of the dome wall thickness was cracked, and yet no progressive effect was seen. At this particular point, the crack width grows to about 0.3 mm. When all loads are considered, the dome still remains stable. The deformations at this stage are shown in Fig. 7, the crack opening being clearly visible, including the effect at the tip inside the stone. In view of these results, the crack length has not been varied, nor has the exact location been modified, and further analysis becomes irrelevant.

Restoration As the present state of deterioration of the domes and other limestone parts of the Southern Pressure House in Antwerp cannot be due to frost, the cause must reside in chemical attack due to increase of CO2, thus favouring the dissolution of the material. Due to the nature of limestone, the calcium carbonate may dissolve if the pH of rainwater is sufficiently low because of CO2 content. Therefore, refurbishment should preferably make use of soft lime mortar to close the surface cracking. Deeper and larger cracks, endangering further decay and disintegration of the parts, may be treated by injection of epoxy-based products. Former calculations have shown that injection pressure may easily reach 5 bars (0.5 MPa). However, these epoxy-based products are harmful to the limestone as they have little permeability and can become rather rigid in the stone. Hence, they should be used in-depth only and after the surface treatment of cracks with lime cement is complete. After successive inspections and temporary measures to avoid accidents, the restoration of the Pressure House is presently being considered. The project will require more extensive evaluation of the various repair methods. However, it may have become clear that water ingress and frost are not the main reasons for the degradation.

Conclusions Recent inspections have revealed that important limestone parts of the Southern Pressure House, a heritage building in Antwerp, show large cracking and may fall from the building. Water ingress and frost are thought to be the cause. The domes show horizontal cracks that might be of particular concern during future restoration. An extensive numerical model has been used to

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predict cracking due to frost. Various approaches to model the effect of water ingress and frost have been considered. Among these, the approach based on the successive stages during ice growth, the presence of a water film separating ice from the surrounding stone and the internal water flow toward the ice front seems the most successful. Application of this approach clearly shows that the effect of frost is incapable of fostering progressive cracking as both the tensile stress at the crack tip and the compression stress at the surface are sufficiently small. In addition, crack width may increase with depth, and this quantity also remains small.

References [1] Himler A. The Southern Pressure House and 7 other hydraulic stations” (in Dutch). Monumenten en Landschappen 1985; 4(6): 8–28. [2] Fisher L. An experimental study of the Washburn equation for liquid flow in very fine capillaries. J. Colloid Interface Sci. 1979; 69(3): 486–492. [3] Vlahou I, & Worster M. Ice growth in a spherical cavity of a porous medium. J. Glaciol. 2010; 56(196): 271–277.

107 Chapter

6.10 The Gothic Tower of Freiburg Minster, Germany: Analysis and Repair

Rainer Barthel, Prof. Dr.-Ing. Partner, Barthel & Maus, Beratende Ingenieure GmbH, München, Germany Joram Tutsch, Struct. Eng., Dipl.-Ing. Technische Universität München München Germany Joseph Jordan, PhD, Struct. Eng., Dr.-Ing. Partner, Barthel & Maus, Beratende Ingenieure GmbH, München, Germany

Introduction The construction of the Freiburg Minster began around 1200 in the Romanesque style, and from 1230 onward, the master builders adopted the Gothic style. The tower was completed around 1330. It is 116 m in height and has survived until the present without major damage or alteration. The outstanding feature of the tower is the filigree construction of the octahedral-pointed spire, which has no internal supports (Fig. 1). Since its construction, no major alterations were undertaken, and no strengthening measures have been required. It survived several catastrophes, including one of the most destructive earthquakes in Northern Europe in 1356. It also survived the bombing raids of November 1944. Nevertheless, the masonry and the tracery had to be repaired at regular intervals, for instance, in the 1920s and 1960s. In 2009, a scaffold was erected once again after small pieces of stone fell onto the viewing platform. Originally, the intention was to undertake local repairs and stone conservation, but further cracks were discovered, which proved to be much more dangerous than expected. In particular, the cornerstones of the main struts of the octagon, which are structurally essential, showed several cracks. The crucial questions were what were the causes of this cracking and what kind of remediation measures would be necessary.

Construction The lower part of the tower is square in plan and very solid, with only a few openings. At 40 m, there is the so-called star gallery and the belfry. Above the belfry, at a height of 55 m, there is an internal platform. From there, the tower is octagonal and free from any internal struc-

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ture—there are no walls, only pillars and high tracery windows. At the height of 72 m, there is a further gallery on the outside. Above that level, the octagonal spire rises. The spire is subdivided into a solid base, seven stories of tracery elements between levels 1 and 8 and the pinnacle incorporating the finial. Circumferential wrought-iron ties are situated on eight levels.

Damage to the Structure When the first cornerstone was removed, it was found to be completely destroyed; what remained was a mere stump. Numerous cornerstones showed similar damage, and some were found to have been repaired rather crudely in former times. It is difficult to repair such a cornerstone in an adequate way. The vertical load on a cornerstone is up to 400 kN. The initial assumption was that corrosion of the iron ties was the cause Fig. 1: Freiburg Minster: View from the of the cracks, and indeed, in some chords 1–2 m octagon level inside the spire long, significant corrosion of the ties was found. Water had infiltrated through open joints between the coping stones and was trapped in the tie channel. Thus, water freezing could also cause damage. However, corrosion of the iron ties does not sufficiently explain all the cracks and defects. Generally speaking, the damage inside the tracery was not found to be alarming. There is little more than a few displacements and minor spalling at some joints (Fig. 2a). Fortunately, only a small number of stones had developed cracks parallel to the outer surface of the tracery panel, which would be dangerous. While there are some cracks that seem to be due to tensile stresses, more often, the cracks indicate bending (Fig. 2b). All the visible damage and deformations were recorded. Especially important was the need to identify the repair measures carried out in former (a)

(b)

Fig. 2: Typical damage inside the tracery. (a) Relative displacement; (b) bending crack

STRUCTURAL ANALYSIS

109

repair campaigns. Substantial repairs were undertaken in the 16th century, in the 19th century, in 1920 and again in 1963. The quality of these measures differs greatly. A full 3D computer model of the entire structure was built. Every stone, every joint and every metal piece is modeled as a separate element; every crack and other anomalies are also fully modeled. All historical alterations are also included. The model was created using a photogrammetric survey that was completed by hand measurements.

Structural Analysis Several different methods of modeling the structure were tested in order to find an appropriate way to conduct structural analysis calculations. The first approach was a finite-element model using simple plate elements for the tracery panels with a reduced stiffness. A more complex model was also created consisting of beam elements and special gap elements at the joints in the tracery, with separate truss elements for the iron ties. This model is very cumbersome, and the results are not easy to check. Therefore, a much simpler model was also developed to gain a better understanding of the overall statical behavior. The tracery panels are substituted by simple truss elements, and their stiffness was derived from a detailed analysis of the various types of tracery under vertical and lateral shear forces. The truss elements can transfer only compressive stress; in addition, the stress–strain relation in compression is nonlinear.

Dead Load The total weight of the spire is 6310 kN. For comparison, the total weight would be 9470 kN if the structure were of the same thickness but with solid masonry walls. The tracery panels are not only ornamental—they support the weight of the entire structure above. The load paths through the tracery panels result in a concentration of forces along the vertical edges. The pattern of the tracery causes horizontal forces that provoke a certain increase in the circumference of the octagon. On the other hand, the overall shape of a pyramid gives rise to horizontal compressive forces, which hold the structure together. The resultant tensile forces in the wrought-iron ties therefore remain small. One feature of the construction is particularly surprising. The only structural elements connecting the tracery panels with the struts are the iron ties. However, the struts and the tracery panels do not have the same stiffness in the vertical direction. Different displacements due to elastic deformation or shrinkage can thus cause significant shear forces in the ties and the adjacent stones. The tie becomes a “shear pin”, which can give rise to local stress peaks and tensile stresses in the stones. This may well account for the vertical splitting of numerous stones in the horizontal chords adjacent to the struts.

Wind Load Because there is no information on assumptions regarding wind loads on such a structure, wind tunnel tests were conducted on a physical model. Wacker Engineers undertook experiments on a 1 : 100 scale (600 mm) model of the entire octagonal tower and spire. Further models at 1 : 40 scale were made of smaller sections to determine the distribution of forces around the circumference of the spire. A peak velocity wind load of 1.21 kN/m2 is assumed, which corresponds to a velocity of around 44 m/s with a 50-year return period. The resultant wind force on the structure is astonishingly large; indeed, the force is much higher than on a spire that is not perforated.

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The wind force corresponds to a force coefficient of roughly 1.4. The forces acting parallel to the surface are particularly high due to the roughness of the surface. The suction forces on the structure are relatively small. The forces in the ties and their connection to the masonry are much larger than those due to the dead load. At the fixings, the maximum tensile force is 226 kN, which is nearly three times that under self-weight. The tracery panels parallel to the wind direction act as shear walls. At the cornerstones, two effects occur. First, the forces in the ties have to be diverted, causing forces inward; second, a proportion of the forces have to be anchored in the stone. Both effects lead to tensile stress across the full thickness of the stones.

Seismic Loads Vibration measurements were conducted on the model and determined that the vibration period of the first and second eigenmode is around 1 Hz. Assuming the seismic zone and the foundation behavior according to Eurocode 8, the equivalent static lateral seismic load was found to be higher than the total wind load. A story-by-story or even stone-by-stone assessment of the effects of this load within the statical model is currently being implemented.

Material Tests A great deal of materials testing was undertaken. Mechanical properties of the original and new mortar, the lead, the sandstone and the wrought iron were determined. In addition, some fullsize copies of structural elements were tested in the laboratory. Some nondestructive testing was also undertaken to investigate internal cracks in the stone. One result of fundamental importance was revealed by this series of tests; it was found that the coefficient of thermal expansion of the historic sandstone and of the wrought iron is the same, indicating that these two materials fit together very well.

Repair Two repair philosophies were discussed. The first proposed using external ties or even steel cables to embrace the whole structure horizontally. These ties are positioned on the outside of the structure at the level of the chords and post-tensioned to eliminate the tension forces in the original ties. No drilling is required. At the cornerstones, steel brackets are required to bear the forces. The cornerstones are thus loaded in three-dimensional compressive stress. This ensures that the repair of the damaged cornerstones is easier, and more of the original cornerstones can be retained. The chords are also loaded in compression, which assists the flat-arch action under local wind loading. This repair philosophy aimed for the minimum of interventions and alteration to the historic structure. However, this solution would generate entirely new load paths inside the chords due to the post-tensioning. In statical terms, this would be a major change; it could cause further unpredictable displacements, and even damage, due to the inhomogeneity of the structure arising from the numerous repair measures completed in the past. A second philosophy was developed that will maintain the original statical situation, and this is the approach now being implemented. The stones and the joints will be repaired locally and, if necessary, strengthened to meet the local requirements. Twelve cornerstones show small cracks, and a frame made of titanium was designed to hold them together and to provide adequate safety under vertical and horizontal loads. Eight cornerstones are badly damaged and must be

CONCLUSIONS

111

removed and replaced by new ones. Split stones located in one third of the horizontal chords have to be replaced in order to achieve sufficient shear stiffness—a precondition for the flat-arch action (Fig. 3). All historic repairs that do not meet the statical requirements have to be replaced. When implementing this kind of in-depth repair, it is possible to strengthen the overall structure and to increase substantially the robustness and level of security. However, if the original ties do not meet the required level of safety, additional ties are inevitable. The Fig. 3: Repair plan: example for chords of sto- final decision depends on the investigations ries 6 and 7 (the wrought-iron tie ring and stone mentioned above, which still have to be executed. The ties would consist of titanium replacements are dark colored) with a diameter of 20 mm and would not be post-tensioned. Thus, they will not change the stress distribution and load paths in the original structure. Two alternative ways of introducing these new ties are being considered. They could be positioned inside the upper part of the chords and anchored in the struts directly above the cornerstones. This would require drilling holes at least 35 mm in diameter over a length of about 5 m. Alternatively, to minimize drilling, the ties could be positioned directly above the chords, necessitating penetration of three or four tracery stones. The diameter of the drilling hole could be reduced to 24 mm. These ties would hardly be seen from below. Apart from being resistant to corrosion, a further advantage of titanium is that its Young’s modulus is roughly half that of steel, which reduces the change of forces in the ties due to temperature variation. These additional ties will be inserted, if necessary, after the repair of all the stones. The implementation of the various repair measures began in 2014. Due to the construction of the scaffolding, the work progresses from top to bottom. Currently, the repair measures have been completed in the upper third of the spire. One of the remaining major challenges is the design of the temporary steel support structures that will allow the removal and replacement of several cornerstones (Fig. 4).

Conclusions The spire on the tower of Freiburg Minster is an invaluable monument of architectural and construction history. The analysis of the construction is an interdisciplinary research effort. The tracery is a filigree masterpiece of medieval art, and at the same time, it is a substantial structural element that must transfer both vertical and horizontal forces. Even the repair measures from the 15th and 16th century are witness to the level of technical development and understanding. Thus, it is worth assessing the construction to an extent that goes far beyond the normal in order to avoid repair or strengthening measures, that would alter the historic substance. The tower has proven its stability for nearly 700 years. Such a statement is frequently used to justify the argument against undertaking any strengthening measures. However, 700 years existence does not prove that the tower is still safe or will continue to be safe in the future. The statical calculations and the tests show that the overall structure and the dimensions of the structural elements

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Fig. 4: (a) Three-dimensional (3D) model of repaired stereotomy at a cornerstone. (b) 3D model of temporary steel structure for replacement of cornerstones correlate more or less with the forces determined theoretically. However, the reliability of the numerous structural elements cannot be proven completely. Stress concentrations or a weak sediment layer in the sandstone or slag inclusion in the wrought-iron ties cannot be excluded. In addition, the repair measures during previous centuries led to a much larger total number of stones and joints than in the original structure. That has weakened the structure and makes it impossible to assume the original level of safety. Even after repairing all the damage that was detected, it will not be possible to achieve the level of safety of the original structure. Thus, extreme wind loads or a large earthquake can be a real threat. It will not be possible to strengthen the structure to an extent that removes all the risks completely, according to our contemporary understanding of safety, without implementing major strengthening measures. This would destroy the original monument. The proposed strengthening by means of additional ties could reduce the risk of major damage or collapse substantially. The final decision of whether this is acceptable must be made by consideration of the various values and points of view regarding historic structures.

113 Chapter

6.11 The Municipal Public Bath at Strasbourg (1905–1908): A Cultural Heritage in Reinforced Concrete

Christiane Weber, Prof., PhD; Leopold-Franzens-Universität Innsbruck, Innsbruck, Austria Alexandre Kostka, Prof., PhD; Université de Strasbourg, Strasbourg, France

Introduction In Strasbourg in Alsace, France, a municipal public bath has survived till this day almost in its original form: Les Bains Municipaux.1 The complex was conceived as a “municipal public bath” in the years prior to World War I. At the time, Germany had annexed Strasbourg as the “Reichsland Elsass-Lothringen” as a consequence of the Franco-German War of 1870–1871 and the Frankfurt Peace Treaty. On 17 June 1901, the municipal chief architect Johann Karl Ott presented the first proposal to build the public bath, suggesting the grounds of the erstwhile Nikolaus barracks on Nikolausring to be a suitable location.2 With the appointment of a large number of socialists to the city council following the 1902 elections, the project for the municipal public bath was promoted with even more enthusiasm, which led to a new proposal on 3 February 1904. On 28 September 1904, the city council agreed to adopt a modified version of the Bauinspektor (municipal building inspector) Fritz Beblo’s scheme presented earlier that year.3 The building was completed between 1905 and 1908 (public bath); a wing specially dedicated to public health was opened in 1910. Beblo’s plans provided for two separate pools: one for men (14.4 m × 26.6 m) and one for women (10.3 m × 18.4 m). Arranged perpendicular to each other, the two swimming baths were characterized by their tall half-hipped roofs. Situated in between were the Turkish baths, complete with a steam bath and a so-called Wildbad (cold water bath). In addition, there were 54 shower and bathtub rooms, which were not purposed for swimming but for practicing personal hygiene. They were arranged across three levels according to class and divided by gender, respectively. They were situated in the two wings on either side of the oval-shaped foyer that projected out from the facade. The building in Strasbourg was developed as a reinforced concrete skeleton structure.4 Several reasons may have led to this decision. The Strasbourg building authorities were very open to innovation and thus endorsed the use of new construction types, such as reinforced concrete. Eduard Züblin, one of the top reinforced concrete design engineers at the time, even relocated

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to Strasbourg to establish his construction company in 1898,5 further evidence of the city’s experimental construction climate at the turn of the 20th century. Züblin’s endeavors to establish the French Hennebique construction system in Strasbourg were not least crowned with success because the municipal building authorities had been restructured in line with the German administrative model. That the city building department played a key role in the authorization of the reinforced concrete structure for the public bath manifests itself in the fact that its officials were responsible for evaluating the building application. The load-bearing analysis enables us to identify the edifice as a reinforced concrete skeleton structure in line with the Hennebique system, even if it is not explicitly named. From the point of view of structural engineering, the barrel-shaped ceiling vaults spanning the two swimming baths for women and men, respectively, presented a highly innovative solution. As had been the case in Munich’s Müllersches Volksbad, built using the construction system of Monier, and with the public bath in Colmar,6 which Züblin built in 1904, a decision was made in favor of reinforced concrete structures over an iron structure, which was popular above all in England. The reason was twofold: first, reinforced concrete vaults were less susceptible to corrosion, and second, they offered additional heating advantages. Moreover, the swimming bath roofs in Strasbourg were conceived as a double shell in order to prevent condensation. In order to be able to realize vaults spanning 16.90 m over the male pool and 17 m over the female pool, girders (so-called sickle-shaped binders) (Fig. 1) were positioned at 5.25 m (male pool) and 4.4 m (female pool) intervals. Longitudinal ribs were placed between the main beams to support two “covers”—one at the top and one at the bottom, leading to the space-defining shells of a maximum thickness of 80 mm. In addition, the plans show that the lower shells were hung from the upper longitudinal ribs between these girders.3 Accordingly, the structure cannot be regarded as a “shell” in the strict sense of the technical term as this shell does not itself perform any supporting action from a load-bearing perspective and, therefore, has not been designed as such. The reinforced concrete roof structures are visible neither in the female nor in the male pools, just as

Fig. 1: Eduard Züblin’s sickle-shaped binders over the swimming pool in the bath5 (AVCUS 843 W 488)

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INTRODUCTION

(a)

(b)

Fig. 2: (a) Fritz Beblo’s municipal public bath at Strasbourg. (b) Barrel vaults over the swimming baths they are invisible in the foyer, which boasts a dome likewise made of reinforced concrete. The ceilings are embellished with stucco work and colored borders (Fig. 2). The second notable innovation by Eduard Züblin concerns the design of the pool. In 1900, the company built the first public bath featuring a pool made of “béton armé” (reinforced concrete) in the Alsatian town of Gebweiler/Guebwiller.7 Until then, swimming pools had been made of tamped concrete or unreinforced concrete. This kind of construction was prone to stress cracking in the case of fluctuations in temperature, which led to leakages in the pool. Here, Züblin was able to capitalize on his engineering experience in designing silos.8 For Gebweiler and for the public bath at Strasbourg six years later, he came up with a structure with a thickness of just 150 mm, which was reinforced on the outer wall by ribs made of reinforced concrete. The pool is mounted freely on supports and separated from the structure by an expansion joint to prevent tension caused by temperature-related changes in lengths. Züblin’s innovation was duly noted in the technical press; Fritz von Emperger published a paper on the pool in Gebweiler in 1902 in his journal “Neuere Bauweisen und Bauwerke aus Beton und Eisen” (State-of-the-art construction methods and buildings made of concrete and steel).7 The builders of the Strasbourg public bath were not given much time to see their creation in action. After fewer than ten years in operation, Alsace once again became French, or perhaps Alsatian to be more accurate; the “old Germans” were hounded out, among them the pool architect Fritz Beblo, who moved back to Munich where he took up the post of head of city architecture. The Swiss engineer Eduard Züblin emigrated to Zurich, where he died in 1916. The municipal bathhouse of Strasbourg is exceptional in France; it represents the only example of a public bath dating from the period of German rule in Alsace (1871–1918) that is still functioning in its original form today. It is also the only public pool located directly in Strasbourg city center, and its place in the collective consciousness is, if possible, even more prevalent. Since 1908, the imposing building that houses the pool for men and women has dominated the residential area on the former Nikolausring, today known as the Boulevard de la Victoire. The location lies on the border between the medieval city center and the “Neustadt” or “German New town” that began to develop from the 1880s to the northeast of the city, and which is now being integrated in the UNESCO preserved area of the city of Strasbourg. In 1910, this impressive building was extended to incorporate a medical wing, which housed sports facilities and medical

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baths, as well as a treatment center for tooth and gum infections. The uneven trapezium form of the plot still determines the facet of the baths today. The whole front length of the elevated high baroque façade is visible from the street.1 A preservation report, recently commissioned by the city of Strasbourg, lists only minor damage to the plaster, caused by humidity.9 To the rear of the building, there is an area that backs onto Rue Prechter and is hardly used today. Feasibility studies, hotly debated at the time in Strasbourg on a political level, have proposed this area for a possible extension. A preservation report by the Atelier Oziol-de Micheli, dated February 2016, is the first attempt after the building was declared a listed monument on 10 October 2000.2 Today, the bathing facilities, including the sauna area of the municipal baths, are still retained from the original. Only minor details, like the closing mechanisms in the changing rooms for example, were redeveloped in the interwar years. The room datasheet also documents moisture damage on the wood floor in the changing cabins.9 The glass windows are also from the original. In the same way, the slightly more playful women’s bath (18 m long) has also retained all of its original features.2 Both the men’s and women’s pools are equipped with fully functioning showers with fittings from the original period. Also dating from the pre-World War I period is the ventilation system, in a slightly altered state but still functioning today.9 The reinforced concrete constructions of the pools were well-known for long-lasting stability, with no need for any repairs. The preservation report mentioned only corrosion of some reinforcing bars on the expansion joint of the female pool. The reinforced concrete roof structures, also designed by Züblin, were of the highest standard technically achievable at that time and have been maintained with particular care. These very complicated features call for a sophisticated restoration scheme, which the authorities were able to present only six years after the first preparation meetings in 2010. The main problem impeding rapid decision making was the question of a partial privatization of the bath, which—according to earlier plans—would comprise at least the steam bath and the sauna. However, bowing to public pressure, at a meeting on 24 June 2016, Strasbourg’s mayor Roland Ries, accompanied by the department heads of finance, health and sport, as well as the staff of the municipal building institutions, presented a plan that will keep the bath in the public domain. The estimated renovation cost of 30 million euros will be partly financed by earnings on the maintenance cost and from the rent of the former engine building to a public health company. The former health building, to the left of the structure, is not included in the renovation plan. As it has the greatest financial value due to its strategic position on the avenue, speculations are ongoing about its future destination.

References [1]

[2] [3]

Kostka A. La genèse transnationale des Bains municipaux de Strasbourg. In Strasbourg De la Grande-île à la Neustadt: un patrimoine urbain exceptionnel, Cassaz D, Eberhardt S (eds) Lieux Dits: Lyon, 2013; 113–120. Fritsch F. Bains Municipaux de la Ville de Strasbourg. Strasbourg: Direction Regionale des Affaires Culturelles. Unpublished document, 2011. Weber Ch. Les Bains Municipaux at Strasbourg (1905–1908): an example of cultural and technical transfer between France and Germany. In Proceedings of the Second Conference of the Construction History Society Queens’ College, Campbell JWP, James-Chakraborty K (eds), Cambridge, 20–21 March 2015, 2015; 199–208.

REFERENCES

[4]

117

Weber Ch. Der Ingenieur Eduard Züblin in Straßburg: Erste Überlegungen zu bautechnischen Transferphänomenen. METACULT. No. 2, 2014; 39–44. [5] Everts-Grigat S, & Fuchs K. Züblin: 100 Jahre Bautechnik 1898–1998 Eduard Züblin AG: Stuttgart, 1998. [6] Triboux P. Strasbourg, Colmar, Mulhouse: les programmes de bains municipaux en Alsace au début du XXe siècle. Une politique volontaire d’hygiène publique. Livraisons de l’histoire de l’architecture 2007; 14: 81–93. [7] Emperger F. Neuere Bauweisen und Bauwerke aus Beton und Eisen, vol. 2 Lehmann & Wentzel: Wien, 1902. [8] Kostka A, Weber Ch. Municipal baths at the beginning of the twentieth century: an example of Franco-German cultural and technical transfer in the Upper Rhine Region. Proceedings of the Fourth International Meeting of the European Architectural History Network, Dublin/Ireland, 2–4 June 2016, 2016; 146–161. [9] Atelier Oziol-de Micheli. Les Bains Municipaux Boulevard de la Victoire Strasbourg: Diagnostic Patrimonial, Strasbourg. Unpublished document, 2016. [10] Franck E. Städtisches Schwimm- und Medicinalbad in Straßburg i. E. Bauzeitung für Württemberg, Baden, Hessen, Elsass-Lothringen, vol. 5, no. 41, 1908; 325–328. [11] Grandvionnet Ph. Les bains municipaux de Strasbourg (1894–1911) dans l’architecture européenne des bains publics. METACULT. No. 4, 2015; 20–27.

119 Chapter

6.12 History and Rehabilitation of Reinforced Brick Ceiling

Michael Fischer, Prof., PhD, Struct. Eng., Dr. Lorenz & Co. Bauingenieure GmbH, Berlin, Germany

Introduction This paper provides a current assessment of the fire resistance of a real-world example of a Kleinesche Decke. Knowing the slab’s construction history is essential for its assessment. In Germany, Johann Friedrich Kleine obtained the patent for the first and still well-known reinforced brick floor (Fig. 1) in 1892. By 1910, more than 60 different slab systems of that kind came up here. For many years, this diversity outpaced that of reinforced concrete slabs developed at about the same time. However, above all, reinforced brick floor systems were also more widely used. Easy to build and inexpensive, reinforced brick floors shaped multistory construction worldwide since the early 20th century.1

Current Structural Condition The former Albert Schweitzer School in Hannover was constructed in 1896–1897. The building is to be converted into a residential building. Although all floor slabs are designed as a

Fig. 1: Exemplary illustration of a Kleinesche Decke1

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Fig. 2: Schematic diagram: slab structure of the housing space

Kleinesche Decke, they vary slightly from room to room. This fact entails, to some extent, different fire resistance ratings. Generally, there are two types of slabs: slabs in the housing space and those in the corridors. The wood strip flooring in the housing space (Fig. 2) is covered with different floor coverings, such as magnesite flooring or linoleum. Furthermore, the smaller rooms were constructed using floor girders with reduced dimensions due to shorter spans. However, these variations are not relevant to the fire resistance classification. All slabs above the corridors, excluding the top slab, comply with the schematic diagram variant 1 (Fig. 3). Variant 2 for the top slab (Fig. 4) differs with respect to the unconfined floor girder’s top flange, entailing a reduced fire resistance period.

Fire Resistance Classification Fig. 3: Schematic diagram: slab structure of the corridor—variant 1

Fig. 4: Schematic diagram: slab structure of the corridor—variant 2 (top slab)

Generally, it is not easy to determine the fire resistance of the present slabs as the Kleinesche Decke type is not listed in the German national standard DIN 4102—Brandverhalten von Baustoffen und Bauteilen (DIN 4102—behavior under fire).2 The following classification is based on comparisons with similar constructions listed in the DIN as well as on evaluations of about 30 load tests on historical reinforced brick floors carried out in recent years.1 The slabs are assigned different fire resistance classifications due to their differences in structure. There are two different classification criteria: slab bay and floor girder (Table 1, Fig. 5).

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FIRE RESISTANCE CLASSIFICATION

Room

Housing space

Corridor variant 1

Corridor variant 2 (top slab)

Min. in accordance with DIN 4102-4 F 30 See table 27, row 1.2 With a brick course d=100 mm (Fig. 5) F 60 According to table 27, row 2.1 Centre distance u = 15 mm from 30 mm reinforcing bar to lower edge (Fig. 5) F 30 See table 27, row 1.2 With a brick course d = 100 mm (Fig. 5)

Slab bay Floor girder Max. in Recommended In accordance Recommended accordance fire resistance with DIN fire resistance with DIN classification 4102-4 classification 4102-4 Classification F 90 F 30 F 30* not possible See table 29 With a brick course d = 100 mm (Fig. 5) F 60 F 30 F 30 See table 29 Bottom flange plastered with 20–30 mm lime cement (MGII)

F 30

Classification not possible

F 30*

* Load tests on reinforced brick floors of different construction types.

Table 1: Fire resistance classifications with reference to DIN 4102 as well as to the evaluations of load tests

Load tests (experimental load-bearing capacity tests) on reinforced brick floors of different construction types (particularly on the slab type Kleinesche Decke) were conducted by different institutions in the last few years. They showed that these slabs can normally carry considerably heavier loads than the loads principally calculated (Table 1). There are different reasons. For example, for the calculations, slab bays are usually assumed to be simply supported between the girders, whereas in practice, slab bays are often partially fixed. However, above all, the slab

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bays carry a considerable part of the load due to the arch action. Additionally, this observation is supported by the fact that failure due to bending occurred almost always simultaneously with the crushing of the compression area in the present case. As the slab bays enhance the structural performance of steel girders due to their composite structure, part of the brick ceiling can be considered to be an effective width of the floor girder.1 Therefore, it can be assumed that in the current case, where the top flange (housing space and corridor variant 2) is merely inadequately confined, Fig. 5: Core sample taken from the slab there is no immediate danger of a floor collapse, examined showing 100 mm bricks and even in case of fire loading on the girder’s com30 mm reinforcing bar pression area. There are several historical reports of fire tests conducted on reinforced brick floors of the Kleinesche Decke. As a result, these slabs and girders, which were mainly plastered with lime cement, were assigned a “high fire resistance” at temperatures of at least 1000°C. Through load tests carried out after the fire tests, it was also proved that the load-bearing capacity of the slabs remained unaffected.3 One of these reports describes a fire test that was discontinued after 70  min while the slab remained undamaged.4 Unfortunately, these reports show the tendency for the Kleinesche Decke’s behavior only under fire conditions. However, these reports cannot be used within the scope of current standards.

Summary and Conclusion It is not possible to determine unambiguously the fire classification of the present Kleinesche Decke built in 1897 by using the current German national standard DIN 4102—Brandverhalten von Baustoffen und Bauteilen (DIN 4102—behavior under fire).2 By comparing the given example with the slab types documented in the DIN 4102, as well as by evaluating numerous experimental load-bearing capacity tests on reinforced brick floors, it can be recommended that the present slab bays should be categorized into class F 60 for parts of the corridor and into class F 30 for parts of the housing space. Moreover, it is recommended that the present steel girders should be assigned class F 30. Therefore, as a precaution, it is recommended that class F 30 should be applied for the entire system. The partial fixity of slab bays along the bearing area, proven by experimental load-bearing capacity tests and, in particular, the arch action of the slab bays, grant additional safety benefits with respect to a fire load [refs 5 to 9].

References [1] Fischer M. Steineisendecken im Deutschen Reich 1892–1925, Cottbus, Dissertation, 2008. [2] DIN 4102-4. Brandverhalten von Baustoffen und Bauteilen – Teil 4: Zusammenstellung und Anwendung klassifizierter Baustoffe, Bauteile und Sonderbauteile Beuth: Berlin, 1994. [3] Lange W. Konstruktive Neuerungen aus dem Gebiet des Hochbauwesens. Winter: Bremen, 1896. [4] Kolbe E. Die wichtigsten Decken und Wände der Gegenwart. Kühne: Oberhausen, 1905.

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[5] Ahnert R, & Krause KH. Typische Baukonstruktionen von 1860 bis 1960, zur Beurteilung der vorhandenen Bausubstanz. Bauwesen: Berlin, 2001. [6] Mittmann T, Bermes B. “Brandprüfungen an historischen Stahlsteindecken”. Sonderdruck FeuerTrutz Magazin 5, 2012. [7] Pötke W. Tragfähigkeitsnachweise an Stahlsteindecken für die Umnutzung alter Gebäude. Selbstverlag: Berlin, 1998. [8] Promat. Bauen im Bestand, Bautechnischer Brandschutz für Massivdecken. Eigenverlag: Ratingen, 2012. [9] Steller F, Fiedler, L.-D., & Quade J. Nachweis der Tragfähigkeit von Stahlsteindecken am Beispiel der Leipziger Pianofortfabrik. Bautechnik 1996; 73: 8–14.

125 Chapter

6.13 Reconstruction of the Neues Museum in Berlin

Gerhard Eisele, Prof. Dipl.-Ing., Professor, University of Applied Sciences, Potsdam, Germany Josef Seiler, Dipl.-Ing., Partner, Ingenieurgruppe Bauen, Karlsruhe, Germany

Introduction The Neues Museum in Berlin, Germany, was built between 1841 and 1859 under the management of Friedrich August Stüler, a pupil of Karl-Friedrich Schinkel. Although designed with a solid appearance to the outside observer, the building’s interiors were a compelling combination of the latest cast-iron technology and ancient lightweight construction techniques. However, shortly after its opening, the museum building began to show settlement damage. This settlement activity persisted and reached a depth of 400 mm at the most unfavorable location. In 1943, during World War II, the central staircase hall was bombed. The northwest wing, the Egyptian courtyard and the southeast dome suffered the same fate in 1945. Some parts of the building were left fully exposed to the elements for over 40 years. The significance of the remaining fabric was recognized in the mid-1980s, prompting a decision to reconstruct the Neues Museum; however, significant portions of the damaged building sections had to be demolished. Some historic structures are unsuitable for a formal evaluation solely based on generally accepted verification methods or modern codes and standards. For this reason, experimental methods had to be considered at an early stage in order to support the structural stability analysis required for the historic elements.1 The verification methodology was defined at the concept planning stage and implemented experimentally in close cooperation with Prof. Steffens, Ingenieurgesellschaft mbH (PSI), Bremen.

Aspect of Structural Design during Reconstruction Following the early use of iron in buildings in the 1790s in England, the Neues Museum was one of the first prestigious buildings in Berlin in which the use of iron became a distinct feature in both structural and architectural terms. Because of the issues that arose from the unstable ground, dead loads had to be minimized, and masonry ceilings built on “clay pots” were

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thus used. Given the history of the building, most parts of the surviving original ceilings were found to be in astonishingly good structural condition. However, real problems arose in some of the floor bays where weather exposure had damaged the fabric or where significant sagging occurred in central sections due to the removal of lateral supporting members. The client requested that all ceilings should be upgraded to fulfill current requirements so that they could withstand service loads of up to 5 kN/m2 in accordance with DIN 1055. Estimates and information given in the original building documentation give rise to the assumption that load-bearing capacities of 200 kg/m2 (2 kN/m2) were considered sufficient at the time of construction.2 The structural design aimed to preserve the historic structures as a technical monument and to return them to their original purpose, as undisturbed as possible, while also responding to the client’s requests. The remaining original structures took priority so that the exhibition layout could be adjusted to the specific situation as and when required. Structurally supporting members, such as large sections of the iron structures, were evaluated using modern verification concepts. The investigations revealed that some of these structures provided significant load-bearing reserves for their original purpose.

Assessment of the Load-Bearing Capacity of Clay Pot Ceilings The concave design of the ceiling areas was based on an ancient technique that used cylindrical, completely closed, hollow clay “bricks” laid in gypsum mortar, which were referred to as clay pots in the project documents. This method provides an extremely low weight-per-unit area at remarkably high load-bearing capacities (Figs. 1 and 2).

Fig. 1: Condition of the Calotte ceiling consisting of clay pots prior to reconstruction (courtesy: Ingenieurgruppe Bauen)

The clay pots were manufactured with only 7–10 mm thick walls and lids. They were used as bricks for various purposes, again held together with a gypsum mortar. Among other features, this construction method was used for the calotte ceilings consisting of transverse arches and brickwork pendentives interspaced with spherical domes of around 4.5 m in diameter, barrel vaults with 5–6 m spans (Fig. 3) and vaulted ceilings between steel beams.

Clay pots h ~ 16 cm, ø 12 cm Clay pots h ~ 20 cm, ø 13 cm Clay pots h ~ 23 cm, ø 14 cm 2–3 Solid clay bricks h = 26 cm

Fig. 2: General structure of a clay pot vault

Structural Analysis In the initial step, the loads acting on the existing clay pot ceiling systems (calotte ceilings, barrel vaults and vaulted ceilings) were estimated based on preliminary calculations.

ASSESSMENT OF THE LOAD-BEARING CAPACITY OF CLAY POT CEILINGS

For this purpose, assumptions had to be made regarding material characteristics, such as the modulus of elasticity, load-bearing capacity and stiffness of the system. All reference documents found in the literature were used. The analyses of a historical load test performed on a single-bay vault3 were compared with the results of a calculation using a three-dimensional (3D) finiteelement (FE) model. Parametric studies carried out for structurally determinate subsystems were used to vary the derived assumptions for the material characteristics and to analyze the results of the calculations. The basic findings from this work were as follows:

127

Fig. 3: Soffit of new clay pot barrel vault after removal of falsework (both illustrations courtesy: Ingenieurgruppe Bauen)

• The highest loads acting on the clay pot structures are in the barrel vaults. • Due to the relatively low dead loads, the effects of loads that vary from bay to bay (“kinematics”) must also be considered for the barrel vaults because they form multibay systems. • The design can be interpreted as a combination of two load-bearing effects: a diaphragm effect in the plane of the pot lids and a more flexible honeycomb structure in the crosssection. • The service loads that the ceilings may potentially withstand cannot be determined without supplementary experimental tests.

Experimental Tests The findings of the structural analysis were used to develop the following program to estimate the load-bearing capacity of the clay pot ceilings: • • • •

Preliminary load test on an existing four-bay barrel vault to identify the system. Basic tests on small specimens with associated numerical analyses. Load test on a newly built sample vault. Development of an appropriate computation model and structural verifications for all clay pot systems. • Confirmation of the computation model, and thus of the load-bearing capacity, using load tests in selected locations. • Inclusion of the plaster floor forming part of the historic ceilings in the load-bearing capacity analysis and evaluation of its contribution to the ceiling areas to be reconstructed.

Preliminary Load Test on an Existing Four-bay Barrel Vault A four-bay barrel vault with spans of approximately 6 m was chosen for the preliminary load tests. Two bays were alternately loaded in order to analyze the stiffness of the overall system, deformation behavior, the modulus of elasticity of the clay pot mortar matrix, torsion of the

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transverse arches, continuity effect and biaxial structural effect. Mobile load frames were used to generate service loads that varied from bay to bay. Online measuring equipment and an associated acoustic emission analysis (AEA) were used to ensure that the testing was nondestructive. The system for subsequent FE calculation was derived from the measured deformation and deflection values.

Basic Tests on Small Specimens In addition to conserving and repairing the existing ceilings, two of the original seven bays of a barrel vault system were to be complemented by five new clay pot floor bays replicating the original design. This meant that the clay pots and the gypsum mortar mixes had to be selected in order to ensure that their mechanical properties and appearance largely corresponded to the original materials. To achieve this goal, laboratory tests were conducted on about 30 small specimens of various “pots” and mortars in different combinations and load cases. An AEA of these small specimens was performed for calibration purposes. The materials ultimately used for the reconstruction work were selected based on these tests. The tests and associated calculations with a refined model based on an elastoplastic material law were used to prove the existence of a redundant structural system. After failure of the rigid outer shell (i.e., pot lids breaking away), the load shifts to the honeycomb structure formed by the pot walls and the mortar within the cross-section; this is associated with a corresponding increase in deformation.

Sample Vault Because the original vault could not be used for limit load tests, a new full-scale two-bay sample vault was constructed within the building. This structure also provided an opportunity to test specific techniques and work sequences. In the first test series, the effect of a partially loadbearing plaster layer was investigated. A supplementary load-bearing plaster floor was included in subsequent testing. The structure was loaded to failure in the course of the second series of measurements and included the structural effect of the plaster. The results complemented the values calculated for the existing and newly designed floor bays and ultimately confirmed that the load-bearing capacities were sufficient for museum use.

Reinforcement of Cast-Iron Girders with CFRP Sheets In keeping with the trend of the time, the original building was constructed with many cast-iron components. This is unproblematic wherever such structural members are loaded mainly in compression. However, cast-iron sections were also used as joists, between which the infill brickwork could be inserted very easily to form vaulted ceilings. These joists are subjected to bending with a marked tensile bending zone, which is why they also had to be verified for the service loads required by modern use patterns. The tensile strength of the original cast iron amounts to only 30–40% of its compressive strength. Inhomogeneities caused by the manufacturing process (shrinkage cavities) weaken the tension zones, thus leading to a dangerous susceptibility to brittle failure. Approximate calculations using design methods specified in the literature3 resulted in theoretically permissible service loads between 1.0 and 2.0 kN/m2 assuming undamaged structural components—quite optimistic given the history of the building. These values

CONCLUSIONS

129 are insufficient if the building is to be used as a museum. Historic cast iron cannot be welded, and bolted steel fish plates were not an option owing to the shape of the elements. One possible solution was to reinforce the iron with carbon fiberreinforced plastic (CFRP) sheets in the tensile zone (Fig. 4). This method is widely known in concrete construction and complies with conservation requirements because mechanical interventions in the member to be reinforced are not necessary. In addition, installation of the reinforcement is reversible. No prior experience existed regarding reinforcement measures for this combination of materials. For this reason, a verification concept was developed jointly with the Institute of Concrete Construction and Fire Protection at Braunschweig University of Technology. This concept is based on the method used for unreinforced beams developed by Frey and Käpplein.3

The first step was to obtain basic information on Fig. 4: Section of ceiling above the ves- the behavior of cast-iron beams. New beams were tibule consisting of clay pots between cast for this purpose. In our high-tech society, it cast-iron girders (300 mm deep). Below: is not at all easy to produce grey cast iron to the detailed section showing CFRP sheet rein- lower quality standard equivalent to the original forcement underneath the historic soffit condition. The beams were partially damaged lining made of zinc (courtesy: Ingenieur- prior to testing and subjected to experiments to determine their load-bearing capacities in the gruppe Bauen) reinforced and nonreinforced condition. Based on the test results, a realistic design method was developed that proved a sufficient degree of postreinforcement safety, even for previously damaged cast-iron beams. The reinforcing CFRP sheets were selected and dimensioned on this basis (Fig. 4): they are 1.4 mm thick and 50 mm high. For verification purposes, on-site confirmation tests were performed in selected trial bays after installation of the reinforcement. These tests provided impressive proof of its effectiveness. The specified service load of 5 kN/m2 was thus confirmed for all historic ceilings. References [4, 5] give a more detailed account of this section.

Conclusions Increasingly, construction engineers need to strike a balance between historic structural designs and modern use requirements. Although these challenges are usually mastered (virtually anything is possible from a purely technical point of view), thorough understanding of historic structures and conservation objectives is not widespread. However, such an understanding is key to the successful treatment of buildings with high conservation significance. In the case reported in this paper, the most important responsibility of the engineers was to recognize, at an early stage, that purely theoretical approaches would not deliver the intended result and that all parties involved in the project—such as the client, user, architect and required experts—needed

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to engage in the discussions, which also had to be facilitated. Key services that needed to be provided included the development of verification concepts, the planning and design of the required tests in a cross-disciplinary approach and coordination of all the activities with the supervising authority.

References [1] Steffens K. Experimentelle Tragsicherheitsbewertung von Bauwerken. Grundlagen und Anwendungsbeispiele. Ernst & Sohn: Berlin, 2001 (in German). [2] Hoffmann CW. Die feuerfesten Decken des Neuen Museums hierselbst. In Notizblatt des Architektenvereins Berlin, 1846 (in German). [3] Frey A, & Käpplein R. Beitrag zum rechnerischen Nachweis der Tragfähigkeit alter Biegeträger aus Gusseisen. Stahlbau 1993; 62(8): 221–230 (in German). [4] Eisele G, Gutermann M, Seiler J, & Steffens K. Wiederaufbau des Neuen Museums in Berlin 2 Tragwerksplanung pro Baudenkmalpflege. Bautechnik 2004; 81(6): 407–422 (in German). [5] Eisele G. Tragfähigkeitsbewertung an Natursteinsäulen am Neuen Museum in Berlin. In Natursteinsanierung Stuttgart 2006. Neue Natursteinrestaurierungsergebnisse und messtechnische Erfassungen, Grassegger G, Patitz G (eds) Fraunhofer IRB: Stuttgart, 2006; 19–28 (in German). [6] Lorenz W. Das Neue Museum Berlin (Historische Wahrzeichen der Ingenieurbaukunst in Deutschland, 15) Bundesingenieurkammer: Berlin, 2014 (in German).

131 Chapter

7.1 The Necessity for Construction History to Assess Historic Bridge Bearings

VolkerWetzk, BTU Cottbus-Senftenberg, Chair of Construction History and Structural Preservation, Cottbus, Germany

Introduction With existing bridge structures having to be maintained or refurbished, we find that historic steel bridge bearings are reentering the engineers’ perception. Due to their sturdiness, they are mostly found to be in sound condition despite having served for more than a century, often negligently maintained and carrying increasing loads. If still in use, however, we have very little reliable information as to their structural assessment. This uncertainty often leads to the costly replacement of bearings that look intact. Such premature exchanges contribute to a permanent loss of historic fabric.

Historic Bridge Bearings With hindsight, we can recognize three generations of bridge bearings, which are distinguishable with regard to their mode of action and to their material: wood, iron/steel and synthetic materials. This article deals with the second generation, that is, those made of iron and steel. They were introduced in the same period that saw iron being widely used for bridges, which allowed for new dimensions in bridge building that were hardly dreamt of only few years before. Rollers, pins and pivots came to characterize this generation of bearings in a very short time; these prominent features, together with the optimized bearing geometry, give this generation its specific aesthetic value. Initially, the bearings were used to provide movability in a longitudinal direction, and subsequently in the lateral direction too. Occasionally, we do not find any fixed bearings in these bridges at all.1 This second generation is characterized by two main materials—cast iron and steel, the latter produced by casting or by forging. The compact bearing plates with complex geometrical designs were initially made of cast iron. However, bearing technology was an early instance of appropriating steel castings. Beginning in the 1870s, for both tilting and bearing plates, steel castings became a serious competitor for the last domain of iron castings in bridge building. By 1880, steel castings were ranked as excellent, albeit expensive, substitutes for cast iron. From 1920 onward, the former had fully replaced cast iron. Historic bearings still in use tend to be

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(b)

Fig. 1: (a) Moveable bearing of the second Dirschau Bridge (1889–1891). The pivots and stilts with a simple geometric design for absorbing heavy loads were forged from expensive crucible steel ingots, whereas the other main parts of the bearings were already Martin steel castings. (b) Fixed bearing at Hamburg Brooks Bridge (1887) with stiffened ribs ordinarily used2 made of steel castings. Establishing steel casting also resulted in a specific geometry for the castbearing parts. Initially, the molds developed for iron casting were used, but soon, foundry practice required castings with an almost equal thickness. Plates with stiffened ribs became characteristic for bearings cast with steel (Fig. 1). This measure was to prevent large shrinkage holes. Nevertheless, massive bearing castings without ribs were used well into the 20th century. If the casting was performed incorrectly, such bearings might contain significant shrinkage holes.2

Structural Assessment of Historic Bearings In compliance with the practice in structural engineering, assessing historic bearings requires knowledge to evaluate their load-bearing capacity and serviceability. Because of the particular task of moveable bearings as part of the entire structure, however, the issue of serviceability is as important as that of the load-bearing capacity: A single nonfunctional bearing—regardless of the individual cause—has to count as a failure of the entire bearing, and this in turn may entail serious consequences for the level of safety in the substructure and/or superstructure. According to the ICOMOS-Charter of Victoria Falls,3 the knowledge of the fabrics’ history is extraordinarily relevant to the structural assessment of historic fabric. Such an approach might be timeconsuming; nevertheless, it is essential for producing the relevant qualitative and quantitative knowledge. This holds true for the assessment of historic bearings as well. Most quantitative statements will be based on material testing performed on the bearing on-site (Fig. 2). For both choosing the correct methodology and evaluating the results, knowledge of the historic practices with regard to technology and engineering procedures provides indispensable guidance.

Assessment of Load-Bearing Capacity Dependable statements concerning the load-bearing capacity of bridge bearings require information about their mechanical properties as well as the textural properties of the bearing material. Knowledge about the material’s texture can be obtained on site without any problems. Experience shows that surface flaws are very rare, whereas indicators for the existence of volumetric

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ASSESSMENT OF LOAD-BEARING CAPACITY

Fig. 2: Material and textural investigation at Teltow-Kanal Bridge, Berlin; from left to right: Hardness measurement, magnetic crack testing, ultrasonography investigation4 flaws are found much more often (Fig. 3). Adopting a historical perspective may help understand the problem behind such flaws. Early 20th-century literature—when bearings made from steel castings were most popular—addressing technological issues reveals that equalizing shrinkage to avoid holes during production was very complicated.5 However, if compared with foundry products required at that time for applications in mechanical engineering, the shape casting of steel-bearing elements was not a big challenge. This may have led to something of a “routine attitude” among foundry men, when it came to casting bridge bearings that led to imprecisions during production, which in turn could cause significant volumetric flaws.2 This means that a responsible structural assessment of volumetric flaws is particularly significant. Experience yields a first and comforting observation: even bearings with a considerable shrinkage hole have performed reliably and coped with stresses for many decades. In addition, it turns out that a shrinkage hole mostly occurs in the core region of a cast part during production. In most cases, they are small and thus insignificant with regard to the overall dimension of the bearing part and the distribution of stresses. For example, in the case of the shrinkage hole shown in Fig. 3, the flaw was only found to exist in the middle fifth of the plate’s longitudinal direction. Knowledge about the material’s mechanics can only be gathered in situ by means of nondestructive testing procedures; tests concerning hardness measurements revealed (a)

(b)

Fig. 3: (a) Moveable bearing cast c.1939. (b) Slice taken from bearing plate (dashed in left figure). In spite of the shrinkage hole, plastic deformations occurred in the contact region between plate and roller (dashed in right-side figure)— a clear indicator of the very high level of overall stiffness of the bearing plate4

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(a)

(b)

Fig. 4: (a) Laboratory microstructural investigation in the peripheral area of a historic bearing made of steel casting; the decarburization close to the surface can be seen as well as the outer layer of tinder.8 (b) Surface of a bearing plate made of steel casting prepared on site for examination of material. The polished layer of tinder is visible (middle) as well as the removed layer close to the periphery (right) (Photograph courtesy: Ref. [4])

the potential of the Leeb method for assessing the tensile strength of historic bearings material.6 The extraction of a small sample for further tests in the laboratory is only possible in single cases. Successful nondestructive access to the bearings presupposes detailed knowledge of how steel castings were produced in different periods. For normalizing the brittle cast texture, all casting blanks were subjected to an extended heat treatment. For a complete textural transformation, unalloyed cast steel had to be annealed at a temperature depending on the carbon share of the material. The entire process of the thermal treatment, however, was only scientifically proven as late as 1915. This means that in the case of early steel castings with low carbon share, a complete textural transformation as part of the thermal treatment at production is unlikely.7 A negative side effect of this heat treatment was the decarburization of the peripheral area, which can be distinguished in Fig. 4a by the increased share of ferrite toward the edge. Furthermore, the annealing yielded a thin, but very hard, layer of tinder enveloping the comparably soft ferritic margin layer (Fig. 4a).7 Grinding down this peripheral area is a precondition for successfully applying nondestructive tests. Further treatment may be required depending on the examination procedure selected. For example, if hardness is to be measured, the surface has to be sanded in conformity with the applicable standards (Fig. 4b).

Assessment of Serviceability Any assessment of the serviceability will mostly concern moveable bearings. The main focus is on the contact zone between the rolling elements and the bearing plates as any plastic deformations of these areas determine the rolling resistance of the bearing. Since the introduction of this bearing generation, a great body of research has addressed this issue. It has also been central to a recent research collaboration between BTU Cottbus and BAM Berlin, yielding a number of publications, which also address the historical development of the contact issue.4,9,10 History provides useful insights when it comes to assessing the contact issue and thus the serviceability. Suffice to say that the rolling elements in the 19th century were more or less dimensioned based on empirical procedures and provide load-bearing capacity reserves if compared with roller sizes arrived at via current design approaches (Fig. 5). Furthermore, history reveals that the careless attitude toward maintaining bridge bearings, often complained about today, dates back

135

REFERENCES

Required Geometry of Rollers

90

Cast Iron

80

Cast Steel

70

Wrought Iron and Steel

60

High-Strength Steel

50 40 30 20 10 DIN 1050, 1937

DIN 18800-1, 1990

B.E., 1925

B.E., 1922

Minister, 1923

Schaper, 1922

Kollmar, 1914

Schaper, 1908

Bernhard, 1911

Vianello, 1905

Kübler, 1900

Tetmajer, 1905

Weyrauch, 1894

Bach, 1889

Deslandres, 1893

Tetmajer, 1889

Reuleaux, 1889

Steiner, 1882

Haeseler, 1888

Laissle, 1876

Winkler, 1875

Baentsch, 1876

Baldermann, 1871

Fränkel, 1869

Köpcke, 1869

Schwedler, 1861

Werder, 1857

0

Fig. 5: Development of the rollers’ radii according to the calculations in Germany4

to the early period of employing iron and steel bearings. Apparently, owners of bridges have not been aware of the machine-like nature of bearings that require regular monitoring and at least some cleaning and maintenance.11 Without these, the loss of serviceability may lead to critical levels of safety in the sub- and/or superstructure.

Value of Construction History Knowledge about the history of bearings as well as about the general conditions of technology and engineering of specific historic periods is essential for assessing the structural quality of bridge bearings made of steel. It provides the base for a successful approach for both the analysis of materials and textures as well as their appropriate evaluation by engineers.

References [1] [2]

[3]

[4] [5]

Wetzk V. Brückenlager. 1850–1950. Dissertation Thesis BTU Cottbus. https://opus4. kobv.de/opus4-btu/frontdoor/index/index/docId/2006, 2010. Wetzk V. The use of steel castings in mechanical and civil engineering—Germany. 1850–1950. In Proceedings of the Fifth International Congress on Construction History, Friedman D, Bowen B, Leslie T, Ochsendorf J (eds), Chicago, 3–7 June 2015, vol. 3, 2015; 585–592. ICOMOS. ICOMOS-Charter—Principles for the Analysis, Conservation and Structural Restoration of Architectural Heritage. Charter of Victoria Falls. Victoria Falls, Zimbabwe, 2003. Wetzk V, Eisenkolb T, & Mehdianpour M. Bewertung historischer Brückenlager – Das Kontaktproblem – Teil 1. Stahlbau 2011; 80(6): 404–412. EMPA. Schweizer Verband für die Materialprüfungen der Technik (Ed.): Der Stahlguss als Baustoff, Bericht Nr. 36, Zürich, 1929.

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Wetzk V, Schüle P. Assessing historic bridge bearings—the potential of hardness measurements for characterizing cast steel. In Proceedings of the Tenth International Conference on Structural Analysis of Historical Constructions, Balen, K v, Verstrynge, E (eds), Leuven, 13–16 September 2016, vol. 3, 2016; 828–831. [7] Wetzk V. Historic bridge bearings—material research on cast steel. In Proceedings of the Fourth International Congress on Construction History, Campbell J, Pan Y, Baker N, Driver M, Heaton M, Tutton M, Yeomans D, Rosoman T (eds), Paris, 3–7 July 2012, vol. 3, 2012; 243–252. [8] BAM. Microstructural Investigation of Bearings made of Steel Castings. Without report, 2013. [9] Eisenkolb T, & Mehdianpour M. Bewertung historischer Brückenlager – Das Kontaktproblem – Teil 2. Stahlbau 2012; 81(7): 510–518. [10] Eisenkolb T, & Mehdianpour M. Bewertung historischer Brückenlager – Experimentelle Untersuchungen zur Rollreibung. Stahlbau 2013; 82(12): 890–897. [11] Wetzk V. Editorial to themed issue on bridge bearings. Proceedings ICE—Engineering History and Heritage, vol. 168, EH2, 2015; 53–54.

137 Chapter

7.2 Refurbishing of the Nibelungen Bridge in Worms, Germany

Eberhard Pelke, Head of Structural Engineering Department, Hessen Mobil, Wiesbaden, Germany

State of the Structure and Historical Assessment The original bridge was opened to traffic in 1900. It consisted of three, two-centered steel arches, with the carriageway superimposed, which were supported on pillars with caisson foundations. The shore bridges are solid, three-centered arches made of tamped concrete faced with natural stone. The present Nibelungen Bridge in Worms forms part of federal highway 47 and links the municipalities of Worms and Bürstadt. The bridge has a total length of 745 m and is divided into three part structures of differing construction consisting of the same 109 m long shore bridge on the left side of the Rhine in Rhineland-Palatinate, the 351.8 m long center part of the bridge crossing the Rhine (Fig. 1) and the shore bridge on the Hesse side of a total length of 295.5 m. The current traffic volume amounts to some 23 000 vehicles every 24 h, with a moderate heavy vehicle share of 8.7%. In the case of the shore bridges, the 12 three-centered arches made of tamped concrete are still in existence. Solid sandstone faces the front side of the 11.4 m-wide arches and the areas directly in front of the hinges. The thickness of the arch lies between 0.67 m at the apex and c. 1 m at the quarter points of the arches. The arches are designed as compound curves with a radius of between 33 m in the case of the largest arch and 26 m in the case of the smallest one. The transverse prestressed carriageway plate made of B 450 quality concrete, incorporated in 1953, is supported over the whole surface in the crown area and above the masonry segments of the arches in the other areas. It is connected three times above the crown and impost hinges in each arch. Traffic used to drive directly on the carriageway plates, as was quite usual for the first prestressed concrete bridges. Between 1972 and 1974, the bridge was completely sealed using a mastic seal, and in the 42 transverse joints, single-seal expansion joints were provided. In the area of the shore bridges, the expansion joints had to be extensively touched up in 1981. Other preservation measures are in keeping with normal maintenance practice. In his lecture at the general meeting of the German Concrete Association (DBV) in Berlin in May 1952, Finsterwalder1 himself presented the fundamental design idea of cantilevering in prestressed concrete that

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Fig. 2: Finsterwalder’s design idea from 19312 dated back to the year 1930. On the occasion of the competition for the construction of a new Dreirosen Bridge in Basle, his company, Dyckerhoff & Widmann, had proposed two Fig. 1: Nibelungen Bridge, Worms, 1953 half arches connected rigidly above the pillar, the crowns of which were to be short-circuited via a tension member made of 60 mm thick wire ropes without connection. The prestressing was generated independently here by the dead weight (Fig. 2). The further historical development of prestressed concrete bridges and the outstanding position of the Nibelungen Bridge are acknowledged in Ref. [3]. Around 1948, Finsterwalder4 found the right material for his single prestressing bar in the self-hardening St 90 steel, known as St 60/90 shortly afterward, from the Krupp Rheinhausen steel works. With nearly double the tensile yield strength, the steel was unsusceptible to brittle fracture and stress corrosion. Finsterwalder succeeded in rolling a screw thread onto the approximately 26  mm thick rods, thus making them suitable for anchoring and connections, which he joined ingeniously simply using plates, sleeves and screws. Furthermore, Finsterwalder’s single bars had the advantage that there was nearly no slippage when the prestressing jacks were removed, which was the prerequisite for cantilevering in short sections.5 Tied to the position of the caisson foundations of the destroyed steel bridge, the Nibelungen Bridge crosses the Rhine at Worms in three large spans with effective widths of 101.65, 114.20 and 104.20  m. The cantilever girders protrude like monoliths from the reinforced concrete hollow pier, following Finsterwalder’s idea formulated in 1931 of a “cantilever whose vault thrust is cancelled out by tensioned, straight cables”.2 Two hollow boxes connected through the carriageway plate with structural depths of between 6.5  m at the pier cut and 2.5  m in mid-span form the 13.5  m wide cantilever girder cross-section (Fig. 3). A vertically prestressed joint, transmitting transverse forces, with stilted cast steel roller bearings avoid any reciprocal displacement of the cantilever girder ends.

Fig. 3: Cross-section of Finsterwalder’s longitudinal and transverse prestressing

While the superstructure grows out of the river piers simultaneously on both sides in sections of 3 m toward the middle of the span, thus keeping the moments of difference to be absorbed for the subsoil small, the end piers had to be ballasted to control the overturning moment from the growing superstructures or were hung back via the prestressed structural components. This was helped by the existing founda-

STEPS TO REFURBISHMENT

139

tions that had absorbed the horizontal thrust of the destroyed steel arch bridge. “The key to the construction” Finsterwalder1 observed. Finsterwalder used his well-tried St 90 single bars for prestressing. He graded the prestressed reinforcement for the superstructures cantilevering out up to 57.1 m in accordance with the reduction of the bending moment toward mid-span. The haunch helped him keep the shearing stresses constant over the length of the structure. Under full load, with the most unfavorable live load conditions, Finsterwalder allowed for a tension wedge that was later called limited prestressing. In total, 486 bars with a diameter of 26 mm were necessary in order to be able to resist the fixed end moment of the full load at center piers (Fig. 3). At the end of each section, on average, 24 bars were stressed and anchored.1 One vertical reinforcement tendon per web directly alongside the cantilever joints absorbed the tensile splitting forces from the anchored tendons. The concrete grade of B 450 was not only a technical but also a logistical challenge for the first postwar years. After 22 months of construction, the bridge was opened to traffic on 30 April 1953. In the opinion of the early prestressed concrete engineers, no tensile stresses should be permitted in prestressed concrete components as far as possible. This led to prestressed stirrups in order to avoid principal tensile stresses. Creeping and shrinking were known; however, engineers were still uncertain about how to determine prestressing losses. Thus, assumed global reductions of 120–150 MPa were usual until the end of the 50s, which went back to the Frankfurt Trials by the Neue Baugesellschaft Wayss & Freytag in 1936. As there was no danger from salt used for thawing ice, friction and not protection from corrosion, was the central topic for consideration during construction with subsequent bonding. Limiting the concrete tensile stresses in a transverse direction by an appropriate choice of system or transverse pretensioning led the engineers of that time to the conviction that the concrete would remain crack free and not require any sealing. Following Freyssinet in this tradition, the Nibelungen Bridge is prestressed three dimensionally; however, as a result of his lower high tensile strength prestressing bars, Finsterwalder did not achieve full prestressing for every load position. The design of the bridge was based on the seventh draft of DIN 4227 but also included the discussion process still in progress. With the exception of the more precise proof of shear reinforcement in the case of exceeding the permissible main tensile stresses, the seventh draft was essentially like the definitive first German prestressed concrete standard. A minimum shear reinforcement was introduced with the additional provisions for DIN 4227 by the federal authorities 12 years later, in 1966. With the haunched cross-section design, the principal tensile stresses could be maintained nearly constant and were limited to omit any reinforcement. Nevertheless, Finsterwalder ordered a low shear mesh reinforcement and mild longitudinal and transverse reinforcement all over the whole cross-section.

Steps to Refurbishment The planning for the refurbishment of the Nibelungen Bridge was subdivided into five sections: 1. Fundamental expertise on the state of knowledge and possibilities of application of the prestressed concrete method of construction at the time of execution. 2. Technical building material examinations as well as examinations of the tendons and hinge prestressing of the center part of the bridge. 3. Checking of the bridge with the findings from and preparation of variants for strengthening the Nibelungen Bridge into German bridge class 60/30, satisfying present day traffic. 4. Refurbishment design.

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5. Follow-on special tests and examinations during building work to evaluate design in 2.4.

Assessment of the State The state of the center part of the bridge is outlined as follows6: • • • • • • • •

Favorable crack situation without shear cracks Good concrete quality, however, without subsequent hardness Usual contamination with chloride and degrees of carbonating Flaking of concrete only locally in the area of the crown elements as well as humidity penetration on the wearing parts of the expansion joints Locally inadequate degree of grouting of the tendons due to the then-too small ducts and the too narrow construction of the tendon sleeve coupling Tendons of the tieback to compensate for the cantilever moment on the land pier on the Hesse side inadequately grouted and corroded Severe corrosion and wear phenomena on the crown hinges coupling the individual cantilever systems and their tie rods endanger traffic safety Unsuitable drainage system (open gutter inside the hollow box along with free fall system)

The durability of the shore parts of the bridge is reduced to a greater extent through the defective expansion joints fitted later and the defective drainage system. The jointed carriageway plates are no longer a match for today’s aggressive environmental influences.

Refurbishing Measures The refurbishing of the center part of the Nibelungen Bridge is based on an economic viability check and on the finding that the bridge’s structural stability is not endangered. This enables a structural strengthening without reinforcing any shear deficits to avoid any structural damage to the longitudinal existing prestressing bars. Its extent can be outlined as follows: • Cleaning of the dirty parts (pier and crown hinges soiled by bird droppings) • Demolition of the railings, crash barriers, lighting, curbs and carriageway surfacing • Check of the defective building material quantities after demolition of the sealing and before awarding the contracts for further works • Examination of the tendons, including the regrouting • Reinforcement of the superstructure by means of straight, external tendons (Figs. 4 and 5) • Substitution of the existing stilt bearing to spherical bearing, including bracing the hinge • Renovation of the existing expansion joints in the crown hinge area, as well as in the transition to the separating piers • Renovation of the existing drainage system • Repair of the concrete in the damaged areas • Renovation of sealing and surfacing, curbs, crash barriers and lighting.

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Fig. 4: Reinforcing the cantilever beams with external longitudinal tendons6

Fig. 5: Detail of the anchorage of the external additional prestressing tendons: (a) cross-section of a hollow box at end of the cantilever; (b) detail of the anchorage block with transverse prestressing bar St 950/1050 With the choice of lightweight concrete, as a result of the continuous carriageway plate of the shore part of the bridge, the restraints are clearly diminished as both the coefficient of thermal expansion and the dead weight of the carriageway plate are reduced, and thus, the deformation of the plate and the horizontal force are decreased as a result of the friction. Expansion joints are only envisaged at the plate ends. The carriageway plate is given sliding supports in the outer spans by the arrangement of fibrated concrete slabs between the superstructure and reinforced concrete head beams on the masonry. The renovation of the curbs, seal, surfacing and vehicle restraint systems; the repair of concrete and masonry surfaces; and the fitting of a closed drainage system complete the measures for the shore parts of the bridge. In the land pier on the right bank of the Rhine, the cantilever moment is dissipated into a force couple via cross girders through connecting compression columns and tiebacks. The tiebacks consist of two edge tension members with 14 single prestressing bars, each with a diameter of 26 mm, and a middle tension bar made up of 34 single prestressing bars. The tendons were detected with the highest degree of corrosion and grouting error damage. Monostrands had to be added and anchored by means of core drill holes in the foundation and the upper tieback transverse girders. Recesses in the middle of the tieback accommodate the tensioning wedge for prestressing the additional

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tendons. Further monostrand tendons serve to strengthen the tieback transverse girder. Further measures for both land piers, such as repairing the natural stones and their joints, improvement in accessibility or renovating damaged manhole covers, are routine tasks. In conclusion, the land pier on the Hesse side will be given a new, external staircase tower.

References [1] Finsterwalder U. Bau der Strassenbrücke über den Rhein in Worms. Beton- und Stahlbetonbau 1953; 48(1): 1–5. [2] Dischinger F. Elimination of bending tensile stresses in R.C. Bridges. IABSE, Second Congress Munich, Pre-Report. IVb2, 1936; 775–798. [3] Pelke E. Pre-Stressing of Bridges in Germany up to 1965 Part I and Part II. Proc. Inst. Civil Eng., Eng. History Heritage 2011; 164(2/4): 99/211–108/218. [4] Finsterwalder U. Dywidag-Spannbeton. Bauingenieur 1952; 27(5): 142–158. [5] Kern G. Das DYWIDAG-Spannverfahren. In Dyckerhoff & Widmann A-G. München (Herausg.) Festschrift Ulrich Finsterwalder 50 Jahre für DYWIDAG G. Braun: Karlsruhe, 1973. [6] Pelke E, & Zichner T. Ertüchtigung der Nibelungenbrücke Worms. Beton- und Stahlbetonbau. 2015; 110(2): 113–130.

143 Chapter

7.3 Early Prestressed Steel–Concrete Composite Continuous Bridges in Belgium

Y. Rammer; B. Espion; Professor, Université Libre de Bruxelles, Brussels, Belgium

Introduction Two Belgian post-tensioned composite steel–concrete continuous bridges built in the 1960s are currently undergoing heavy repair due to corrosion of the main steel girders and severe degradation of the concrete slabs due to deicing. The bridges are located on important European highways. The authors were involved in the assessment of the residual bearing capacity of the cantilever sidewalks of one of these bridges during temporary deviation of the traffic on the bridge. This assessment was undertaken before the renovation started, and the authors discovered that the highway administration implemented the compression stress values that were computed in the original calculation notes. This puzzled the authors and led to the need for further historical research about this original, but now obsolete, continuous bridge construction method that actually induces high prestressing losses. Only recently was the historical development of composite structures taking into account the connection of the steel members with concrete parts fully addressed:1 during the postwar period (1950–1975), referred to as “the classical phase” by those authors, standardized testing and calculation methods resulted in numerous bridges and buildings. Continuous and cantilever composite bridges are affected by hogging bending moment regions in the vicinity of intermediate supports, causing tensile stresses in the deck concrete slab and affecting the durability of the deck due to flexural cracking.2 Initial ideas for avoiding these tensile stresses involved the introduction of some kind of “precompression” in the concrete deck slab, either by (a) jacking the supports or (b) prestressing the concrete slab by tendons (c) before or after connecting the steel and concrete parts of the structure. Creep and shrinkage effects were, already at that time, known to induce redistribution of stresses between the steel girders and the concrete deck slab. Regarding continuous bridges, theoretical development seems to have started after World War II,3 and presumably, the first full-scale bridge of that type was constructed across the Ruhr River in Herdecke.4 This road bridge has three spans (48.2 m + 64.2 m + 48.2 m = 160.6 m) with an overall uniform depth of 2.4 m and a deck width of 17.8 m (five steel I girders of 2.0 m depth

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and a concrete slab of about 400 mm). The sequence of construction was: (a) erecting the steel structure on temporary supports; (b) lowering the supports in order to introduce some “prebending” in the steel; (c) installing the deck slab, placing the reinforcement and tendons; (d) lowering the supports in order to introduce compression in the concrete slab; and (e) post-tensioning of the STUP-Freyssinet 12ϕ5 tendons (the contractor was Wayss und Freytag, and the 12ϕ7 were not available at that time). The bridge was opened in March 1951. The fact that this bridge was equipped with STUP tendons gave the authors the motivation to look further into the French literature and to try to discover when the original idea of prestressing continuous composite bridges arose. The first occurrence was found in a report quoting tests conducted by the SNCF (the French National Railway Company) on composite bridges : “Des tabliers continus en béton armé, associés à des poutres métalliques peuvent être construits, à condition d’annuler, par précontrainte du béton, les tensions aux droits des appuis. Cette précontrainte peut être obtenue simplement par dénivellation d’appui”.5 At the end of World War II, Ridet, referring to a conference held in May 1944, stated that STUP-Freyssinet presented an alternative proposal for a two-span bridge (two spans of 35.9 m) at Donchery (Fig. 1). Longitudinal tendons were to be placed on the top and bottom of the slab.7 This 1944 proposal was developed and further explained in an article on continuous composite bridges,6 using post-tensioning to introduce compression stress in the concrete deck slab (before live loads) of 9 MPa (Fig. 2).

Herstal and La Louvière Bridges In Belgium, post-World War II economic reconstruction was fast as the public and industrial infrastructure was hardly damaged. However, after the Universal Exposition in 1958, the country

Fig. 1: Donchery Bridge elevation6

Fig. 2: Donchery Bridge cross-section6

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entered a period of economic, social and political unrest. Major infrastructure programs were delayed. However, some projects were pursued, including the two bridges at Herstal (Fig. 3) and La Louvière (Fig. 4), which are currently undergoing heavy rehabilitation (Table 1). The Herstal Bridge (no. OA27) overpassing the Meuse River has a similar, but shorter, adjacent bridge crossing the Albert Canal (no. OA26). Both are, in fact, twin decks (one in each direction). The structure is statically determinate. The reasons for this are possible mining subsidence (Fig. 5). The sequence of construction was: (a) erecting the steel structure on temporary supports (Fig. 3); (b) concreting the cantilever central span; (c) lowering the cantilever span temporary

Fig. 3: Herstal Bridge during construction8

Spans Type of span Calculation Geometry Width (of each parallel twin bridges) No. of steel girders Depth of slab Formwork for slab Method of erection Longitudinal tendons Transversal tendons

Fig. 4: La Louvière Bridge during construction9

Herstal (Bridge OA27) 3 (65 m + 110 m + 65 m = 240 m) Continuous (40 m cantilever span) Statically determinate Variable depth (2–5.5 m) 12.75 m

5 230 mm Wood on scaffolding Temporary supports 224 STUP-Freyssinet 12ϕ7 STUP-Freyssinet 12ϕ7 per 600 mm Position of tendons Inside slab Shear connection Friction by transversal posttensioning Jacking/prebending Yes Opening to traffic 1964 Designer Alexandre Birguer Steel contractor Ateliers de Jambes-Namur Table 1. Main bridge data

La Louvière (Bridge nr 34) 3 (50 m + 109 m + 50 m = 209 m) Continuous Statically indeterminate Variable depth (2–5.5 m) 18.20 m 6 190 mm Precast concrete planks Incremental launching 27 STUP-Freyssinet 12ϕ7 N/A Under slab with deviators By shear connectors Yes 1967 Antoine Van Der Vloet Ateliers de Jambes-Namur

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Fig. 5: Herstal Bridge longitudinal section and elevation; note the 40 m suspended span (points C and D are hinges)10

Fig. 6: Herstal Bridge transversal section (original drawing from Birguer office, Administration archives)

Fig. 7: La Louvière Bridge : transversal section11 supports in order to introduce a “prebending” 100 ton force in the steel; (d) installing the deck slab, including placing the reinforcement and tendons; (e) transversal post-tensioning (Fig. 4) for shear connecting; and (f) longitudinal post-tensioning of the STUP-Freyssinet 12ϕ7 tendons. Anchor heads are situated under the deck slab for longitudinal tendons and embedded in the sidewalks for the transversal tendons (Fig. 6). The La Louvière road bridge also has three spans with a similar shape, but the bridge is strictly continuous and statically indeterminate. The sequence of construction was: (a) erecting the steel structure with a cantilever construction (Fig. 4), (b) lowering the end supports in order to introduce some prebending in the steel, (c) installing the deck slab using precast concrete planks and placing the reinforcement, (d) installing the tendons under the deck, (e) jacking up the

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end supports in order to introduce some compression in the concrete slab (f) and, finally, posttensioning of the STUP-Freyssinet 12ϕ7 external tendons protected by plastic ducts (Fig. 7). Tendons are slightly deviated under the deck by means of steel profiles connected to the main steel girders. Anchor heads and blocks are situated under the deck slab.

Conclusion The examples studied suggest that the idea of prestressing continuous composite beams should probably be attributed to the STUP Company during World War II, not very long after the development of Freyssinet’s 12ϕ5 anchorage and tendon. However, the construction method of the four bridges mentioned in this paper (Donchery, Herdecke, Herstal and La Louvière) is quite complex due to the mixed use of supports jacking and post-tensioning sequences. Designers at that time were not aware of the prestressing losses over a long period or of the time-dependent effects during construction sequences on the redistribution of stresses between steel and concrete.12 When investigating such bridges with the view of extending their lifetime, engineers should have sufficient knowledge of “old” calculation methods and standards in order to identify discrepancies in actual knowledge of the time-dependent structural behavior. Further research is necessary to try to understand how those complex structures (i.e., the different phases, including partial strutting, jacking, lowering and tensioning) were calculated and, furthermore, what would be the results of modern calculations of prestressing losses and redistribution. Today’s techniques of expertise however leave one essential issue unresolved: how can the actual residual prestressing in the structure be assessed?13

Acknowledgements The authors acknowledge the assistance of ir.Pierre Gilles and ir.Françoise Taquet from the Walloon Administration for allowing convenient access to their archives for these bridges.

References [1] Pelke E, Kurrer K-E. On the evolution of steel-concrete composite construction. Proceedings of the Fifth International Congress on Construction History, Chicago, 2015. [2] Ernens M, Cremer J-M, Dotreppe J-C. Cracking and durability of concrete slabs of composite bridges. IABSE Report, No. 999, 1997; 187–192. [3] Dischinger F. Stalbrücken in Verbund mit Stahlbetondruckplatten bei gleichzeitiger Vorspannung durch hochwertige Seile. Der Bauwingenieur 1949; 24(11): 321–376. [4] Homberg H, & Köhling E. Die neue Ruhrbrücke Herdecke, eine durchlaufende Verbundträgerbrücke mit Vorspannung. Der Bauingenieur 1951; 26(5): 129–176. [5] Ridet J. La construction mixte acier-béton armé dans les ouvrages d’art. Mémoires de l’AIPC 1947; 8: 171–194. [6] Guérin J , Pigeau H. La construction mixte fer-béton dans les ouvrages d’art à travées continues. Annales de l’Institut Technique du Bâtiment et des Travaux Publics, No. 157, November 1950, 1950. [7] Ridet J. La construction mixte fer-béton dans les ouvrages d’art. Annales de l’Institut Technique du Bâtiment et des Travaux Publics. Circulaire Série 1, No. 48, May 1947, 1945.

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[8] Birguer A. Constructions composites et précontraintes en acier-béton. Annales de l’Institut Technique du Bâtiment et des Travaux Publics, No. 221, May 1966, 1966. [9] Laviolette M. Pont n°34 sur l’autoroute de Wallonie. Acier-Stahl-Steel, No. 6, Juin 1968, 1968; 290–295. [10] Fougnies R, Mahieu L. Evolution récente des ponts en béton précontraint en Belgique: le Pont de Herstal. Annales des Travaux Publics de Belgique No 3, June 1969, 1969; 215–216. [11] Fougnies R, Mahieu L. Evolution récente des ponts en béton précontraint en Belgique: le Pont de La Louvière. Annales des Travaux Publics de Belgique No 3, June 1969, 1969; 207–208. [12] Ducret J-M. Étude du comportement réel des ponts mixtes et modélisation pour le dimensionnement. PhD Thesis Nr 1738. École Polytechnique Fédérale de Lausanne, 1997. [13] Rammer Y, & Espion B. A case study of replacement of external post-tensioning cables. Bridge Eng. 2015; 167(BE3): 183–192.

149 Chapter

7.4 Making Rennie’s 1796 Lune Aqueduct Watertight Againi

Leslie Clarke, CEng, FICE. Principal Engineer, Canal & River Trust, Leeds, UK

Introduction and History The Lune aqueduct carries the Lancaster Canal across the River Lune just to the north of the city of Lancaster. It is a magnificent, monumental, five-span, masonry structure constructed between 1793 and autumn 1796 under the auspices of John Rennie. The aqueduct is now a grade I listed structure and forms part of the estate of the Canal & River Trust (Fig. 1). Leakage from the aqueduct canal trough has been a continuing problem since construction, as can be seen from the buildup of calcite deposits and the staining on the structure. Calcite deposition by means of precipitation is a slow process that takes many years. The process requires slightly acidic water as an initiator and carrier—just the type of conditions brought about by the Industrial Revolution of the 1700s and industrial production of the 1800s. On the north abutment of the Lune aqueduct, the calcite has formed a surface glaze or flowstone over the masonry. Over that time, quantities of lime have gradually been leached out of the mortar, not only of the canal trough structure but also the aqueduct structure itself. Leakage has occurred from beneath the arches on the upstream and downstream sides, from the pier faces, from the spandrel walls, from the wing walls and from below the ledges at towpath level.

Aqueduct Structure The masonry of the aqueduct is sandstone of the millstone grit series that was sourced from several quarries local to the site. The stone has some variation in grain size and coloration consistent with different sources. The masonry piers and abutments are founded on piled timber rafts. Although the structure above the piers looks very solid and bulky, it is in fact hollow. The arch supports a series of vaults springing from two longitudinal walls built from the top of the arch (extrados) within the structure. The canal is contained within a masonry trough 2.3 m deep i

This essay is a reduced version of a paper published in Engineering History and Heritage. Please see the original for full details in Ref. [1].

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Fig. 1: The Lune aqueduct, 1797. Engineer: John Rennie. The aqueduct carries the Lancaster Canal across the River Lune, near Lancaster, UK and 6.2 m wide. The trough is a flattened, widened U-shape formed from two ellipses, and the greater axis is the width between the outside retaining walls and the lesser depth of the canal. The trough comprises two layers of masonry, an outer rubble course (229 mm thick) and an inner-facing course of ashlar blocks (305 mm thick), all underlain by a 914 mm minimum thickness of puddle clay, which is contained within the masonry spandrel walls on either side, each spandrel wall being 1.524 m thick. The gap between the spandrel walls and the back of the canal through walls is filled with puddle clay. The base of the puddle clay is supported on the top of a series of internal stone vaults within the aqueduct structure. These vaults are formed from two 914 mm thick internal walls, springing off the extrados of the arch, and these support three internal Gothic arches. The inside of the aqueduct is thus partly hollow, thereby reducing the loads on the piers and abutments and thus the foundations. Each pier contains a series of secured longitudinal wrought-iron chain bars between the upstream and downstream ends, one at the level of the stone course below low water (of the river) and the other under the level of the arch springing. In addition, each arch contains four secured wrought-iron bars running from the upstream side to the downstream side. The ironwork was intended to assist in holding the structure together.

Problems Caused by Leakage Quantities of water leaking through an aqueduct can have considerable deleterious effects on the fabric of the structure over time. Lime can be leached from the joints between the masonry blocks, causing gradual small movements in position. Freeze–thaw cycles can cause delamination of layers of stone and cracking within individual blocks, as well as erosion of lime mortar joints. Freezing water within the masonry fabric can cause major movement of elements of the structure. An increase in the moisture content of contained fill can lead to major structural movement at stress concentration points. All of these effects are visible on the Lune aqueduct in various places. Over time, these effects can cause the structure to deteriorate gradually, both in appearance and in structural performance. In the northeast arch at river water level, drips of water from the canal are visible. On the next two piers and buttresses, damp patches can be observed. Damp is visible on the spandrel wall. Calcite deposits are clearly visible generally. Vegetation can be seen growing on the structure, a clear sign that water is present. Figure 2

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shows the southeast abutment with the start of the arch springing, showing leakage, calcite deposits from leached lime binder, cracked masonry blocks and delaminated blocks due to freeze– thaw cycles on wet stone. On 15 September 1798, there was an embankment breach failure at the southeast approach to the aqueduct.2 The embankment was reconstructed and sealed. On 31 October 1798, the canal trough rent (fissured) at the end of the south abutment, with a similar situation occurring at the north end.2 The back of the abutment was excavated and repuddled with clay. On 23 November 1798, Rennie recommended that the copings on top of the canal trough Fig. 2: Damage to the south- should be taken up, and the puddles trenched over on both sides of the aqueduct.3 This would only have been conducted as a coneast arch springing sequence of leakage. Between 1800 and 2012, there was general leakage of varying quantities from the canal trough through the aqueduct, with water wetting parts of the face of the aqueduct, dripping into the river from the arches and onto the river towpath from the arch on the southeast. After 1900, localized repointing with cementitious mortar was carried out (precise dates unknown). In April 2006, there was major leakage from the embankment, arch and east wing wall at the south end of the aqueduct. In November 2008, there was further major leakage at the south end of the aqueduct in the same area as in April 2006.

Recent Leak Sealing Works Maintaining canal structures that are over 200 years old in a robust, functioning and reasonably watertight condition, such as the Lune aqueduct, is a difficult task when funds are limited and with a network that extends across England and Wales. A risk-based approach is adopted with regard to this asset management issue, with priorities being allocated to individual problematical assets. With respect to the Lune aqueduct, there has been a significant number of recent, major leakage problems dating from 2006, described below.

April 2006 Severe leakage appeared from the embankment in the area of the southeast wing wall. A hole of 100 mm diameter was discovered in the center of the canal bed very close to the embankment and canal trough junction. There was an additional hole under the adjacent towpath approach wall on the southwest. As a quick, cost-effective, temporary measure, the holes were filled with general-purpose grout under gravity; the existing clay bed of the canal was removed over a 10 m length from the end of the aqueduct trough, and new puddle clay was placed over the approach to the aqueduct. The clay was taken partially up the masonry approach walls and over the start of the aqueduct trough.

November 2008 Leakage from the south abutment was first noted in November and progressively worsened over a number of days. In early December, the leak became significant, and canal water also began to

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flow from the base of the southeast embankment close to the interface with the masonry wing wall of the aqueduct, in the same area as the 2006 problem. This became a cause of increasing concern, and the canal was dewatered. Once dewatered, the canal was inspected. No significant holes or fissures were noted in the clay of the canal bed. On further investigation, voiding was discovered below and behind the towpath masonry approach wall at the aqueduct transition. Leakage water was exiting into the void, flowing under the canal Fig. 3: Southeast end leak sealing, Novem- bed to the opposite side through the embankment to the southeast and emerging near the base of the ber 2008 wing wall. A more permanent repair was made, consisting of a short transition length of water-retaining channel from the end of the aqueduct trough onto the embankment (Fig. 3).

January 2011–2012 For leak sealing of the aqueduct trough, a series of grouting works was planned. This choice of solution was arrived at partly due to the classification of the aqueduct as a grade I listed structure, a structure of great heritage value and importance, and additionally following lengthy discussions and consultations with the Canal & River Trust heritage advisor, Lancaster City Council heritage officer and English Heritage. The result of these consultations was that the use of an applied, internal, watertight sealing system on the internal face of the trough masonry was precluded, even though this would have produced a canal trough that would have been virtually watertight. Reconstruction of the trough was also considered an option, but this would have been too expensive and time-consuming.

Grouting Works, First Stage: February/March 2011 The first stage of grouting works, the purpose of which was to seal the joints in the canal trough masonry, was undertaken with the canal out of water. Following the stage 1 grouting, the overall amount of seepage from below the aqueduct had been reduced by approximately 90–95% and had been confined to certain areas. However, it was felt that the top two to three courses of wall masonry had not been dealt with sufficiently, mainly due to the method adopted. Therefore, a second stage of grouting works was proposed.

Grouting Works, Second Stage: June 2011 The purpose of this grouting was to fill the upper two to three courses of masonry in the offside wall, where there were still thought to be leakage problems that had not been completely addressed by the internal trough grouting works, and as had previously been deduced by monitoring variations in canal water operating levels and leakage rates. The same type of grout as used in the first stage was injected from the top of the offside wall along the whole wall length

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through the rear face of the coping stones. Following the grouting, a further slight reduction in leakage was observed, to around 95% of the original.

Grouting Works, Third Stage: June 2012 In the course of the major improvement works previously completed in April 2012, damaged coping stones along the offside edge of the canal trough had been removed for replacement. During this process, it was possible to inspect the top of the canal trough walls. The inspection showed that the joint between the two masonry layers was in poor condition, with an almost complete loss of lime binder, leaving the mortar effectively as a loose saturated sand containing silt inclusions from canal water. Following the stage 3 grouting, the residual seepage, compared with that after stage 2, was reduced by approximately 40%.

Observations: Grouting and Leak Sealing From the works carried out and the observations made during the aqueduct restoration works, it is apparent that the joint between the ashlar and rubble masonry courses of the canal trough is a potential seepage path for water. This can occur through the smallest of shrinkage or separation cracks between mortar/grout and the ashlar stone blocks, crack widths that are not visible to the naked eye. As an alternative, the application of a waterproof coat on the inside of the canal channel trough, rather than further grouting, would give more certainty of outcome in terms of eliminating the residual seepage. However, this rests on the assumption that listed building consent could be obtained for this approach, which, judging by the discussions with heritage advisers from the Canal & River Trust, Lancaster City Council and English Heritage, would not be supported or granted for a structure of this importance.

Conclusions There had been leakage between the stiff structure of the aqueduct and the soft embankment approaches since the canal opened in 1797. It is hoped that incorporating water-retaining reinforced-concrete channels on either side of the original masonry trough of the aqueduct will permanently eliminate this leakage. The grouting operations to the canal trough along the length of the aqueduct have been very successful. Leakage has been reduced by 95–98% of the levels observed before restoration began. Although the canal trough does still exhibit residual seepage, the quantity is very small and will not lead to further deterioration of the masonry structure.

Lessons for Consideration The matters discussed in this paper relate to a well-known, monumental, historic structure. However, lessons can still be learned that may apply to aspects of other projects, not only to repair or renovation work but also to new work. These lessons are as follows: • understand the history and nature of the structure • understand the context of the site • identify the effects of problems

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• • • •

investigate and understand the causes of the problems when the causes are known, only then define the solutions solutions should be sympathetic and not have unintended consequences be flexible in approach, do not stick rigidly to predetermined solutions in light of new or additional evidence • observe, monitor and review the results and use this information to confirm or revise the remaining works • disseminate the information for others to benefit from.

If historic structures and assets are to be valued, treasured and retained for the nation, as the Canal & River Trust believes the canal system should be, then they require regular, thorough and systematized inspection and risk management processes so that problems can be identified at an early stage, and measures can be put in place and undertaken to remedy them at an appropriate time. Understanding and expertise are required in dealing with these problems so that appropriate solutions are put into effect. This expertise needs to be passed on to future generations in order to sustain this approach.

References [1] Clarke L. Making Rennie’s 1796 Lune aqueduct watertight again. Proc. Inst. Civil Eng. Eng. History Heritage 2014; 166(EH4): 198–206. [2] Lancaster Canal Navigation Company. Minutes of the Committee Meetings (1798–1813). RAIL 844/231, The National Archives, (1798). [3] Rennie J. Specification for the Mason Work for the Lune Aqueduct. Lancaster Maritime Museum, LANLM. 1985.76.1, 1793.

155 Chapter

7.5 Restoration of Robert Maillart’s Reinforced Concrete Bridges in Switzerland

Eugen Brühwiler, Professor, EPFL – Swiss Federal Institute of Technology, Lausanne, Switzerland

Introduction Bridges of high cultural value and aesthetic quality deserve respectful treatment and, consequently, construction interventions must balance these assets with the severe requirements of utilization. This is particularly relevant to structural engineers and bridge owners involved in rehabilitation or modification interventions. This contribution presents, by means of restoration of bridges designed by the famous Robert Maillart, how interventions can be performed with adequate respect for cultural value while complying with the demands of modern traffic use. It demonstrates how noninvasive and thus low-cost interventions can be performed on “old” concrete structures with adequate respect for cultural and aesthetic values in order to improve them in view of a second service duration. This goal of noninvasive interventions can only be achieved by using advanced engineering methods (as allowed in standards valid for existing structures) and intervention technologies specifically suited for existing concrete structures.

Robert Maillart Robert Maillart (1872–1940) was a Swiss civil engineer who strongly influenced design and construction using reinforced concrete. Robert Maillart was born in Berne, Switzerland, and studied at the Swiss Federal Institute of Technology (ETH) in Zurich. His main mentor was Professor Wilhelm Ritter from whom he learned to develop structural shapes that could be easily handled by structural analysis. Maillart could rarely test his original designs prior to construction, and thus former EMPA director Mirko Ros who performed load testing on many of Maillart’s bridges, held an important role in validating Maillart’s original design approach. Maillart’s main inventions are the threehinged arch and the deck-stiffened arch designs for bridges, as well as the beamless floor slab for

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industrial buildings, supported by columns with mushroom-like heads for continuous force transmission. His design approach and principles as well as his slender bridges changed the aesthetics and engineering of bridge construction significantly and are influencing engineers until today.

Examination and Noninvasive Intervention to Improve Durability Based on the standards valid in Switzerland for existing structures,1 examination of the structural performance of Maillart’s bridges presented here was conducted using updated values for action effects (dead load, road traffic) and resistance of structural members. The results showed that the requirements for structural safety are fulfilled in view of today’s and future traffic demands. The overall condition of the bridges was generally “satisfactory to good” despite the fact that almost no maintenance has been conducted. As was to be expected from more than 80-year-old exposed concrete, carbonation depth was significantly beyond the first layer of steel rebars (rebar cover of about 20 mm). Consequently, there was likelihood of steel rebar corrosion if concrete humidity was sufficiently high (i.e., higher than 80%). In addition, few local zones showed visible rebar corrosion, for example, along edges where it was difficult to correctly position the rebar and compact the concrete. Given this condition of the exposed concrete, a noninvasive concept was proposed and executed to improve the durability of reinforced concrete, consisting of two major aspects: • Restoration of the local zones showing corroding rebars using a mortar composed of sand and gravel of similar origin, as well as using timber boards for the formwork similar to the ones used for the initial construction. • In-depth hydrophobic treatment of rain-exposed concrete surfaces with the objective to prevent ingress of rainwater into the concrete. This treatment allowed the concrete humidity to be maintained at a rate lower than 75%. It is effective in time as the water-repellent agents penetrate more than 5 mm into the concrete where they are protected from ultraviolet sun radiation and leaching effects due to rainwater. Thorough preliminary tests were conducted to identify the restoration mortar that fits best to the existing surface texture and color and to validate the success of the in-depth hydrophobic treatment for the given concrete. Products for in-depth hydrophobic treatment appeared more than ten years back in the construction domain because it was possible to produce water-repellent nano-size agents, allowing for easy penetration into concrete by capillary suction.

Schwandbach and Rossgraben Bridges In 1933, Robert Maillart designed and built two bridges located close to each other in a remote area near Schwarzenburg, south of Berne, in Switzerland. The Schwandbach bridge (Fig. 1) is the most well-known deck-stiffened arch bridge of Maillart because it is like a spatial structure carrying a curved roadway. The Rossgraben bridge (Fig. 2), with its arch span of 82 m, is the second largest open-box, three-hinge arch structure, and the world-famous Salginatobel bridge is the most important three-hinged arch bridge. Both bridges have high cultural and aesthetic values. Both reinforced concrete structures showed satisfactory performance in terms of structural resistance and durability. Therefore, after more than 70  years of being in service, limited

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Fig. 1: Schwandbach bridge, after restoration (2005)

Fig. 2: Rossgraben bridge, after restoration (2005) intervention was necessary to restore their durability according to the noninvasive intervention concept described above. Rehabilitation works performed in 2005 included improving the entire water drainage system, placing a waterproofing membrane on the deck slab, locally repairing zones where steel rebars were damaged by corrosion and protecting the exposed concrete surfaces with in-depth hydrophobic treatment. This low-impact and cost-effective intervention brought no visible change in the structures, although it significantly improved the service life of these bridges. Ten years after the intervention, the bridges’ condition is good, and the surface protection is still effective.

Schrähbach Bridge The Schrähbach bridge is also located in a remote area where it is part of an only 3–4 m-wide agricultural road around an artificial lake created by the construction of a dam. There is only limited traffic, including single heavy agricultural vehicles. There are no plans to change this traffic regime in the future. The bridge was designed and built in 1923 by Robert Maillart (Fig. 3). It is the first realization of the structural system called “deck-stiffened arch” invented by Maillart for the purpose of reducing structural dimensions and thus construction costs. This structural system allows building a thin arch on a light scaffold, which is cheaper to build.

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(a)

(b)

Fig. 3: Schrähbach bridge in 1925 after filling of the spandrels (a); original project by Maillart (b) The necessary stiffness of the structure is provided by the bridge girder with a U-shaped crosssection appropriate to carry concentrated vehicle wheel loads (particularly those located at the quarter span of the arch). The 59 m long and 3.6 m wide bridge structure carries a 3 m wide single roadway. The bridge comprises three parts—two short approach viaducts and the deckstiffened arch structure. The arch has a span of 28.8 m and a rise of 4.0 m (rise-to-span ratio of 1 : 7.2). The deck girder (with a height of 1.3 m) and the arch (of a thickness varying from 0.18 to 0.22 m from rise to abutment) are connected monolithically through 150 mm thin spandrel walls spaced by 2.43 m. The thickness of the deck slab is 0.17 m and carries a 200 mm thick concrete overlay pavement added in 1935. Some months after construction and load testing, the spandrels of the arch bridge and the first opening of the approach viaducts were filled with bricks that have no structural function (Fig. 3a). As this intervention is not reported, one may suspect that these fillings were executed—most probably without asking Maillart—for architectural reasons as there was an overall architectural concept for all engineering works around the lake implying massive construction. In addition, Maillart’s slender structures were not respected and acclaimed by most of his contemporary engineers and architects.

Examination and Intervention Concept In view of its renovation, an examination of the Schrähbach bridge was performed. The results show that the structural safety for all structural members is verified for unrestricted road traffic, and limitation to the utilization (such as a limitation of allowable axle loads or gross vehicle weights) is not necessary. The reinforced concrete of the bridge can be reconditioned and protected according to the concept described above and has been already applied to the Schwandbach and Rossgraben bridges. The intervention concept also aims to restore the

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Fig. 4: Schrähbach bridge: present condition structure according to Robert Maillart’s original plans (Fig. 3b), namely, to remove the ugly spandrel filling after 90 years! However, as of today, the Schrähbach bridge has still not been rehabilitated (Fig. 4), it is actually threatened by demolition and replacement, as decided by the owner and his consulting engineer. Subsequently, restoration of this bridge unfortunately is in court and the case is still under way, and even technical and economic arguments do not seem to make the “law”. This case shows once again the extent to which professionals in charge of civil works need sensitization and education about the cultural values of their works as well as modern engineering methods and technologies to preserve cherished structural engineering heritage structures worldwide, like the ones by Robert Maillart.

Conclusions The examples of three bridges designed by Robert Maillart show that rehabilitation interventions on bridges of high cultural value can meet the severe requirements of utilization while respecting historical value and aesthetic quality. The objective of the interventions is to apply so-called noninvasive or “soft” methods to restore and protect reinforced concrete exposed to environmental action. There are many “undiscovered” and “ignored” bridges built over the last 60 years that deserve similar recognition as the ones by Maillart. Structural engineers and bridge owners need to be more aware of these aspects when conducting rehabilitation or modification interventions. Structural engineering with the ultimate goal of limiting construction interventions to a strict minimum is thus intertwined with the interest of preserving monuments and limiting costs to bridge owners. It also means giving value to bridges as well as appreciating the art of structural engineering and the identity of structural engineers.

References [1] Brühwiler E, Vogel T, Lang T, & Lüchinger P. Swiss standards for existing structures. Struct. Eng. Int. 2012; 22(2): 275–280. [2] Brühwiler E. Les ponts en béton armé de Robert Maillart – intervenir pour pérenniser. In La Sauvgarde des Grandes Œuvres de l’Ingénierie du XXe Siècle Cahiers du TSAM, PPUR – Presses Polytechniques et Universitaires Romandes: Lausanne Suisse, ISBN 978-2-88915113-4; 2015, 126–141.

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7.6 Examination of Two Riveted Railway Bridges over the River Rhine

Eugen Brühwiler, Professor, EPFL – Swiss Federal Institute of Technology Lausanne, Switzerland

Introduction Riveted steel bridges were built over a period of more than 100 years up to the 1950s. Several of them are considered historical and should be preserved as heritage of structural engineering. Often, an important future service life may be identified such that, economically, it is not justified to replace a riveted bridge because of some arbitrary age criterion, as has been often done in the past. This contribution deals with the examination of two railway bridges in riveted wrought-iron and early steel construction. Both were built in the 19th century and span over the River Rhine. They are still in service accommodating the modern-day railway traffic of the Zurich suburban railway. Both bridges have been examined recently to verify the structural and fatigue safety for long-term future utilization while preserving the cultural values of the bridges. The standards valid in Switzerland for existing structures were applied:1 updated railway traffic load models, updated data regarding the fatigue behavior of riveted joints and information from in situ deformation measurements were used to verify the structural and fatigue safety based on precise bridge-specific information.

Railway Bridge over the River Rhine between Koblenz (Switzerland) and Waldshut (Germany) Bridge Structure The investigated bridge (Fig. 1) crosses the Rhine river in northern Switzerland to carry a onelane railway line between Koblenz (Switzerland) and Waldshut (Germany). It was designed by Robert Gerwig and built in 1858–1859 by the German company Benckiser. It comprises riveted

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wrought-iron members. The straight lattice truss structure is one of the last examples of a construction type that was typical for the railroad construction boom in Europe during the third quarter of the 19th century.

Fig. 1: Railway bridge over the River Rhine between Koblenz (Switzerland) and Waldshut (Germany)

The wrought-iron structure was designed as a continuous girder over three spans of 37.5, 55 and 37.5 m, with a total length of 130 m supported by abutments and piers of natural stone masonry. The bridge girder carries a single track by an open deck carriageway, that is, the timber sleepers are directly fixed to the stringers. The bridge was initially designed to carry two tracks; however, it always only carried one track.

Cultural Values The Rhine river bridge Koblenz–Waldshut is considered the oldest riveted railway bridge still in service in Continental Europe. This bridge is generally accepted as an engineering monument of high value. In 1994, it was given a Brunel Award, which is the most important award for railway architecture. The cultural values of this bridge may be evaluated as given below.

Historic Value The multiple lattice girder structure is one of the last representatives of a type of construction that was typical of the pioneer’s time of railway construction in the third quarter of the 19th century. The structure, which is still in its original condition, is an important reference in the work of Robert Gerwig (1820–1885), who was also the builder of the north ramp of the Gotthard railway and other important railways in Central Europe. Robert Gerwig is considered one of the most important engineers of railway construction in the 19th century in Switzerland and southern Germany.

Aesthetics The bridge is an aesthetically pleasing by virtue of the transparency of the lattice girder structure and its interrelation with the massive river piers and abutments of natural stone masonry (Fig. 2). The wrought-iron structure is characterized by the riveted construction. It has filigree and bold appearance despite the strong appearance as a continuous beam of constant height. The massive river piers and abutments contribute significantly to the impression of stability. The bridge’s slenderness and the transparency of the lattice girder visualize technical efficiency. The symmetry and repetition of identical structural elements contribute to uniformity and order. This functional structure set in natural surroundings was planned as a simple structure and appropriately designed. Any decorative elements were omitted. The green color of the corrosion protection painting is ideal as it is one of the possible colors of iron.

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Fig. 2: Details showing the interrelation between the wrought-iron lattice girder and natural stone pier and abutment

Relation to the Surroundings The bridge stands across the Rhine River with great visibility. The sober continuous girder bridge with its severe lines stands in contrast to the natural river landscape. The piers and abutments and the subsequent approaching masonry viaduct located on the Swiss side create a harmonious transition of the riveted structure characterizing a technical object to the natural surroundings.

Appreciation This bridge stands for the highest engineering efficiency in all matters: short time of construction, low material use, minimized cost of construction and a sober and flawless appearance. Its cultural values are assessed as being very high. This bridge belongs undoubtedly to the most important existing riveted bridges in Europe. It is a monument to the art of structural engineering.

Examination of Structural Performance In 1999, the bridge was upgraded to accommodate the modern railway traffic of the Zurich metropolitan area. To estimate the fatigue life of the bridge structure, a detailed examination was performed using realistic past and future traffic models as well as advanced knowledge of the fatigue behavior of riveted wrought-iron details. It could be proven that the bridge structure was safe, and its service life could be considerably extended for the foreseen passenger train traffic.2 More recently, the bridge was again examined in view of a long future service life of 80  years and increasing future passenger train traffic. The examination of the bridge performance revealed that criteria of fatigue safety and structural safety are fulfilled, including a future fatigue life theoretically longer than 80 years. No extraordinary interventions need to be performed to keep the bridge in service. To guarantee the bridge’s durability over the next 80 years, future rehabilitation works, including rehabilitation of the open railway track, were outlined. Preservation and further utilization of the more than 150-year-old bridge are significantly more

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economical in terms of both costs for maintenance interventions and life-cycle costing, compared to the hypothetical option of bridge replacement.3

Railway Bridge over the River Rhine at Eglisau (Switzerland) Bridge Structure The railway bridge across the River Rhine at Eglisau in Switzerland was built between 1895 and 1897 for single-lane railway traffic. The bridge was designed by Robert Moser and chief engineer E. Züblin, distinguished railway engineers during the main period of railway construction in Switzerland in the second half of the 19th century. The central part of the 457 m long bridge is a riveted steel truss structure made of early mild steel, built by the steel construction company Buss from Basel, Switzerland. The truss girder has a span of 90 m and a height of 9 m. Multiple arch approach viaducts in natural stone masonry, with piers up to 50 m in height, follow in the north and south of the steel truss (Fig. 3). During 1982–1983, the original carriageway (that consisted of a ballasted track on Zores iron profiles) was replaced by a steel trough with ballast. Several joints of the truss girder were also strengthened using posttensioned bolts, and the corrosion protection painting of the steel construction was renewed entirely.

Cultural Values This almost 500 m long bridge that is 50 m high above the river valley is very dominant in the landscape. The high massive piers of the masonry arch approach viaducts and the powerful riveted truss beam in between confer a certain boldness to the bridge. The overall appearance is characterized by the hybrid structure, that is, lightweight steel beam of long span over the river and massive masonry multiple arches of shorter spans for the approaching viaducts. This

Fig. 3: Railway bridge across the River Rhine at Eglisau, Switzerland. Scaffolding at mid-span and at the abutment was installed during the monitoring campaign

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type of hybrid bridge construction was very frequent for railway lines built in the 19th century and before the use of reinforced concrete. Typical in the railway domain, this bridge also stands for the highest engineering efficiency in all matters: short time of construction and low cost of construction. This bridge is still in its original constitution. It is considered an engineering monument of high value by the authorities for cultural heritage.

Examination of Structural Performance Long-term monitoring of the structural elements was conducted over one year4 with the objective to gain precise information about the railway action effects on structural members. Monitored deformation values were exploited by rain flow analysis and served as the basis for fatigue safety verification. As the locations of measurements are generally not identical to the cross-sections of verification, measured strains were translated to the relevant verification cross-section by means of factors that were determined by detailed structural analysis. Using these values, all fatigue-relevant structural details were first verified with respect to a fatigue limit of riveted joints of 51 MPa. Then, damage accumulation calculation according to the Palmgren–Miner Rule was performed for the few elements where the fatigue safety check, with respect to the fatigue limit, was not fulfilled. Sufficient fatigue safety could finally be verified for the entire riveted structure, and additional service duration of more than 50 years for this riveted structure could be validated. The examination showed that after almost 120 years of service, there is no notable fatigue damage in the riveted structure. Taking into account even higher future traffic loading, a second service life may thus be expected. Consequently, the implemented approach to determine the updated action effects allowed for explicit consideration of data from long-term monitoring. Monitored data were used to determine accurately fatigue-relevant stresses in fatigue-prone structural elements. Hence, uncertainties in the determination of updated action effects were reduced. The performed examination based on longterm monitoring was economic as the cost of the long-term monitoring and accompanying theoretical studies was only a small fraction of the cost of hypothetical major strengthening or replacement.

Conclusions The two riveted railway bridges are important monuments of structural engineering, and they will remain in service for modern railway traffic despite their relatively long past service life. Extending the service life essentially means giving value to bridges as well as appreciating the art of structural engineering and the identity of structural engineers. Bridges dating to the 19th century are commonly considered “old”. The present examples show that examination based on modern structural engineering for existing structures may reveal that riveted bridges can stay in service for a long future service life. There is no “old” bridge, and structural performance is the sole relevant and adequate criterion to keep a bridge in service. In the past, riveted bridges were systematically replaced. Even now they are considered by some railway authorities to be “old” and prone to fatigue and thus as candidates for bridge replacement. In addition, cultural and aesthetic values are often disregarded by structural engineers. Consequently, a change in paradigm is still needed. Structural engineers have to understand that modern topical discipline and competence is to examine existing structures using advanced methods while respecting cultural values and financial constraints.

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References [1] Brühwiler E, Vogel T, Lang T, & Lüchinger P. Swiss standards for existing structures. Struct. Eng. Int. 2012; 22(2): 275–280. [2] Keller A, Brühwiler E, Hirt MA. Assessment of a 135-year-old riveted railway bridge. Proceedings, IABSE Symposium in San Francisco, IABSE Report, vol. 73/2, 1995; 1029–1034. [3] Brühwiler E. Examination of fatigue safety of a 150-year old riveted railway bridge. Proceedings, IALCCE’12, Vienna, 3–6 October 2012, 2012. [4] Brühwiler E, Bosshard M, Steck P, Meyer C, Tschumi M, Haldimann S. Fatigue safety examination of a riveted railway bridge using data from long term monitoring. Proceedings, IABSE Conference, Rotterdam 2013: Assessment, Upgrading and Refurbishment of Infrastructures, 2013.

167 Chapter

7.7 The Rendsburg High Bridge across the Kiel Canal

Matthias Bartzsch, Struct. Eng., Karsten Geißler, Prof.; GMG Ingenieurgesellschaft Dresden Germany

Overview of the Structure The Rendsburg High Bridge is one of the most important technical monuments in Germany and a landmark of the town Rendsburg. This older than 100-year-old bridge leads the railway line Hamburg–Flensburg (–Denmark) across the Kiel Canal. This railway line is the main line to Scandinavia, which lies under a very heavy railway traffic route. The viaduct was built between 1911 and 1913 using a design proposed by Friedrich Voß and facilitates a clear passage height for shipping of 42 m. Due to the great importance of the bridge for national and international railway traffic, the bridge is being extensively retrofitted by its owner, the Federal Water and Shipping Administration (WSV), as well as by the German railway company Deutsche Bahn (DB) (Fig. 1). The structure was built as a riveted steel construction with an entire length of nearly 2.5 km. It consists of several parts: the main bridge and the northern and southern transition bridges. The main bridge (“canal bridge”) is situated in the middle of the structure. It has a length of 294.6 m

Fig. 1: Rendsburg High Bridge with the “canal bridge” (the main bridge, left) and the “loop bridge” (right)

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and a free span of 140 m above the canal. The main structure of the canal bridge was built as a framework, while both longitudinal and transverse girders were built as solid-web girders. The canal bridge is linked by the connecting piers to the northern and southern transition bridges. The transition bridges consist of a chain of piers and superstructures—51 piers and 105 superstructures, each a short superstructure (11.50  m) on the pier and a long superstructure (26.50–28.50  m) between two piers. The superstructures were constructed as single-span solid-web girders. The substructures were built as truss piers. The northern transition part additionally houses another bridge of 75 m length, the so-called “loop bridge”. As the railway line needs to reach the Rendsburg train station at the north of the viaduct but still has to overcome a height difference of about 30 m, the line is routed in a wide loop. The line crosses itself at the so-called loop point. The loop Fig. 2: Transporter Bridge bridge, a trussed frame structure, is situated there. The construction material of the viaduct is steel from the beginning of the 20th century (“Flusseisen nach 1900” according to the German standard). Its strength characteristics are similar to today’s steel S235 but with a larger scatter. The remaining service life of the bridge is estimated to be more than 50 years. A special feature is the additional transporter bridge at the canal bridge. It consists of a segment of roadway (a gondola) that is carried by cables, which are fixed to an upper carriage. The upper carriage, which is driven electrically, runs on special rails between the pylons of the canal bridge. Up to four cars, but primarily pedestrians and cyclists, can be transported by the transporter bridge (Fig. 2).

Development of Traffic Loads The bridge was originally designed for the so-called “Preußischer Lastenzug A” (LZ A— Prussian load arrangement A). Additionally, a reserve of 20% referred to LZ A was regarded with farsightedness for later load increases at the design of the canal bridge, the loop bridge and the piers. The load arrangement LZ A consists of two locomotives (axle load 17 t and distributed load 71  kN/m), two tenders (13  t and 65  kN/m) and single-sided wagons (13  t and 43 kN/m). In the future, the bridge will be used with the following load arrangements:1 a double-tracked traffic with a freight train of load class D2 (axle load 22.5 t and distributed load 64 kN/m) on one track and a lightweight passenger train (DRZ) on the other track or2 a single-tracked traffic with a freight train of load class D4 (22.5 t and 80 kN/m). In terms of distributed loads, the vertical forces of the former load arrangement LZ A and those of today’s loads D2/DRZ (double-tracked) and D4 (single-tracked) are almost the same. Only

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the axle loads are higher today. However, a considerable increase concerns the horizontal (longitudinal) forces caused by braking and acceleration. While the braking forces were determined by 1/7 of the vertical loads in the past, today they are determined by 1/4 of the vertical loads—that is, nearly doubling of the braking forces. In addition, an acceleration force of 1000 kN (transferred on a length of 30 m) has to be considered on the second track. These high horizontal forces lead to a great load increase for the high and slender bridge. This applies especially to the acceleration force, whose load length of 30 m nearly matches the structural length of a truss pier with its associated (longitudinally fixed) long superstructure.

Horizontal Load Transfer The viaduct is divided into single structures in longitudinal direction. The horizontal (longitudinal) forces may be transmitted between these single structures only by the rails and the friction bearings of the superstructures. The friction bearings are plated steel on steel with a friction coefficient of μ = 0.2–0.4, which may transmit horizontal loads under the effect of vertical loads. That horizontal load transfer by the rails and the friction bearings along the bridge enables a load distribution of concentrated horizontal loads, and these are primarily the acceleration forces. A direct application of the high acceleration forces and braking forces to the analysis model would cause a numerical overloading of the single structures, mainly the truss piers. Thus, a realistic load transfer/load distribution needs to be considered. The longitudinal load transfer was determined by a nonlinear analysis model of the whole bridge, including the rails. The analysis model takes into account load-dependent, nonlinear force-displacement functions between the rails and the railroad sleepers and the girders, as well as at the friction bearings. The nondeterministic parameters of the force-displacement functions were varied by numerous calculations. The results of the analysis are the realistic horizontal forces undertaken by the single structures. For example, the local induced acceleration force of 1000 kN may generally be reduced to 400 kN per single structure. The remaining load is distributed to the nearby single structures. The computation was verified by in situ measurements.

Strengthening Concept The structural analysis yielded some typical cases of overstress at the bridge under today’s traffic loads: • members that are directly affected by the higher acceleration and braking forces, for example, the main diagonal bars of the truss piers and the foundations of the truss piers (overturning of the piers), • members that are affected by the higher axle loads of the trains, for example, the longitudinal and transverse girders of the deck, • members that participate unintentionally in the primary load-carrying system, for example, wind bracing and deck elements. The overstressed members need to be strengthened. Typical strengthening measures at the riveted construction are (Fig. 3): • strengthening plates on the truss members—the strengthening plates need to be integrated into the truss joints,

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Fig. 3: Strengthening by additional plates (a, b); replacement of wind bracing (c) • latticing of open cross sections in order to increase the torsional stiffness (lateral torsional buckling), • replacement of rivets against fitted bolts if the shear capacity is exceeded, • replacement of whole truss members—generally only possible for secondary members , for example, the wind bracing. The (well-tried) static system of the bridge construction should not be changed. Fig. 4: Working under traffic load

The execution of the strengthening measures at the riveted framework construction with manifold graded cross sections is technically very challenging. Often, additional connecting and filler plates are necessary. Welding of the old material is not intended. Most of the strengthening measures are carried out under railway traffic. Until 2014, the bridge had been used for single-track traffic; since the beginning of 2015, the bridge has been used for doubletrack traffic (Fig. 4).

Conclusions With extensive repair and strengthening measures, the over 100-year-old Rendsburg High Bridge is being retrofitted for many years to come. Today’s railway traffic loads, especially the acceleration and braking forces, are significantly higher than the original design loads. Sophisticated computations and dynamic measurements make it possible to identify and to verify remaining load capacity. Only using that can the bridge be retrofitted in a technically and economically feasible way. The measures are usually carried out under railway traffic, which makes high demands of their design, planning and execution. The Rendsburg High Bridge is a masterpiece of civil engineering. Preserving it is an important contribution to building culture.

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References [1] Geißler K , Bartzsch M. The Rendsburg High Bridge across the Kiel Canal. Proceedings of the IABSE Conference – Structural Engineering: Providing Solutions to Global Challenges, Geneva, Switzerland, September 2015, 2015; 466–473. [2] Bartzsch M, Geißler K, & Schmachtenberg R. Die Ertüchtigung der Rendsburger Eisenbahnhochbrücke über den Nord-Ostsee-Kanal. Stahlbau 2015; 84(3): 171–181.

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7.8 Steel Viaduct Refurbishment Inspired by the Original Structure and Its History—The Best Solution with Regard to Structural, Economical and Heritage Requirements

Werner Lorenz, Professor, Chair of Construction History and Structural Preservation, BTU Cottbus-Senftenberg, Cottbus, Germany

Introduction The preservation and strengthening of bridges protected by conservation orders is a structural engineering field that is likely to cause conflicts. The cultural significance of these edifices imposes an obligation to fulfill heritage requirements. However, load-bearing capacity, fatigue resistance and cost effectiveness still need to be ensured. The extensive refurbishment of the elevated viaduct for Berlin’s metro line No. 2, built from 1909 onward, is an impressive example of the efficiency of the principle of “intervention close to the original”. This approach philosophy is inspired by the original structure and develops the structural design of an intervention from a comprehensive understanding of the history of the structure and aims for a solution that systematically picks up on the strengths of the original fabric.

History and Significance The 1.7 km long viaduct carrying today’s metro line No. 2 in the Prenzlauer Berg district of Berlin was built in two phases, the first beginning in 1909. Trains started running on this section in 1913 (Fig. 1), and an extension to Pankow, the end of the line at that time, followed in 1927– 1930. The concept, design and layout of the viaduct and stations were the result of an intensive collaboration between engineer and architect, which, even then, was hailed as exemplary in contemporary publications. For example, “a form in which the technical has become aesthetic …, a simplicity that has bearing ...” was how Karl Scheffler described it in 1914,2 and in 1922, Paul Wittig wrote “engineered structures with a modern expression ... in which it is hardly possible to tell where the activities of the engineer end and those of the architect begin”.1 The chief engineer was Johannes Bousset (1865–1945), and the architect was Alfred Grenander (1863–1931) from Sweden, who was responsible for the architecture of Berlin’s railways above and below ground for 30 years and who knew how to give them dignity and significance. Protected by a preservation order since 1978, today, the viaduct is an artery in and an emblem of Prenzlauer Berg.

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Structure, Details and Materials Distinct structural and constructional differences between the two construction phases can be seen in the primary structure. The reason for these differences can be found in the dynamic development of structural steelwork after World War I. In 1909, the primary system was still made up of an alternating series of two-pin frames with cantilevers supporting Fig. 1: View of the viaduct, first phase, 1909– intermediate beams. In 1928, the designers selected fixed-base hollow-box columns car1913, photograph pre-1920 (see Ref. [1]) rying beams in the form of balanced “rocker arms” on pinned supports, with longer spans of 28.50 m. On the other hand, in both phases, the permanent way, consisting of track, sleepers and ballast, was laid on a deck of curved plates, the narrow ends of which changed to bent plates in double curvature (Fig. 2). As they were stressed like membranes, thin plates were possible; contrary to recommendations at the time, 7 mm was chosen instead of 8 mm. Owing to the different plan shapes (rectangular and trapezoidal) and the various dimensions, the approximately 2200 plates Fig. 2: Removal of historic deck plates (cour- that had to be fabricated were divided into tesy: Lorenz & Co. Structural Engineers, more than 400 different types. The 547(!) 2009) bridge bearings, with 12 different basic types, are worth a special mention. The reasons for the high number and many different types included the short spans and the differing boundary conditions of the load-bearing structure. Most of the original bearings are still in place. Types of steel common at the time of construction were used (1909–1913: mild steel; 1927–1930: grade St 37 steel). The properties of mild steel were nearly the same as the grade St 37 used later. Rivets were used for most connections.

Diagnosis and Safety Evaluation The development of the refurbishment concept followed detailed inspections, carried out from 1999 onward, to ascertain the condition of the structure. Calculations and loading tests, some performed by the Federal Institute for Materials Research & Testing in Berlin, enabled the compilation of a highly differentiated record of the state of damage and fatigue. Overall, despite intensive use over a period of up to 100 years plus the higher axle loads of modern trains, the results showed no reason to consider replacing the viaduct; the robust historic form of construction had stood the test of time. Therefore, construction technology and heritage conservation saw themselves as partners with essentially similar interests: preservation instead of

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rebuilding! Nevertheless, various steel members needed considerable repairs, a number of loadbearing components had to be replaced, and above all, the corrosion protection needed complete renewal. The most alarming thing, however, was the condition of the deck. Corrosion had led to some plates having rusted through almost completely, and numerous cracks near the supports definitely pointed to a fatigue problem (see below).

Refurbishment Concept The refurbishment concept had to take into account the fact that the viaduct is important in different ways. The task was to ensure that the viaduct remained a safe part of the transport infrastructure. At the same time, however, the prominent cultural significance of this historical legacy had to be taken seriously in every respect. The engineers in particular had a great responsibility: planning the engineering works was no longer just a technical assignment but a heritage conservation one as well! With conflicting priorities, it was vital to agree on the fundamental heritage preservation goals and the elements constituting the heritage assets themselves as early as possible: What is it exactly that makes it “historic”? What are the particularly valuable “hotspots”? What has to be tackled especially carefully? Besides the structure, form, silhouette and color of the viaduct, the list included its aesthetic significance, the multitude of different bridge bearings and the characteristic form of the deck—precisely those elements that needed attention! As a result, the heritage conservation planning parameters were summarized in a few principles: As little as possible, as much as necessary! Minimally invasive interventions! Repairs by way of “homoeopathically” improved replicas while preserving the appearance! Otherwise, the plans proceeded along the lines of the three-phase method of the ICOMOS Charter “Principles for the Analysis, Conservation and Structural Restoration of Architectural Heritage”3,4—dating from 2003—and the strict approach derived from that: diagnosis–safety evaluation–design of intervention.4

An Example—Renewing the Deck A more accurate survey of the cracks in the deck plates revealed a number of obvious defects already inherent at the time of building. For example, the transition from the curve of the ballast plate to its horizontal bearing strip often did not lie directly on the supporting flanges of the longitudinal or transverse beams as intended but protruded instead by up to 35 mm owing to excessive construction tolerances. In reality, instead of acting as a membrane, the thin plate was being loaded as a cantilever; the additional bending stresses that occurred every time a train passed made fatigue cracks here inevitable. Above all else, it was this small detail defect that, in the end, forced the replacement of the entire historic deck! As a replacement, the client initially favored abandoning the ballast track and swapping to a slab track; in doing so, the old plates that would be released from their structural function could, however, remain in place. Two options were discussed: the “concrete on steel” solution, in which slabs with twin-block sleepers cast on trapezoidal profile sheeting would be supported on the existing transverse beams of the viaduct (Fig. 3), and an alternative “steel on steel” system, with longitudinal steel beams guaranteeing that the loads would be transferred from the rails in their highly elastic mountings to the existing transverse beams. However, there were considerable difficulties with both solutions. Those difficulties were due to the departure from the flexible permanent way with its ballast bed and, in particular, incompatibilities between the different movement joint requirements of the rails, the

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Fig. 3: Option 1: Slab track “concrete on steel” (courtesy: Lorenz & Co. Structural Engineers, 2011)

Fig. 4: Option 3: Replacement of deck plates, changed in detail “homoeopathically” (courtesy: Lorenz & Co. Structural Engineers, 2011)

slab track and the historic steel load-bearing structure plus the associated load paths for loads due to braking and accelerating. Therefore, this author developed a third option that essentially replicated the historic deck plates but avoided the flaws diagnosed in the damage survey through precise optimization of the details of the historic model (Fig. 4). This required the development of a solution that could handle more than 400 different plate geometries with one tolerance standard that would prevent the unacceptable cantilevering of the original plates and the ensuing fatigue problems. The key to success was, on the one hand, the compilation of a detailed plate database in which the geometry of every one of the roughly 2200 existing plates was recorded. This database enabled sensible clusters to be formed for the replicas by specifying a maximum cantilever of just 10 mm. By increasing the plate thickness as well, from 7 to 9 mm, it was thus possible to verify the durability of the relevant stress cycles with a utilization of merely 88% even under the most unfavorable conditions. On the other hand, a method that permitted economic fabrication of the number of different plate clusters required to meet this specification had to be found. The answer came from the steelwork contractor RW Sollinger Hütte GmbH, who proposed fabricating the double-curvature plates by using hydraulic cold forming to bend an initially flat plate. In the meantime, this method could be easily adapted to the different geometric boundary conditions and could thus comply with the necessary erection tolerances.

Heritage and Construction History and the Structural Engineer’s Responsibility Complete refurbishment of the viaduct for the U2 line, including the two high-level stations, was completed on schedule in the spring of 2011 after more than ten years of preparations, planning and building work (Figs. 5 and 6)—and without exceeding the budget of approx. €78 million. The project emphasized the fact that construction technology and heritage conservation do not necessarily have to contradict each other, even with a transport infrastructure project such as this one. Instead, constructive dialogue between the partners can lead to new solutions that are interesting both technically and economically. It also confirms the thesis that the closer refurbishment concepts adhere to the specification of the historic structure itself, the better they are.

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Fig. 5: Refurbished viaduct with renewed deck plates (courtesy: Lorenz & Co. Structural Engineers, 2011)

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Fig. 6: Refurbished bearing supports (courtesy: Lorenz & Co. Structural Engineers, 2011)

This project also impressively demonstrates that when developing an intelligent and truly sustainable refurbishment concept, the design engineers need both engineering science and construction history skills during all phases of the design process in order to: • recognize the construction history significance of the historic structure and use this as a basis for respectful treatment, • locate the specific design forms in their contemporary context and use these to understand load-bearing structure, details and load paths, • identify the typical weaknesses and flaws in the forms of construction of the period and thus devise upgrading strategies based on the historic structure and • decide on the “hotspots” that require especially careful heritage conservation treatment in such an engineered structure, determined primarily by its historic design. Historic bridge structures such as the viaduct in Prenzlauer Berg are not simply complex evidence of feats of human achievement. They are also, and principally, authentic testimony to the history of the art of engineering, the history of the engineers themselves. Dealing with these structures respectfully requires engineers to take on much more responsibility than the heritage conservationists. Without knowledge and awareness of construction history, however, it is not possible to assume that responsibility.

References [1] Wittig P. Die Architektur der Hoch- und Untergrundbahn in Berlin. Zirkel ArchitekturVerlag: Berlin, 1922. [2] Scheffler K. Gute und schlechte Arbeiten im Schnellbahngewerbe. In: Der Verkehr. Jahrbuch des Deutschen Werkbundes, Jena, 1914; 42–47. [3] International Council of Monuments and Sites (ICOMOS). Principles for the Analysis, Conservation and Structural Restoration of Architectural Heritage. Charter of Victoria Falls, 2003.

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[4] International Council of Monuments and Sites (ICOMOS). Recommendations for the Analysis, Conservation and Structural Restoration of Architectural Heritage. Guidelines on the Charter of Victoria Falls, 2003. [5] Roca P. The study and restoration of historical structures: from principles to practice. In: Proceedings of the Fifth International Conference on Structural Analysis of Historical Constructions, Lourenço PB, Roca P, Modena C, Agrawal S (eds), New Delhi, 6–8 November 2006, 2006; 9–24. [6] Fischer M, & Lorenz W. Stahlbau unter Denkmalschutz – Grundinstandsetzung von Viadukt und Bahnhöfen der Hochbahnlinie U2 in Berlin-Prenzlauer Berg. Stahlbau 2011; 80(6): 419–427 (incl. further references).

179 Chapter

7.9 The Main Avenue Bridge, Cleveland, Ohio, USA

Dario A. Gasparini, Professor Emeritus of Civil Engineering, Case Western Reserve University, Cleveland, Ohio, USA William Vermes, Professional Engineer, Jones Stuckey, A Division of Pennoni, Cleveland, Ohio, USA

Introduction The Main Avenue Bridge in Cleveland is a remarkable engineering work in many ways. It is a large-scale, complex design and has an interesting social history. It embodies many structural innovations, and it was carefully detailed with consistent aesthetic principles. It was built with great efficiency in 17 months, and its performance over 77 years has been excellent. The bridge has a total length of approximately 1800 m (or 2440 m with approaches) with at least five horizontal curves and several vertical curves. The bridge was built to provide an east–west transportation link that did not require motorists to go through downtown Cleveland streets. It replaced the Main Avenue swing bridge over the Cuyahoga river, which was a traffic bottleneck, and it relieved traffic from its southern neighbor, the Detroit-Superior Bridge.

Planning and Design Planning for the bridge began in 1928, but the Great Depression and failure of a county bond levy in 1930 halted the project. However, in September 1937, it became one of the initial projects funded by the Federal Emergency Administration for Public Works, whose charge was to fund meritorious public works with the intent to “provide stimulus” to the American economy. Engineering staffing began in August 1937 and was completed in December. The Cuyahoga County Engineer’s Office received over 130 applications, many from graduates of leading US engineering schools. About 35 engineers were hired to design and supervise construction at a typical salary of $400 per month. At this time, John O. McWilliams was the Cuyahoga county engineer, W. E. Blaser was county bridge engineer, and Wilbur J. Watson was the project consulting engineer. The person who led all aspects of the design was the chief design engineer Fred L. Plummer. Prior to joining the County Engineer’s Office, Plummer had been an associate

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professor of structural engineering at the Case School of Applied Sciences in Cleveland. He was a member of the American Welding Society and a strong advocate of welding. He authored two books, Soil Mechanics and Foundations and Fundamentals of Indeterminate Structures. Given the focus of his structural book, it is understandable that Plummer set the structural theme for the project: continuity of structural forms for improved structural efficiency. This theme evoked aesthetic principles that were consistently followed while detailing the bridge. Construction of the bridge began on 12 May 1938, and the bridge was dedicated 17 months later, on 6 October 1939. Its total cost, including $1.6M for land acquisition, was $7.2M.

Structural Forms Plummer and his design engineers used a variety of structural forms, including: • Plate girders, continuous over four spans, for the lakefront ramp • Eight “continuous cantilever” riveted rigid frames for the eastern approach from West 3rd street to West 9th street • Continuous beams on rigid frame bents plus one simply supported truss for the eastern approach from West 9th street to “Pier 10” • Ten “continuous cantilever” trusses • Four spans of continuous reinforced concrete beams on concrete rigid frames • Riveted plate girder for the West 25th street overpass • Continuous riveted rigid frames for a “subway ramp” overpass • Continuous barrel-type concrete rigid frames for the West 28th street subway ramp overpass • Three-span welded rigid frame bridges for the West 28th street overpasses.

length ≈ 262 m length ≈ 366 m length ≈ 213 m length ≈ 768 m length ≈ 55 m length ≈ 27 m length ≈ 69 m length ≈ 17 m length ≈ 36.6 m

In this brief paper, it is not possible to provide a complete description of all these structural forms. The following are brief highlights of some of the innovative aspects.

Continuous Plate Girders Reference [1] described the design of the lakefront ramp of the eastern approach. The ramp has a 4.15% grade and accommodates a horizontal curve. The 16.7 m-wide roadway is supported by three plate girders, continuous over four spans. Figure 1 shows the 82.6 m span plate girder, which at that time was the longest plate girder span in the Americas. Its depth over the piers is 4.78 m.

Fig. 1: Plate girders of 82.6 m span on Main Avenue Bridge lakefront ramp

The ramp is at a 57° skew with respect to its piers, which are aligned with the railroad tracks below. The transverse joists were also made continuous over the three girders. Steelgrid decking, later filled with concrete, was welded directly to the joists and provided lateral bracing to the top flanges of the girders. Stress resultants in the continuous girders were determined using Hardy Cross’ moment

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distribution method of analysis, published in 1933, and later checked using the slope-deflection method. The girders were fabricated by Bethlehem Steel in Bethlehem, Pennsylvania, and were shipped by train to the site in sections that were up to 42.7 m long.

Continuous Cantilever Trusses After the lakeside ramp, the bridge continues with a set of eight spans of continuous riveted rigid frames and continuous beams on rigid frame bents. The structural form changes to a set of ten truss spans near the eastern bank of the Cuyahoga river, as shown in Fig. 2. The trusses are of “continuous cantilever” construction; that is, alternate spans have two cantilever arms that support “drop-in” spans. The longest truss span, over the Cuyahoga river, is 122 m. The trusses have a deviation in their alignment to accommodate a horizontal curve. At the location of the deviation, special details were developed to allow for radial thermal movements.2 Several design decisions were made based on aesthetics, including the ratios of the truss depths at midspan to those over the piers. To provide a “modern” appearance, no laced sections were used, and to minimize changes in cross-sectional dimensions, higher-strength “copper bearing silicon steel” was used where required by greater element forces.

Welded Steel Rigid Frame Bridges Two separate bridges were built to pass over West 28th street. As shown in Fig. 3, each bridge is formed by two rigid frames, with a total length of 36.6 m and a main span of 21.3 m. Although rolled sections were used for both the beams and the columns, the beam-to-column connections, the splices and the joist and deck connections were all of welded construction; no riveting was used (except for the fascia plates). Reference [3] provided a full discussion of the design and construction processes. Welding processes were, of course, developed much earlier in the 20th century, and applications to shipbuilding and aircraft fabrication were pioneered in Europe. In the USA, Ref. [4] noted that “serious commercial development of structural welding commenced in 1926”. By that time,

Fig. 2: Continuous cantilever trusses of the Main Avenue Bridge (courtesy: Cleveland Memory Project)

Fig. 3: Welded rigid frame bridge over West 28th street

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processes for the economic production of heavily covered electrodes had been perfected, and interested companies, such as Westinghouse Electric, General Electric, and Lincoln Electric, heavily promoted welding technologies. Reference [4] described an all-welded steel plate girder railway bridge and an all-welded truss bridge built in the USA in 1928 as well as welded highway bridges completed in Poland and Czechoslovakia in 1928 and 1931, respectively. Reference [5] described international developments on welded bridges, especially the famous Belgian Vierendeel frames. Reference [6] discussed German all-welded highway bridges; by 1939, “150 railroad bridges and 500 highway bridges” had been welded in Germany.7 Many were plate girders, but other forms were also built. Although a few welded plate girders and truss bridges were built in the USA in the early 1930s, US engineers, in general, were slower to accept all-welded highway bridges, primarily because of concerns over fabrication-induced stresses, fatigue and brittle fracture. The American Welding Society (AWS), which was founded in 1919 and which has published The Welding Journal continuously since 1922, published their first bridge welding code in 1936.8 The James F. Lincoln Arc Welding Foundation was also established in Cleveland in 1936 to promote and disseminate information on welding technologies. The American Association of State Highway Officials (AASHO) also had separate provisions on welding bridges by the end of 1935, but these were not included in their 2nd Edition of the Bridge Code, published in 1935. AASHO and AWS collaborated on revisions, which were incorporated into their 1941 revised codes. The design of the West 28th street bridges must have followed the AASHO load provisions and either the AWS or the AASHO welding provisions. Results of a survey of state highway officials on welding practices were reported in the March 1939 issue of The Welding Journal. Although most states were using welding for repair, strengthening and attaching “secondary members”, of the 41 states that responded, not one reported using welding for “primary members”. Therefore, the West 28th street overpasses of the Main Avenue Bridge, completed in 1939, may be the oldest extant welded rigid frame bridges in the USA.

Piers and Foundations The piers and foundations for the bridge were challenging because of the restrictions imposed by the railroads, the presence of “construction fill” near the Lake Erie shore and the potential instability in the riverbanks under the loads imposed by the trusses. The piers for the lakefront ramp, visible in Fig. 1, were especially innovative. Because of size limitations within the railroad right-of-way, the designers used composite sections; that is, steel outer shells with appropriate shear transfer attachments were filled with reinforced concrete. To transfer moments in the piers to the foundation, two layers of steel grillages were fastened at the bases of the steel pier shells. A rectangular sheet-piling wall was then driven, and the grillages were embedded in concrete. The piers Fig. 4: Hyperbolic paraboloid surfaces on for the trusses, visible in Fig. 2, were hollow concrete piers for trusses (Cleveland Memory sections with a wall thickness of 686 mm, supported by pile foundations. Curiously, one Project)

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of the faces of each pier is a hyperbolic paraboloid surface, as shown in Fig. 4. Although increasing cross-sectional dimensions from top to bottom is structurally sensible, affecting this by a warped surface seems to have primarily been an architectural flourish.

Performance The foundations, piers and superstructures of the Main Avenue Bridge were carefully designed and have performed exceptionally well. However, two design decisions, coupled with uneven maintenance and liberal use of deicing salt in the severe Cleveland winters, caused problems. The first decision was to use a concrete-filled, steel-grid deck, welded directly to the stringers. The second was to provide roadway drainage by allowing water to flow through open finger joints in the deck to a collection system below. Over time, the drainage system failed at many locations, allowing salt-laden water to flow over structural members, causing corrosion. The water also caused corrosion in the steel-grid deck, which in turn led to buckling of the pavement and closure of expansion joints. This distress necessitated a series of nighttime closures and emergency repairs. In 1991, the bridge was closed completely, and an18-month rehabilitation was performed. The entire 25 m-wide, steel-grid deck and the supporting stringers (to which the deck was welded) were replaced. The bridge now has a reinforced concrete deck over new stringers. Superstructure components were repaired or replaced as required, including the replacement of 40% of the floor beam cantilever brackets. Sealed expansion joints with a new drainage system were also installed. The total cost of this rehabilitation was $65 million. For the past 24 years, the Main Avenue Bridge has served the public well. In 2007, a complete repainting of the truss spans revealed significant section loss in two truss lower chord box members requiring emergency strengthening. Since 2014, a series of other rehabilitation projects have been performed, including strengthening of select gusset plates following a recent structural load rating and revised section loss measurements. During the 77-year service of the Main Avenue Bridge, no repairs have been performed on corrosion-resistant silicon steel truss members or on the welded frame superstructures of the West 28th street overpasses.

References [1] Plummer FL. Girder span record boosted to 271 ft. Eng. News-Record 1941; March 27: 50–52. [2] McWilliams JO, Blaser WE, & Plummer FL. Features of Cleveland’s Main Avenue Bridge. Roads and Streets 1939; December. [3] Plummer FL. Welded rigid frames, European style. Eng. News-Record 1940; July 18: 55– 57. [4] Fish GD. Arc-Welded Steel Frame Structures McGraw-Hill Book Co.: New York, 1933. [5] Grover LM. Foreign countries lead U.S. in welded bridges. Eng. News-Record 1936; May 14: 703–709. [6] Schaper G. New German bridges. Welding J. 1937; September: 32–39. [7] Kommerell O. Bridge welding in Germany. Welding J. 1939; August: 472–474. [8] American Welding Society. Specifications for Design, Construction, Alteration and Repair of Highway and Railway Bridges by Fusion Welding AWS: New York, 1936.

185 Chapter

7.10 Renovation of a Historic Railway Lift Bridge

Jurgen Voermans, Struc. Eng., Royal Haskoning DHV, Rotterdam, The Netherlands, Jaco Reusink, Struct. Eng., Engineering Department, Municipality of Rotterdam, Rotterdam, The Netherlands

Introduction The Koningshaven bridge in Rotterdam is a vertical lift-type, movable railway bridge. The bridge was completed in 1927 and was replaced by a tunnel in 1993. The bridge was designated as a national monument in 2000. To preserve the bridge for future generations, an extensive renovation project is under execution. This paper elaborates on the history, the design, the structural assessment and major challenges of the structural retrofit.

Brief History The construction of the Koningshaven bridge was part of a major project extending the connection of the Amsterdam–Rotterdam railway line to the Moerdijk–Antwerpen railway line. This part of the project involved the accomplishment of a double-track railway through the densely populated Rotterdam inner city and the crossing of the Nieuwe Maas river. The Koningshaven bridge was completed in 1877 connecting the southern part of the river and canal crossing between the northern shore of the Nieuwe Maas river through Noordereiland and the southern shore of the Koningshaven (Fig. 1). The Koningshaven bridge consisted of a steel arch with a span of 80 m on both sides of a symmetrical swing bridge with a total length of 54.5 m. Openings of 20 m allowed vessels to pass on either side of the central pivot pier (Fig. 2). As time progressed, the swing bridge could no longer meet the requirements of the busy navigation and railway traffic. The width of the bridge openings was too narrow, and the bridge had to be opened frequently. Both navigation and railway traffic were seriously obstructed. Several collisions occurred as a result. The collision on 2 November 1918 of the German steamship Kandenfels was decisive in the discussion to replace the swing bridge with a vertical lift bridge.

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Fig. 1: Map of Rotterdam in 1888. The location of the bridge is indicated by the red arrow Fig. 2: Swing bridge crossing the Koningshaven In 1927, the swing bridge was replaced with the current vertical lift bridge designed by ir. P. Joosting (1867–1942), chief engineer of the Bridge Construction Department of the Dutch Railways. In 1993, a 2796 m long four-track railway tunnel was opened, and the railway bridges spanning the Maas River became superfluous. After fierce protests against the proposed demolition, the Koningshaven bridge was designated as a national monument. The municipality of Rotterdam obtained the ownership of the bridge from Dutch Railways. At that time, the bridge had already suffered from a decade’s lack of proper maintenance. Today, the bridge is highly admired as a memory to the Industrial Era, with a dense concentration of harbor activities at the inner city river south bank. The bridge is regarded by the public as a national icon.

Historical Design Until 1927, the approach spans of the swing bridge remained in place. The new lift bridge consists of two towers with a movable bridge span in between, which is moved up and down by means of ropes. The lift span is balanced by counterweights and covers a span of 53.5 m; the distance between the central planes of the main trusses is 8.8 m. Towers rise 60 m from the base to the top. The vertical clearance at mean high water level provided under the soffit of the lift span is 45 m. The complete steel superstructure consists of built-up steel members made of plates, angles and channels riveted together. The drive system applied is innovative. Instead of placing the drive machinery on top of the lift span in accordance with a Waddell-type span drive vertical lift bridge that was commonly applied at the time, it was placed in a machine room at the southern tower. This resulted in a significant reduction of structural weight of the lifting part. The lift span is suspended by 48 counterweight ropes with a diameter of 40 mm, 12 ropes at each corner. The ropes pass over eight cast-iron sheaves at the top of the towers and continue down from the other side of the sheaves to the counterweights. The sheaves have a diameter of 3.60 m and contain six sheave grooves (Fig. 3). Lever-type equalizers are used at the connections to the lift span to ensure equal loading of the ropes (Fig. 4). To pull the span up and down, eight operating ropes with a diameter of 26 mm are used (Fig. 5). The ends of these ropes are attached to geared operating drums in the machinery room. The four uphaul ropes extend from the drums upward and run around intermediate sheaves to sheaves at the top of the southern tower and then to the lift span. At both ends of the lift span, they make 90° turns around deflector sheaves upward to the top of the northern tower where they are attached.

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Fig. 3: Cast-iron sheave supported by a spherFig. 4: Lever-type equalizer ical roller bearing

Fig. 5: Course of counterweight and operating ropes: (a) downhaul rope; (b) uphaul rope; (c) counterweight rope1

Fig. 6: (a) Counterweight ropes; (b) course of leveling ropes1

The four downhaul ropes are wound in the opposite direction on the drums and run around intermediate sheaves at the base of the southern tower to the lift span. At both ends of the lift span, they make 90° turns around deflector sheaves downward to the base of the northern tower where they are attached. Leveling ropes are applied in order to maintain the two ends of the span at the same elevation during operation to prevent unsynchronized movement. These ropes consist of two pairs of ropes with a diameter of 26 mm and a Z-shaped course. The length of these ropes does not change during raising and lowering of the span (Fig. 6). Two ropes run from the base of

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the southern tower around deflector sheaves at both ends of the lift span to the top of the northern tower; the other two ropes run from the base of the northern tower to the top of the southern tower. In the machinery room, one direct current motor of 200 HP drives through a reduction gearing and a shaft of two pinions. These mesh with the ring gears of both operating drums. At both points, cast in situ drums with brakes with a diameter of 2 m are attached. The machinery can move the lift span at a speed of 0.9 m/s.

Renovation In 2016, the bridge was subjected to an extensive renovation. The purpose of the renovation was technical and durability lifetime extension of minimum 15 years. During the renovation, minimal hindrance of the navigation traffic was accepted. The scope of the renovation was determined by technical inspections and both structural and risk assessments (technical and personal safety), which were required for movable bridges in the Netherlands. The structural assessment was carried out according to the Eurocodes (2011+NA), in combination with the Dutch NEN 8700 code covering the structural reliability assessment of existing structures in case of retrofit and disapproval. A reliability level of β = 3.3 for renovation was applied. The structural assessFig. 7: Removing of the lift span ment focused mainly on the towers as the load-bearing capacity of the approach spans and lift span proved not to be critical. Distinction has been made between normal operational use and the temporary renovation period. Only the latter is discussed here. During renovation, the old lead-based paints were fully removed by blasting and were replaced by a new corrosion protection system. To facilitate proper conservation application circumstances and to prevent contamination of the environment due to paint, the steel structure had to be fully enclosed and conditioned. To achieve this, a scaffold was erected to allow the structure to be wrapped in plastic foil. Lowering the lift span and consequently raising the counterweights in case of high wind speeds would conflict with the scaffold. Therefore, a decision was made to remove the lift span during renovation (Fig. 7). The counterweights were fastened above to the towers by a steel frame. This procedure has multiple advantages: • • • •

Renovation of the lift span in a conditioned environment enhancing the quality of the conservation Enhancing safe working (not at height) Reduction of wind load effects on the towers No obstruction to navigation traffic by the lift span that needs to be lowered halfway at high wind speeds

In comparison with the situation during normal use, the area exposed to wind was increased, thus increasing the wind load on the towers as the scaffold is horizontally supported by the

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towers. Although the lift span was absent, the total wind load on the towers increased significantly. The high wind pressure factors of the truss towers caused higher wind forces than in the wrapped situation and it was decided that for large truss structures, the Eurocode wind loads are generally conservative. Minor uplift may occur at SLS (Serviceability Limit State) during extreme wind gusts, because of the absence of the dead load of the lift span that would act favorably to fix the towers at their supports. Therefore, work was not permitted on the scaffold at a wind speed ≥ 9 Beaufort. It has been recognized from previous projects that, after blasting, the scope of steel renovation may be extended to other parts. In the contract, a procedure was included to cope with unforeseen situations.

Conclusions The following conclusions can be drawn: • Extending the lifetime of historical movable bridges that are designated as monuments is difficult as the structural modifications due to the technical and personal safety requirements (e.g., safety stairs or elevator) are often contradictory to the appearance of the protected monument bridge. • The wind load on large truss structures according to the Eurocode is generally conservative. • The driving gear only requires minor worn-based replacements, such as cables and sheaves. • Special attention and nonstandard procedures are required for the sensitive high-quality application of the full new corrosion protection system on historic riveted structures; some of the locations are difficult to reach for quality blasting and painting, and the steel surface can be rough due to corrosion. • Elaborate technical inspections and recalculation proved essential in describing the necessary renovation scope.

References [1] Archive Nederlandse Bruggenstichting: historic photographic material. [2] De Boode A, & Van Oudheusden P. De ‘Hef’ – biografie van een spoorbrug. Uitgeverij De Hef: Rotterdam, 1985. [3] Joosting P. De in aanbouw zijnde hefbrug over de Koningshaven te Rotterdam. De Ingenieur. 1927; 42(6): 89–103. [4] Oosterhoff J, Coelman BH, & De Wagt WA. Bruggen in Nederland 1800 – 1940 Beweegbare bruggen. Matrijs: Utrecht, 1999. [5] Voermans J, & Reusink J. Renovation of a historic railway lift bridge. In IABSE Conference Geneva, 2015 – Structural Engineering: Providing Solutions to Global Challenges. IABSE: Zurich, 2015; 474–481.

191 Chapter

7.11 An (Almost) Extinct Engineering Heritage Asset—The Case of the Reichsautobahn Bridges

Roland May, Chair of Construction History and Structural Preservation, BTU Cottbus-Senftenberg, Cottbus, Germany

Introduction In early May 2015, a motorway bridge dating from the 1930s was demolished near Pfungstadt. Refurbishment had been ruled out, and the bridge had to make way for a replacement. A routine matter hardly worth a mention, replacing old bridges along motorways and major roads has been an everyday task for many decades. The headline to an article in the local newspaper announcing the impending demolition work was therefore correspondingly laconic: “Facelift for South Hesse’s motorway bridges”.1 The demolition, which went almost unnoticed by experts in this field, however, was a milestone in the story of the treatment of one of the most important heritage assets in the history of 20th-century transport. This unspectacular structure was indeed the last remaining historic bridge on the oldest section of the German motorway network.

The Reichsautobahn and Its Bridges At the time, the Reichsautobahn was probably the most ambitious traffic infrastructure project in the world. Work on this motorway network began in the autumn of 1933—only a few months after the National Socialists had seized power. Although there was plenty of experience from previous motorway plans to fall back on, these roads were declared to be “roads of the Führer” and were instrumentalized as symbols of a new order. Nevertheless, even wary foreign countries followed the rapid construction of an unprecedented road network almost 4000 km long, purely for motorized traffic, with increasingly unconcealed enthusiasm. Today, the Reichsautobahn is quite rightly regarded as the defining blueprint for modern motorways. Initially, the motorways project followed primarily economic goals. Soon, however, cultural aspects increasingly became the focus of attention, with the motorway network supposedly demonstrating the reconciliation between nature and technology. However, exploiting this for propaganda purposes proved to be quite complicated at first; after all, although the motorways were “thousands of kilometres long, they were also rather flat” (Ernst Bloch). Thus, besides the very ambitious integration into the landscape, the count-

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less bridges, as the most significant landmarks, became central elements in the propagandistic exploitation (Fig. 1). Unfortunately, the first bridges, including the aforementioned bridge near Pfungstadt, were an utter fiasco in terms of their appearance. Therefore, the architect Paul Bonatz was appointed as artistic adviser; he had already enjoyed great successes in cooperating in the design of engineering structures. Together Fig. 1: Landscaping and bridge building in with the engineer Karl Schaechterle and the 1938: motorway in the Wisenta valley near architect Friedrich Tamms, Bonatz supplied Schleiz crucial ideas for developing a truly high-class bridge design philosophy for the motorway network.2 In contrast to almost all other building projects carried out by the National Socialists, these motorways were widely acclaimed internationally. One remarkable feature was the diversity of the bridges. Modeled on different principles, the bridge designs embodied conflicting ideas, ranging from pure creative engineering in steel and reinforced concrete to “vernacular” and even monumental structures in stone. Over a period of not quite ten years, some 6000 bridges and culverts were completed along these motorways, with another 2000 or so at various stages of completion. The catchphrase in the propaganda of the National Socialists at that time was therefore the “land of bridge-building”.3 And indeed, the motorways offered a unique insight into the various possibilities of bridge building in the second quarter of the 20th century.

A Story of Continuous Losses Toward the end of World War II, more than just a few motorway bridges were destroyed by the Wehrmacht in order to hamper the advance of Allied troops. Nevertheless, much of the damage had been already repaired by the mid-1950s. One real problem for the retention of the Reichsautobahn as a unique infrastructure heritage asset in the coming years, however, was the growing volume of traffic, particularly in former West Germany. Wider carriageways and increasing traffic loads frequently led to bridges having to be demolished and replaced by new structures. As the term heritage began to be applied more widely, engineering structures and facilities started to attract the attention of the conservationists. The first motorway bridges were declared monuments in the early 1980s, and the first scientific monograph on the Reichsautobahn appeared at the same time4—since followed by many other publications. However, these measures could not stop the ongoing loss of cultural assets, especially after this trend was given new impetus by the unification of East and West Germany. A gigantic avalanche of investments was now underway under the heading of “German Unity Transport Projects”, the intention of which was to upgrade the ailing transport infrastructure of the former GDR. This resulted in a remarkable paradox. Although the “untouched state” of the motorways in the east of the country was praised with enthusiasm,5 this did not change the fact that, very soon, their appearance matched that of motorways in the west. Countless bridges were demolished in the course of modernization measures, including many outstanding examples of German engineering, but their potential value as heritage assets was not seriously considered. Only the intended demolition of the bridge over the Teufelstal (Devil’s valley) provoked some opposition. This bridge, formerly Germany’s largest arch bridge in rein-

THE DIFFICULTY OF PRESERVING HISTORIC TRANSPORT INFRASTRUCTURE ASSETS

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Fig. 2: Examples of the loss of outstanding motorway bridges. Top, left to right: River Elbe, Dresden (1934–1935, demolished 1995); Schkeuditz interchange (1935–1936, demolished 2000); Elbe floodplain, Hohenwarthe (1934–1937, demolished 1994). Bottom, left to right: Lauter valley near Kaiserslautern (1934–1937, demolished 2015–2016); Devil’s valley near Stadtroda (1936–1938, demolished 1999–2000); Danube, Leipheim (1934–1937, demolished 1999) forced concrete, had been protected since 1993 and had even been named a potential UNESCO World Heritage candidate in 1997.6 However, although prominent experts testified that the bridge could be refurbished, even this icon of the Reichsautobahn was demolished at the turn of the 21st century. At the same time, demolition continued unabated in the west of the country. Especially bitter here was the loss of the Danube bridge at Leipheim, the most important example of the contemporary adoption of Robert Maillart’s concept of three-pin arch bridges (Fig. 2).

The Difficulty of Preserving Historic Transport Infrastructure Assets The problem was definitely not restricted to former motorway bridges and certainly did not go unnoticed. For example, in 1999, a publication by the German National Committee for Heritage Preservation drew attention to the frightening scale of the destruction of cultural assets in the realm of transport infrastructure.7 However, to date, we have seen no substantial change in policy. One reason for this state of affairs can be found in the administrative structures, which make the preservation of heritage assets such as motorways extremely difficult in Germany. Here, the fundamental responsibility for issues regarding motorway bridges lies with the highways and heritage conservation authorities, organized on the level of the separate federal states. Heritage conservation authorities are normally involved in building measures, even smaller projects, but even today, they only rarely consider construction history aspects. The reasons for this are, on the one hand, that some heritage conservation authorities show no particular interest in becoming involved in such matters. On the other hand, their work is hampered by a lack of strategic preservation plans. Thus, decisions regarding demolition or retention are frequently left solely to the engineers in the highways authorities. There is no doubt that they have become aware of the early motorway bridges’ significance and that they certainly base their decisions on the best of their knowledge and belief. However, an unfortunate mix of a lack of construction history knowledge, overcautious safety concerns regarding the “theoretical service life” and a prefer-

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ence for new structures over refurbishment in the public financing system leads them to favor the demolition of a historic structure in most instances. As far as this author is aware, Germany does not yet have an official register of all heritage assets from the time of the Reichsautobahn. So, it is not surprising that, so far, the group of protected motorway bridges seems arbitrary. Conspicuous here is the dominance of large stone arch viaducts. Apparently, from the standpoints of both engineering (good ability to carry higher loads) and heritage protection (especially vivid depiction of National Socialist monumentality), these bridges seem to represent the “ideal” heritage asset when it comes to motorway bridge building. The clear preference for a certain type of bridge is, however, highly problematic because this means that one vital element of Reichsautobahn bridge building, namely, the surprising diversity, can no longer be seen in an adequate number of examples. The situation regarding underpasses and overpasses is particularly frustrating. Seen from the driver’s viewpoint, although the latter are much more important than large bridges carrying the motorway, they were and still are being poorly treated. The fact that such bridges normally constitute a series along motorway segments has only been acknowledged once so far, with “route 46” being protected since 2003.8 This motorway segment was never completed, and this fact undoubtedly simplified the granting of such comprehensive protection. However, the fragments spread across remote forest areas over a length of about 30 km lack one essential element: the “experience” of a connecting road. An example from North Rhine-Westphalia shows just how difficult it is to preserve overpasses on roads that are in use. The “Weg Hesseler” overpass at Beckum, built in 1938, was one of the first bridges in the world using the Freyssinet prestressing system. A preservation order for this bridge was granted in 1991, and so, it survived the upgrading measures carried out shortly before the turn of the century, whereas an overpass built at the same time just a few kilometers away using Ulrich Finsterwalder’s rival system quietly disappeared in 1996. After considerable doubts arose regarding the structural safety of the Beckum bridge, a decision was made to relocate the superstructure in 2012. Owing to the considerable costs, this measure, no doubt carried out with the best of intentions, led to a storm

Fig. 3: Attempts to deal with the motorway bridge-building inheritance: the “Weg Hesseler” prestressed concrete overpass (1938) following its relocation to the Vellern motorway rest area; a preserved segment of welded superstructure from the Mühlenfliess Bridge (1937/1938)—now an exhibit in the motorway history collection at Erkner Motorway Maintenance Depot; the extension (2003–2005) to the Saale valley bridge at Jena (1938–1941) with an “appropriate” design language

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of public protest. Not totally blameless here was undoubtedly the presentation of the “torso” on a nearby motorway rest area in a manner that can hardly do justice to the heritage idea. This is just another instance in a whole series of seemingly almost desperate attempts to preserve at least some of the motorway bridge-building inheritance (Fig. 3).

Outlook An example that demonstrates that a different approach is possible, despite considerable traffic, is Merritt Parkway in Connecticut, which is protected in its entirety—a length of over 60 km. However, in the meantime, it would be nearly impossible to find a comparable segment of the Reichsautobahn that has not been extensively reshaped. Most of the historic sections have been upgraded or enclosed between noise barriers or given new structures. These days, gaining some kind of authentic impression of the earlier “adventure of the motorway”9 is virtually only possible on routes outside the country, in former German territories in Eastern Europe. However, it is probably only a question of time before these examples also vanish. It would appear that preserving the last original parts of the early motorway network (and compiling a meaningful record of structures to be demolished) is only possible when a number of fundamental ideas recently proposed in a remarkable dissertation10 are quickly put into practice. The most important element here would be the compilation of a national register containing facts on the general state of preservation in addition to substantiated information on the historical, construction history and cultural relevance of individual motorway segments. With such a basis, it would then be possible to develop targeted preservation plans. However, in Germany, a fundamental improvement to the situation regarding the retention of historic transport infrastructure can only succeed when the players involved join forces in some kind of association, such as the USA’s Historic American Engineering Record (HAER), which has been around since 1969. We can already see a first glimmer of hope: the series Wahrzeichen der Ingenieurbaukunst (landmarks in the art of engineering) published by the Federal Chamber of Engineers has already had a lasting impact on German construction engineers’ awareness of their engineering heritage. The recently founded Gesellschaft für Bautechnikgeschichte e.V. (German Construction History Society) is emerging as a competent partner for authorities when it comes to construction history issues. There are also many voluntary groups performing valuable documentary work. Critical, however, is the fact that German structural engineers must see themselves as advocates of their own history to a greater extent. The (almost complete) disappearance of the motorway heritage asset vividly demonstrates the consequences of a lack of awareness of history among this profession. It is true that the early German motorways are cumbersome in historic and technical terms, but only when engineers fully appreciate the value of construction history for their current everyday engineering will they perhaps succeed in preserving a symbolic segment of the Reichsautobahn for the future.

References [1] “reh”. Frischekur für Südhessens Autobahnbrücken. Darmstädter Echo 2015; 10 April. [2] May R. Pontifex maximus. Der Architekt Paul Bonatz und die Brücken. MV-Wissenschaft: Münster, 2011. [3] Gruber E, & Schütz E. ‘A land of bridges’. On the conception and presentation of bridges for the Reichsautobahn in the Third Reich. Daidalos 1995; 57: 20–33. [4] Stommer R (Ed.). Reichsautobahn. Pyramiden des Dritten Reichs Jonas: Marburg, 1982.

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[5] Lucka W. Autobahnbrücken aus der Zeit des Reichsautobahnbaus im Wesergebirge. Berichte zur Denkmalpflege in Niedersachsen. 1989; 9(3): 130–135. [6] DeLony E. Context for World Heritage Bridges. ICOMOS: Paris, 1997. [7] Gympel J. Schrittmacher des Fortschritts – Opfer des Fortschritts? Bauten und Anlagen des Verkehrs. Deutsches Nationalkomitee für Denkmalschutz: Bonn, 1999. [8] Stockmann D. Strecke 46. Die vergessene Autobahn, 3rd edn. Stockmann: Veitshöchheim, 2007. [9] Harz H, & Menzel H. Das Erlebnis der Reichsautobahn. Ein Bildwerk Callwey: Munich, 1943. [10] Kriest M. Die Reichsautobahn. Konzeption, räumliche Struktur und Denkmaleigenschaft eines historischen Verkehrsnetzes. Petersberg: Imhof, 2016.

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7.12 Construction Technology of Chinese Woven Timber Arch Bridges

Yan Yang, PhD ; Baochun Chen, Prof.; Shozo Nakamura, PhD ; College of Civil Engineering, Fuzhou University, China

Introduction According to the structural types of the existing timber arch bridges, they can be classified into three main forms, that is, rib arch, truss arch, woven arch.1–3 The woven arch is a unique structure and is only built in China, so it is also called Chinese woven timber arch.3 According to their present situation, location and structural details, Chinese timber arch bridges can be further divided into two types: one is the nonextant ancient Bianhe rainbow bridge and the other is the extant Min-Zhe timber arch bridge.4,5 The historical records show that the first ancient Bianhe rainbow bridge was built in China between 1032 and 1033.4 The Chinese timber arch bridges were widespread in the 11th and 12th centuries over the Bian and Fen rivers, but none of them survived, and no details of their design and construction technologies have been

(a)

(b)

Fig. 1: Two branches of Chinese timber arch bridges: (a) Bianhe rainbow bridge; (b) Min-Zhe timber arch bridge

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recorded. The structures can only be seen from a bridge in the famous painting “Chhing-Ming Shang Ho Thu” (Festival of Pure Brightness on the River), as shown in Fig. 1a, by Zhang Zeduan who was an artist who lived during the Northern Song Dynasty (1119–1125).6,7 Fortunately, more than 100 Min (short for Fujian Province)-Zhe (short for Zhejiang Province) timber arch bridges still exist in mountainous areas in the northeast of Fujian Province and in the southeast of Zhejiang Province, as shown in Fig. 1b.8 A Chinese woven timber arch bridge achieves large spans by weaving straight logs together in a special way without nails and ropes, in which the main arch consists of two different longitudinal polygonal arch systems connected by transverse systems, and the construction is convenient because the structural members are light and need little processing.8 Due to its long history and ingenious conception, the Chinese woven timber arch bridge was listed in the world heritage tentative list by China in 2012. Chinese timber arch bridges are designed and built by bridge craft workers. The technology has been handed down from masters to their apprentices, many being father and son, and has thus formed some timber arch bridge families with stable characteristics in their construction technologies. However, today, there are only a few old masters as fewer young people prefer to learn this skill because it is difficult to find a job. This construction technology is at risk of being lost, and hence, it was listed in the Urgent Safeguarding List of Intangible Cultural Heritage by UNESCO in 2009.9 It is urgently important to record the construction techniques, which is the purpose of this paper. Because no ancient Bianhe rainbow bridge survived, and no detailed records on the construction technology have been found, this paper will introduce only the construction technology of the MinZhe timber arch bridges.

Structure of Chinese Woven Timber Arch Bridges Typical single structures of the two kinds of Chinese timber arch bridges are shown in Fig. 2. The main structures are similar with small difference, while the Min-Zhe timber arch bridge has a deck system and covering house.10 The bearing structure of a Min-Zhe timber arch bridge (Fig. 2b) is constructed using a woven arch consisting of longitudinal and transverse straight logs assembled in a special manner. There are two longitudinal systems—one is a three-line polygonal arch with three groups of longitudinal straight logs of the same length connected with two transverse beams, and the other is a (a)

(b) Covered house 60

30 30 30

830

Transverse beam of 2nd system Transverse beam of 1st system Spandrel structure (horse-leg) Longitudinal beam

60

21 × 45 = 945

Spandrel protection plates X-bracing

40 

Transverse beam of 2nd system 2nd system of arch ring 1st system of arch ring

The first system

The second system

Fig. 2: Sketch of Chinese woven timber arch bridges: (a) Bianhe rainbow bridge; (b) Min-Zhe timber arch bridge

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CONSTRUCTION TECHNOLOGY OF CHINESE TIMBER ARCH BRIDGE Upper transverse beams of 2nd system Level arch ring of 2nd system Longitudinal beams Upper slant rib of 2nd system General column

Level arch rib of 1st system

Transverse beams of 1st system Below slant rib of 2nd system Slant arch rib of 1st system

Straight tenon joint

Swallow Tail tenon joint

2nd system Swallow Tail tenon joint Straight tenon joint Swallow Tail tenon joint Straight tenon joint 1st system

Fig. 3: The mortise and tenon node five-line polygonal arch with five groups of shorter longitudinal straight logs connected with four transverse beams. The longitudinal members are mainly subjected to compressive forces and take full advantage of the compressive strength of timbers parallel to their fiber. The transverse members connect the two longitudinal systems into an integral structure. All the components are connected with the mortises and tenon nodes without nails and ropes, and two kinds of mortise and tenon nodes are used, including swallow tail tenon and straight tenon, as shown in Fig. 3.

Construction Technology of Chinese Timber Arch Bridge In the traditional Chinese society, similar to other construction engineering activities, timber arch bridge construction also has some important religious rituals and folk belief behavior.11 However, this section concentrates on the construction technology, including the following five main steps.9

Selection of Bridge Location Selection of a bridge location generally follows Fengshui (wind and water) to meet a quest for an auspicious location in ancient China. The bridges are located at the site called Shuikou (the mouth of water), the downstream of a river of a village. It is a belief in Fengshui that this can cause peaceful lives and prospects for the local people. Many of China’s surviving timber arch bridges can be seen as proof of the reasonability of the traditional site selection method. Some rules of Fengshui reflect the consideration of the hydrological and geological conditions of the bridge site. The bridge site selection also relies on the rich experience, high-level techniques and wisdom of the masters. In some bridges, the arches are directly erected on a natural cliff and crag with shallow carves without an abutment, as shown in Fig. 4.

Construction of Abutments and Piers

Fig. 4: The abutment

Most abutments and piers of the Chinese timber arch bridges are built with big gravels or block stones on a spread foundation. These structures were all built by manual methods. There was no advanced equipment for elevation measurement in

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the past. A half-section bamboo pipe (the knots were cut off) filled with water was used. If the bamboo is not long enough for the bridge span, several bamboos may be used with temporary supports. The bamboos are connected through overlapping and sealed with yellow wet clay in the joint bottom to prevent the water from seeping out. The level can be reached by adjusting the height of the bamboos in the supports.

Selection of Materials and Treatment of Structural Members Chinese fir is a kind of tree popular in the Min-Zhe areas. The fir tree grows fast, and its wood is easily processed and is not easily subjected to decay or easily eaten by moths. Moreover, its mechanical performance is more stable than other types of wood. Consequently, it becomes the first choice for the main construction material by craft masters. Trees with suitable sizes in the local area are strictly selected, accompanied by some important religious rituals and folk beliefs to show their best wishes. The selected trees are cut down and transported to the bridge site. Then, they are constructed according to the design of the craft master. Only simple processes are needed on the raw materials. All the steps are carried out by manual methods with traditional tools such as the Luban rulers, carpenter’s ink markers, wooden fork horse, axes, chisels, planers and saws.

Erection of Arch Ring Erection of the arch ring is the most important step in the construction. It consists of four steps for a single span bridge (without piers), as illustrated in Fig. 5. The four steps are as follows: (1) erection of the first system (three-line polygonal arches), (2) erection of vertical columns (also called general column in Chinese Folk) on the abutment as elevation scales, (3) erection of the second system (five-line polygonal arches) and (4) installation of X-bracings. Because no modern lifting equipment was available in ancient times, primitive wood winches were used for erection, and the wooden brackets were used to support the springing member

1

2

3

Fig. 5: The process of erection of the arch ring

4

CONSTRUCTION TECHNOLOGY OF CHINESE TIMBER ARCH BRIDGE

(a)

(b)

(c)

(d)

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Fig. 6: Erection of the arch ring: (a) the bracket, (b) wood winch, (c) lifting arch ring members and (d) installing transversal beam and arch rings during construction. Two brackets made of two main columns, a cross beam and several diagonal strut members, and located near the two knee positions of the first system are built, as shown in Fig. 6a. The members in the first system are erected by wood winches (Fig. 6b) and supported by two brackets (Fig. 6c). After all the slat springing members in the first system are erected in position, two transverse beams are hoisted up (Fig. 6d), and tenon joints of the members are inserted into straight mortises of the transverse beam. All the members on one side are joined together and form two frames laid on the brackets. Then, the crown members are inserted into the swallow tail mortise of the transverse beams to connect the two springing frames together and form three-line polygonal arches. The second system of the five-line polygonal arch ring is easier to build after the completion of the first system. Its longitudinal members are erected on gaps of the first system from the springings. When all the crown members of the second system are installed to close the arch, the main arch construction is completed, as shown in step 3 in Fig. 5. In order to improve the spatial stability of the main arch, two X-bracings are employed, with one being inserted into transverse beams with the swallow tail tenon and the other being inserted into vertical columns in the abutment with a straight tenon. Finally, wood blocks are inserted between springing members to

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enhance the integrality of the arch ring. It should be pointed out that, in order to prevent serious damage of the wood members during construction, all the tools, including punner and hammers, are made of wood instead of iron or steel.

Construction of Spandrel Structures and Covering House The spandrel structure of the Min-Zhe timber arch bridges, also called horse-leg in Chinese tradition, consists of a pair of inclined members standing on the springing and two or three vertical or inclined members standing on a quarter transverse beam in the second system. The members are connected with mortise and tenon joints. The deck system consists of deck transverse beams, longitudinal beams and deck slabs. Generally speaking, there are six deck transverse beams (three for each side). One of them is close to the abutment and is also used as the transverse beam of the general column, while the other is located in quarter span and also serves as the transverse beam of the horse-leg. The transverse beam near the crown usually utilizes the upper transverse beam of the second arch ring system. A covering house is similar to a local general house and is built from the central part to both sides. Names of craft masters and their chorography and pedigrees are written on the ridge of the covering house for recognition of their participation and contribution. During the construction of the covering house, raising of the ridgepole is a high point that follows a ritual as in building houses and temples in Chinese traditional folk customs. When the bridge is completed, a ceremony of completion will be held on an auspicious day. After that, the bridge is open to the public.

Concluding Remarks Chinese woven timber arch bridges are not only an essence of architecture but also an important heritage structure in China and even in the world. The traditional construction technology is a precious intangible cultural heritage handed down from ancient generations. Acquiring the construction technology of Chinese timber arch bridge is the key issue in maintaining the existing bridges and building of new ones. Recording the construction technology may not only bring the benefit of learning the technology and attracting more young people to learn, thus preventing its disappearance in our generation, but it could also be a reference to create innovative construction techniques for the construction of modern arch structures.

References [1] Fernandez Troyano, L., 2003. “Bridge Engineering—A Global Perspective”. Thomas Telford. [2] Chen B, Yang Y. Introduce foreign timber arch bridge. Proceedings of the Third China International Symposium on the Covered house Bridge of Timber Arch Structure in Pingnan, China, October 2009, 2009; 237–241 (in Chinese). [3] Yang Y, Chen B. Comparative study on the timber arch bridge in China and abroad. Proceedings of the Third Chinese Colloquium on Ancient Bridge, Nanjing, China, 2010; 103– 110 (in Chinese). [4] Huangcheng Tang. 2000. History of Science Technology in China, Bridge Volume Science Press. Beijing, China. (in Chinese).

REFERENCES

[5]

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Huangcheng Tang. 2010. Chinese Timber Arch Bridge. China Building Industry Press (in Chinese). [6] Ceraldi C, Ermolli ER. Timber arch bridges: a design by Leonardo. Arch Bridges IV— Advances in Assessment Structural Design and Construction, Barcelona, Spain, 2004, 2004; 69–78. [7] Yang Y, Chen B, Gao J. Timber arch bridges in China. Proceedings of the Fifth International Conference on Arch Bridge, Madeira, Portugal, September 2007, 2007; 171–178. [8] Yan Yang, Shozo Nakamura, Baochun Chen and Takafumi Nishikawa: 2012 A survey on existing China timber arch bridges, J. Civil Constr. Mater. (Jpn. Soc. Civil Eng.), Vol. 28, (61—68). [9] Fengfang Zhou,Zeqi Lu,Xudong Su, 2011. Traditional Construction Technology of China Timber Arch Bridges, Zhejiang People’s Publishing Press. (in Chinese). [10] Yan Yang, Shozo Nakamura, Baochun Chen and Takafumi Nishikawa. 2014. The origin of timber arch bridges in China, J. Jpn. Soc. Civil Eng., 2, 54-61. [11] Ronald G. Knapp, Peter Bol, A. Chester Ong. 2008. Chinese Bridges: Living Architecture from China’s Past, Tuttle Publishing, America.

Afterword: Learning from the Past to Build the Future

The present SED is a compilation of contributions devoted to the vast topic of history of structural engineering as well as interventions on heritage structures and structures of high cultural values. Various, sometimes opposed, viewpoints and approaches are expressed and presented. IABSE Working Group 9 “Construction History” is aware of the rather heterogeneous and controversial nature of the content of this SED. However, this shall stimulate and provoke lively discussions within the structural engineering community who needs to increase the awareness of historical and cultural aspects of structures and structural engineering. Current structural engineering methods and practice are only at the very beginning of effective engineering integrating historical and cultural aspects in the assessment of existing structures and in intervention projects to adapt or modify structures of cultural values for future demands. Current structural engineering is predominately driven by a spirit to design and build new structures “out in the green”. Today’s structural engineers’ vocation still is to design and build, even when dealing with existing structures ! For many structural engineers, the opinion still prevails that an existing structure has a finite service life of 80–100 years and then needs to be replaced by a new structure. While this spirit was maybe rational 50 years ago, it is nowadays far away from modern society’s demands calling for a focused approach on existing structures, in particular those of high cultural values. Existing structures are an asset and wealth of a society, and structural engineers are called upon to maintain and enhance the existing structures effectively, within the availability of limited (public) funds … instead of replacing existing structures by new construction. The main problem is that most structural engineers have little or no education in the engineering of existing structures, including history of structures. They are not even aware of the opportunities available for the effective modern engineering of existing structures. This problematic situation is due to traditional civil engineering curricula at most of the technical universities still focusing largely on the design of new structures in reinforced concrete, steel and may be timber following provisions of current codes and standards. Considering this rather bureaucratic and uninspiring design education of structural engineers, it is not surprising that most design engineers are nowadays considered and treated as “code checkers”. They often have a limited understanding of the broader context of their design solutions and insufficient skills to collaborate with other professionals like architects and environmental engineers.

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AFTERWORD: LEARNING FROM THE PAST TO BUILD THE FUTURE

IABSE Working Group 9 “Construction History” largely discussed these professional issues during its meetings and excursions, and concluded that structural engineers definitely need to learn from the past to build the future ! However, this discussion is not specifically reflected in the present SED, and as a conclusion, WG 9 decided to highlight this issue in this afterword. Two topical issues should be developed further in the near future within IABSE and its Working Groups: •

•

Education of structural engineers needs a fundamental change. Modern curricula should be based explicitly on the needs of “Engineering of existing structures”. Design of new structures should be relegated. In addition, “History of structures and structural engineering” needs to become a mandatory fundamental engineering discipline. Greater emphasis should be given to principles comprising the essentials of all construction materials in both existing and new structures. Obviously, new technologies like monitoring of structures, advanced computational models for structural analysis as well as novel high-performance materials and structural systems are part of a modern curriculum. Information and data regarding ideas and solutions of structural engineering in the past should be scientifically analyzed and exploited. This “mining” process shall produce and enhance novel knowledge and know-how to design innovative interventions on existing structures and to create new structures. In the past, several innovative ideas could not be realized because of lack of appropriate means (materials, methods and tools) available in former times. Current and future technologies, in particular the computer-based ones, may help to implement and enhance former structural systems using high-performance materials. Understanding of the past is a rich source of inspiration for structural engineers.

Knowing the past is indispensable for modern structural engineering ! With the present SED, the IABSE Working Group “Construction History” wanted to make a contribution to this important goal. Eugen Brühwiler, Professor at the Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland, Vice-Chairman of IABSE Working Group 9 “Construction History” August, 2017

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List of SEDs Available Following SEDs can be purchased at the IABSE Onlineshop: SED 15 - Engineering History and Heritage Structures Viewpoints and Approaches Authors: Eberhard Pelke, Eugen Brühwiler, 2017 SED 14 - Sustainable Structural Engineering Editors: J. Anderson, C. Bucher, B. Briseghella, X. Ruan, T. Zordan, 2015 SED 13 - Use of Timber in Tall Multi-Storey Buildings Authors: Ian Smith, Andrea Frangi, 2014 SED 12 - Case Studies of Rehabilitation, Repair, Retrofitting, and Strengthening Editors: M.M. Bakhoum, Juan A. Sobrino, 2010 SED 11 - Design for Robustness Authors: Franz Knoll, Thomas Vogel, 2009 SED 10 - Structural Use of Glass Authors: Matthias Haldimann, Andreas Luible, Mauro Overend, 2008 SED 9 - Cable Vibrations in Cable-Stayed Bridges Author: Elsa de Sa Caetano, 2007 SED 8 - Use and Application of High-Performance Steels for Steel Structures Author: Hans-Peter Günther (Editor), 2005 SED 7 - Use of Fibre Reinforced Polymers in Bridge Construction Author: Thomas Keller, 2003 SED 6 - Structural Bearings and Expansion Joints for Bridges Author: Günter Ramberger, 2002 SED 5 - Introduction to Safety and Reliability of Structures Authors: Jörg Schneider and Ton Vrouwenvelder (3rd reviewed and extended edition, 2017) SED 4 - Ship Collision with Bridges - The Interaction between Vessel Traffic and Bridge Structures Author: Ole Damgaard Larsen, 1993 SED 3 - Vibrations in Structures - Induced by Man and Machines Authors: Hugo Bachmann, Walter Ammann, 1987 SED 2 - Dynamic Response of Reinforced Concrete Buildings Authors: Hajime Umemura, Haruo Takizawa, 1982 SED 1 - Concrete Box-Girder Bridges Authors: Jörg Schlaich, Hartmut Scheef, 1982

www.iabse.org/onlineshop IABSE Members can download SEDs in ePDF format for free in the Members Area at: www.iabse.org

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About the Authors

Structural Engineering Documents Objective:

Eberhard Pelke earned his civil engineer diploma from Darmstadt University. He is Head of the Department of Bridge Engineering at Hessen Mobil Road and Traffic Management in Wiesbaden, Germany. He is a Fellow of IABSE and was from 2013-17 Chair of IABSE WG9 Construction History.

To provide in-depth information to practicing stuctural engineers in reports of high scientific and technical standards on a wide range of structural engineering topics.

IABSE Bulletin Board: H.Subbarao, (Chair), D. Laefer, (Vice Chair), M. Bakhoum, C. Bob, M.W. Braestrup, N.P. Hoej, H.H. Snijder, R.von Wölfel, R. Mor, M.G. Bruschi, I. Payá-Zaforteza, S. Kite, M. Garlock.

Topics:

Eugen Brühwiler is professor of structural engineering at the EPFL—Swiss Federal Institute of Technology in Lausanne, Switzerland. His activities include modern methods to examine and enhance structures of high cultural value. He is a Fellow of IABSE and was from 2013-17 Vice-Chair of IABSE WG9 Construction History.

The International Association for Bridge and Structural Engineering (IABSE) operates on a worldwide basis, with interests of all type of structures, in all materials. Its members represent structural engineers, employed in design, academe, construction, regulation and renewal. IABSE organises conferences and publishes the quarterly journal Structural Engineering International (SEI), as well as reports and monographs, including the SED series, and presents annual awards for achievements in structural engineering. With a membership of some 4,000 individuals in more than 100 countries, IABSE is the international organisation for structural engineering.

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With Contributions From: E. Pelke, T.F. Peters, M. Traykova, R. Vergoossen. A. Bögle, W. Lorenz, E. Brühwiler, N. Janberg, J. Romo, B. Addis, M.J. Beiersdorf, J. Steiner, E. Vianen, R. Spaan, J.F. Duntemann, B.R. Greve, A. Traykov, D. Partov, N. Winterbottom, B. Heres, T. Chardakova, D. Wendland, P. van Bogaert, R. Barthel, J. Tutsch, J. Jordan, C. Weber, A. Kostka, M. Fischer, G. Eisele, J. Seiler, V. Wetzk, Y. Rammer, B. Espion, L. Clarke, M. Bartzsch, K. Geißler, D. Gasparini, W. Vermes, J. Voermans, R. May, Y. Yang, B. Chen, S. Nakamura.

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The International Association for Bridge and Structural Engineering (IABSE) was founded as a non-profit scientific association in 1929. Today it has more than 300 members iQ over 0 countries.IABSE’s mission is to promote the exchange of knowledge and to advance the practice of structural engineering worldwide. IABSE organizes conferences and publishes the quarterly journal Structural Engineering International, as well as conference reports and other monographs, including the SED series. IABSE also presents annual awards for achievements in structural engineering.

For further Information: IABSE c/o ETH Zürich CH-8049 Zürich, Switzerland Phone: Int. + 41-44-633 2647 Fax: Int. + 41-44-633 1241 E-mail: [email protected] Web: www.iabse.org

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Engineering History and Heritage Structures – Viewpoints and Approaches Structural Engineering Documents

The present Structural Engineering Document (SED) is a compilation of contributions devoted to the vast topic of history of structural engineering as well as interventions on heritage structures and structures of high cultural values. Various, sometimes opposed, viewpoints and approaches are expressed and presented. The rather heterogeneous and controversial nature of the content of this SED shall stimulate lively discussions within the structural engineering community who needs to increase the awareness of historical and cultural aspects of structures and structural engineering. Current structural engineering methods and practice are only at the very beginning of effective engineering, really integrating historical and cultural aspects in the assessment of existing structures and in intervention projects to adapt or modify structures of cultural values for future demands. Knowing the past is indispensable for modern structural engineering !

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Engineering History and Heritage Structures – Viewpoints and Approaches

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Structural Engineering Documents

15 Engineering History and Heritage Structures – Viewpoints and Approaches Eberhard Pelke Eugen Brühwiler

International Association for Bridge and Structural Engineering (IABSE)

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