Retrofiting For Earthquake Of Safe Building

RETROFITING FOR EARTHQUAKE SAFE BUILDINGS A Project Submitted In Partial Fulfilment of the Requirements For the Degree of Bachelor of Technology In Civil Engineering SUBMITED BY NAME

ROLL NO.

MOHD. ALTAMASH

110107108

GAURAV CHAURASIA

110107068

IMRAN BAIG

110107077

DEEPAK TOMER

110107058

PRAMOD CHAUDHARY

110107135

DEPARTMENT OF CIVIL ENGINEERING SHARDA UNIVERSITY (GREATER NOIDA) 2015

A Project Submitted In Partial Fulfilment of the Requirements For the Degree of

Bachelor of Technology In Civil Engineering SUMITED BY NAME

ROLL NO.

MOHD ALTAMASH

110107108

GAURAV CHAURASIA

110107068

IMRAN BAIG

110107077

DEEPAK TOMER

110107058

PRAMOD CHAUDHARY

110107135

Under the guidance of MR.SAYED EMAD UDDIN AHMED

DEPARTMENT OF CIVIL ENGINEERING IIMT COLLEGE OF ENGINEERING (GREATER NOIDA) 2013

CERTIFICATE This is to certify that the project entitled “RETROFITING FOR EARTHQUAKE SAFE BUILDINGS ” submitted by MOHD. ALTAMSH , GAURAV CHAURASIA , IMRAN BAIG , DEEPAK TOMER , PRAMOD CHAUDHARY in partial fulfilment of the requirements for the award of bachelor of technology degree in Civil engineering at the SHARDA UNIVERSITY (GREATER NOIDA) is an authentic work carried out by them under my supervision and guidance. To the best of my knowledge the matter embodied in the project has not been submitted to any other university/institute for the award of any degree.

Date: 15-04-2015 MR. SYED EMAD UDDIN AHMAD Department of Civil Engineering (

SHARDA UNIVERSITY (GREATER NOIDA)

ACKNOWLEDGEMENT

We would like to express our profound sense of deepest gratitude to our guide and motivator SYED EMAD UDDIN AHMAD assistant prof. SHARDA UNIVESITY(GREATER NOIDA)for his valuable guidance, sympathy and co-operation for providing necessary facilities and sources during the entire period of this project. We wish to convey our sincere gratitude to all the faculties of Civil Engineering Department who have enlightened us during our studies. The facilities and co-operation received from the technical staff of Civil Engineering Department is thankfully acknowledged. We express our thanks to all those who helped us in one way or other. Last, but not least, we would like to thank the authors of various research articles and books that were referred to.

MOHD. ALTAMASH (110107108) GAURAV CHAURASIA (110107068) IMRAN BAIG (110107077) DEEPAK TOMER (110107058) PRAMOD CHAUDHARY (110107135)

CO N T E N T S

Chapter No.

Title

Page No. 1

General Principles for the Design of Concrete Buildings for Earthquake Resistance 1.1

Introduction

1.2

Seismic

2

Seismic Assessment and Retrofitting of Existing Concrete Buildings 2.1

Introduction

2.2

Circumstances

2.3

Why Retrofitting

2.4

Retrofit Performance Objectives

2.5

Public Safety Only

2.6

Structure Survivability

2.7

Structure Functionality

2.8

Structure Unaffected.

2.9

Need in earthquake vulnerable building

2.10

Seismic evaluation of buildings

2.11

Component of seismic evaluation methodologies 2.11.1 QUALITATIVE METHODS 2.11.2 AN ANALYTICAL METHOD

2.12

Basic Concepts at (CEB, 1997)

3

2.13

Structural damage due to lack of deformation

2.14

Classification

Retrofitting of masonry structures 3.1

Introduction

3.2

Why Retrofitting

3.3

Defects of masonry

3.4

Necessity of retrofitting of existing masonry

3.5

Retrofitting schemes depend upon

3.6

FAILURE MODE OF MASONRY BUILDINGS 3.6.1

O UT – O F – P L A N E

3.6.2

IN–P L ANE FAI LURE

3.6.3

DIAPHRAGM FAILURE

3.6.4

FAILURE OF CONNECTION

3.6.5

P O U N D I N G

3.6.6

FAI L U R E O F N O N - S T R U C T U R A L C O M P O N E N T S

Chapter No.Title

FAI L U R E

Page No.

4

RETROFITTING OF MASONRY BUILDING 4.1

INTRODUCTION

4.2

METHODS FOR RETROFITTING OF MASONRY BUILDING

4.2.1

Repair

4.2.2

Local/Member Retrofitting

4.2.3

Structural/Global Retrofitting

4.3

REPAIRING TECHNIQUES OF MASONRY 4.3.1

Masonry Cracking

4.3.2

Masonry deterioration

4.4

THROUGH STONES/BOND STONES

4.5

CEMENT GROUTING

4.6

MASONRY DETERIORATION

4.7

RE-POINTING

4.8

MEMBER RETROFITTIN

4.9

TYPES OF SHORTCRETE 4.9.1 4.9.2

4.10

WET MIX DRY MIX OR GUNITE DESIGN MIX

ABSTRACT

The seismic retrofitting of reinforced concrete buildings not designed to withstand seismic action is considered. After briefly introducing how seismic action is described for design purposes, methods for assessing the seismic vulnerability of existing buildings are presented. The traditional methods of seismic retrofitting are reviewed and their weak points are identified. Modern methods and philosophies of seismic retrofitting, including base isolation and energy dissipation devices, are reviewed. The presentation is illustrated by case studies of actual buildings where traditional and innovative retrofitting methods have been applied.

KEYWORDS: Pushover Analyses, Seismic Vulnerability, Seismic Retrofitting, Base Isolation

CHAPTER- 1

General Principal for the Design of Concrete Building for Earthquake Resistance

1.1 INTRODUCTION Seismic retrofitting of constructions vulnerable to earthquakes is a current problem of great political and social relevance. Most of the Italian building stock is vulnerable to seismic action even if located in areas that have long been considered of high seismic hazard. During

the past thirty years moderate to severe earthquakes have occurred in Italy at intervals of 5 to 10 years. Such events have clearly shown the vulnerability of the building stock in particular and of the built environment in general. The seismic hazard in the areas, where those earthquakes have occurred, has been known for a long time because of similar events that occurred in the past. It is therefore legitimate to ask why constructions vulnerable to earthquakes exist if people and institutions knew of the seismic hazard. Several causes may have contributed to the creation of such a situation. These are associated to historical events, fading memory, greed, avarice, poverty and ignorance. Among historical events particularly relevant are wars, epidemics, and natural disasters which may limit, in a significant way, the available resources of a country. In such circumstances there is a tendency to build with poor materials and without too much attention to good construction techniques and safety margins. A situation of this kind occurred in Italy and in Japan after the Second World War and similar situations have occurred in Italy many times in the past. In such a situation it is possible that the phenomenon of fading memory occurs and past memories are easily erased. In Italy commercial profits often result from the employment of poor material and workmanship rather than of the optimal utilization of the production factors. The depressing situation of poor quality control and material acceptance also falls into this framework, which, in most cases, results only in paper work devoid of substantive value. Among causes arising from ignorance there may be both an inadequate knowledge of the seismic hazard and design errors due to insufficient knowledge of the earthquake problem; also the inability to correctly model the structural response to the seismic action. While considerable progress has been made in recent years by the research community in dealing with the above problems, it has become more difficult to transfer the results to the seismic engineering profession and the situation can only deteriorate in the near future. Recent changes in the curricula of engineering schools are leading to a general impoverishment of the basic knowledge and operational capabilities of our engineering graduates. A final cause of vulnerability is connected with the maintenance of constructions; it is obvious that if a construction is not regularly maintained, much as happens for a motorcar, the mechanical properties of the materials may undergo local and global degradation with a significant loss of resistance of the 22 Seismic Retrofitting of Reinforced Concrete Buildings Using Traditional and Innovative Techniques structural members and of the entire construction. Also, changes in service conditions, often made arbitrarily, may lead to substantial changes in the structural behaviour resulting in a degradation of the structural response to the expected loading conditions. On the basis of what has been presented so far, it is not surprising that in areas long known to be subject to the seismic hazard it is not infrequent to find constructions vulnerable to

earthquakes. In the following sections some procedures used for the evaluation of the seismic resistance and vulnerability of reinforced concrete buildings will be described together with traditional and innovative techniques of seismic retrofitting of the same structures. The paper ends with a description of the seismic retrofitting of two reinforced concrete residential buildings in the village of Solation, near Syracuse, in Sicily. The buildings belong to the Institute Autonomic Case Popularise (IACP) of Syracuse. As will be clear from following arguments the aim of the paper is not to discuss in depth the state-of the-art of seismic retrofitting, but rather to give a general overview. The aim is also to focus on a few specific procedures which may improve the state-of-the-art practice for the evaluation of seismic vulnerability of existing reinforced concrete buildings and for their seismic retrofitting by means of innovative technique.

1.2 SEISMIC ACTION Seismic vulnerability is not an absolute concept but is strongly related to the event being considered. The same construction may not be vulnerable to one class of earthquakes and yet be vulnerable to another. Therefore, before attempting a seismic vulnerability evaluation of a given construction, the seismic action that will affect that construction must be fully specified.All seismic codes specify the seismic action by means of one or more design spectra. These are a synthetic and quantitative representation of the seismic action which, besides depending on the characteristics of the ground motion, depends on some intrinsic characteristics of the structure such as the fundamental mode of vibration and its energy dissipation capacity.The elastic design spectrum depends on the vibration periods of the structure and on the available damping. In Figure 1 the elastic spectrum of Eurocode 8 (CEN, 1998) is drawn for three different values of damping. A new draft of Eurocode 8 (CEN, 2003) became available in 2003, but is not being used here because some of the Eurocode 8 material relevant to the present work is still questionable and not generally accepted. The value of the spectral pseudo-acceleration, corresponding to a vanishing small period, corresponds to the peak ground acceleration (PGA). In fact, for T = 0 the structure is rigid and, therefore, subject to the same acceleration as the ground. This acceleration, called the maximum effective ground acceleration or PGA, depends directly on the seismic hazard at the construction site and acts as the anchoring acceleration of the spectrum. This value is generally prescribed by seismic codes as a function of the seismic hazard at the construction site. Furthermore, four regions may be identified for the elastic spectrum, each defined by a lower and upper period. In the first region, (0 .T .TB ) , the spectral ordinates increase linearly with the period; in the second (TB . T .TC ) , these are independent of the period; in the third (TC . T .TD ) , the spectral ordinates decrease rapidly with the period, that is with the reciprocal of the period T according to Eurocode 8; and finally in the fourth region (T . TD ) , they decrease even more rapidly, with the reciprocal of the period squared according to Eurocode 8. More details on the elastic design spectrum may be found in the seismic codes (CEN, 1998), in specialized publications and in the treatises on dynamics of structures and seismic engineering (Chopra, 2001; Clough and Penzias, 1993). The separation periods TB ,TC ,TD depend on seismological factors and on local site conditions. For instance Euro code

8 specifies them as a function of three subsoil classes: A (firm soil), B (medium soil), C (soft soil).

CHAPTER-2

Seismic Assessment and Retrofitting of Existing

Concrete Buildings

2.1 INTRODUCTION In many parts of the world, including Europe, design of new buildings for earthquake resistance is a relatively recent development. In those regions, resistance of buildings to lateral forces resulted in the past only from wind considerations. Provisions for seismic design and detailing of members and structures resembling those found in modern seismic codes did not appear before the mid-1970s in US standards, or the mid-1980s in European

national codes. So, in the light of our current knowledge, the building inventory of many seismic regions worldwide is by and large substandard and seismically deficient. Although today and for the years to come the major earthquake threat to human life and property comes from existing substandard buildings, the emphasis of earthquake engineering research, practice and code-writing has been, and still is, on new construction. Policy makers hope that the problem of existing buildings will be solved gradually by attrition (sometimes accelerated by urban renewal and redevelopment). This may be a socio-economically optimal solution for those regions where the rate of occurrence of moderate to strong earthquakes is much lower than the attrition rate of old buildings. Although seismic resistance adds very little to the construction cost of a new building, the cost of seismic upgrading an existing one, including disruption of use, relocation of tenants, removal and replacement of non-structural parts, etc., is normally a large fraction of the building replacement cost and may be prohibitive for private owners or difficult for the local economy to bear.

2.2 CIRCUMSTANCES (2.2.1) earthquake damaged buildings (2.2.2) earthquake vulnerable buildings

2.3 WHY RETROFITTING This proves to be a better option catering to the economic consideration and Immediate shelter problems rather than replacement of buildings

2.4 RETROFIT PERFORMANCE OBJECTIVES With the development of Performance based earthquake engineering (PBEE), Several levels of performance objectives are gradually recognized:

2.5 PUBLIC SAFETY ONLY The goal is to protect human life, ensuring that the structure will not collapse upon its occupants or passers-by, and that the structure can be safely exited. Under severe Seismic conditions the structure may be a total economic write‐off , requiring tear‐down and replacement.

2.6 STRUCTURE SURVIVABILITY The goal is that the structure, while remaining safe for exit, may require extensive repair (but not replacement) before it is generally useful or considered safe for occupation. This is typically the lowest level of retrofit applied to bridges.

2.7 STRUCTURE FUNCTIONALITY

Primary structure undamaged and the structure are undiminished in utility for its primary application. A high level of Retrofit, this ensures that any required repairs are only "cosmetic"‐for example, minor cracks in plaster, drywall and stucco. This is the minimum acceptable level of retrofit for hospitals.

2.8 STRUCTURE UNAFFECTED This level of retrofit is preferred for historic structures of high cultural significance.

2.9 NEED EARTHQUAKRE EVULNERABLE BUILDINGS (a) The buildings have been designed according to a seismic code, but the code has Been upgraded in later years (b) Buildings designed to meet the modern seismic codes, but deficiencies exist in the design or construction (c) Essential buildings must be strengthened like hospitals historical monuments and architectural buildings (d) Important buildings whose service is assumed to be essential even just after an earthquake (e) Buildings the use of which has changed through the years (f) Buildings are expanded, renovated or rebuilt.

2.10 SEISMIC EVALUATION OF BUILDINGS   To assess the seismic capacity of earthquake vulnerable buildings or earthquake 

damaged building for the future use. Helpful for degree of intervention required in seismically deficient structure

Methodologies (2.10.1) Qualitative methods (2.10.2) Analytical methods

2.10.1 QUALITATIVE METHODS  Based on the background information available of the building and its construction site     

Architectural and structural drawings Past performance of similar buildings under severe earthquakes Visual inspection report Some non Destructive test results.

Methods    

Field Evaluation Method, Rapid Visual Screening Method, ATC 14 methodologies etc.

2.10.2 AN ANALYTICAL METHOD Based on consideration of the capacity and ductility of buildings on the basis of available drawings.

Methods    

Capacity/Demand (C/D) method, Screening method, Pushover analysis, Nonlinear inelastic analysis etc.

Evaluation procedure should be very simple and immediate based on synthetic information that can prove suitable for risk evaluation on large populations. Therefore, qualitative evaluation of the buildings is generally being carried out.

2.11 COMPONENTS OF SEISMIC EVALUATION METHODOLOGY

2.11•1 CONDITION ASSESSMENT (i) Data collection or information gathering of structures from architectural and Structural drawings.

(ii) Performance characteristics of similar type of buildings in past earthquakes. (iii) Rapid evaluation of strength, drift, materials, structural components and structural details.

2.12 BASIC CONCEPTS at (CEB, 1997): (a) Up gradation of the lateral strength of the structure; (b) Increase in the ductility of structure; (c) Increase in strength and ductility. It is suggested that the cost of retrofitting of a structure should remain below 25% of the replacement as major justification of retrofitting.

2.13 STRUCTURAL DAMAGE DUE TO LACK OF DEFORMATION  

Limited amount of ductility. The inability to redistribute load in order to safely withstand the deformations imposed upon in response to seismic loads

Columns In reinforced concrete columns several interaction mechanism influences its lateral load behaviour. The main actions are associated with axial, flexure, shear, and bond.

2.14 CLASSIFICATION

CHAPTER 3 RETROFITTING OF MASONRY STRUCTURES

3.1 INTRODUCTION Masonry Buildings –most common construction extensively employed in India. Bricks were first fired around 3500 BC, in Mesopotamia, present-day Iraq, one of the highrisk seismic areas of the world. The ziggurat temples at Erode, possibly the world’s first city, have withstood not only earthquakes but also wars and invasions. From Roman aqueducts and public buildings to the Great Wall of China, from the domes of Islamic architecture to the early railway arch bridges, from the first 19th century American tall buildings to the 20th century nuclear power plants, bricks have been used as structural material in all applications of building and civil engineering.

3.2 WHY RETROFITTING   

This proves to be a better option catering to the economic considerations and Immediate shelter problems rather than replacement of buildings Flexible to accommodate according to prevailing environmental conditions. Easily available

3.3 DEFECTS OF MASONRY Low seismic resistance –extensive damage thanks to the possibility it offers to erect robust structures based on limited size blocks assembled with a mortar, the unreinforced masonry (URM) technique is widely used every where around the world. Nevertheless, the URM system remains suffering of intrinsic weaknesses concerning tensile and/or shear strength capacities. As a consequence, structural engineers involved in URM projects have to carefully consider potential interactions with the environment, namely the soil.

3.4 NECESSITY OF RETROFITTING OF EXISTING MASONRY BUILDINGS   

Majority of seismically deficient buildings Economic considerations & immediate shelter requirements Earthquake damaged buildings can’t be replaced or rebuilt in a short time.

3.5 Retrofitting schemes depend upon:1) Material of parent construction 2) Type of masonry 3) Location and amount of damage

3.6 FAILURE MODE OF MASONRY BUILDINGS 1) Out of plane failure 2) In plane failure 3) Diaphragm failure 4) Pounding 5) Connection failure 6) Failure of non-structural components

3.6.1) OUT –OF –PLANE FAILURE: Structural walls perpendicular to seismic motion subjected tout-of-plane bending.Vertical cracks at corners and middle of walls. Although unreinforced masonry is an ancient building material, effective methods for modelling its structural behaviour remains an active research issue. One particularly difficult aspect is the out-of-plane response of unreinforced masonry walls to seismic loading, which Parlay and Priestley have described as “one of the most complex and ill-understood areas of seismic analysis” (Parlay 1992, p. 623). The complexity arises from the fact that the behaviour is highly non-linear, governed primarily by cracking and instability rather than material failure. Most studies of out-of-plane failure have emphasized analysis of one-way span conditions (e.g. Kariotis 1981, Lam 1995). Design procedures typically neglect the twoway spanning action that occurs near intersecting perpendicular walls, which provide support along a vertical line (Boussabah 1992). Neglecting the two-way action is conservative, but may significantly underestimate the strength of the wall. Towards the objective of developing a method appropriate for the two-way dynamic analysis of unreinforced masonry walls, this paper describes finite element studies of the one-way static condition. The study is motivated by an on-going archaeological investigation concerning the reconstruction of the ancient city of Pompeii following an earthquake in 62 AD, seventeen years prior to the famous eruption of Mt. Vesuvius (Dobbins 1994), however the results have broader applications to the seismic assessment and renovation of unreinforced masonry structures.

CAUSE  

Inadequate anchorage of the wall into the roof diaphragm Limited tensile strength of masonry and mortar.

RESULT 

Resulting flexural stress exceeds tensile strength of masonry

Outer plan fail exist wall

3 .6 .2) IN –P LA N E FAILU RE:Structural walls parallel to seismic motion –in-plane forces. This thesis presents the results of an experimental investigation into the strength of brickwork under biaxial tension-compression. Since there is insufficient experimental evidence available on the strength of brickwork under biaxial stress to explain the behaviour of brick masonry walls under in-plane loads, experiments were carried out on one-sixth scale model brickwork panels under uniform stress conditions. An idealized failure surface is suggested based on experimental results and the effect of shear bond strength and tensile bond strength on the results is discussed. An iterative plane stress finite element computer programme incorporating the above information is used to simulate the in-plane behaviour of brickwork. Brickwork is treated as an elastic, isotropic material with limited capacity when stressed in a state of biaxial tension-compression. The model reproduces the non-linear behaviour of masonry produced by progressive cracking. Shear wall tests have been used to test the validity of the analytical model. Sensitivity analysis of elastic constant used in the model are performed to illustrate their influence on the calculated stresses Bending -horizontal cracks

Shear -diagonal cracks CAUSE  excessive bending or shear RESULT  double diagonal (X) shear cracking. This cracking pattern frequently found in cyclic loading indicates that the planes of principal tensile stress in the walls remain incapable of withstanding repeated load reversals leading to total collapse. As the ground motion takes place for a short duration the walls are subjected to only one or two significant loading reversals and do not collapse totally.

In plan failure

3.6.3) DIAPHRAGM FAILURE

 

Rare phenomenon in the event of seismic motion. Damage to the diaphragm never impairs its gravity load

carrying capacity

CAUSE -Lack Of tension anchoring produces a non-bending cantilever action at the base of the wall resulting from the push of diaphragm against the wall. The in-plane rotation of the diaphragm ends and the absence of good shear transfer between diaphragms and reacting walls

RESULTDamage at the corners of the wall. In strengthened buildings, separation remains worse at or near the centreline of the diaphragm

Diaphragm failure 3.6.4) FAILURE OF CONNECTION

Seismic inertial forces that originate in all elements of the building are delivered to horizontal diaphragms through structural connections.

FORCE DISTRIBUTION d i a p h r a g m > f o u n d a t i o n .    

v e r t i c a l

e l e m e n t s >

Transfer in-plane shear stress from the diaphragms to the vertical elements To provide support to out-of-plan forces on these elements Diagonal cracks disposed on both the walls ‘edges causing separation and collapse of corner zones. Inadequately strengthened openings near the walls ‘edges and by floors insufficiently connected to the external walls.

Connection failure

3 . 6 . 5 )

P O U N D I N G

While building pounding is commonly reported after earthquakes, scientific understanding of the phenomenon and its consequences is very limited. Many researchers have used numerical modelling of pounding to gain further insight into the process. Typically the modelling is similar to that shown in Figure 1 (Anagnostopoulos 1988; Maison and Kasai 1992; Jankowski 2006). A contact element is placed between two buildings at each floor, with the floors modelled as a single lumped mass. Alternatively the buildings’ frames may be explicitly modelled, but the floors’ diaphragms are rigidly slaved together so no diaphragm oscillation or mass distribution effects can occur. The specifics of the collision element vary but it typically comprises of a very large stiffness being activated once a specified gap has closed. Modelling of this type does not usually include allowances for floor-to-column pounding.

Pounding failure in building

3 . 6 . 6 FAI L U R E O F N O N - S T R U C T U R A L C O MP O N E N T S . Non-structural components in the context of this paper refer to architectural features, mechanical/electrical equipment providing services to the building and building contents (refer Table 1). Widespread damage to non-structural components in buildings continues to be observed in recent earthquakes. Whilst statistical cost data for non-structural damage are scarce, it is widely agreed and reported that the economic effects of all non-structural damage combined generally exceed those of structural damage in an earthquake (Brunsdon& Clark, 2001). For example, in a survey of 355 high-rise buildings after the 1971 San Fernando earthquake, it was Shown that in dollar value terms, 79% of the damage was non-structural (Arnold et al, 1987). Despite this, earthquake engineering research worldwide has been directed mainly to performance issues associated directly with the structural elements or the building structure as a whole.

Non structure component

CHAPTER 4 RETROFITTING OF MASONRY BUILDING 4.1 INTRODUCTION IS 13935 To upgrade the earthquake resistance up to the level of the level of the present day codes by appropriate techniques. CEB 1995Concepts including strengthening, repairing and remoulding Newman , 2001It is an upgrading of certain building system, such as mechanical, electrical, or structural, to improve performance, function or appearance EBUILDINGS.

4.2 METHODS FOR RETROFITTING OF MASONRY BUILDINGS Broadly classified into three categories on the basis of their effect on structural performance (1) Improving the existing masonry strength and deformability, not related to any specific objective which is similar to the REPAIRING process of masonry structures (2) Improving the in-plane strength of the wall or any weak zone of the section akin to LOCAL/MEMBER RETROFITTING (3) Improving the structural integrity of the whole structure intermesh offing-plane and outof-plane strength or only against out-of-plane forces very much like the GLOBAL/STRUCTURAL RETROFITTING

4.2.1 Repair Process to preserve the mechanical efficiency of a masonry structure and to increase shear resistance of wall having large internal voids The commonly employed repairing techniques of masonry are :1) Concrete or epoxy injection 2) Reinforced injection 3) Grouting with cement or epoxy 4) Insertion of stones 5) Re-pointing of mortar.

4.2.2 Local/Member Retrofitting

It enhances the shear resistance of un-reinforced masonry components especially against inplane forces. Feasible retrofitting technique:1) Surface coating 2) Concrete overlays or adhered fabric with wire mesh or FRP materials 3) Use of RC and steel frames in opening

4.2.3 Structural /Global Retrofitting Improving the response of existing un-reinforced masonry buildings to both gravity and seismic loads it provides them “box type” behaviour and increases the flexural strength of un-reinforced walls and piers. The most common techniques are:(i) Addition of reinforcement (ii) External binding or jacketing (iii) Priestess (iv) Confinement with RC element and steel sections (v) Strengthening of wall intersections and (vi) Strengthening of connection between walls and floors.

4.3 REPAIRING TECHNIQUES OF MASONRY Main two problems solved during the repairing process are:(i) Masonry cracking, (ii) Masonry deterioration.

4.3.1 Masonry Cracking “Break, split, fracture, fissure, separation, cleavage, or elongated narrow opening visible to the normal human eye and extending from the surface and into a masonry unit, mortar joint, interface between a masonry unit and adjacent mortar joint or into a joint between masonry and an adjacent construction element”.

CAUSE 

Movement or strain induced by imposition of loads by restraint of volume changes in masonry materials seismic vibrations.

Repair of GO and GI grade cracks To repair cracks up to a width of 5 mm :

Pressure injection of cement grout containing admixtures against shrinkage or epoxy is recommended.

For fine cracks up to 1mm width - epoxy injection is preferred

Repair of G2 grade cracks The repairing process remains much similar to the previous technique with an exception to insert reinforcement in every injecting hole.

Repair of G3 grade cracks Cracks due to loss of connection among the multi-wythe masonry walls may be categorized as G3 grade cracking. More susceptible to out-of-plane forces resulting in collapse of the outer leaf of multiple leaves stone masonry walls. Two possibilities of Damage –a) and b) in Fig.

4.4 THROUGH STONES/BOND STONES "Through" stones of full-length equal to wall thickness may be inserted at an interval of 0.6 m in vertical direction atI.2m in horizontal direction. In the non-availability of full-length stones, stones in pairs each of about3/4 of the wall thickness may be used providing an overlap between them. use of "S" shape elements of bars 8 to 10 Ø or a hooked link with a cover of 25 mm from each face of the wall or wooden bars of size 38 mm x 38 mm cross section or equivalent.

4.5 CEMENT GROUTING       

Used to repair and strengthen masonry walls having large voids or to fill the space between adjacent portions of masonry. Commonly used -epoxy and cement grouts. Grout injection binds the inner and outer withes together establishing a composite action between them for an improved of-plane moment capacity. The selection of grout depends on the desired strength, properties and on the size of the crack network or void system. Cement grout consisting of 1 part of Portland cement, ½part type S hydratedlime,1/2 part type fly ash may be used for repairing earthquake- reinforced masonry building. Problem -lateral pressure exerted by the grout collapse. Low lifting is preferred as it reduces the hydrostatic pressure, which prevents the outward thrust of the grout from displacing one of the withes.

4.6 MASONRY DETERIORATION 

Most common-

UNITS – 

Due to water penetration and freeze thaw cycles in Mortar due to poor quality.

REPAIR TECHNIQUES UNITS – 

Replaced by new units –same appearance, material property

MORTAR –

 Weak or deteriorated mortar is the cause of failure of masonry buildings. -before retrofitting, improvement in strength of

4.7 RE-POINTING:     

Carried out when the quality of the mortar happens to be poor but the units remain in good condition. Involves removal of the existing mortar up to 1/3 of the walls thickness or at least7+ inches from the joints on one or both sides of the wall, Proper cleaning of the surfaces by compressed air brush or steam of water Insertion of new mortar Steel reinforcement in bed joints improve the ductility and energy dissipation capacity

4.8 MEMBER RETROFITTIN G1) RETROFITTING TECHNIQUES SHOTECRETE:Used for:   

Weak masonry Absence of enough solid piers to resist seismic loads Applied on the inside or outside of wall

SHORTCRETE IS A CONCRETE MIX PNEUMATICALLY APPLIEDTO A SOLID SURFACE

4.9 TYPES OF SHORTCRETE 1) WET MIX For:  Large volume and massive sections 2) DRY MIX OR GUNITE:  For lesser volume, thinner sections and confined spaces  Better handling control due to good control of material flow For effective use of Short Crete:  Design of concrete  Selection of correct process  skilled workmanship

4.10.DESIGN MIX SHORTCRETE MIX:   

Part Portland cement and 3 parts sand by volume Must have compatible stiffness values to the masonry walls 4 to 5 inch shortcrete sufficient

SUMMARY AND CONCLUSIONS After an introduction which explains why there are so many vulnerable structures in areas of high or moderate seismic hazard around the world, the authors consider the specific case of Eastern Sicily. The paper proceeds with an illustrative description of the seismic action and then addresses the problem of evaluating the seismic resistance and vulnerability of engineering structures. The application of the methodology presented to reinforced concrete buildings in Eastern Sicily clarifies the concepts discussed. In particular, the concepts of seismic resistance, seismic vulnerability and seismic over-resistance become easily understood and appreciated. The paper then considers the retrofitting of buildings vulnerable to earthquakes and briefly describes the main traditional and innovative methods of seismic retrofitting. Examples drawn from the professional, editorial and research activity of the senior author are used to illustrate the problems in a simple way. Among all the methods of seismic retrofitting, particular attention is devoted to the method which is based on stiffness reduction. This method is carried out in practice by application of the concept of springs in series, leading in fact to base isolation. One of the two springs in series represents the structure and the other represents the base isolation system. The application of the concept to two buildings in Eastern Sicily concludes the presentation. The enhanced resistance of the buildings to the design earthquake clearly shows the effectiveness of the method, while a generally improved seismic performance also emerges from the application. In conclusion it is hoped that the material presented in this paper will be useful in increasing the understanding of the earthquake engineering problem and of seismic retrofitting.

References [1] http://help.solidworks.com/2012/English/SolidWorks/cworks/c_Definitions_Response_Spectra.ht m

[2] A. Meher Prasad: “Response Spectrum”, Department of Civil Engineering, IIT Madras [3] Bobby Motwani: “Are We Ready for El Centro” [4] Pankaj Agarwal, Manish Shrikhande: “Earthquake Resistant Design of Structures”, PHI Learning Private Limited, 2011 [5] David T. Finley, Ricky A. Cribbs: “Equivalent Static vs Response Spectrum – A comparision of two methods” [6] Durgesh C. Rai, “Seismic Evaluation and Strengthening of Existing Buildings”, IITKGSDMA –EQ24-V2.0 [7] http://www.microstran.com/faq_dynamics.htm#ResponseSpectrumAnalysis [8] Joao Luis Domingues Costa: “Standard Methods for Seismic Analyses”, Report BYG.DTU R-064, 2003 [9] IS 1893 (Part 1):2002, “Criteria for Earthquake Resistant Design of Structures” [10] “Manual on Seismic Evaluation and Retrofit of Multi-Storeyed RC Buildings”, 2005 [11] http://theconstructor.org/structural-engg/strengthening-of-r-c-beams/1930/