Department Of Civil Engineering, Kjcoemr

Retrofitting of Structures

CHAPTER 1 INTRODUCTION Retrofitting is modification of existing structures to make it more resistant to external forces like seismic forces, wind force and vibrational forces. Generally, we have to take decision that whether to demolish the building or retrofit it. It will depend upon the stressing level of the structure. The need to improve the ability of an existing building to withstand seismic forces arises usually from the evidence of damage and poor behavior during a recent earthquake. It can arise also from calculations or by comparisons with similar buildings that have been damaged in other places. While in the first case the owner can be rather easily convinced to take measures to improve the strength of his building, in the second case dwellers that have much more stringent day-to-day needs are usually reluctant to invest money in the improvement of seismic safety. The problems of repairs, restoration and seismic strengthening of buildings are briefly stated below: (i) Before the occurrence of the probable earthquake, the required strengthening of seismically weak buildings is to be determined by a survey and analysis of the structures. (ii) Just after a damaging earthquake, temporary supports and emergency repairs are to be carried so that precariously standing buildings may not collapse during aftershocks and the less damaged ones could be quickly brought back into use. (iii) The real repair and strengthening problems are faced at the stage after the earthquake when things start settling down. At this stage distinction has to be made in the type of action required, that is, repairs, restoration and strengthening, since the cost, time and skill required in the three may be quite different. The decision as to whether a given building needs to be strengthened and to what degree must be based on calculations that show if the levels of safety demanded by present codes and recommendations are met. Difficulties in establishing actual strength arise from the considerable uncertainties related with material properties and with the amount of strength deterioration due to age or to damage suffered from previous earthquakes. Thus, decisions are frequently based on gross conservative assumptions about actual strength. The method of repair and strengthening would naturally depend very largely on the structural scheme and materials used for the construction of the building in the first instance, the Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures technology that is feasible to adopt quickly and on the amount of funds that can be assigned to the task, usually very limited. Some methods like “splints and bandages” “wire mesh with gunite” “epoxy injection” etc., have already been tried and applied in a few countries for repairing as well as strengthening earthquake damaged buildings. Depending upon the conditions, various methods of retrofitting can be used, but these can be chosen as per experience. Some methods of retrofitting are by using steel plates and jacketing of steel to structural elements, using steel bars bonded to structural elements external prestressing for the bridge girders, chemical methods (filling up the cracks by chemicals or adhesives) and using Fiber-Reinforced Polymer (FRP) composites bonded to surface of concrete. One of the techniques out of these for strengthening is externally bonded glass fiber reinforced sheets applied externally by wet layup method. Inclined GFRP sheet were used for retrofitting of beams weak in shear.

Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures

CHAPTER 2 LITERATURE REVIEW

1) Amol Suresh Satpute, Dr. Mahavir Balmukund Varma (2017) “Retrofitting of Beams Using Externally Bonded Glass Fiber Reinforced Polymer (GFRP) Wraps”

The research work related to retrofitting of building and civil structural elements had been done by many engineers. It is an essential medicine required to be applied for enhancing the structural health of a structural element over a serviceability period of life. In general a beam or slab needs to carry an additional load as the purpose of occupancy has been changed over a period of time for a specified area in a building and it needs to be replaced for a very short difference in its load carrying capacity; in such case the application of the externally bonded Glass Fibre Reinforced Polymer (GFRP) wraps can be a remedy or solution over the problem. In present study a detailed investigation on the concrete beam specimens (5.90 in. [150 mm] width × 5.90 in. [150 mm] depth × 27.56 in. [700 mm] length) made with different steel reinforcement configuration and strengthened with glass fiber reinforced polymer (GFRP) wraps in single, double and triple layer was carried out after 28 days of water curing. The Glass Fiber Reinforced Polymer can be used in various patterns i.e. related to orientations of the fibers, shape of the wrapping and locations of the wrappings to make effective use of the materials and ensure the desired purpose of imparting long service life of the selected technique. One of these new and advanced techniques is the externally bonded GFRP wraps, which consists of wrapping the concrete beams externally with the help of a resin matrix. The purpose of this study is to retrofit the beam to enhance the load carrying capacity. The beam specimens were tested under four point load test to find out the ultimate load and deflection in the member. From the observations, a considerable increase in load carrying capacity was recorded. 2) Gugulothu Rambabu, Pushadapu Prudhvija, Kusuma Sundar Kumar (2016) “Strengthening of reinforced concrete beams using glass fiber reinforced polymer”

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Retrofitting of Structures Worldwide, a great deal of research is currently being conducted concerning the use of fiber reinforced plastic wraps, laminates and sheets in the repair and strengthening of reinforced concrete members Fiber-reinforced polymer (FRP) application is a very effective way to repair and strengthen structures that have become structurally weak over their life span. FRP repair systems provide an economically viable alternative to traditional repair systems and materials. Experimental investigations on the flexural and shear behavior of RC beams strengthened using continuous glass fiber reinforced polymer (GFRP) sheets are carried out. Externally reinforced concrete beams with epoxy-bonded GFRP sheets were tested to failure using a symmetrical two point concentrated static loading system. Two sets of beams were casted for this experimental test program. In SET I three beams weak in flexure were casted, out of which one is controlled beam and other two beams were strengthened using continuous glass fiber reinforced polymer (GFRP) sheets in flexure. In SET II three beams weak in shear were casted, out of which one is the controlled beam and other two beams were strengthened using continuous glass fiber reinforced polymer (GFRP) sheets in shear. The strengthening of the beams is done with different amount and configuration of GFRP sheets. Experimental data on load, deflection and failure modes of each of the beams were obtained. The detail procedure and application of GFRP sheets for strengthening of RC beams is also included. The effect of number of GFRP layers and its orientation on ultimate load carrying capacity and failure mode of the beams are investigated.

3) Lalin Lam, Qudeer Hussain, Panuwat Joyklad, and Amorn Pimanmas (2015) “Behavior of RC Deep Beams Strengthened in Shear using Glass Fiber Reinforced Polymer with Mechanical Anchors”

This paper examines the effect of glass chopped strand mat fiber composites (GCSM) with the mechanical anchor on the shear strength of reinforced concrete deep beams. Two types of matrix system were used to provide stresses between the fibers and also between the fiber composites-to-concrete interface. Epoxy and polyester resin were investigated and compared to find the suitable resin matrix. Mechanical expansion anchor system which was recently proposed by the author was used in this study. The experimental results indicated that using GCSM composites with mechanical anchors led to enhancement of load-carrying capacity and stiffness of the beams. Epoxy resin system was found to be more effective Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures compared to Polyester resin. The ultimate shear capacity of the RC deep beams strengthened with epoxy system was increased up to 68% compared to the control specimen. Continuously wrapped the GCSM fiber composites over the bottom and both sides of the beam in the form of a U-wrapped provided additional anchorage at the bottom end of fiber composites. This leads to the prevention of debonding and the increase of loading capacity. Providing additional bond strength of the bond interface by using mechanical anchor found to be more effective since it leads to more usage of the composites. Strengthening technique using FRP wrapped with mechanical anchors supposedly confined the compressive strut which is able to increase the loading capacity.

4) C. V. R. Murty, Rupen Goswami, A. R. Vijayanarayanan, Vipul V. Mehta “Some Concepts in Earthquake Behavior of Buildings”

This book explains concepts in behavior of buildings during earthquakes. The book dwells on basic concepts in earthquake resistant design of buildings, first describes these at a conceptual level and then articulates further with numerical examples. It is an attempt to respond to some of the frequently asked questions by Architects and Structural Engineers regarding behavior of Reinforced Concrete (RC) and Steel buildings under the action of lateral loads, especially during earthquakes. Since most buildings built in India are made of RC, the dominant set of examples used is of RC buildings. But, with no loss of generality, the broad concepts discussed in this document are valid for both RC and Steel buildings. Also, the discussion is limited to normal buildings without any special devices, like base isolation and other energy absorbing or dissipating devices. Also, specialized systems (like post-tensioning slab systems and nuclear power plants) are not in focus. 5) A.K. Mittal Handbook on "Construction of Earthquake Resistant Buildings"

This handbook explains that to avoid a great earthquake disaster with its severe consequences, special consideration must be given. Engineers in seismic countries have the important responsibility to ensure that the new construction is earthquake resistant and also, they must solve the problem posed by existing weak structures.

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Retrofitting of Structures Most of the loss of life in past earthquakes has occurred due to the collapse of buildings, constructed with traditional materials like stone, brick, adobe (kachcha house) and wood, which were not particularly engineered to be earthquake resistant. In view of the continued use of such buildings, it is essential to introduce earthquake resistance features in their construction. 6)

National Institute of Building Sciences Building Seismic Safety Council, Washington DC

“Earthquake-Resistant

Design

concepts

-

An

Introduction

to

the

NEHRP

Recommended Seismic Provisions for New Buildings and Other Structures.” 7) S. K. Duggal “Earthquake Resistant Design of Structures”

Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures

CHAPTER 3 3.1 Necessity of Seismic Retrofitting: Buckling and bulging are the common phenomenon of RC column failure. For a flexural member like Beam bending and deflection are the common phenomenon of RC column failure. The joint has been always considered as weaker section of the structure. If sufficient care is not taken for the beam-column or slab-column connection at designing stage as well as at the construction stage, it may lead to the degradation of the building in early age. Factors responsible for the degradation of RC element are: Longitudinal reinforcement is insufficient, Sufficient cover is not provided, Lack of ductile detailing, Not designed for seismic loading, Unexpected overloading, Lateral ties or stirrups are not provided at the required spacing, Poor quality of material used, Quality of workmanship is inferior, Ignorance of vertical or diagonal cracks, spalling of concrete, corrosion in the reinforcement, dampness of surface, Unexpected impact loading, vibration etc., Lack of ductile detailing, Poor concreting at the connection, insufficient maintenance etc.

3.2 Retrofit Performance Objectives: 

Public safety only: The goal is to protect human life, ensuring that the structure will not collapse upon its occupants or passersby, 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.



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.



Structure functionality: Primary structure undamaged and the structure is undiminished in utility for its primary application.



Structure unaffected: This level of retrofit is preferred for historic structures of high cultural significance.

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Retrofitting of Structures

3.3 Need of Retrofitting in Existing Earthquake Vulnerable Buildings: 

Buildings have been designed according to a seismic code, but the code has been upgraded in later years.



Buildings designed to meet the modern seismic codes, but deficiencies exist in the design and/or construction.



Essential buildings must be strengthened like hospitals, historical monuments and architectural buildings.



Important buildings whose services are assumed to be essential just after an earthquake like hospitals.



Buildings, the use of which has changed through the years.



Buildings those are expanded, renovated or rebuilt.

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Retrofitting of Structures

CHAPTER 4 TECHNIQUES USED FOR RETROFITTING Retrofitting Techniques

Global

Local

Adding Shear Wall

Jacketing of beams

Adding infill wall

Jacketing of Columns

Adding Bracing

Jacketing of beamcolumn joints

Adding wing wall Mass Reduction

Strengthening of individual footings

Wall thickening Base Isolation Mass Dampers

4.1 Global Retrofitting Techniques: 4.1.1 Adding Shear Wall: Reinforced concrete (RC) buildings often have vertical plate-like RC walls called Shear Walls (Figure 1) in addition to slabs, beams and columns. These walls generally start at foundation level and are continuous throughout the building height. Their thickness can be as low as 150mm, or as high as 400mm in high rise buildings. Shear walls are usually

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Retrofitting of Structures provided along both length and width of buildings (Figure 1). Shear walls are like verticallyoriented wide beams that carry earthquake loads downwards to the foundation.

Figure 1: Reinforced concrete shear walls in buildings - an excellent structural system for earthquake resistance. Advantages of Shear Walls in RC Buildings: Properly designed and detailed buildings with shear walls have shown very good performance in past earthquakes. The overwhelming success of buildings with shear walls in resisting strong earthquakes is summarised in the quote: "We cannot afford to build concrete buildings meant to resist severe earthquakes without shearwalls." -Mark Fintel, a noted consulting engineer in USA

Shear walls in high seismic regions require special detailing. However, in past earthquakes, even buildings with sufficient amount of walls that were not specially detailed for seismic performance (but had enough well-distributed reinforcement) were saved from collapse. Shear wall buildings are a popular choice in many earthquake prone countries, like Chile, New Zealand and USA. Shear walls are easy to construct, because reinforcement Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures detailing of walls is relatively straight-forward and therefore easily implemented at site. Shear walls are efficient, both in terms of construction cost and effectiveness in minimizing earthquake damage in structural and non-structural elements (like glass windows and building contents). 4.1.2 Adding infill wall: After columns and floors in a RC building are cast and the concrete hardens, vertical spaces between columns and floors are usually filled-in with masonry walls to demarcate a floor area into functional spaces (rooms). Normally, these masonry walls, also called infill walls, are not connected to surrounding RC columns and beams. When columns receive horizontal forces at floor levels, they by to move in the horizontal direction, but masonry walls tend to resist this movement. Due to their heavy weight and thickness, these walls attract rather large horizontal forces (Figure 3). However, since masonry is a brittle material, these walls develop cracks once their ability to carry horizontal load is exceeded. Thus, infill walls act like sacrificial fuses in buildings; they develop cracks under severe ground shaking but help share the load of the beams and columns until cracking.

Earthquake performance of infill walls is enhanced by mortars of good strength, making proper masonry courses, and proper packing of gaps between RC frame and masonry infill walls. However, an infill wall that is unduly tall or long in comparison to its thickness can fall out-of-plane (i.e., along its thin direction), which can be life threatening. Also, placing infills irregularly in the building causes ill effects like short-column effect and torsion.

Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures 4.1.3 Adding Bracing: An effective solution when large openings are required. • Potential advantages for the following reasons: Higher strength and stiffness, Opening for natural light, Amount of work is less since foundation cost may be minimized Adds much less weight to the existing structure.

4.1.4 Base isolation: The concept of base isolation is explained through an example building resting on frictionless rollers. When the ground shakes, the rollers freely roll, but the building above does not move. Thus, no force is transferred to the building due to shaking of the ground; simply, the building does not experience the earthquake. Now, if the same building is rested on flexible pads that offer resistance against lateral movements, then some effect of the ground shaking will be transferred to the building above. If the flexible pads are properly chosen, the forces induced by ground shaking can be a few times smaller than that experienced by the building built directly on ground, namely a fixed base building. Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures

The flexible pads are called base-isolators, whereas the structures protected by means of these devices are called base-isolated buildings. The main feature of the base isolation technology is that it introduces flexibility in the structure. As a result, a robust medium-rise masonry or reinforced concrete building becomes extremely flexible. The isolators are often designed to absorb energy and thus add damping to the system. This helps in further reducing the seismic response of the building. Several commercial brands of base isolators are available in the market, and many of them look like large rubber pads, although there are other types that are based on sliding of one part of the building relative to the other. A careful study is required to identify the most suitable type of device for a particular building. Also, base isolation is not suitable for all buildings. Most suitable candidates for base-isolation are low to medium-rise buildings rested on hard soil underneath; high-rise buildings or buildings rested on soft soil are not suitable for base isolation. It is easiest to see this principle at work by referring directly to the most widely used of these advanced techniques, which is known as base isolation. A base isolated structure is supported by a series of bearing pads which are placed between the building and the building's foundation. A variety of different types of base isolation bearing pads have now been developed. For our example, we'll discuss lead–rubber bearings. These are among the frequently–used types of base isolation bearings. A lead–rubber bearing is made from layers of rubber sandwiched together with layers of steel. In the middle of the bearing is a solid lead "plug." On top and bottom, the bearing is fitted with steel plates which are used to attach the

Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures bearing to the building and foundation. The bearing is very stiff and strong in the vertical direction, but flexible in the horizontal direction.



EARTHQUAKE GENERATED FORCES: To get a basic idea of how base isolation works. This shows an earthquake acting on

both a base isolated building and a conventional, fixed–base, building. As a result of an earthquake, the ground beneath each building begins to move. In Figure 13, it is shown moving to the left.

Each building responds with movement which tends toward the right. We say that the building undergoes displacement towards the right. The building's displacement in the direction opposite the ground motion is actually due to inertia. The inertial forces acting on a building are the most important of all those generated during an earthquake. It is important to Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures know that the inertial forces which the building undergoes are proportional to the building's acceleration during ground motion. It is also important to realize that buildings don't actually shift in only one direction.

Because of the complex nature of earthquake ground motion, the building actually tends to vibrate back and forth in varying directions. So, Figure 3 is really a kind of "snapshot" of the building at only one particular point of its earthquake response In addition to displacing toward the right, the un–isolated building is also shown to be changing its shape– from a rectangle to a parallelogram. We say that the building is deforming. The primary cause of earthquake damage to buildings is the deformation which the building undergoes as a result of the inertial forces acting upon it. The different types of damage which buildings can suffer are quite varied and depend upon a large number of complicated factors. But to take one simple example, one can easily imagine what happens to two pieces of wood joined at a right angle by a few nails, when the very heavy building containing them suddenly starts to move very quickly — the nails pull out and the connection fails. 

SPHERICAL SLIDING ISOLATION SYSTES:

As we said earlier, lead–rubber bearings are just one of a number of different types of base isolation bearings which have now been developed. Spherical Sliding Isolation Systems are another type of base isolation. The building is supported by bearing pads that have a curved surface and low friction During an earthquake, the building is free to slide on the bearings. Since the bearings have a curved surface, the building slides both horizontally Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures and vertically. The force needed to move the building upwards limits the horizontal or lateral forces which would otherwise cause building deformations. Also, by adjusting the radius of the bearing's curved surface, this property can be used to design bearings that also lengthen the building's period of vibration. For more information read this article titled Protective Systems for Buildings: Application of Spherical Sliding Isolation Systems as it describes one particular type of spherical sliding isolation system, and its successful use in making some structures more earthquake resistant.

4.1.5 Mass Dampers: Another approach for controlling seismic damage in buildings and improving their seismic performance is by installing seismic dampers in place of structural elements, such as diagonal braces. These dampers act like the hydraulic shock absorbers in cars - much of the sudden jerks are absorbed in the hydraulic fluids and only little is transmitted above to the chassis of the car. When seismic energy is transmitted through them, dampers absorb part of it, and thus damp the motion of the building. Dampers were used since 1960s to protect tall buildings against wind effects. However, it was only since 1990s, that they were used to protect buildings against earthquake effects. Commonly used types of seismic dampers include viscous dampers (energy is absorbed by silicone-based fluid passing between pistoncylinder arrangements), friction dampers (energy is absorbed by surfaces with friction between them rubbing against each other), and yielding dampers (energy is absorbed by Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures metallic components that yield). In India, friction dampers have been provided in a 18-storey RC frame structure in Gurgaon.



FLUID VISCOUS DAMPERS: Once again, to try to illustrate some of the general principles of damping devices, we'll

look more closely at one particular type of damping device, the Fluid Viscous Damper, which is one variety of viscous dampers that has been widely utilized and has proven to be very effective in a wide range of applications. The article, titled Application of Fluid Viscous Dampers to Earthquake Resistant Design, describes the basic characteristics of fluid viscous dampers, the process of developing and testing them, and the installation of fluid viscous dampers in an actual building to make it more earthquake resistant. Damping devices are usually installed as part of bracing systems. Figure 16 shows one type of damper brace arrangement, with one end attached to a column and one end attached to a floor beam. Primarily, this arrangement provides the column with additional support. Most earthquake ground motion is in a horizontal direction; so, it is a building's columns which normally undergo the most displacement relative to the motion of the ground. Figure 16 also shows the damping device installed as part of the bracing system and gives some idea of its action.

Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures

 TUNED MASS DAMPERS: A tuned mass damper, also known as a harmonic absorber, is a device mounted in structures to reduce the amplitude of mechanical vibrations. Their application can prevent discomfort, damage, or outright structural failure. They are frequently used in power transmission, automobiles, and buildings.

(A schematic of a simple spring–mass–damper system used to demonstrate the tuned mass damper system.) Tuned mass dampers stabilize against violent motion caused by harmonic vibration. A tuned damper reduces the vibration of a system with a comparatively lightweight component so that the worst-case vibrations are less intense. Roughly speaking, practical systems are tuned to either move the main mode away from a troubling excitation frequency, or to add damping to a resonance that is difficult or expensive to damp directly.

4.1.6 Mass Reduction: • In this process removing one or more storey of building as shown in the figure. • Decrease the load at foundation. Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures • Increase the life and strength.

4.1.7 Wall Thickening: • Increase the thickness by adding bricks, concrete and steel reinforcement. • It can bear more vertical and horizontal loads. • Does not cause sudden failure of the wall.

4.1.8 Adding of Wing Wall: • To increase lateral strength, ductility and stiffness of structure. • The wing walls are placed on the exterior side of an existing frame.

Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures

4.2 Local Retrofitting Techniques: 4.2.1 Jacketing of Columns: Jacketing of columns consists of added concrete with longitudinal and transverse reinforcement around the existing columns. This type of strengthening improves the axial and shear strength of columns while the flexural strength of column and strength of the beam-column joints remain the same. It is also observed that the jacketing of columns is not successful for improving the ductility. A major advantage of column jacketing is that it improves the lateral load capacity of the building in a reasonably uniform and distributed way and hence avoiding the concentration of stiffness as in the case of shear walls. This is how major strengthening of foundations may be avoided. In addition the original function of the building can be maintained, as there are no major changes in the original geometry of the building with this technique. The jacketing of columns is generally carried out by two methods: (i)Reinforced concrete jacketing and (ii) Steel jacketing (iii) FRP jacketing.

Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures (i) Reinforced Concrete Jacketing: Reinforced concrete jacketing can be employed as a repair or strengthening scheme. Damaged regions of the existing members should be repaired prior to their jacketing. There are two main purposes of jacketing of columns: (i) Increase in the shear capacity of columns in order to accomplish a strong columnweak beam design and (ii) To improve the column's flexural strength by the longitudinal steel of the jacket made continuous through the slab system are anchored with the foundation. It is achieved by passing the new longitudinal reinforcement through holes drilled in the slab and by placing new concrete in the beam column joints as illustrated in figure 1. Rehabilitated sections are designed in this way so that the flexural strength of columns should be greater than that of the beams. Transverse steel above and below the joint has been provided with details, which consists of two L-shaped ties that overlap diagonally in opposite corners. The longitudinal reinforcement usually is concentrated in the column corners because of the existence of the beams where bar bundles have been used as shown in figure. It is recommended that not more than 3 bars be bundled together. Windows are usually bored through the slab to allow the steel to go through as well as to enable the concrete casting process.

Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures

(ii) Steel Jacketing:

Addition of steel often applied in the form of plates or jackets. 

Local strengthening of columns has been frequently accomplished by jacketing with steel plates.



Advantage of steel include that it does not add significant weight to the structure in comparison with concrete and it saves on construction time(no curing).



The main disadvantage of this type are linked to construction issues steel can be labor intensive and it require heavy equipment‘s to handle thousands of tons and as well as having a more difficult maintenance.

(iii) FRP Jacketing: Several researchers have investigated the possibility and feasibility of fibre reinforced polymer composite jackets for seismic strengthening of columns winding them with high strength carbon fibres around column surface to add spiral hoops (figure no. 3) The merits of this method are:

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Retrofitting of Structures • Carbon fibre is flexible and can be made to contact the surface tightly for a high degree of confinement; • Confinement is of high degree because carbon fiber is of high strength and high modules of elasticity are used; • The carbon fibre has light weight and rusting does not occur.

Limitations: There are some disadvantages associated with the column jacketing techniques well, • In some cases the presence of beams may require majority of new longitudinal b to be bundled into the corners of the jacket; • With the presence of the existing column it' difficult to provide cross ties for new longitudinal bars which are not at the corners of the jackets; • Jacketing is based mostly on engineering judgment as there is a dearth of guidelines. 4.2.2 Jacketing of Beams: Jacketing of beams is recommended for several purposes as it gives continuity to the columns and increases the strength and stiffness of the structure. While jacketing a beam, its flexural resistance must be carefully computed to avoid the creation of a strong beam-weak column system. In the retrofitted structure, there is a strong possibility of change of mode of failure and redistribution of forces as a result of jacketing of column, which may Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures consequently causes beam hinging. The location of the beam critical section and the participation of the existing reinforcement should be taken into consideration. Jacketing of beam may be carried out under different ways; the most common are onesided jackets or 3- and 4-sided jackets. At several occasions, the slab has been perforated to allow the ties to go through and to enable the casting of concrete. The beam should be jacketed through its whole length. The reinforcement has also been added to increase beam flexural capacity moderately and to produce high joint shear stresses. Top bars crossing the orthogonal beams are put through holes and the bottom bars have been placed under the soffit of the existing beams, at each side of the existing column. Beam transverse steel consists of sets of U-shaped ties fixed to the top jacket bars and of inverted U-shaped ties placed through perforations in the slab, closely spaced ties have been placed near the joint region where beam hinging is expected to occur.

Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures

CHAPTER 5 CONCLUSIONS • Seismic retrofitting is a suitable technology for protection of a variety of structures. It has matures in recent years but the expertise needed is not available in the basic level. • Decrease the working space of concrete structure due to extension in structural elements and affect the appearance. Optimization techniques are required to know the most efficient retrofit for a particular structure. • The main challenge is to achieve a desired performance level at minimum cost, which can be achieved through a detailed nonlinear analysis. • Proper design codes are required to be published as code of practice for professionals related to this field.

Department of Civil Engineering, KJCOEMR

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Retrofitting of Structures

CHAPTER 6 REFERENCES 1) Amol Suresh Satpute, Dr. Mahavir Balmukund Varma (2017) “Retrofitting of Beams Using Externally Bonded Glass Fiber Reinforced Polymer (GFRP) Wraps”

2) Gugulothu Rambabu, Pushadapu Prudhvija, Kusuma Sundar Kumar (2016) “Strengthening of reinforced concrete beams using glass fiber reinforced polymer”

3) Lalin Lam, Qudeer Hussain, Panuwat Joyklad, and Amorn Pimanmas (2015) “Behavior of RC Deep Beams Strengthened in Shear using Glass Fiber Reinforced Polymer with Mechanical Anchors”

4) C. V. R. Murty, Rupen Goswami, A. R. Vijayanarayanan, Vipul V. Mehta “Some Concepts in Earthquake Behavior of Buildings”

5) A.K. Mittal Handbook on "Construction of Earthquake Resistant Buildings" 6)

National Institute of Building Sciences Building Seismic Safety Council, Washington DC

“Earthquake-Resistant

Design

concepts

-

An

Introduction

to

the

NEHRP

Recommended Seismic Provisions for New Buildings and Other Structures.” 7) S. K. Duggal “Earthquake Resistant Design of Structures.” 8) Shri. Pravin B. Waghmare “Materials and jacketing technique for retrofitting of structures.”

Department of Civil Engineering, KJCOEMR

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