SEISMIC ANALYSIS WITH SHEAR WALLS A PARTIAL FULFILMENT OF M.TECH- STRUCTURAL ENGINEERING PRESENTED BY ABHISHEK HAZRA STRUCTURAL ENGINEERING DIVISION DEPARTMENT OF STRUTURAL ENGINEERING NARULA INSTITUTE OF TECHNOLOGY

CONTENTS INTRODUCTION BACKGROUND DISCISSION CLASSIFICATION OF SHEAR WALLS BEHAVIOUR UNDER SEISMIC LOADING LOCATION OF SHEAR WALLS IN A BUILDING STEPS FOR SHEAR WALL DESIGNING DETAIS OF SHEAR WALLS CONCLUSION REFERENCES

INTRODUCTION SHEAR WALL Shear wall represent the most efficient structural element to take lateral force acting on a multi-storey building and to transfer them to foundation. Shear wall is a structural element used to resist lateral/horizontal/shear forces parallel to the plane of the wall by: cantilever action truss action “We cannot afford to build concrete buildings meant to resist severe earthquakes without shear walls.” :: Mark Fintel, a noted consulting engineer in USA

BACKGROUND Initially shear walls are used in reinforced concrete building to resist wind force. Earlier ,tall building were made only for steel as bracings to take lateral wind loads could be easily provide in steel construction. However science resent observation have consistently shown the excellent performance of building with shear wall even under seismic force, such walls are now extensively used for all earthquake resistance design. The most important property of shear walls for seismic design ,as different from design for wind ,is that it should have good ductility under reversible and repeated overloads. Besides they impart lateral stiffness to the system and also carry the gravity load.

DISCUSSION For building over 20 stories, shear walls may become imperative from the point of view of economy and control of lateral deflection. Shear wall need adequate foundation .the foundation of one of several interacting structural walls does not affect its own stiffness relative to the other walls

CLASSIFICATION OF SHEAR WALLS SIMPLE RECTANGULAR TYPE , BARBELL AND FLANGED WALLS COUPLED WALLS RIGID FRAME SHEAR WALLS FRAMED WALL WITH INFILLED FRAMES COLUMN SUPPORT SHEAR WALLS CORE TYPE SHEAR WALLS

FIGURE- A SIMPLE RECTANGLE AND BAR BELL TYPE FREE STANDING WALLS

1. SIMPLE RECTANGULE TYPE AND FLANGED (BARBELL TYPE)WALL The simple rectangular shear walls ,under the action of in plane vertical loads and horizontal shear along its length, are subjected to bending and shear. Barbell type of wall are formed when a wall is provide monolithically between two column. The columns at the two ends are then called the boundary elements. The barbell type walls are stronger and more ductile than the simple rectangular type of uniform section. Also they never fail in shear but only by yielding of steel in bending. One of the disadvantage of this type of shear walls is that as these walls are rigid during an earthquake they attract and dissipate a lot of energy by cracking, which is difficult to repair.

2. COUPLED TYPE WALLS If two structural walls are joined together by relatively short spandrel beams, the stiffness of the resultant wall increases; in addition the structure can dissipate most of the energy by yielding the coupling beams with no structural damage to the main walls. It is easy repair these coupling beams than walls. These walls should satisfy the following two requirements: The system should develop hinges only in the coupling beam before shear failure The coupling beam should be designed to have good energy-dissipation characteristics .

FIGURE-B

3. FRAMED WALLS WITH INFILLED FRAMES Framed walls are cast monolithically, whereas in filled frames are constructed by casting frames first and infilling it with masonry or concrete block later. 4.COLUMN SUPPORTED SHEAR WALLS For architectural reasons to discontinue shear walls at floor level the wall to carry by widely spaced column. In such column supported shear wall, the discontinuity in geometry that level should be specially taken care of in the design 5. CORE TYPE SHEAR WALLS In some building ,the elevators and other service areas can be grouped in a vertical core which may serve as device to withstand lateral loads.

CLASSIFICATION ACCORDING TO BEHAVIOUR SQUAT STRUCTURAL WALLS SLENDER WALL ORDINARY-MOMENT SHEAR WALLS DUCTILE-MOMENT SHEAR WALLS DUAL SYSTEMS

1.SQUAT STRUCTURAL WALLS Squat structural walls with a ratio of height to length of less than 2 or 3 find wide application in seismic force resistance of low-rise building. In this walls in which deflection and strength are controlled by shear. 2. SLENDER WALL Slender wall usually have a height to length ratio is grater than 2. They behaves like a vertical slender cantilever beam. 3.ORDINARY-MOMENT SHEAR WALLS Ordinary moment shear walls in which deflection and strength are controlled by flexure. These are usually high rise shear walls to resist high wind and cyclones.

4.DUCTILE-MOMENT SHEAR WALLS Ductile –moment shear walls are special walls meant for seismic region and which have good energy dissipation characteristics under reversal loads. 5.DUAL SYSTEMS When lateral force resistance is provided by the combined contribution of frames and structural walls, it is customary to refer to them as a dual system Ductile frames, interacting with walls can provide a significant amount of energy dissipation ,particularly in the upper stories of a building .on the other hand ,as a result of the large stiffness of walls, good story drift control during an earthquake

BEHAVIOUR UNDER SEISMIC LOADING Depending on the height to width ratio , a shear wall may be behave as a slender wall a squat wall or a combination of two. In slender wall primary mode of deformation is bending. Shear deformation are small and can be neglected . Flexure strength usually governs the design of such wall .They are usually subjected to low nominal shear stress. They develop a predominantly horizontal crack pattern in the lower hinging region after a few cycle of inelastic deformation Squat wall show significant amount of shear deformation as compared to bending deformation. Shear strength usually governs the design of such walls. They are usually subjected to high nominal shear stress. They develop inclined cracks in the web that form a diagonal compression strut system for each direction of loading.

FIGURE- C

LOCATION OF SHEAR WALL IN A BUILDING Shear walls are usually provided between column line, in stair wells, lift wells and in shaft . When design for wind loading the location of the wall with in the building plan does not play an important role. Incase of seismic loading ,however ,wall location are a critical factor .Under wind loading a fully elastic response is expected ,while during strong earthquake significant in elastic deformation are anticipated . A wall configuration which has very little eccentricity between the centre of building mass and stiffness and results in a reasonably uniform distribution of inelastic deformation under seismic loading For the best torsional resistance ,as many of the walls as possible should be located at the periphery of the building

SHEAR WALLS

DESIGN STEPS FOR SHEAR WALL Step -1: Review of the layout of cantilever wall systems. Step-2: Derivation of gravity loads and equivalent masses Step- 3: Estimation of earthquake design force Step-4: Analysis of the structural systems Step- 5: Determination of design action Step- 6: Design for flexural strength Step: 7: Design for shear strength Step:8: Detailing of reinforcement

DETAIL OF SHEAR WALL

CONCLUSION The torsional effects in a building can be minimized by proper location of vertical resisting elements and mass distribution. Shear walls should be employed for increasing stiffness where necessary and be uniformly distributed in both principal direction Multi –storied RCC building shear walls are now fast becoming as popular as an alternate structural form for resisting the earthquake force.

REFERENCES www.weikipedia.com www.google.com IS 1893, Criteria for Earthquake Resistant Design of Structure-Part1:2002 IS 13920, Ductile Detailing of Reinforced Concrete structure subjected to seismic force, 1993 IS 456(2000) Code of practice for plain and reinforced concrete

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