SEISMIC ANALYSIS WITH SHEAR WALLSSEISMIC ANALYSIS WITH SHEAR WALLS

A PARTIAL FULFILMENT OF A PARTIAL FULFILMENT OF

M.TECH- STRUCTURAL ENGINEERINGM.TECH- STRUCTURAL ENGINEERING

PRESENTED BY

ABHISHEK HAZRA STRUCTURAL ENGINEERING DIVISION

DEPARTMENT OF STRUTURAL ENGINEERING

CONTENTSCONTENTS 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

INTRODUCTIONINTRODUCTION

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

BACKGROUNDBACKGROUND

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.

DISCUSSIONDISCUSSION

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

1. SIMPLE RECTANGULAR TYPE , BARBELL AND

FLANGED WALLS

2. COUPLED WALLS

3. RIGID FRAME SHEAR WALLS

4. FRAMED WALL WITH INFILLED FRAMES

5. COLUMN SUPPORT SHEAR WALLS

6. 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

1. SQUAT STRUCTURAL WALLS

2. SLENDER WALL

3. ORDINARY-MOMENT SHEAR WALLS

4. DUCTILE-MOMENT SHEAR WALLS

5. 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