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SHEAR WALL

INFLUENCES ON STRUCTURAL FORMS  From

engineer point of view, the structural forms are selected on the basis of : the resistance of different structural elements to gravity and horizontal loads  In reality, the choices of structural forms uses is strongly influenced by:  Internal planning  Material and method of construction  External architectural treatment  The planned location and routing of the service system

CONTI…. 

It may be noted that taller and more slender is the building; the more important is the selection of structural factors become and more necessary is to choose the appropriate structural forms.

WEIGHT OF STEEL IN TALL BUILDING  The

efficiency of the structures can be roughly compared by their weight per unit floor area.  Weight of the floor is influenced by floor span.  Buildings up to ten stories can accommodate wind loading without increase in member sizes because of the flexibility in permissible stresses set by the design codes.  However, for more then ten stories the additional materials required for wind resistance increases non-linearly.

WEIGHT OF STEEL IN TALL BUILDING

INTRODUCTION TO SHEAR WALL For tall buildings, it is necessary to provide adequate stiffness to resist the lateral forces caused by wind and earthquake  When such buildings are not properly designed for these forces, there may be very high stresses, vibrations, and side-sway when the forces occur  The results may include not only severe damage to the buildings but also considerable discomfort for their occupants 

In structural engineering, a shear wall is a structural system composed of braced panels (also known as shear panels) to counter the effects of lateral load acting on a structure. Wind and seismic[1] loads are the most common loads that shear walls are designed to carry.  It provide lateral stability to structures by resisting the in-plane shears and bending moments caused by the lateral forces 

DEFINITION 

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Shear Wall is a Structural Element used to resist Lateral / Horizontal / Shear forces parallel to the plane of the wall by: Cantilever Action for slender walls where the bending deformation is dominant Truss action for Squat / Short Walls where the shear deformation is dominant

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The basic requirements of shear walls designed for high seismic forces is to ensure flexure rather than shear-controlled design

In reinforced concrete framed structures the effects of wind forces increase in significance as the structure increases in height  Codes of practice impose limits on horizontal movement or sway  Limits must be imposed on lateral deflection to prevent: • Limitations on the use of building, • Adverse effects on the behaviour of non-load bearing elements, • Degradation in the appearance of the building, • Discomfort for the occupants 

One way to limit the sway of buildings and provide stability is to increase the section sizes of the members to create a rigid, moment-resisting frame. However, this method increases storey heights, thus increasing the building cost. It is rarely used for more than 7 or 8 storeys  Another way is to provide stiff, shear resisting walls liked to a flexible frame. These can be external walls or internal walls around lift shafts and stair wells (a core) or sometimes both are provided 

PLACEMENT OF SHEAR WALL 

The shape and plan position of the shear wall influences the behaviour of the structure considerably. Structurally, the best position for the shear walls is in the centre of each half of the building. This is rarely practical, however, since it dictates the utilization of the space, so they are positioned at the ends

This shape and position of the walls give good flexural stiffness in the short direction, but relies on the stiffness of the frame in the other direction

This arrangement provides good flexural stiffness in both directions.

However, this arrangement lacks the good torsional stiffness of the previous arrangements due to the eccentricity of the core

SHEAR WALL PLACEMENT IN BUILDING

On most occasions, it is not possible to use shear walls without some openings in them for doors, windows, and penetrations for mechanical services  The wall sections on the sides of these openings are tied together by beams enclosed in the walls, by the floor slabs, or by a combination of both  Although shear wall designs are often handled with empirical equations, they can be appreciably affected by the designer’s previous experience 

A structure with reinforced concrete shear walls is going to be quite stiff and, thus, will attract large seismic forces  If the shear walls are brittle and fail, the rest of the structure may not be able to take the shock  If the shear walls are ductile, however (and they will be if properly reinforced), they will be very effective in resisting seismic forces 

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The depth of the beam from the compression end of the wall to the center of gravity of the tensile bars is estimated to be about 0.8 times the wall length, lw, as per ACI Section 11.10.4. The commentary (R11.9.9) says that in low walls, the horizontal shear reinforcing is less effective, and the vertical shear reinforcing is more effective

QUASI-STATIC TESTING OF SHEAR WALL

RESEARCH STUDIES: PERFORMANCE-BASED DESIGN OF SQUAT REINFORCED CONCRETE SHEAR WALLS VIA HYBRID SIMULATION Catherine Whyte Postdoctoral Researcher

Bozidar Stojadinovic Professor and Chair of Structural Dynamics and Earthquake Engineering

Department of Civil, Environmental and Geomatic Engineering Swiss Federal Institute of Technology (ETH) Zürich nees@berkeley Workshop May 27, 2014

OVERVIEW Motivation to study squat shear walls in nuclear facility structures  Hybrid simulation method and suitability for testing squat shear walls  2 hybrid simulation tests at UC Berkeley  Comparison to quasi-static cyclic test at SUNY Buffalo 

HYBRID SIMULATION FOR SQUAT NUCLEAR FACILITY WALLS Well-suited for testing walls in very massive structures so the mass associated with the structure can be simulated  One physical wall component can be tested at large scale 

CONCLUSIONS Displacement controlled hybrid simulation using a high-precision digital encoder for displacement feedback is an effective way to perform largescale hybrid testing of stiff specimens  Tested two walls with different ground motion loading sequences and observed same progression of failure modes and similar hysteretic behavior  Hybrid simulation results were consistent with quasi-static test results in terms of global behavior response 

ACI PROVISIONS FOR SHEAR WALLS

EXAMPLE 

Design a reinforced concrete shear wall shown in figure, if fc’ = 3000 psi and fy = 60,000 psi

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