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Learning

23 Earthquake Design
Earthquake Tip and

Construction

Why are Buildings with Shear Walls preferred in Seismic Regions?

What is a Shear Wall Building structural elements (like glass windows and building
Reinforced concrete (RC) buildings often have contents).
vertical plate-like RC walls called Shear Walls (Figure 1) Architectural Aspects of Shear Walls
in addition to slabs, beams and columns. These walls Most RC buildings with shear walls also have
generally start at foundation level and are continuous columns; these columns primarily carry gravity loads
throughout the building height. Their thickness can be (i.e., those due to self-weight and contents of building).
as low as 150mm, or as high as 400mm in high rise Shear walls provide large strength and stiffness to
buildings. Shear walls are usually provided along both buildings in the direction of their orientation, which
length and width of buildings (Figure 1). Shear walls significantly reduces lateral sway of the building and
are like vertically-oriented wide beams that carry thereby reduces damage to structure and its contents.
earthquake loads downwards to the foundation. Since shear walls carry large horizontal earthquake
forces, the overturning effects on them are large. Thus,
design of their foundations requires special attention.
Shear walls should be provided along preferably both
length and width. However, if they are provided along
only one direction, a proper grid of beams and
RC columns in the vertical plane (called a moment-resistant
Walls frame) must be provided along the other direction to
resist strong earthquake effects.
Plan Door or window openings can be provided in
shear walls, but their size must be small to ensure least
interruption to force flow through walls. Moreover,
openings should be symmetrically located. Special
RC design checks are required to ensure that the net cross-
Foundation Shear sectional area of a wall at an opening is sufficient to
Wall carry the horizontal earthquake force.
Figure 1: Reinforced concrete shear walls in
buildings – an excellent structural system for Shear walls in buildings must be symmetrically
earthquake resistance. located in plan to reduce ill-effects of twist in buildings
(Figure 2). They could be placed symmetrically along
Advantages of Shear Walls in RC Buildings one or both directions in plan. Shear walls are more
Properly designed and detailed buildings with effective when located along exterior perimeter of the
shear walls have shown very good performance in past building – such a layout increases resistance of the
earthquakes. The overwhelming success of buildings building to twisting.
with shear walls in resisting strong earthquakes is
summarised in the quote:

“We cannot afford to build concrete buildings meant Unsymmetric
to resist severe earthquakes without shear walls.” location of
shear walls
:: Mark Fintel, a noted consulting engineer in USA not desirable

Shear walls in high seismic regions require special
detailing. However, in past earthquakes, even Symmetry of building in
plan about both axes
buildings with sufficient amount of walls that were
not specially detailed for seismic performance (but had Symmetric location of
enough well-distributed reinforcement) were saved shear walls along the
perimeter of the
from collapse. Shear wall buildings are a popular building is desirable
choice in many earthquake prone countries, like Chile,
New Zealand and USA. Shear walls are easy to
construct, because reinforcement 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 Figure 2: Shear walls must be symmetric in plan
minimizing earthquake damage in structural and non- layout – twist in buildings can be avoided.
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