the shear walls by the beams. In addition to these
cantilevers.
When a lateral force is applied, the
axial forces, the beams develop moments and shears
spandrels act as struts that flexurally deform to be
that contribute to the walls resisting overturning. The
compatible with the deformation of the cantilever
magnitude of the resisting beam bending moments
piers. It is relatively simple to determine the forces
and vertical shears is dependent on the relative
on the cantilever piers by ignoring the deformation
stiffnesses of the walls and the coupling beams. It
characteristics of the spandrels. The spandrels are
should be noted that the foundation itself functions as
then designed to be compatible with the pier
a coupling beam.
Accurate determination of the
deformations. In Figure 7-3B, the piers are relatively
resisting
forces
can
be
complex;
therefore,
flexible compared with the spandrels. The spandrels
approximate methods are generally used.
One
are assumed to be infinitely rigid, and the piers are
method may be used for calculating the axial forces,
analyzed as fixed-ended columns. The spandrels are
and another method may be used for calculating
then designed for the forces induced by the columns.
bending moments and shears to ensure that the
The overall wall system is also analyzed for
structural elements are not underdesigned.
overturning forces that induce axial forces into the
columns. The calculations of relative rigidities for
(5)
Construction joints and dowels.
The
both cases shown in Figure 7-3 can be aided by the
contact faces of shear wall construction joints have
charts in Figure 7-4. For cases of relative spandrel
exhibited slippage and related drift damage in past
and pier rigidities other than those shown, the
earthquakes.
Consideration must be given to the
analysis and design become more complex.
location and details of construction joints, which
must be clean and roughened.
Shear friction
(3)
Methods of analysis.
Approximate
reinforcement may be utilized in accordance with
methods for analyzing walls with openings are
ACI 318. For this procedure, a coefficient of friction
generally acceptable. For the extreme cases shown in
of 0.6 is suggested for seismic effects.
Figure 7-3, the procedure is straightforward.
For
other cases, a variety of assumptions may be used to
e.
Out-of-Plane Effects.
determine the most critical loads on various elements,
thus resulting in a conservative design. (Note: In
(1) Lateral forces. Walls and partitions must
some cases, a few additional reinforcing bars, at little
safely resist horizontal seismic forces normal to their
additional cost, can greatly increase the strength of
flat surface (Figure 7-5, part a). At the same time,
shear walls with openings.)
When, however, the
they must resist moments and shears induced by
reinforcement requirements or the resulting stresses
relative deflections of the diaphragms above and
of this approach appear excessively large, the strut
below (Figure 7-5, part b). The normal force on a
and tie procedure indicated in paragraph 7-2d (2) or a
wall is a function of its weight. Equations for the
more rigorous analysis may be justified.
determination of the force are provided in Paragraph
10-1b(1); however, wind forces, other forces, or
(4) Coupled shear walls. When two or more
interstory drift will frequently govern the design.
shear walls in one plane are linked together by
coupling beams, interactive forces are transmitted to
7-15
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