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

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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