in which the deflections of portions of walls are

performs the function of a plate girder web, the

combined usually are adequate.

pilasters or floor diaphragms function as web

stiffeners, and the integral reinforcement of the

(a) Wall deflections. The rigidity of a wall

vertical boundaries functions as flanges.

Axial,

is usually defined as the force required to cause a unit

flexural, and shear forces must be considered in the

deflection. Rigidity is expressed in kips per inch.

design of shear walls. The tensile forces on shear

The deflection of a concrete shear wall is the sum of

wall elements resulting from the combination of

the shear and flexural deflections (see Figure 7-1). In

seismic uplift forces and seismic overturning

the case of a solid wall with no openings, the

moments must be resisted by anchorage into the

computations of deflection are quite simple; however,

foundation medium unless the uplift can be

where the shear wall has openings, as for doors and

counteracted by gravity loads (e.g., 0.90 of dead

windows, the computations for deflection and rigidity

load) mobilized from neighboring elements. A shear

are much more complex.

An exact analysis,

wall may be constructed of materials such as

considering angular rotation of elements, rib

concrete, wood, unit masonry, or metal in various

shortening, etc., is very time-consuming. For this

forms. Design procedures for such materials as cast-

reason, several short-cut approximate methods have

in-place reinforced concrete and reinforced unit

been developed. These do not always give consistent

masonry are well known, and present no problem to

or satisfactory results. A conservative approach and

the designer once the loading and reaction system is

judgment must be used.

determined.

Other materials frequently used to

support vertical loads from floors and roofs have

(b) Deflection charts. The calculation of

well-

established

vertical-

load-

carrying

deflections is facilitated by the use of the deflection

characteristics, but have required tests to demonstrate

charts. See Figure 7-4 for fixed-ended corner and

their ability to resist lateral forces. Various types of

rectangular piers. Curves 5 and 6 are for cantilever

wood sheathing and metal siding fall into this

corner and rectangular piers. The corner pier curves

category. Where a shear wall is made up of units

are for the special case where the moment of inertia,

such as plywood, gypsum, wallboard, tilt-up concrete

units, or metal panel units, its characteristics are, to a

large degree, dependent upon the attachments of one

unit to another, and to the supporting members.

(1)

Rigidity analysis.

For a building with

rigid diaphragms, there is a torsional moment, and a

rigidity analysis is required. It is necessary to make a

logical and consistent distribution of story shears to

each wall. An exact determination of wall rigidities

is very difficult, but is not necessary, because only

7-9

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