Page 439 - Design of Reinforced Masonry Structures

CHAPTER 7
SHEAR WALLS

7.1 INTRODUCTION

All structures must have some means of resisting lateral forces, such as wind or seismic,
and transfer them to the ground. In the vertical plane, several types of force-resisting sys-
tems are commonly used to resist lateral loads, such as shear walls, braced frames, moment
frames (also called rigid frames), or a combination of these called dual systems. These
systems are commonly referred to as lateral force–resisting systems (LFRS). When used
to resist wind forces, these systems are referred to as main wind force–resisting systems
(MWFRS); they are called seismic force–resisting systems (SFRS) when used to resist
earthquake forces. Shear walls can be used in all types of buildings, from low-rise to high-
rise, and from ordinary warehouse to multistory apartment buildings. They form an integral
part of lateral load–carrying systems commonly known as bearing wall systems (known in
the past as the box system), and are also used in conjunction with other seismic force–resisting
systems referred to as building frame systems and dual systems. Essentially, a bearing wall
system refers to a structural support system wherein major load-carrying columns are omit-
ted and the walls and/or partitions are of sufficient strength to carry gravity loads. When
used as SFRS, shear walls must be designed by engineered methods; this chapter presents
analysis and design of such walls.
A bearing wall system offers unique advantages over other load-resisting systems and
provides an economical alternative to structural frame system. It not only eliminates the need
for a structural frame but also provides the enclosure walls for the building. Architectural
units can be used to provide a durable, aesthetic finish for both exterior and interior walls
thus eliminating the need for additional surface treatments. Additional costs of fireproof-
ing and soundproofing are also eliminated. The walls and partitions supply in-plane lat-
eral stiffness and stability to resist wind, earthquake, and any other lateral loads. Shear
wall structures are inherently stiff and capable of limiting deformation and damage during
extreme lateral loads. As such, shear walls form an important topic in building design and

construction. Figure 7.1 shows a typical multistory shear wall system.
Braced and moment frames are generally constructed from steel or reinforced con-
crete. Shear walls may be constructed from a variety of materials like reinforced concrete,
reinforced masonry, wood frame [with various kinds of sheathing material—plywood,
gypsum wallboard, drywall, interior and exterior plaster (stucco), fiberboard, and lumber
sheathing], and steel plates. In typical wood-frame buildings, the shear walls are built from
sheathed wood panels, which are called shear panels. Shear walls made from masonry
(clay or concrete units) may be unreinforced or reinforced. This chapter presents a discus-
sion of analysis and design of reinforced concrete masonry shear walls.

7.1