Civil Engineering Reference
In-Depth Information
columns” with the result that the slenderness requirements of Section 10.10 of the Code
will have to be met. An alternative procedure for slender walls is presented in ACI Sec-
tion 14.8.
Walls with
k
u
/
r
greater than 100 (and for which a theoretical analysis is required)
are rather common, particularly in tilt-up wall construction. The Portland Cement Associ-
ation has available a design aid that is particularly useful for such cases.
2
18.5
SHEAR WALLS
For tall buildings it is necessary to provide adequate stiffness to resist the lateral forces
caused by wind and earthquake. When such buildings are not properly designed for these
forces there may be very high stresses, vibrations, and sidesway when the forces occur.
The results may include not only severe damages to the buildings but also considerable
discomfort for their occupants.
When reinforced concrete walls with their very large in-plane stiffnesses are
placed at certain convenient and strategic locations, they can often be economically
used to provide the needed resistance to horizontal loads. Such walls, called
shear
walls
, are in effect deep vertical cantilever beams that provide lateral stability to struc-
tures by resisting the in-plane shears and bending moments caused by the lateral
forces.
As the strength of shear walls is almost always controlled by their flexural resistance,
their name is something of a misnomer. It is true, however, that on some occasions they
may require some shear reinforcing to prevent diagonal tension failures.
The usual practice is to assume that the lateral forces act at the floor levels. The stiff-
nesses of the floor slabs horizontally are quite large as compared to the stiffnesses of the
walls and columns. Thus it is assumed that each floor is displaced in its horizontal plane
as a rigid body.
Figure 18.2 shows the plan of a building that is subjected to horizontal forces. The
forces are applied to the floor and roof slabs of the building, and those slabs, acting as
large beams lying on their sides, transfer the loads to the shear walls A and B. Should the
shear walls
A
C
D
B
Figure 18.2
2
Portland Cement Association, 1980, “Tilt-Up Load Bearing Walls—A Design Aid,” EBO74D (Skokie, IL), 28 pp.
