Standard Shear Walls - The Analysis of Irregular Shaped Structures - page 350

Compression perpendicular to the grain has been exceeded for two studs bearing
on the first-floor wall bottom plate. The allowable tension stress in the boundary studs
should also be checked at the net section. The addition of studs will reduce the resisting
moment arm length x , which will increase the overturning force. The forces on the wall
are approaching the high end of the demand that should be required of the wall. The
wall length should be increased if the forces increase. ▲

9.8 Interior Shear Walls

A basic discussion of interior shear walls was presented in Chap. 2. The distribution of
lateral forces into interior shear walls that are oriented parallel to the trusses is rela-
tively easy because the trusses can be used as the collector elements. However, walls
that are installed perpendicular to the trusses create framing conditions that make the
installation of a continuous collector very difficult. Most texts do not discuss this condi-
tion or provide solutions to this problem. Interior shear walls are usually required when
the allowable diaphragm aspect ratio has been exceeded, or when it is desirable to
reduce the load to an end wall. A typical layout is shown in Fig. 9.17. The installation of
the interior shear wall, in effect, creates two separate diaphragms. The interior wall acts
as a support for both diaphragms and therefore defines a diaphragm boundary. A full-
length collector must be installed to support the remaining depth of the diaphragms on
both sides of the wall, in accordance with the code.
When trusses or rafters are oriented perpendicular to exterior shear walls, the trans-
fer of the diaphragm forces to the shear walls is typically accomplished with full-height
solid blocking. However, at interior shear walls or stub-heel trusses at an exterior wall,
the distance from the top plate of the shear wall to the roof sheathing prevents the use
of solid blocking. Whenever this condition occurs, other methods must be used to com-
plete the load path. One method commonly used is to require preengineered truss-
blocking panels designed and constructed by the truss manufacturer. The designer of
the lateral-force-resisting system is responsible to provide the shear loads to the truss
manufacturer and typically places the loads applied to the panels on the construction
drawings. Another method often used is to install site-built shear panels consisting of
plywood or OSB sheathing nailed to lumber blocking between the trusses to transfer
the diaphragm shears down into the wall. Figure 9.14 shows a typical arrangement of
these panels. The shear panels act as mini-shear walls that resist shear and overturning.
In extreme cases, the height of the panels can even exceed 12 ft if the trusses are sloped
and the shear wall is located near the ridge. The analysis of the shear wall and panels
can follow the procedure covered in Sec. 9.7 by applying the shear force at the sheathing
level or by transposing the forces down to the top of the wall. The shear blocking panels
making up the upper wall section must be connected to the lower shear wall just like a
second-floor shear wall, including overturning hold-down anchors or straps. It is
important to note that the force being transferred, similar to typical shear walls, is a per
lineal foot diaphragm load which, in most cases, is transferred through the shear panels
into a continuous top plate of the shear wall below. The shear panels shown in the pho-
tograph in Fig. 9.15 are 2 ft wide (actually 22.5″ wide) by 8 ft high. Assuming that a
uniform shear of 200 plf is applied at the top of the panels, the counteracting shear force
acting vertically on each end of each panel, neglecting dead load, is equal to 1600 lb.
This overturning force must be resisted by an equal and opposite shear force or a