Discontinuous Shear Walls - The Analysis of Irregular Shaped Structures - page 407

F i g u r e 11.2 Photograph of in-plane offset shear walls. ( Courtesy, Willdan Engineering. )
The upper wall section B, in Fig. 11.1, is vertically discontinuous to the foundation.
Its overturning force on the left side of the wall must be transferred through the sup-
porting header, into the jamb studs supporting the header on each side of the opening,
and then down into the foundation at locations B and C. The header, jamb studs, and
their connections must be designed as elements supporting discontinuous walls, in
accordance with ASCE 7-05 1 Sections 12.3.3.3 and 12.10, using the overstrength factor,
as applicable. The overturning force at the left side of wall section B also affects the
design of the hold-down located at the right side of wall section C. The first-floor pier
on the right side of the window opening is assumed, in this case, not to meet the
required aspect ratio to function as a shear wall and therefore cannot be used as part of
the lateral-force-resisting system. It is, however, required to support the right side of
the discontinuous wall above. Two configurations for the support and tie-down for the
right side of wall segment B are shown in the figure.
Figure 11.3 shows a similar condition where a perforated shear wall is located over
a segmented shear wall of lesser width. In this case, hold-downs are only required at
each end of the perforated shear wall above. Since the first-floor full-height section on
the right side of the opening is too narrow to meet the code-required aspect ratio, it
cannot be used as part of the first-floor shear wall to resist lateral forces. The second-
floor wall is vertically discontinuous on the right side of the wall. The end studs of
section B are supported at the first floor by multiple studs which must be designed as
elements supporting discontinuous walls. These studs must be designed for tension and
compression forces using the overstrength factor, as applicable, and must transfer the
overturning forces from the upper wall into the foundation. The intermediate tie-downs
at the full-height segments, as required by SDPWS 2 Section 4.3.6.4.2.1, must be transferred
into the continuous rim joist and then into the wall header below.
Figure 11.4 shows a two-story shear wall, where the wall at each level is designed
in accordance with the force transfer around the opening (FTO) method. The upper
wall is shown having a length that is less than the first-floor wall to demonstrate how