Shear Wall Design
The perforated shear wall (PSW) design methodology is similar to the segmented shear wall (SSW) method but
only requires two hold-downs for each wall (one at each end), thus eliminating the
intermediate overturning restraints located adjacent to window and door openings in the SSW method.
The PSW method recognizes that the entire
wall acts to resist overturning, rather than a series of individual full-height segments. The
result is a wall with slightly lower capacity (a function of the sizes of openings)
and reduced cost in material and labor due to elimination of intermediate
hold-downs. Intuitively, a PSW with a small opening would have
nearly the same capacity as the same wall without
openings. As the size of the opening(s) increases, the capacity is
correspondingly reduced. In many cases wood-framed walls have
excess capacity when designed according to the SSW methodology, while the PSW method results in a more economical
Determining the capacity of a PSW, or shear wall with
unrestrained openings, is similar to the SSW method.
However, in the PSW method all sheathed portions of the shear wall (shaded in green) are assumed to provide
resistance to lateral loads. PSW capacity is based on the capacity of the wall
from the SSW method, reduced by an opening adjustment factor that is related to the percentage
of full-height sheathing in the wall.
The first step in PSW design is to determine the unit shear capacity
(v) of the SSW using IBC Table 2306.4.1 or UBC Table 23-II-I-1, as was demonstrated previously for segmented
shearwalls. Next, the shear capacity adjustment factor (Co) must be calculated using
the tabulated information below. Note that the value of Co is
always less than or equal to unity since a PSW has
fewer hold-downs than a SSW.
The unrestrained opening height is the vertical dimension of any opening
in the wall. The maximum unrestrained opening height is the vertical dimension of the tallest opening in the wall,
expressed as a fraction of the total shear wall height (h). Openings may be located vertically between two sheathing
elements (windows), between a sheathed element and the floor (doors), or
between the top of the wall and the floor (large doors, or windows and doors without structural sheathing
above/below openings). Any
areas of the wall that are not sheathed with structural panels such as plywood or OSB are
considered unrestrained openings. The PSW method makes the conservative
assumption that all unrestrained openings in the wall have the same
height as the maximum vertical opening dimension in the wall.
Once the shear capacity adjustment factor (Co) is determined, it is used to calculate the allowable shear capacity of the perforated shear wall (VPSW) as follows:
VPSW = Co v Sbi
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