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According to SDPWS 4.3.5.6 and Equation 4.3-5 the total shear capacity Vn of a perforated shear wall is
Vn = vn Co Sbi
where Co is the shear capacity adjustment factor calculated using equation 4.3-6 and Sbi is the sum of the shear wall segments, adjusting for narrow segments as per 4.3.3.4.
Equation 4.3-6 is
Co = Awall / (3Ao + Afhs),
where Awal, Ao and Afhs are the area of the wall, the total opening area, and the total full-height sheathing, respectively.
The unit design shear capacity can be written
vn Co Sbi / Sb
where Sb is the actual length of valid full-height sheathing segments in the wall, so Sbi / Sb can be considered the Aspect Ratio adjustment factor for perforated walls.
The Shear Design table of the Design Results shows Co and Sbi / Sb for each perforated wall.
Design for Unknowns
Since Co and Sbi / Sb are determined on a wall-by-wall basis, it is possible for walls on the same shear line to have different Co and values. If some design values are unknown and all walls on the shear line are considered to have identical materials, the program designs for the wall with the critical combination of Co factor, and applied force. If walls can have differing materials, they are designed separately.
Shearwalls 2019 and Earlier
The SDPWS calculation of the Co factor changed for SDPWS 2021, implemented in Shearwalls 2023 (Version 13). Earlier versions in of the program offered a choice in the Design Settings between using earlier SDPWS Equations 4.3-5,-6, and using Table 4.3.3.5 to calculate this factor.
In this method, Co depends upon the ratio of the total length of full-height sheathing to the total length of the wall. Using the Table, the maximum opening height the wall is also required; using the Equations, the total area of openings is used. The values in the Table are arrived at by using the maximum opening height as the height of each opening, and is thus a conservative approximation of the Co arrived at via the Equations.