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Important Note – These are descriptions to changes implemented in WoodWorks Shearwalls for version 9 and may not reflect current behavior.
This section pertains to the allowable loads in psf for out-of-plane bending design of sheathing members subject to component and cladding wind loads.
For all previous versions of Shearwalls, design values were taken from Table 7A of the Wood Frame Construction Manual if they were close to those in the SDPWS, when factored as explained below.
Two anomalous values were taken from the SDPWS - 12” spacing, perpendicular to the supports, 19/32"and 23/32" thicknesses. These anomolies were due the fact that SDPWS included shear effects in the analysis as well as bending.
The values in the WFCM table are unfactored for load duration, and a footnote says they can be multiplied by 1.6 for wind design.
The values were published as Allowable Stress Design (ASD) values, so no conversion was necessary for Shearwalls ASD design.
The values assume the sheathing is supported in 3 spans by the studs.
For all but the cases given below, the design values are now taken from SDPWS Table 3.21.
Values for lumber sheathing are taken from the WFCM 2001, as SDPWS does not list these values. Values for 5/16” sheathing are taken from the 1995 WFCM as they are in neither the SDPWS nor the 2001 WFCM.
The SDPWS values incorporate a wind load duration value of 1.6. In Shearwalls, the values are multiplied by the ratio between the user-input load duration value from the Design Settings and 1.6. (Note that NDS Table 2.3.2 refers to 1.6 as a “frequently used load duration factor”, indicating there is some latitude for designers to change this value, hence the override in Shearwalls)
WFCM values for 5/16 plywood are multiplied by the user-input load duration factor.
Lumber sheathing values from the WFCM are multiplied by the 1.4 factor given in WFCM table 4A, multiplied by the ratio of between the user-input load duration factor and the standard load duration factor of 1.6.
The values are divided by 1.6 for ASD design in Shearwalls, in accordance with SDPWS 3.2.1.
The WFCM values were based upon the assumption of two span stud support, the SDPWS is based on three spans. Refer to SDPWS C3.2 for the reason for this change.
The program now allows you to select which assumption you prefer based on the characteristics of your building.
Radio buttons 2-span and 3-span have been added to a new data group called Out-of-plane sheathing assumption in the Design settings.
The default value for new files is 2-span, in accordance with SDPWS. The value for existing files from previous versions is 3-span, so as to retain the design results for those files.
When 3-span is selected, the factored tabulated values are multiplied by 1.25.
The span assumption appears below in the legend below the Components and Cladding by Shearline table.