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Important Note – These are descriptions to changes implemented in WoodWorks Shearwalls for version 9 and may not reflect current behavior.
The following changes implement the new requirements in Table 4.3.4 for fiberboard – that it now is allowed to have a 3.5:1 aspect ratio, where it was previously limited to 1.5:1, but a penalty is applied to shear resistance for ratios between 1:1 and 3.5:1.
The design group for the Allow 3.5:1 height-to-width ratio setting has been renamed to Seismic wood panels, and fiberboard from Seismic design. If it is checked, then the program allows fiberboard to be 3.5:1, otherwise it is restricted to 1:1. Previously fiberboard was always restricted to 1.5:1.
Separate factors for wind and seismic design are calculated according to note 3 of Table 4.3.4, and applied to the capacity of a shearwall side that has fiberboard materials.
For seismic design, fiberboard height-to-width factors are shown in the same columns for exterior and interior sides as the structural wood panel height to width factor, which now also contains the unblocked Cub factor. For wind design, a similar column has been added to the table, and the column for low-rise wind case has been removed to make space for it.
The height-to-width factor is incorporated into the shear resistance that is output for each side of the shearwall.
When we are allowing 3.5:1 height to width ratios, fiberboard is treated as a structural wood panel when determining whether to ignore non-wood-panel contributions, otherwise it is treated as a non-wood panel.
This is because when fiberboard has a 3.5:1 maximum ratio, there is no advantage to ignoring it when combined with structural ratio, which as the same h/w ratio. When it is restricted to 1:1, it is ignored along with gypsum sheathing so that short segments are not discarded when they can contribute to structural sheathing capacity.
An exception to the above rule takes place when the setting Ignore non-wood-panel contribution for all walls is checked for seismic design. In this case, fiberboard is considered a non-wood panel, because the purpose of that setting is to exclude those materials that might contribute adversely to the value of the seismic response modification factor R from ASCE 7 Table 12.2-1.
A small extension to the … when combined with structural wood panels label called (including fiberboard) appears after the seismic checkbox, and is disabled and enabled to show whether fiberboard is considered a structural panel for this purpose . In most cases, this applies to wind design as well.
The following applies to shearwalls with unblocked structural wood panels on at least one side. Unblocked shearwalls are new to this version of the program, see item 6 above.
The program restricts the height-to-width ratio for the new unblocked structural wood panels to 2:1, in all cases, as per SDPWS Table 4.3.4. Narrower unblocked panels are not considered full-height segments and do not contribute to shear resistance. Blocked panels continue to have a H-W ratio of 3.5, with reduced capacity for seismic design when between 2 and 3.5.
The Setting Ignore non-wood when combined with structural wood panels, does not include unblocked shearwalls among the structural wood panels. There is no advantage to ignoring gypsum and other non structural wood materials when combined with unblocked walls, as they have the same height-to-width ratio.