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Re: Plywood Diaphragm Values

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The diaphragm shear values in the UBC are listed for minimum nominal panel thickness. If thicker sheathing is used, the values do not increase (per the UBC) because the values are controlled by nail allowable lateral forces.  If thinner sheathing is used (say 15/32"), then the values in the code for that thickness govern.  The max. nail size listed in the
diaphragm table is 10d common, applicable to 15/32" or thicker panels.

If you use the NDS for "principles of mechanics," then you will find that the lateral load increases as the panel thickness increases, for a specific nail size such as 10d common. These increases haven't been considered in the UBC diaphragm table. The current revision to APA Report 138 on diaphragms shows how the NDS values compare with the UBC values for
diaphragm design.

Hope this helps.

John Rose/APA

Kipp Martin wrote:

> I am working on a project where we are using 3/4" plywood for the roof sheathing.  UBC Table 23-II-H gives diaphragm values for up to 19/32" (5/8") sheathing.  Are values for thicker plywood published by someone?  I've been told that I can use the values for the thinner plywood.  Is that true?  As you can tell, it's been a while since I worked with plywood.
> --Kipp Martin, P. E.
> Portland, Oregon