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Re: Plywood Floor Diaphragm Shear Values

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Allowable diaphragm shear load values are tabulated based on minimum
nominal panel thicknesses, and for specific nail sizes and penetration
which typically control the diaphragm shear value.  Thus, for thicker
wood structural panels, it is most common to use the tabulated values.

The tabulated value may need to be reduced for a specific application,
such as when the nail penetration is reduced below the minimum specified
in the code or evaluation report, as sometimes occurs with engineered
wood framing which may have 1-1/2" or thinner wood flanges; or if a
lower density species other than Douglas fir or southern pine is used
for framing.

Since diaphragm design also can be based on principles of mechanics, it
may be possible to increase the tabulated design shear in some cases by
using the allowable lateral nail load based on NDS formulas, which
include consideration of panel thickness, but this is time-consuming and
generally not worth the effort to do this more sophisticated analysis.
In this case, it would also be necessary to check allowable diaprhagm
shear load based on panel shear through the thickness, using a method as
described in APA Report 138.  (The tabulated allowable diaphragm design
shear loads in the code already have been checked for compliance with
this condition.)

John Rose
APA-Retired
Tacoma, WA


Paul Crocker wrote:

>    Part 1.1Type: Plain Text (text/plain)


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