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Re: Horizontal plywood diaphragms

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David -

I've never seen horizontal values for a 48" span of unblocked 3/4" plywood, 
which doesn't mean they don't exist.  You may try calling APA.  As a side 
note, I think that 3/4" plywood is only rated to span 48" maximum for roof 
vertical loads when the edges are blocked, unless you use T&G plywood or 
panel clips.  See Table 23-I-S-1 in the 1994 UBC.  This may force the 
blocking issue anyway.

Bruce Resnick, SE
Parker Resnick Str. Eng.

In a message dated 4/2/99 10:42:04 AM Pacific Daylight Time, DHLAssoc(--nospam--at) 

<< I have a commercial project where the architect wants to use exposed 3/4" 
 plywood over exposed 4x rafters at 48" o.c. He does not want to see any 
 blockings between the rafters. Prelim calcs show maximum diaphragm shear to 
 be around 150 plf. Does anyone know--- for plywood horizontal diaphragm 
 values; if there is any place in the UBC where one can find diaphragm shear 
 values for framing member spacing more than 16" o.c.?