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RE: Diaphragm deflection for plywood floor

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It is not clear which code you are referring to, but the requirements for
using diaphragm in rotation are in section 2315.1 of UBC. Basically the
depth normal to open side is limited by 25 feet or 2/3 of the open side. The
2/3 ratio can be exceeded up to 2:1 if drift calculations are provided. If
the building has to resist seismic loads it needs to comply with the above,
regardless of wind controlling the base shear. However the drift would be
calculated based on the seismic loads not the wind load. 

In regard to engineer stamping the plans and not complying with the code,
your answer is right on.

Ben Yousefi, SE
San Jose, CA

	-----Original Message-----
	From:	edjonson [SMTP:edjonson(--nospam--at)email.msn.com]
	Sent:	Wednesday, July 05, 2000 8:47 AM
	To:	seaint
	Subject:	Diaphragm deflection for plywood floor

	A building official friend of mine asked me to look at a set of
house plans.  Is concern was lack of shear walls at the front of the garage.
Looking at the calculations the engineer is cantilevering the plywood floor
diaphragm 20 feet to the garage back wall.  The diaphragm shear stresses are
580 plf (wind controlled).  There is a second story on top of the garage.  I
told the building official to tell the engineer to verify the drift is
within the UBC requirements.  My questions is, am I asking to much for
verifying the drift?  Also this same engineer told the building official
that since he was stamping the plans he did not have to meet the 3 1/2 to 1
height to width ratio for plywood shear walls.  I said BS.  
	Your comments are much appreciated.  Thanks
	Ed Jonson

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