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Re: Seismic Loads in Ceiling

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Bring your plywood floor diaphragm over to 2' from the bearing walls to blocking between your floor joists. Add sill plates and cripple walls with plywood up to the rafters.  transfer the shear to the roof diaphragm through blocking and boundary nailing at the roof plywood.
Hope this helps.
Ray Shreenan  SE
----- Original Message -----
From: Bill Allen
To: Seaint
Sent: Monday, December 22, 2008 8:47 AM
Subject: Seismic Loads in Ceiling

Just curious, but I'm interested in how others address transferring the ceiling dead load to lateral force resisting elements in residential construction. I haven't worried about this too much in the past, but I have a project now which consists of a high pitched roof and the owner wants to use the attic space as a floor. Of course, the problem is that I can't connect the floor diaphragm to the top plate of the exterior wall because the roof rafters are in the way. I can't use the ceiling joists in weak axis bending because they do not clear span the structure. Besides, they only run one direction. I'm concerned about using the GWB ceiling as a diaphragm because of what it may do to my R value and that I have a low level of confidence in quality of construction with regards to the installation of drywall fasteners. I have visualized all sorts of complicated (and convoluted) shear transfer details which I would rather not draw nor present to the architect.





T. William (Bill) Allen, S.E.


Consulting Structural Engineers
V (949) 248-8588 ? F(949) 209-2509