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[SEAOC] Re: [SEAOC] Wood Screw Capacity[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)power.net
- Subject: [SEAOC] Re: [SEAOC] Wood Screw Capacity
- From: BCASE1356(--nospam--at)aol.com
- Date: Fri, 19 Jul 1996 01:49:07 -0400
In a message dated 96-07-18 12:04:27 EDT, you write: << Subj: [SEAOC] Wood Screw Capacity Date: 96-07-18 12:04:27 EDT From: jimdane(--nospam--at)ix.netcom.com (JAMES ARDEN DANE) Reply-to: seaoc(--nospam--at)power.net To: seaoc(--nospam--at)seaoc.org I have a retrofit application where I have been asked to attach drag strap blocking to 5/8" plywood using a series of A35 clip angles. I am trying to find a wood screw with an established shear capacity when attached to 5/8" plywood. The intent is to avoid the removal of light weight concrete and carpet when the office is in use. Has anyone used a similar application? ... >> I have seen a few jobs where an A35 was used to screw to 3/8" plywood. I am not sure I believe in this detail. According to NDS and the 1994 UBC a screw needs to have 7d in order to have full design values for shear. This limits you to a 6d (0.138" diameter) and 7d (0.151" diameter) screws at approximately 50% of their full capacity when screwing into 5/8" plywood. I know that APA has some published values for screws in plywood which would have to be reduced for working stress by some factor of safety. I think that you would be better off telling the owner they need to remove the lightweight concrete. Another approach might be to epoxy a flat block to the underside of the plywood, you could still screw A35's to the block and plywood, but I would have more faith in the epoxy glue. The glue is good for 50-75 psi in shear (typical failure of plywood is rolling shear = 75 psi) and the usual failure is the wood and not the glue. Fire consideration is probably the downfall in using strictly epoxy. ___________ glued interface. ____________/_________ ___________/__________ <--------plywood sheathing [_______] <------ flat blocking | | | <------ A35 for shear transfer between blocking | | <------ vertical blocking === <------ drag strap (assumed nailed to blk'g) (hope the above illustration is readable) Michael Cochran Brian L. Cochran Associates, Inc. Los Angeles, CA ...
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