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RE: Discontinuous Shear Wall

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You could not develop more strength in the shearwall than the ultimate
capacity of the holdown i.e. the wall could not take more shear if the
holdown failed.

So for example if you had A36 threaded rods used in your holdown, the
ultimate capacity is about 100% greater, then the overstrength factor
would be:

"Omega" = (fu/fy)(Tn/Tu)= (70ksi/36ksi)(Tn/Tu) = 1.9 Tn/Tu
	 < 2.8 for UBC wood framed shearwalls

Where Tn = nominal tensile capacity of the rod and Tu = the ultimate
demand calculated by analysis. If the design is 100% efficient then
phi*Tn = Tu and:

"Omega" = 2.0 / phi = 2.0 / (0.9) = 2.2 

Michael Bryson, SE

-----Original Message-----
From: David Merrick [mailto:MRKGP(--nospam--at)winfirst.com] 
Sent: Tuesday, October 03, 2006 9:18 AM
To: SEAINT
Subject: Re: Discontinuous Shear Wall

The omega factor is usually the best choice in wood design because of 
the uncertainty of the maximum strength. Maximum force of the walls 
above are to equal their ultimate failing capacity. Wood framed shear 
panel maximum capacity can very high when bounded by framing. It is not 
just the nail capacity.

Even unrated gypsum wall board have a substantial failure capacity, from

my poor memory, tests result in maximum capacity exceeding 200 plf. 
Unintended shear walls are a problem in failure but hopefully the 
intended walls are long, stiffer and will receive most of the load 
before much is transferred into the unintended walls.

David Merrick, SE
Sacramento, CA

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