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[SEAOC] RE: [SEAOC] Gyp. board shear walls in LA

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It is my understanding that the LA reductions are a combination of several 
things:

1. Over estimated capacity of Gyp board shear wall.
2. Lack of inspectors.
3. Poor construction quality.

The truth is that a gyp board is worth much more than 30 plf. Until LA city 
finds out what that value is, they decided to lower it to 30 plf. Actually, 
what I heard is that after Northridge earthquake, they were going to 
prevent use of gyp board shear walls. However, the gyp board industry lobby 
negotiated a 30 plf value. Something is better than nothing.

Shafat


----------
From: 	Stephen & Karen Fisher[SMTP:skfisher(--nospam--at)mother.com]
Sent: 	Monday, June 17, 1996 8:47 PM
To: 	seaoc(--nospam--at)power.net
Subject: 	[SEAOC] Gyp. board shear walls in LA

I have recently been working on a seismic evaluations of both 2 and 3 story 
wood framed apartment buildings in LA.  I am curious as to the rational 
used
in the drastic drop in the allowable shear value for gyp. board.  According 
to research the allowable shear value of a 5/8" blocked gyp. board shear 
wall
with 6d @4"o.c. has been modified in recent codes as follows:

		Prior to 1988 UBC:		175plf

		1988 UBC thru current:		1/2 * 175plf = 87.5plf

		Current LA requirements:	30plf max

I understand that gyp. board will tend to crack and can therefore not 
handle
cyclic loading very well.  Also, accoriding to some of the articles I have
read if the nails are overdriven and break through the surface of the gyp.
board there will be less capacity.

My question is with the current 30plf allowable in LA.  Is that the true
capacity of the qyp. board?  If so was the original 175plf a complete over
estimate of the gyp. boards real capacity?  If the 175plf was an 
overestimate
then it was so by a factor of almost 6:1.

Any thoughts you might have on this topic would be greatly appreciated.

Stephen Fisher, PE

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