Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

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

[Subject Prev][Subject Next][Thread Prev][Thread Next]
>
>I have been using all plywood shear walls ever since the initial capacity 
>reductions were made as a response to the Northridge earthquake damage. As a 
>result I was not aware that gyp board shear values were reduced even to 30 plf!
>Although that is _something_, it seems to me that 30 plf is practically 
>nothing...as far as I can recall, whenever there's been even a generous amount 
>of wall to utilize as gyp board shear wall, typical construction seldom results
>in stresses being much lower than about 50 plf ... so basically gyp board has 
>been practically eliminated as a shear wall option.
>
>Perhaps someone else can comment on this-
>
>Thomas D. Honles, S.E.
>Phone: (213)367-0006   LADWP, Los Angeles, California, USA
>Internet e-mail: thonle(--nospam--at)dwp.ci.la.ca.us
>          (also: tdh(--nospam--at)capella.dwp.ci.la.ca.us)
>------------------------------------------------------------------


Thomas,

I was at Cal State Northridge in the weeks after the event.  As part of 
my tasks, I walked through some of the wood framed residence halls on 
campus.  These buildings were constructed in three stages, about five 
years apart.

The first group were two or three stories tall, had plywood shear walls in 
one direction along the corridor and gwb shear walls at the rooms.  These 
buildings performed miserably during the quake.  Nearly all of these 
buildings sustained serious damage and were yellow tagged by the state's 
inspector.

The remaining two sets of buildings were constructed with plywood shear 
walls in both directions.  These performed much better; with one major 
exception.

If the plywood shear wall did not have a hold down, the sill plate 
generally was destroyed.  We surmised that the plywood would continue to 
act as a shear element and the entire wall segment rocked off its 
foundation.

Our conclusion was that it did not matter what the code told us about the 
need for hold downs at the ends of plywood walls, we needed to put 
something in.  The plywood will resist much more overturning than a 
series of anchor bolts at some nominal spacing will provide.  

What nailed it down for us was a wall in a three story hall that had an 
entire bearing/shear wall hanging from the story above.  The wall had 
fractured the sill plate and swung away from the concrete slab;  it was 
just hanging in space.  ( It was with great diplomacy that we encouraged 
the lady working in that office to move to another part of the building.)

My opinion is that GWB is nice and pretty, but it does not have any 
post-earthquake strength.  I will try to stay as far away from that 
material as I can for my clients.

Greg

...