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RE: 2x2 Plate Washers for WSP Shear Wall

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No, Bill, it also occurs in Seismic Zone 2, the land of infrequent large 
earthquakes, but we will have to get our ass kicked with a moderate 
earthquake before the public realizes it and engineers have the guts enough 
to admit that we are susceptible to large earthquakes.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Bill Allen wrote:

. > Paul -
 
. > And this phenomena only occurs in Seismic Zones 3 & 4?
 
. > T. William (Bill) Allen, S.E. (CA #2607)
. > V/F (949) 248-8588
. > San Juan Capistrano, CA

. > -----Original Message-----
. > From: Paul Feather [mailto:pfeather(--nospam--at)SE-Solutions.net] 
. > Sent: Tuesday, August 26, 2003 11:14 AM
. > To: seaint(--nospam--at)seaint.org
. > Subject: Re: 2x2 Plate Washers for WSP Shear Walls (UBC)


. > Bill,
 
. > Examination of failure modes on shear wall sill plates indicated that as
. > the holdown and endpost deflect, there is a general tension field
. > developed along the wall which creates tension on the sill plate in
. > cross grain bending relative to the anchor bolts.  The behavior is
. > similar to the observed failure in masonry or concrete walls as well,
. > principal tensile forces are on the diagonal with internal resolution of
. > the principal shear stresses.  This tension field action was causing
. > sill plates to split along the bolt line thereby losing shear capacity
. > at the bolts.  The idealized analysis model we have always used, direct
. > shear with all tension and compressive forces concentrated at the ends
. > does not adequately account for the actual conditions.
 
. > A rather extensive testing program was conducted, I believe at UC
. > Irvine, that demonstrated the 2" plate washer was an adequate measure to
. > prevent premature splitting of the sill plate and allow our traditional
. > analysis model to remain valid.  I am sure there is probably more
. > information available on the subject then we would ever have time to
. > actually read.
 
. > The shear wall table in chapter 23 is actually closer to the "real"
. > requirement as a result of tests.  Chapter 18, which is horribly
. > out-dated and the "conventional construction" catch all for foundation
. > design, was also updated to require plate washers regardless of
. > application.  The two committees probably didn't talk to each other.  It
. > is one of those code things, like if a two pound hammer is required
. > under this condition, we will make it required under all conditions so
. > they can't screw it up.
 
. > Personally I am a bit conservative with wood shear wall design.  I
. > prefer to maximize the wall lengths where possible and keep demand below
. > the 3" E.N. threshold, preferably 4".  
 
. > Paul Feather PE, SE
. > pfeather(--nospam--at)SE-Solutions.net
. > www.SE-Solutions.net

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