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Re: shearwalls

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I witnessed an experiment at a local university recently where, after the first two cycles of a seismic record input the TOP plate nail connection ruptured like zipper and the full load was carried by the upper half of the studs in the wall (the lower part remained nailed)- apart from massive deflections did very well thank you without failure.  Seeing the experiment not performing as predicted (i.e. bottom sill/anchor distress) they switched it off.  It had me wondering too about our often pre-conceived ideas of how the data will be forthcoming.

Thor A. Tandy   P.Eng,  MCSCE,  MIPENZ
Victoria, BC, Canada
e-mail: <vicpeng(--nospam--at)vtcg.com>

-----Original Message-----
From: chuckuc <chuckuc(--nospam--at)dnai.com>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Friday, September 11, 1998 5:07 PM
Subject: shearwalls


>I guess this is for John Rose.  My reading, testing, and observation
>leads me to conclude that most shearwall test failures initate at the
>sill nailing of the uplift corner.  The deflection of the tie down
>allows separation between the post and sill and this deflection (1/4" to
>1/2") overloads the local sill nails. It can also break the sill in
>cross grain bending. Under cycled loading this usually fails the nails
>in bending fatigue due to the large number of high deflection load
>cycles required by the current test protocol.  Questions: When is APA
>going to test and publish shearwall information using real tie downs? 
>L.A. is apparently requiring testing of tie downs using wood posts
>rather than steel test jigs--how can we get that data? What about using
>Richardo Foschi's computer model to provide us with some parametric
>curves relating shearwall capacity to tie down deflection? Since the
>fasteners and the tie downs seem to account for virtually all of the
>deflection, why not just drop the calculation of panel bending and shear
>deflection and just adjust the nailing coefficient a little? I have
>heard rumors of fatigued nails at Northridge, does anyone know anything
>about it?  If we never see fatigue failures in real earthquakes maybe
>Erol Karacabeyli is right; is the current cycled loading protocol 
>giving us the wrong answers?
>Chuck Utzman, P.E.
>
>
>