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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.