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Re: horiz. diaph. -Reply

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John Rose, you wrote that " the diaphragm and shear wall values for 4-5 ply
(and 3-ply) plywood are equivalent, regardless of the application.  City of LA
currently has a restriction on shear wall values for 3-ply plywood, limited to
200 lb/ft. APA's opinion is that this restriction is overly conservative and
not supported by cyclic (reversed) load testing or monotonic testing."

The greatest test and laboratory for shear walls in California is one of our
frequent earthquakes.  Unlike plywood panels constructed with four and five
plys, forces caused by the Northridge Earthquake tore three-ply panels at their
inner ply seam. This information supports reductions for  3ply panel
construction and is more valuable than mere simulated testing.

Tim McCormick, P.E.
City of Los Angeles