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Stapled Diaphragms under Seismic Load

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Numerous posts over the weekend concern NER-272 and the use of stapled
diaphragms/shear walls.  Most were from west coast engineers, presumably
designing structures which must resist seismic load.  The thread was about
gage, approval, and OSB v. Plywood, and there were enlightening responses,
but I have changed the subject line slightly and am posting this because I
think the discussion failed to touch on a bigger issue.

I designed a building with stapled shear walls per NER-272 some years before
I learned that the ICBO approval was based on small numbers of small scale
static tests.  I stopped using it.  To the best of my knowledge, the
situation has not changed.  In response to what I understand to have been
very poor performance observed in stapled shear walls during the Northridge
earthquake, I believe the City of Los Angeles Department of Building and
Safety to have banned the use of such panels.  I think the Department of the
State Architect and Office of Statewide Health Planning have taken the same
position.

My understanding is that decent scale dynamic load testing had been done
only assemblies using common nails prior to Northridge.  I believe some
testing has been done sense, and more research is underway, but so far as I
know, no one has yet published dynamic tests of shear panels relying on box
nails or staples.  Since deformation/tearing around nails is a common
failure mode, it seems apparent that a shear panel may exhibit dramatically
different behaviour under repeated and reversible loading that it would
under a single slow steady push.  In particular, enlargement of the nail
hole due to tearing of the fibers around it after only a few cycles may put
the shank of the nail into flexure that could lead to strain hardening and
brittle fracure of the shank.  One could imagine that this problem would be
more severe in very small diameter fasteners (e.g., the legs of wire
staples).

Perhaps some one from COLA, DSA and/or OSHPD will comment.  Perhaps ICBO
will correct a misunderstanding or explain/defend the reliance on static
testing.  For all of us practitioners however, IMHO, caution is warranted in
using shear panel values taken from the ISANTA approval (NER-272).  For my
part, I'm avoiding stapled shear panels and/or diaphragms until I see better
data.

Drew Norman, S.E.
Drew A. Norman and Associates