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Re: WARNING against using Staples in shear walls/diaphragms

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well, that sucks...  we typically will overlay sheathing to t&g decking and use shear values from ESR-1539.  This throws that for a loop...  Thanks, Thor.  Good information.  Please keep us informed.

On Feb 5, 2008 10:52 PM, Thor Matteson <thor(--nospam--at)yosemite.net> wrote:
To those of you who specify structural staples for shear walls and
diaphragms---they may fail without warning.  Following are excerpts from a
letter sent by the SEAOC Building Code Committee to the Chair of the CALBO
Seismic Safety Committee:

*************************************
SEAOC Building Code Committee expressed concern that damage to staples from
earthquake lateral forces cannot be visibly evaluated because the staple
crowns showed no visible distress regardless of movement or failure of the
legs.

....the first set of tests was based on COLA/ SEAOSC testing criteria. The
second set of tests was based on the CUREE test protocol. The results showed
the Strength Limit State (SLS) for the 16 ga. staples occurred at 1 inch
drift (0.01h).  The SLS for the 8d common nails at the same spacing was
twice the strength and at 1.6 inch drift (0.016h). Both sets of tests showed
that the staples provide somewhat similar shear value at small panel drifts
up to ½ inch, but at larger drifts beyond 1-inch, stapled sheathing loses
shear values in comparison with common nails.  Beyond 1-1/2 inch panel
drift, using staples, life safety becomes a concern.  Nailed sheathing drift
extends to 3-1/2 inch before becoming a life safety concern.

After the tests, it was noted that failure of the staples occurred between
the back-side of the plywood sheet and the face of studs after only 10 or 12
reversed cycles.  Nails exhibited heavy bending either at the head or in
slots in the plywood face or studs by nail bending.  In contrast, after
staple failure or heavy bending, the crown of the staple showed no sign of
the stapled legs distress, appearing the same as first installed.  Thus, it
would be impossible to evaluate the degree of loss of shear strength in
stapled panels after seismic shaking without partially removing the panel.

In summary, we believe there are sufficient life safety concerns to warrant
notifications to building officials in regions of Seismic Design Categories
C to F within California. Until a formal proposal to the California Building
Standards and/ or the International Code Council can be reviewed and
approved, local jurisdictions in California may adopt amendment to limit the
use of staple fasteners only with the validation tests and approval of
building officials.
**************************************

I'm going to ask permission to post the full text of this letter on my
website, along with other notes from an engineer involved in the testing..

Thor Matteson
www.shearwalls.com


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David Topete, SE