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Re: IBC 2305.3.10 2x2x3/16 plate washers

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The CUREE Wood Frame Project has research results that strongly suggest that
sill plate washers be increased to 3x3x3/8 inch washers for 2x4 sills and
5x5x1/2 inch for 2/6 sills. CUREE is recommending this regardless of the
sill bolt diameter used and regardless of whether the wall does or does not
utilize tiedowns. CUREE found through test results that these larger plate
washers are necessary to delay or eliminate the onset of splitting in shear
wall foundation sills so that the more ductile withdrawal failure mode of
sheathing nails can be assured of being the first mode in shear wall
systems. The thicker, larger plate washers also reduce wall end uplift and
cross-grain bending of the sills due to prying action of sheathing nails.
Diagonal slots in the washers are intended to ease installation in
situations where bolts are not exactly centered on sill plates. This may end
up as a future code change proposal.

As far as sole vs sill plates, CUREE seems to be silent in this respect. But
wouldn't it make sense to use plate washers on any sole plates that are
associated with shear walls that are likely to experience net uplift at the
sole plate? CUREE may not have published test results that address this
aspect just yet.

Fred Turner, Staff Structural Engineer, California Seismic Safety
Commission, a public policy advisory agency, fturner(--nospam--at), 1755
Creekside Oaks Dr. #100 Sacramento, CA 95833 916-263-0582 Phone 916-263-0594

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