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[SEAOC] Re: [SEAOC] wood panel shear wall/frames

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You might check out proposal 248 in the 1997 ICBO proposed code changes which
was approved as revised this winter. It provides pictures of height to width
ratio limitations for wood walls. In a nutshell, if you detail the horizontal
and vertical boundary elements at the corners of the openings in the walls
for the respective force and moment transfer, then the effective height of
the opening can be defined as the clear height at the side of an opening. See
pages 140  and 141 of the March-April 1996 ICBO Building Standards Part III
monograph. You'll need to check with the SEAOC Code Committee to see if there
are any significant challenges to this proposal. If successful, it will be
part of the 1997 UBC. 
Also, the Wood Technical Subcommittee 7 of the BSSC just wrote the following:

Recent testing and observations from Northridge have suggested that holddown
posts experience notable displacement before significant load can be carried
through the holddown connector. The result is a large deformation demand
placed on the nails connecting the sheathing to the framing. This often
results in the nails pulling out of the sheathing at the holddown post corner
and sometimes resulting in an unzipping effect where a significant portion of
the remaining sheathing nailing fails as high loads fail one nailed
connection and move on to overstress the next nail. The most effective
solution currently known is to limit the slip and deformation at the holddown
post by using a very stiff nailed or screwed holddown. When holddown slip is
less than 1/16 in or so, the assumption of wall stiffness porportional to
length is fairly reasonable. For larger holddown slip values, wall stiffness
will move towards being proportional to the square of the wall length; more
importantly, the anchorage will start exhibiting displacement compatibility
problems discussed above. The currently available deflection equations are
known to not always be accurate and need to be updated. Some new deflection
formulas are also proposed in TS7's Proposal 7-7 now undergoing balloting.
Hope this helps.