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Re: Residential Flexible/Rigid Diaphragm Analysis

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Jim Fruit writes:

"Dennis,

Currently the City of San Jose and the City of Palo Alto do penalize the
embedded column with the lower Rw but do not apply the lower Rw to the whole
structure.  I recommend you contact them for their take on the issue.  

Hope this helps.

Jim Fruit, AIA
Carl Mileff and Associates, Inc.
Building Code Services."

Jim,
Most of the building departments that I have submitted structural designs to
and who use the '94 UBC have allowed me to limit the Rw reduction to the line
of shear. I believe that this is valid. 
However, the '97 UBC is more specific and requires compliance of the whole
structure. As with most codes, the final adoption of the code or changes to it
are at the discretion of the local building official.  This causes a problem
is the local official is not an engineer and relies only upon the written code
or upon consultants hired to evaluate each section of the code as it relates
to their locale. 
I don't believe that most consultants (plan check agencies) will take a
position other than the written code unless they have the "clout" of specific
knowledge of SEAOSC's committee work and can take a position which they
believe to be able to justify. This is a very gray area and one we are not
likely to see in the Coachella Valley.

I hope that at the very least, we can start an intelligent discussion both on
the list and in the committee meetings for seismology and wood. We need to
promote that both committees put their collective heads together on this
issue. 
Personally, I hope they will wait until the results are in from CUREe/Caltech
before we start intensifying the design methodology for single family
residences.

Regards,
Dennis Wish PE