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1997 UBC Seismic

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Sasha, Ron and Sadre;

I appreciate your input to my question.  Sorry it has taken me so long
to convey my thanks.  I have been out of touch with the list for the
past week.

There seem to be significant changes to the '97 UBC seismic compared to
the '94.  The greatest of these changes, at least to us "east coast
engineers" in zones 1 and 2, seems to be this omega (i.e. 3R/8) factor
by which the seismic force is multiplied by for design of certain
elements.  I still have a minor point of confusion with part of this
issue.  In section 1633.2.6, collector elements, states that "Em need
not exceed the maximum force that can be  transferred to the collector
by the diaphram and other elements of the lateral force resisting
system."  

In section 1630.1, Em is defined as omega*Eh.  To me, this is saying
that if your diaphram is not capable of transferring Em, then the
collectors, in this case, need only be designed for the force that the
diaphram can transferr (less than Em, but not less than Eh).  So, this
Em is not a strict demand than must be placed on the collectors (and
other elements specified for this particular combination)?  I guess, as
Sasha said, this is some type of "weak link" concept.

Thanks,

George Barclay, P.E.