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Seismology Committee Web page - Rigid/Flexible Part 1

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Part I of III

I read the arguments of the Seismology committee on the www.seaoc.org web
page for the Seismology Committee. The documents goes to great lengths argue
that the provisions of the current code dates back to the sixties. However,
the writers of this document fail do any more than quote sentences which
have been, largely ignored by engineers practicing on wood structures for
some very simple reasons. There was no practical method of analysis for
unblocked diaphragms and there still isn't. However, this in itself is not a
valid argument to design by flexible analysis alone.

The Seismology committee would have us believe that it is the engineer's
responsibility to determine the final design method. They argue that
engineers have always had the latitude to design according to their
professional judgment. They fail to point out that based on the definitions
they provide in the code, small wood diaphragm in wood structures act rigid.
Although a historic argument, not until APA suggested arbitrary multiplier
of 2.5 times the blocked diaphragm deflection to define the deflection of a
flexible diaphragm could the previous codes be enforced.  It is now
enforceable and SEAOC has taken measures to educate the professional
community so that it would be difficult to ague without comparison that the
rigidity of the diaphragm makes little if any difference in the overall
design. In other words, you have to go through the work to responsibly prove
that the work was unnecessary.
While building officials used the lack of appropriate design methods to
calculate the diaphragm deflection in the past, they are now empowered to
enforce the letter of the code as the disqualifying factor has been removed.
Those building departments who do enforce the code are going as far as to
enforce known discrepancies and errors until they are appropriately address
by code revision or publication within ICBO's Building Standards. Those
jurisdictions who are not enforcing compliance are creating potential
liability for those engineers who submit without determination of a
diaphragms rigidity. This last group creates an unmatched competition as
many are gambling that their liability coverage will protect them in the
event that they are sued for non-compliance. Those of us who feel an ethical
responsibility to comply until the code writers act on their ethical
responsibility to correct the errors and ambiguity are losing work in the
process. Personally, I've lost two clients who would rather find an engineer
willing to ignore these provisions in three local cities and the county of
Riverside who will not enforce the code. I know this to be factual as I
provide contract services for one firm that plan checks for these three
cities and have been instructed not to correct non-compliance issues.

see part II of III