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Re: Redundancy Factor

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"As you and others have put forth the question "what has changed since 1988 
UBC to require us to do rigidity analysis on wood floor diaphragm now that 
1997 UBC is in effect?". I still have not seen or heard an answer other than 
"because it was presented in a seminar as an example." If the code language 
regarding rigidity analysis has not changed since 1988 UBC, why are we 
required to do that on residential wood frame diaphragms NOW and not since 
1988? If we are going to be liable now for not doing rigidity analysis, why 
aren't we liable for not doing it since 1988, or are we? Some tribute the 
"change" to the aftermath of Northridge earthquake, but again the requirement 
was there since 1988. I don't believe there is a specific language in the 
1997 code that says "the rigidity analysis is now required for wood frame 
diaphragms as well," so, why consider it now if it was not considered since 
1988 UBC? If the intent of the 1988 UBC was to require such an analysis on 
wood frame diaphragms, why wasn't it advertised or didn't it become known 
then rather than now?

Any official explanation or an explanation of an Official? Maybe the authors 
or presenters of the example presented at the wood seminar last year know the 

Oshin Tosounian, S.E."

(I hate to be "me too" sayer but I can't help it on this one) Well said Oshin.

If you are collecting posting from the list server to present to the 
seismology committee on this issue. I believe this posting by Oshin should be 
on top of the pile since it pretty much sums up the whole argument. If a 
reasonable answer (backed by factual data) for this question is presented by 
those in favor of this methodology, let's hear it, and we will all go on 
doing our business accordingly. Otherwise, the proven standard of care for 
the past few decades should rule.

Ben Yousefi, SE
San Jose, CA