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Re: Taking Questions for Seismology Submission

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Dennis, I have the following two questions in regard to the wood diaphragm 
issue. Please forward to Bill Nelson. (I know we were supposed to send these 
directly to you but there is a little bit of information here that I thought 
may be of interest to the "enlightened" engineers passionately following this 
thread):

1- Is there any documentation (SEAOC Seismology archives) that proves the 
addition of provisions for diaphragm flexibility determination in the 1988 
UBC was intended for wood diaphragms? I remember clearly the Saturday seminar 
I attended in San Diego when the 88 UBC was adopted. Allen Poroush and Nabih 
Yousseff were among the speakers. However, I don't have any recollection of 
hearing anything significant about this issue and whether the new provision 
was intended for wood diaphragms. 

A couple of weeks ago I called ICBO and spoke with Susan Dowty in regard to 
their archives. 
Normally there is a paragraph or two given as "Reason" for any code change 
proposal. However, for that particular year (1987), SEAOC had presented a 
wholesale rehaul (20 pages) of the seismic provisions and according to Susan, 
one brief sentence was given for reason to the effect that "the intent to is 
to update seismic provisions to keep up with the new technology, 
etc........." (nothing specific) She mentioned that Ken Luttrel was the SEAOC 
seismology chair at that time and all questions regarding the code change 
proposal were to have been addressed to him. (I would be very curious to hear 
from Ken in this regard)

I do recall that prior to the 88 UBC we (plan check engineers) always had a 
rough time with metal decks without topping and whether they should be 
assumed as rigid or flexible. So I personally welcomed the new addition to 
the code (the metal deck industry since then developed flexibility 
coefficients for their diaphragms) little did I know that it would someday 
come back to haunt us.

2- (this has been asked many times before) Where is the documentation that 
past performance of light framed wood structures were unacceptable due to the 
erroneous assumption of diaphragm flexibility? And please don not give the 
examples of open front buildings such as Northridge Meadows, since that 
really does not prove anything in this regard and on the contrary proves the 
dangers of using diaphragms in rotation, which rigidity analysis in a way 
legitimizes.

Ben Yousefi, SE
San Jose, CA