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'97 UBC Lateral Design - Envelope Solutions????

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I have assumed the design menthodology of the '97 UBC for wood framed 
structures to be an envelope proceedure - where the results of the flexible 
and rigid diaprhagm shear distribution are forces are distributed based upon 
the worst case condition.

I had a discussion with another engineer who indicated that this is not 
clearly defined in the code and that the analysis should be based on the 
determination if the diaprhagm is rigid or flexible. Inasmuch as the majority 
of wood diaprhagms in residential construction are determined to be rigid, I 
would need to resort to distribution by torsion and may be allowed to neglect 
proportional distribution (flexible) analysis.

The design examples from the 1998 Wood Seminar by SEAOSC uses an envelope 
solution - which I have followed on the designs I have completed. The results 
are, in my opinion, overly conservative at best, based on the knowledge I 
have of good performance based on proper detailing and construction.

The idea of using the diaphragm deflection test as a means to determine which 
method governs is not acceptable to me - especially when the distribution of 
forces may result in a reaction that is less than I historically determined 
from flexible methods. It is not so much a question of policy as it is that I 
have no devloped sense of how the materials will behave torsionally as I have 
from my history of flexible design and the knowledge of the good performance 
of the buildings I have designed.

What are your opinions? Do you interpret the code as requiring the 
distribution by enveloped methods (worst case from each design), or from the 
test applied to the stiffness of the diaprhagm? 

Dennis S. Wish PE