Tuesday, September 13, 2011

ASCE 7-05 Section

Can anyone expand on the second sentence in this section? It seems to mean nothing, considering the requirement of the first sentence. R, Cd , and Ω0 Values for Horizontal Combinations.
Where a combination of different structural systems is utilized to
resist lateral forces in the same direction, the value of R used for
design in that direction shall not be greater than the least value
of R for any of the systems utilized in that direction. Resisting
elements are permitted to be designed using the least value of R for
the different structural systems found in each independent line of
resistance if the following three conditions are met: (1) Occupancy
Category I or II building, (2) two stories or less in height, and (3)
use of light-frame construction or flexible diaphragms. The value
of R used for design of diaphragms in such structures shall not be
greater than the least value for any of the systems utilized in that
same direction.

Maybe I am missing something, but it seems to say in the first sentence that you have to use the least R values (which makes sense), but the second sentence seems to be giving an exception if the three criteria are met, however it still states that the least R values is to be used.

Any thoughts would be helpful.


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