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RE: ASCE 7-05 Section 12.2.3.2

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Jason,
 
The second sentence allows you to use a different R value for each system provided you meet the stated caveats.  The last line is just for the diaphragm. 

Regards, Harold Sprague
 
> From: jason(--nospam--at)wcaeng.com
> To: seaint(--nospam--at)seaint.org
> Date: Tue, 13 Sep 2011 15:43:54 -0600
> Subject: ASCE 7-05 Section 12.2.3.2
>
> Can anyone expand on the second sentence in this section? It seems to mean nothing, considering the requirement of the first sentence.
>
> 12.2.3.2 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.
>
> Jason
>
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