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ASCE 7-05 Section 12.2.3.2
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- Subject: ASCE 7-05 Section 12.2.3.2
- From: Andre Sidler <asidler(--nospam--at)hotmail.com>
- Date: Wed, 14 Sep 2011 08:23:04 -0700
Jason -
This is commonly used in but not only used in residential wood-framed structures. For instance we have a nice house on a bluff with a great view. The owner wants nothing but windows for the view but as an engineer we need a line of resistance so we stick a steel moment frame along that line in an otherwise wood shear wall structure. The wood shear wall has a lower R value than the moment frame but using the exceptions below we can now design the MF using the higher R value associated for the MF while the rest of the structure uses the lower R for the shear walls and diaphragm. Of course nothing is as simple as that but I tried to simplify for example purposes. I hope this helps. Andre Sidler, S.E., P.E. Seattle, WA -------------------------------------------------------------------------- 4 Message:0004 4 -------------------------------------------------------------------------- From: Jason Christensen <jason(--nospam--at)wcaeng.com> To: "seaint(--nospam--at)seaint.org" <seaint(--nospam--at)seaint.org> 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 =D90 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 tha= t you have to use the least R values (which makes sense), but the second se= ntence seems to be giving an exception if the three criteria are met, howev= er it still states that the least R values is to be used.=20 Any thoughts would be helpful. Jason |
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