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RE: Choosing R, Seismic Provisions

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>If you are in Seismic Design Category A, B, or
>C and you choose to use a Response Modification
>Factor greater than 3 - say for example IMRF of
>steel w/ R = 6, how exactly does the code
>technically require you to detail per
>the seismic provisions?  

The intent of the paragraph in Part 1, Section 1 of the 2002 AISC Seismic
Provisions is explained in the Commentary -- last paragraph of Part 1
Commentary Section C1 (top of page 76). IThat paragraph gives you the
summary of what is in effect if you stack up all the various requirements in
the IBC or NFPA 500 and the AISC Seismic Provisions as far as
scope/applicability. It is most clearly stated in that paragraph that you
can choose to use R=3 in SDC A, B and C and not be required to meet anything
in the AISC Seismic Provisions. However, it also clarifies that in SDC D, E
anf F AND whenever you choose to use an R factor higher than 3 in SDC A, B
or C, you must meet the AISC Seismic Provisions. Bottom line: you cannot
take advantage of the benefits of high ductility (a higher R) if you do not
also meet the detailing requirements that give you that high-ductility.

>I realize the detailing reference section is
>listed right there in the table, but when you
>look at the first page of the referenced provisions,
>it says something to the effect of "these
>provisions apply to buildings in category D
>or above... or when required by the EOR."

I agree this statement is a bit confusing and have submitted a change
proposal to the committee to make it more -- and I hope crystal -- clear.

>I was talking to an engineer who swears up and
>down that if you're in SDC A, B, or C, you don't
>need to detail per the provisions - even if you
>pick the higher R

That is flatly wrong.


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