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RE: Choosing R, Seismic Provisions

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The applicable material standard referenced in the 2000 IBC (since you are referring to Seismic Design Category, I'm assuming you're using the IBC) should be consulted to determine the level of detailing required for the seismic-force-resisting system that is chosen for the Seismic Design Category. For example, if you had a concrete structure, ACI 318-99 Sect. 21.2 gives the information you are looking for. In regions of low seismic risk (SDC A and B), Sect. requires that the appropriate seismic detailing in Chapter 21 of the code be provided when intermediate or special systems are utilized. In regions of moderate seismic risk (SDC C), when special systems are used, the appropriate detailing of Chapter 21 must also be provided.

In order to take advantage of the larger R values, the appropriate level of seismic detailing must be provided.

Dave Fanella
Dumb question....

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?  

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 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 - which doesn't make sense to me... I just don't quite understand
the roadmap that ultimately leads to, "not only can you CHOOSE to require
the seismic provisions, but you MUST require them if you choose R>3."




David A. Fanella, Ph.D., S.E., P.E.
Director of Engineering
S.K. Ghosh Associates, Inc.
1856 Walters Avenue, Suite 200
Northbrook, IL 60062
Ph: 847.291.9864
Fax: 847.291.9865
E-mail: dfanella(--nospam--at)
Web Page: 

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