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Steel Moment Frames; "Special vs. Ordinary"

Steel Moment Frames; "Special vs. Ordinary"

Steel Moment Frames; "Special vs. Ordinary"

(OP)
Does anyone know what exactally is the difference between Steel "Special" Moment Frame, & Steel "Ordinary" Moment Frames.  I know there are various stipulations to qualify one as special, but what are they, and where can I find them?

Thanks

RE: Steel Moment Frames; "Special vs. Ordinary"

Look on the AISC web site for a free copy of the seismic provisions.

http://www.aisc.org/WorkArea/showcontent.aspx?id=17638

The basic difference is in the detailing.  A SMF allows you to use a larger "R".  R is in the denominator of the seismic base shear calculation.  Thus the bigger the R the smaller the seismic shear.  The trade off is that a SMF has more stringent detailing requirements.

RE: Steel Moment Frames; "Special vs. Ordinary"

There is a significant change in the moment connection details as a result of the higher R (response modification).  R > 3 will require the SMF connections.  There are several prequalified connection details.  The connections develop 110% of the beam moment capacity and require significant reinforcement.  Except in high seismic areas R = 3 is typically more economical.   

http://www.FerrellEngineering.com

RE: Steel Moment Frames; "Special vs. Ordinary"

Not knowing the extract terminology, I thought a special moment frame was a strong column weak beam frame.

An expert is a man who has made all the mistakes which can be made in a very narrow field

RE: Steel Moment Frames; "Special vs. Ordinary"

rowing..  that's always the goal, regardless of classification..

RE: Steel Moment Frames; "Special vs. Ordinary"

I would have thought that a gravity "normal" frame wouldn't have to meet this requirement. Especially if in a low seismic area, but that just goes to show how little I know about the American way.    

An expert is a man who has made all the mistakes which can be made in a very narrow field

RE: Steel Moment Frames; "Special vs. Ordinary"

(OP)
Thanks Everyone.

RE: Steel Moment Frames; "Special vs. Ordinary"

I agree with Connectegr.  If you are able, use an R of 3 and design connections as you normally would.  See the ASCE 7 and AISC manual (pages 2-4 ff) for limitations.  Sometimes you are required to use the more stringent seismic detailing requirements, I believe in Seismic Design Catagories (SDC) D, E , or F.

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