Steel Moment Frames; "Special vs. Ordinary" 1

[SRO]

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

 

[DHKpeWI]

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.

 

[connectegr]

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

 

[rowingengineer]

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

 

[frv]

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

 

[rowingengineer]

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

 

[SRO]

Thanks Everyone.

 

[DHKpeWI]

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.