Moment Frame Classification

I’m doing a seismic analysis, and running through Chapter 12 of the ASCE 7 05.
In the definition of a moment frame, they classify “Ordinary, Intermediate, and Special moment frames”, with significant impacts on the seismic load. There is little clarification on the differences between them.

Could anyone shed any insight on this issue.


Probably the best description of requirements is contained in AISC 341 (Seismic Provisions). Each frame type has a series of requirements such as width/thickness ratios that must be maintained. Obviously, the higher the allowed R factor, the tighter all of the rules are. IMF and SMF frames also require specific connection design or tested connections.
The document is available for free download from AISC on their website:

Above is a snippet.