When it comes to steel moment frames, there are three types of frames defined in the code — ordinary moment frames (OMF), intermediate moment frames (IMF) and special moment frames (SMF). They are listed in the table below along with their Response Modification Coefficient (R-value), Overstrength Factor (Ωο), and Deflection Amplification Factor (Cd) per ASCE 7.
For Steel Moment Frames
Typically OMF are used in wind regions, where a stiff, non-yielding frame is desired. SMF are typically used in seismic regions where more ductility is needed. Graphics below illustrate the difference in ductility between the three moment frame types.
Expected to withstand limited inelastic deformations
Doesn’t require use of prequalified connections per AISC
Not required to be tested
Typically used in non/low-seismic regions
Expected to withstand moderate inelastic deformations
Require use of prequalified connections per AISC
Must sustain inter-story drift angle of at least 0.02 radians
Typically used in low/mid-seismic regions
Expected to withstand significant inelastic deformations
Require use of prequalified connections per AISC or verified with testing
Must sustain inter-story drift angle of at least 0.04 radians