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Different Types of Moment Frames

Strong Frame Moment Frame

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 (Ωo), and Deflection Amplification Factor (Cd) per ASCE 7.

For Steel Moment Frames

Steel Moment Frames Specifications Diagram

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.

Moment Frame Comparison Chart

OMF

  • 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

IMF

  • 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

SMF

  • 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
  • Typically used in mid/high-seismic regions