July 16, 2015

Ordinary Moment Frame (OMF) Considerations in RISAConnection

Design for seismic connection detailing is done in RISAConnection per the AISC Seismic Design Manual, 2nd Edition (2010) which contains two documents: the AISC 341‐10 Seismic Provisions for Structural Steel Buildings and the AISC 358‐10 Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications.

The AISC 358-10 is specifically for the design of seismic IMF & SMF connections. However, you are allowed to define your connection as an Ordinary Moment Frame (OMF) using any of the AISC 358-10 pre-qualified connection types. In this case, many of the checks will be for reference only as they are not specifically required by the design code.

Seismic OMF 1

OMF Required Strength

Because they are not specifically covered by the AISC 358-10, the strength requirements of an OMF come from chapter E1 of the AISC 341-10.

Moment Strength

Per AISC 341-10 section E1.6b, the flexural strength of an OMF shall be the lesser of:

  • 1*Ry*Mp (LRFD) / (1.1/1.5)*Ry*Mp (ASD)
  • R*Mu (For minimally ductile moment frames, the required moment need not exceed R*Mu based on discussion in the AISC 341 commentary)

Shear Strength

Per AISC 341-10 section E1.6b, the required shear strength of an OMF is computed using the AISC 360-10 (14th edition) load combinations.

When a model is imported from RISA-3D, these values are brought over from the RISA-3D seismic detailing calculations. When a model is created using the stand-alone version of RISAConnection, the user is expected to enter these values.

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