Influence of the gravity framing system on the collapse performance of special steel moment frames

• Collapse performance of moment frames improves when the gravity system is included in the analysis.
• The influence of partially restrained connections is most significant in shorter buildings.
• The influence of gravity column continuity is most significant in taller buildings.
• The improvement in performance reduces when splices are placed in gravity columns.

This paper investigates the influence of the gravity framing system on the seismic performance of special steel moment frames (SMFs). The buildings used in this study were taken from one of the examples that form part of the ATC-76-1 project, which used the FEMA P-695 methodology to assess the collapse probability of SMF systems. Two, four and eight story SMFs were analyzed with and without the gravity frame to quantify their collapse performance. Aspects of the gravity frame that were investigated include the contribution of stiffness and strength of beam to column connections, and the location of splices in the gravity columns. Moreover, this research investigates the potential for the development of inelastic deformations in the gravity columns, and the effect of such deformations on structural response. The results show that gravity connections and gravity column continuity profoundly affect the computed response and collapse probability. The inelastic behavior in gravity columns has a less important effect but should be included in the analysis.