Collapse behavior of steel special moment resisting frame connections

There is a common perception that seismic detailing can improve the collapse resistance of steel frame buildings. However, the effect on connection performance of the potentially large catenary, i.e., tensile, forces that can develop during collapse has not yet been adequately studied. The objective of this paper is to use computational structural simulation to investigate a number of key design variables that influence formation of catenary action in steel special moment resisting frame subassemblages. The numerical model used in the study employs a calibrated micromechanical fracture model and is validated using existing test data. The simulation results demonstrate the ductility of seismically designed special moment frame connections and their ability to deform in catenary mode. It is shown that connection ductility and strength are adversely influenced by an increase in beam depth and an increase in the yield to ultimate strength ratio and that the beam web-to-column detail plays an influential role in connection response. A number of conclusions with practical implications are drawn from the numerical results.