Experimental Results for Seismic Resistant Steel Moment Frame Connections

Steel moment resisting frames were highly regarded for seismic resistant design. This opinion was based on early research and observations of their performance in past earthquakes. Its reputation was tarnished during the 1994 Northridge earthquake, because cracking was noted in many steel frame buildings. Widely divergent opinions have been expressed regarding the causes of this cracking. The present paper examines the results of past experiments to provide a rational evaluation of potential causes of the observed damage. More than 120 experiments are reviewed, and 91 are examined in detail. Comparisons across different test programs and statistical analyses are performed. The results show that flexural ductility of the beam is reduced by shear yielding in the panel zone and increased beam depth. Beam-flange thickness, column orientation, and beam span to depth ratio also influence the flexural ductility. Other factors including welding process, the size and type of weld, and the yield stress and tensile strength of the steel are briefly examined. The implications of these observations to engineering practice are summarized.