SEISMIC RESPONSE OF COMPOSITE MOMENT-RESISTING CONNECTIONS - I - PERFORMANCE

The 1994 Northridge, California, earthquake precipitated numerous unex pected fractures in welded steel moment-resisting frame connections, m ainly in the regions of the bottom girder flanges. This two-part paper reports on research to determine if structural phenomena, primarily t he effect of composite concrete floor slabs, contributed substantially to these failures. The results of cyclic experiments of one bare stee l and two composite full-scale specimens representing typical pre-Nort hridge, interior moment-resisting connections are described, along wit h corroborating analyses. The structural performance of the test speci mens is highlighted in this paper. The connections failed either britt lely at the welded interface of the bottom girder flange and the colum n flange, or with a low cycle fatigue failure emanating from the root of the bottom girder flange access hole. None of the connections achie ved adequate levels of cyclic ductility, and the composite connections did not achieve their calculated strengths when subjected to positive bending moment. In the companion paper, the behavior of the connectio ns and the structural phenomena that contributed to the failures are d ocumented.