Effects of connection fractures on SMRF seismic drift demands

A central portion of an extensive investigation into the effects of beam-column connection fractures on seismic interstory drift demands for steel moment-resisting frame (SMRF) structures is summarized. Nonlinear dynamic analyses are carried out for six SAC Phase II buildings modeled with brittle connections and subjected to the SAC ground motions at two probability levels. Story drift demand statistics for the model structures with brittle connections are compared with those for the model structures with ductile connections. An empirical analysis model for connection fracture is employed, with values for the parameters of the model calibrated by field and laboratory data. The sensitivities of story drift demands to variations in the fracture parameters are explored. In particular, the case when only bottom beam-flange-connections fracture is contrasted with the case of both top- and bottom-flange fractures. Whereas the effects of single-flange (e.g., bottom-flange) fractures alone on story drift demands are perhaps less than anticipated, the additional effects of second-flange (e.g., top-flange) fractures can be substantial. In either case, the effects of connection fractures are more pronounced at higher drift demand levels.