Effects of connection fractures on SMRF seismic drift demands

A central portion of an extensive investigation into the effects of beam-co lumn connection fractures on seismic interstory drift demands for steel mom ent-resisting frame (SMRF) structures is summarized. Nonlinear dynamic anal yses are carried out for six SAC Phase II buildings modeled with brittle co nnections and subjected to the SAC ground motions at two probability levels . Story drift demand statistics for the model structures with brittle conne ctions are compared with those for the model structures with ductile connec tions. An empirical analysis model for connection fracture is employed, wit h values for the parameters of the model calibrated by field and laboratory data. The sensitivities of story drift demands to variations in the fractu re parameters are explored. In particular, the case when only bottom beam-f lange-connections fracture is contrasted with the case of both top- and bot tom-flange fractures. Whereas the effects of single-flange (e.g., bottom-fl ange) fractures alone on story drift demands are perhaps less than anticipa ted, the additional effects of second-flange (e.g., top-flange) fractures c an be substantial. In either case, the effects of connection fractures are more pronounced at higher drift demand levels.