Seismic performance of steel frames with a post-Northridge connection

Seismic performance of steel frames with "post-Northridge" bolted web, welded flange, beam-column connection with adequate ductility (BWWF-AD) and "pre-Northridge" bolted web, welded flange, beam-column connection (BWWF) is comprehensively evaluated using a nonlinear finite element method (FEM). The material and geometric nonlinearities, major sources of energy dissipation, and the flexibility of the connections are considered. The Richard Model is employed to analytically describe the moment-relative rotation (M-theta) curves of BWWF-AD connections using limited available data of full-scale, ATC-24 laboratory experiments. From the limited experimental data, an analytical method is developed to predict and to extrapolate the M-theta curves of BWWF-AD connection with any sizes of beams and columns. This method is used to extend the test results of an individual BWWF-AD connection to a frame with several or more BWWF-AD connections. The inelastic seismic response of two SAC Steel Project benchmark steel moment-resisting frames (SMRF) with BWWF and BWWF-AD connections modeled as partially restrained (PR) and as fully restrained (FR) are calculated and compared. Furthermore, the effects of BWWF and BWWF-AD connections on the frames' maximum top lateral and interstory displacement, maximum connection rotation, drift, and the frames' base shear forces are evaluated and compared. Moreover, the calculated drift and base shear forces of the frames are compared with the 2000 Edition of International Building Code (IBC 2000). This study suggests that the Richard Model captures the experimental M-theta curves of BWWF-AD connections accurately. BWWF-AD connections have significantly larger elastic stiffness than other types of PR connections. Their elastic stiffness is similar to that of bolted, double web angle with top and seat connection, but their ductility is much larger. In most cases, the presence of BWWF-AD connections improved the seismic performance of the steel frames. The proposed method analytically confirmed the beneficial effects of BWWF-AD connections observed in full-scale testing