Seismic demand models and performance evaluation of self-centering and conventional concentrically braced frames

Abstract

Self-centering concentrically braced frame (SC-CBF) systems have been developed to increase the drift capacity of braced frame systems prior to damage. The SC-CBF has a column base detail that permits column uplift at a specified level of overturning moment resulting from lateral forces, softening the lateral force-lateral drift behavior of the system. Restoring forces from vertically-oriented posttensioning bars provides self-centering and reduces residual drift in the SC-CBF. To demonstrate the effectiveness of SC-CBF systems, a comparative study of seismic performance of SC-CBF systems with that of conventional CBF systems is performed using seismic fragility and engineering demand (e.g., peak inter-story drift and residual inter-story drift) hazard curves. First, two prototype buildings are designed with the same configuration, with either CBF or SC-CBF frames as the lateral-load-resisting system. Then both structures are analyzed using nonlinear time history finite element modeling under earthquake records that have various seismic characteristics. The seismic responses are then utilized to build accurate probabilistic demand models for peak inter-story drift and residual inter-story drift. Finally, fragility curves for three performance levels (immediate occupancy, life safety, and collapse prevention) and engineering demand hazard curves are generated using the developed probabilistic demand models. The comparison of the fragilities and engineering demand hazard curves of the two structural systems reveals that the SC-CBF system exhibits better seismic performance than the conventional CBF system.