Seismic Assessment of Self-Centering Rocking Braced Systems with Story Energy Dissipation

Abstract

Self-centering rocking braced (SCRB) system provides enhanced seismic performance and reduced post-earthquake residual drift. However, the effect of higher modes is controversial, affecting shear demands and bending moments in the structure. This functional deficiency is addressed by developing SCRB frames equipped with buckling-restrained columns (BRCs) and buckling-restrained braces (BRBs), performing as exchangeable fuse frames. The system consists of external columns branching off from the main core and connected to it via butterfly-shaped fuses, and BRC and BRB are incorporated into the core at four different height levels to be compared with conventional SCRB as the baseline. Three sets of 12-, 16- and 20-story structures are numerically developed in OpenSees finite element framework with regard to geometrical and material nonlinearities, making a total of 12 SCRB prototypes. The suit of 22 ground motions used in FEMA P695 was scaled to DBE and MCE hazard levels and applied to the structures. Results indicate the capability of the new system in reducing the destructive effects of higher modes, especially in the case of a fuse frame located in the middle of the height. In addition, the core moment and shear force largely reduced, almost 60%, in higher positions of the fuse frame, while those configurations led to large residual drift at the restrained level. However, all structures met the DBE-level 2% drift target. Moreover, increasing structural height nearly reduced seismic demands and increased response reductions. Overall, the system demonstrated acceptable performance in terms of high capacity for energy absorption.