Collapse-resistant capacity evaluation of buckling-restrained braced steel frames with ductile castings

The buckling-restrained braced steel frames with ductile castings are a novel ductile structural system, which replaces welded gusset plates and braces with bolt-connected ductile castings and fabricated buckling-restrained braces respectively. This system eliminates welding residual stress in connections, improves the plastic deformation capacity of brace and the low-cycle fatigue life of the structure, and enables rapid post-earthquake repair. To evaluate the collapse resistance performance of buckling-restrained braced steel frames with ductile castings (CBRBSF), this paper proposes a simplified numerical analysis method based on beam, shell and truss elements, and a 12-story model of CBRBSF with ideal yield mechanism is designed accordingly. The incremental dynamic analysis method is employed to investigate the seismic fragility of the structure under near-field and far-field ground motions. The seismic collapse margin ratio is quantitatively calculated and further compared with that of conventional BRBFs. The results indicate that the simplified numerical model presents high computational accuracy, which can accurately capture the mechanical responses of CBRBSF while reducing computational cost. Furthermore, the designed CBRBSF achieves an ideal yield and energy dissipation mode. Its collapse probability under near-field and far-field earthquakes is no more than 5%, and the corresponding ACMR satisfies the evaluation criteria specified in FEMA P695. In addition, the CBRBSF exhibits obviously superior ductility and collapse resistance margin to traditional BRBFs, with sufficient safety redundancy.