Seismic Performance of Dual Systems with BRBs under Mainshock-Aftershock Sequences

Buckling-restrained braces (BRBs) are employed in new constructions and in the retrofitting of existing frames. They provide additional strength and stiffness to buildings, together with high and stable energy dissipation capacity. BRBs can fail due to excessive maximum and/or cumulative ductility demands. In addition, the use of BRBs can result in large residual drifts in the structure due to their low post-elastic hardening. Moreover, in seismic-prone regions, structures are usually subjected to mainshock-aftershocks (MS-AS) earthquake sequences, often leaving no time for repair or retrofit between events. Ductility demand accumulation and/or residual drifts induced by the MS can affect the structural performance during the following AS. The present study addressed the abovementioned issues by first investigating an optimal design procedure for steel dual systems in which conventional BRB frames are combined with moment-resisting frames. The latter are designed to behave elastically to enhance the self-centering capability of the structure and limit soft-story mechanisms. The design procedure is first presented and applied to a case-study building. The seismic performance of the latter is assessed by means of sequential Cloud Analysis. Both real and artificial MS-AS sequences are used to derive system fragility curves. Results show that the BRBs capacity can be potentially affected by multiple earthquakes, which cause accumulation of plastic strains within the devices. However, the preliminary results show that when accounting for real MS-AS sequences, ASs do not significantly increase the cumulative ductility demands in BRBs.The support of Prof. Katsuichiro Goda that provided real MS-AS sequences, as well as the fruitful discussions on the detailed BRBs OpenSees modeling with Prof. Alessandro Zona and Prof. Quan Gu are gratefully acknowledged