Seismic fragility and loss estimation of self-centering steel braced frames under mainshock-aftershock sequences

This paper highlights the importance of considering local component failure of self-centering braces (SCBs) when examining the seismic fragility and economic performance of emerging self-centering steel braced frames, with a particular focus on the influence of mainshockaftershock (MS-AS) sequences. The design and modelling of the prototype buildings are first presented, where the failure mechanism and simulation technique for single-core and dual-core SCBs are explained. Seismic fragility analysis and economic loss evaluation are subsequently conducted, where the damage state, component fragility, and repair cost of the considered braces are comprehensively discussed. The study confirms that MS-AS sequences have a pronounced influence on various performances of the structures. Under the maximum considered earthquake (MCE), the probabilities of collapse for structures with single-core and dual-core SCBs (structures S-SCF and D-SCF) increase from 18% to 28% and from 10% to 16%, respectively, when aftershock is additionally considered. MS-AS sequences have a small influence on the peak absolute floor acceleration of both structures. When aftershock is additionally considered, the probabilities of exceedance of the 0.5% residual inter-story drift threshold increase from 25% to 31% and from 16% to 19%, respectively, for structures S-SCF and D-SCF; the 50% percentile loss ratio of the two structures increases from 0.09 to 0.16 and from 0.08 to 0.11, respectively; and the expected losses over a 50-year period of the two structures are increased by 25.7% and 22.9%, respectively. Apart from the non-negligible influence of MS-AS sequences, the importance of appropriate modelling of tendon fracture is also highlighted.