Multi-EDP Performance Assessment of a Steel BRBF Under Ground Motion Sequences

The behaviour of Buckling-Restrained Braces (BRBs) is characterised by steady and nearly symmetrical hysteretic loops that provide large energy dissipation capacity. However, their low post-yielding stiffness may result in large residual deformations at the end of the earthquake motion. Moreover, the cumulative ductility demand due to repeated plastic excursions can lead to low-cycle fatigue failure. These two unfavourable conditions could be exacerbated by the occurrence of subsequent earthquakes (e.g., mainshock-aftershock sequences or multiple earthquakes during the design lifetime). Therefore, their assessment requires a framework that considers ground motion (GM) sequences. In this paper, a case study structure subjected to GM sequences is analysed, considering three Engineering Demand Parameters (EDPs) relevant to the performance evaluation of the BRBs and of the frame, namely the maximum ductility demand in the BRBs, the cumulative ductility demand in the BRBs, and the residual inter-storey-drift in the frame. These EDPs are assessed both independently and simultaneously, in order to establish the risk of overpassing any capacity limit that may lead to the collapse or demolition of the structure.