STR-813: FRAGILITY OF LOW-RISE CONTROLLED ROCKING STEEL BRACED FRAMES WITH DIFFERENT BASE ROCKING JOINTS

Controlled rocking steel braced frames (CRSBFs) are resilient seismic force resisting systems that can self-centre the structure and prevent structural damage during design-level earthquakes. Energy dissipation may be provided to limit peak displacements, while post-tensioning provides self-centering after rocking. Previous studies have shown that designing energy dissipation and the post-tensioning components in CRSBFs using a response modification factor of R = 8 is sufficient to prevent collapse of structures during earthquakes higher than the design level. However, designers have unique control over the hysteretic behaviour of the system, even after the response modification factor is selected. Additionally, recent studies have suggested that CRSBFs can be designed using higher response modification factors without a significant reduction in performance. This paper examines how the design of the post-tensioning and energy dissipation components comprising the base rocking joint influences the collapse performance of a three-storey CRSBF using the results of ten incremental dynamic analyses (IDA). Ten different base rocking joints were designed for the frame using different response modification factors, energy dissipation parameters, and post-tensioning parameters. A suite of 44 ground motions was selected and scaled until collapse occurred in at least 50% of the cases, and collapse fragility curves were generated using the truncated IDA curves. The results show that the same CRSBF can have different collapse performances, depending on the parameters selected to design the base rocking joint. However, nine of the ten base rocking joints provided an acceptably low probability of collapse based on the implemented methodology