Risk-based mainshock-aftershock performance assessment of SMA braced steel frames

Abstract

This study presents a methodology to generate probabilistic seismic demand models and hazard curves for steel frames with or without shape memory alloy (SMA) bracing systems under mainshock – aftershock sequences. First, three post-mainshock damage states were defined based on both peak inter-story drift and residual drift ratios. Incremental dynamic analyses (IDA) were performed considering only mainshock events to determine spectral acceleration demands corresponding to each mainshock damage level. Then, aftershock IDA were conducted on the post-mainshock SMRF and SMA frames at three damage states. To estimate the peak and residual drift response of SMRF and SMA braced frames subjected to a mainshock – aftershock sequence, empirical seismic demand models were developed. Next, a risk-based seismic performance evaluation study was conducted to generate seismic demand hazard curves for maximum and residual interstory displacement response. Results reveal the advantages of SMA braces in enhancing post-event functionality of steel frame buildings. In addition, defining damage states based on residual drifts is recommended while comparing the aftershock performance of conventional steel moment resisting frames with self-centering steel buildings.