Effect of SMA prestressing and MRF damping ratio on the seismic collapse capacity of steel moment frames equipped with hybrid SMA-MRF damper

In this paper, the pre-stressing effect on shape memory alloy wires is investigated for a semi-active hybrid shape memory alloy-magnetorheological fluid (SMA-MRF) structural control systems. This novel supplemental damping system can be installed in structural frames, to enhance the seismic performance. Three steel frames of three, six, and nine stories adopted form the second phase of the SAC project are simulated. The vibration control system is analyzed under both non-pre-stressed and pre-stressed conditions corresponding to 5%, 10%, and 15% of activation load of the shape memory alloy. The considered structural systems have three levels of 10%, 20%, and 30% critical damping ratios originated from MR dampers. The frames are evaluated through IDA and fragility curves are constructed based on the collapse points. Subsequently, the collapse margin ratios (CMR) of the frames are calculated in compliance with FEMA P695. Results are compared, demonstrating that in all frames and at every level of damping, as the pre-stress level increases, the collapse margin ratio also increases, leading to an enhancement in the seismic performance of the system. By implementing 15% pre-stressing, the collapse margin ratio is increased by as much as 33%. An adjusting equation utilizing dimensionless parameters is ultimately obtained to estimate the CMR of frames retrofitted with hybrid dampers under various conditions, based on the CMR of frames with no dampers. In this paper, the pre-stressing effect on shape memory alloy wires is investigated for a semi-active hybrid shape memory alloy-magnetorheological fluid (SMA-MRF) structural control systems. This novel supplemental damping system can be installed in ... [2288 chars]