High Performance Superelastic Materials for Seismic Applications

This study proposes a super-elastic memory alloy re-centering damper device and investigates its performance in improving the response of steel frame structures subjected to multi-level seismic hazard. The proposed super-elastic memory alloy re-centering damper (SMARD) count on high performance shape memory alloy (SMA) bars for re-centering capability and employs friction springs to augment its deformation capacity. First of all, this study explores the super-elastic response of NiTiHfPd SMAs under various conditions and illustrates their application into seismic applications. In order to collect experimental data, uniaxial tests are conducted on super-elastic NiTiHfPd SMAs in the temperature range of -55 ºC to +25 ºC, and at the loading frequencies of 0.05 Hz to 1 Hz with four different strain amplitudes. The effects of loading rate and temperature on super-elastic characteristics of NiTiHfPd SMAs are examined. Then, a four-story moment resisting frame with and without supplementary SMA damping elements is designed and modeled. Nonlinear response history analyses are conducted to assess the performance of NiTiHfPd SMAs in mitigating seismic response and limiting residual drifts of steel frames subjected to strong ground motions. The results indicate that the residual story drifts can significantly be reduced when the steel buildings are designed with SMA-bracing systems. It is also found that changing temperature between -35 °C and +25 °C does not affect the performance of NiTiHfPd SMA bracing systems. Additionally, an analytical model of six-story and nine-story steel special moment frame buildings with installed SMARDs in developed to determine the dynamic response of the building. Finally, nonlinear response time history analyses are conducted to assess the behavior of controlled and uncontrolled buildings under 44 ground motion records. Results show that SMARDs can enormously mitigate dynamic response of steel frame structures at different seismic hazard levels and at the same time enhance their post-earthquake functionality.