Development and experimental evaluation of a passive base isolation system using superelastic NiTi SMA springs

Superelastic (SE) response of shape memory alloys (SMAs) offers significant potential for base isolation (BI) systems by reducing superstructure deformations and improving structural safety. This study presents a novel isolation device integrating steel sliding bearings with SE NiTi spring attenuators, designed to provide self-centering capacity and energy dissipation through reversible phase transformations. The attenuator configuration was optimized using a custom-developed algorithm to balance isolation efficiency with displacement control. To evaluate performance, an array of SMA springs was incorporated into a three-story steel frame prototype with three degrees of freedom, tested experimentally on a shake table. For comparison, a conventional elastic spring was also employed, and both systems were subjected to recorded earthquake ground motions. Results for the SE isolation device (SEID) showed that substituting steel with SMA springs reduced structural stiffness by 69%. Calibration confirmed consistent behavior across spring pairs, with maximum deviations of 17.3% due to material nonlinearity. Adoption of shorter springs with fewer coils improved efficiency, reducing oscillating mass by 42%. Modal testing further demonstrated amplitude reductions of 80% under seismic excitations and 91% under forced vibration, validating the SEID as an effective solution for diverse dynamic loading conditions.