Full-scale shaking table test and numerical analysis of structural frames with SMA cable-restrained base isolation

Abstract

Restrainer is a promising solution for deformation control of isolated systems. The present study comprehensively discusses the behavior, design and potential application of a novel superelastic shape memory alloy (SMA) cable-restrained laminated natural rubber (SMA-LNR) bearing. The study commences with a brief introduction of the working principle, and then a quasi-static test on an individual bearing specimen is presented. A full-scale shaking table test is subsequently presented, followed by a comprehensive parametric study, leading to preliminary design recommendations. The quasi-static test shows a two-stage behavior exhibited by the individual SMA-LNR bearing, that is, linear flexible behavior at small displacements and restraining stage beyond initial gap. Under dynamic excitations, the SMA cables swayed smoothly with the shear deformation of the bearings, and experienced fracture beyond the maximum considered earthquake (MCE). The restraining effect is strengthened with increasing number of SMA cables, but this is accompanied by an increase in the acceleration response of the superstructure. An earlier engagement of the SMA cables, that is, smaller initial gap, leads to decreases in the bearing deformation. The acceleration responses of the superstructure and the maximum cable strain are not very sensitive to the initial gap. Using an overly small number of SMA cables has limited beneficial effect on bearing deformation control, and may even increase the deformation under certain excitations; therefore, a lower-bound restraining force offered by SMA cables should be given to ensure an unconditional positive bearing deformation control. Two normalized design parameters and their recommended values are finally proposed to facilitate practical design.