Abstract: This paper proposes novel self-centering (SC) seismic base isolators by utilizing shape memory alloy U-shaped dampers
(SMA-UDs) with favorable superelastic behavior. Two different designs, which incorporate the SMA-UDs into a conventional laminated
rubber bearing with a lead core or that with steel-UDs, are investigated. In both designs, four groups of superelastic SMA-UDs are arranged symmetrically around the rubber bearings. In the SC seismic base isolators, the laminated rubber bearings withstand the high vertical loads from superstructures, and the lead cores or the steel-UDs provide the majority of energy dissipation through hysteresis behavior under cyclic loading. Moreover, the superelastic SMA-UDs spontaneously offer excellent SC force, which can effectively minimize residual deformations and reduce downtime after earthquakes. This study first illustrates the working mechanism and performance of the SMA-UDs in the base isolators through a series of component tests under loadings with different directions (i.e., in-plane and out-of-plane directions), protocols, and frequencies. Subsequently, the principles and performances of the SC base isolators are examined systematically through the quasistatic cyclic loading tests of the conventional and proposed base isolators. Test results demonstrate that these SC base isolators can exhibit satisfactory SC capability and stable energy dissipation. Moreover, the hysteresis characteristics of the SC base isolators are nearly isotropic, thereby enabling the SC base isolators to resist seismic actions in any horizontal direction. In comparison with conventional seismic base isolators, the proposed SC base isolators will provide a promising type of high-performance seismic-resilient devices required by modern civil infrastructure.