Long-stroke shape memory alloy restrainers for seismic protection of bridges

Abstract

To prevent unseating failures and pounding problems in simply supported bridges, steel restrainers that can limit relative displacements of adjacent spans have commonly been used. This study proposes a shape memory alloy (SMA)-based restrainer that can serve as both energy dissipater and restrainer under cyclic tension and compression loading. The proposed device named as, long-stroke SMA restrainer (LSR), consists of a superelastic SMA bar, a steel tube, and a filler material. The SMA bar provides re-centering force and dissipates energy, while steel tube and the infill material prevent buckling of SMA bar under compression. Taking advantages of large strain capacity of SMAs, the LSRs are designed to accommodate large displacement demands for bridge restrainers. The mechanical response of NiTi SMA bars with a diameter of 12 mm was first studied through uniaxial tension and compression testing. Buckling and post-buckling response of the SMA bars were also characterized. Then, a high-fidelity finite element (FE) model was developed and validated to represent the behavior of SMA bars. Next, the buckling mechanism of proposed LSR was studied through FE simulations and a design methodology for the LSR was developed to prevent buckling. Results shows that the LSR can exhibit stable energy dissipation capabilities with excellent self-centering ability both under tension and compression loading and can serve as an effective restrainer in simply supported bridge structures.