An SMA cable-based negative stiffness seismic isolator: Development, experimental characterization, and numerical modeling

Shape memory alloy (SMA)-based seismic isolation systems can successfully reduce the peak and residual displacements of bridges during strong earthquake, but they commonly lead to an increased force demands in substructure. This study explores the development of an SMA cable-based negative stiffness isolator to alleviate this problem. The proposed isolator is composed of superelastic SMA cables and a frictional sliding bearing with convex surfaces. The frictional sliding bearing limit the forces transferred to the superstructure and provides energy dissipation, while its built-in negative stiffness mechanism reduces the force demands in substructure. SMA cables provide critical restoring forces, additional energy dissipation, and displacement-limiting capacity. Based on the force balance, the negative stiffness and restoring requirements of the SMA cable-based negative stiffness isolator were analyzed first. Then, a prototype large-scale isolator was designed and fabricated. Next, the experimental testing of the developed isolator was performed under two different vertical load levels. Finally, finite element modeling of the proposed isolator was conducted, and the simulation results and experimental results were compared and discussed. The proposed isolator generates lower forces than the SMA-based zero and positive stiffness isolators and can exhibit stable energy dissipation capabilities with very good displacement-limiting and self-centering capabilities.