Behavior and Design of Self-Centering Energy Dissipative Devices Equipped with Superelastic SMA Ring Springs

This paper presents a novel type of self-centering energy dissipative device equipped with superelastic shape memory alloy (SMA) ring springs. The fundamental mechanical behavior and analytical solutions for individual SMA rings are first presented, which is followed by a detailed introduction of the working mechanism and fabrication process of the proposed device. Two prototype specimens, varying in the size of their SMA rings, are tested, where the stiffness, strength, self-centering capability, and energy dissipation characteristics are examined in detail. In particular, the behavior of the devices under repeated rounds of testing is evaluated to understand their resistance to strong aftershocks or multiple earthquakes. The specimens are shown to exhibit flag-shaped load-deformation hysteretic behavior with excellent self-centering capability and satisfactory energy dissipation with an equivalent viscous damping ratio of up to 20%. Due to a preload applied to the SMA ring springs, the devices have an initial yield resistance of around 90 kN and initial stiffness of approximately 225 kN/mm. No damage to any component of the devices is observed, although certain degradations of the yield resistance are exhibited. To effectively capture the key behavior of the devices, a design model is finally proposed that is shown to be in good agreement with the test results. Some limitations of the proposed model are also identified.