SMA-Based Multi-Ring Self-Centering Damping Devices for Seismic Retrofit of Structures

One of the effective methods to retrofit seismically vulnerable building structures is the use of supplemental energy dissipation devices. Such devices may decrease the seismic displacement and acceleration demands of the retrofitted structures, thereby mitigating damage to both structural and non-structural components. Due to the unique mechanical properties of superelastic (SE) Nitinol, such as high strength, significant elasticity, substantial energy absorption, and excellent fatigue resistance, various forms/shapes of SE Nitinol have been used to develop self-centering damping devices. SE Nitinol rings are particularly effective because they offer large ductility, can resist compression without buckling, allow multi-directional loading, and are cost-effective. Recently, an innovative class of self-centering damping devices incorporating SE Nitinol rings, termed SMA-based multi-ring (SBMR) devices, has been developed and numerically evaluated by the authors . Each SBMR damping device consist of at least one SE Nitinol ring and at least one supplemental energy dissipating (ED) ring. The rings are concentrically and tightly positioned inside one another such that they deform together. The ED rings are made of metals with high hysteretic damping capacity, such as mild steel or shape memory (SM) Nitinol. Under diametric deformation, both the SE and ED rings absorb energy, whereas the SE ring(s) are primarily intended to provide self-centering. Due to their shape, the SBMR devices may be installed in building frames through a variety of approaches, among which cross bracing is particularly efficient. This presentation evaluates the performance of SBMR devices through an extensive experimental study. This presentation discusses an extensive experimental study on four SBMR damping devices with different ring configurations. The initial test results for two single SM and SE Nitinol rings along with a double-ring device demonstrated the stability of the hysteretic responses of the proposed devices and their effectiveness in providing a balanced combination of damping and self-centering capabilities.