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

Metallic dampers are among the most effective supplemental energy dissipation devices used to retrofit seismically vulnerable structures. Such devices could be even more beneficial if they are equipped with self-centering elements, reducing the residual displacements of the retrofitted structures. This paper introduces an innovative group of self-centering metallic dampers, namely, SMA-based multi-ring (SBMR) devices, and evaluates their effective design and performance through extensive numerical and experimental studies.

The SBMR devices combine superelastic (SE) rings with supplemental energy dissipation (ED) rings (placed inside each other) to achieve suitable levels of self-centering and damping at both small and large deformations. The SE and ED rings are made of SE Nitinol and other metals with high damping capacities, respectively. Here, only double- and triple-ring devices with one ED ring made of either mild steel or shape memory (SM) Nitinol are examined, while in both cases, the ED ring is enclosed/confined by the SE ring(s). The SBMR devices could be loaded in multiple directions without any risk of buckling, thereby being easily implementable in structures via both diagonal and cross-bracing systems.

The proposed variations of SBMR devices are first simulated via 3D finite element models and their effective designs are examined through a parametric study. Then, double- and triple-ring devices with both mild steel and SM Nitinol ED rings are designed, fabricated, and tested under various bidirectional loading scenarios, including quasi-static and dynamic loading. The primary response parameters considered to assess the devices’ performances are effective damping ratio, self-centering efficiency, and maximum strains.