Self-centering and damping capabilities of a tension-compression device equipped with superelastic NiTi wires

The hysteretic damping capacity and high recoverable strains characterizing the superelastic response of shape memory alloys (SMA) make these materials attractive for protection systems of structures subjected to dynamic loads. A successful implementation however is conditioned by functional fatigue exhibited by the SMA when subjected to cyclic loading. The residual deformation upon cycling and the efficiency in material usage are the two most restrictive issues in this sense. In this paper, a device equipped with superelastic NiTi SMA wires and capable of supporting external tension compression loads with optimized properties is presented. It is shown how the introduction of the wires' pre-straining allows for the absorption of deleterious residual deformation without affecting the self-centering capabilities upon unloading, in contrast with what occurs for pre-strained tendons. These features were experimentally verified in an in-scale prototype composed of two 1.2 mm diameter superelastic NiTi SMA wires. In order to numerically assess the dynamic response of a simple structure subjected to seismic excitations, a multilinear superelasticity model for the NiTi wires was developed. (paper)