Mechanical behavior of hybrid self-centering brace: Insights into the role of SMA cables

Shape Memory Alloy (SMA) cables have emerged as promising materials for self-centering devices owing to its remarkable self-centering ability and good energy dissipation capacity. However, the impact of SMA cables on the mechanical behavior of hybrid self-centering devices, particularly concerning pre-tension forces, has not been extensively explored through experimentation. In light of this, this study takes the recently proposed hybrid self-centering brace (HSB) as an example, which comprises Viscoelastic (VE) dampers and SMA cables in parallel, to further investigate its mechanical behavior through in-depth experimental tests. Firstly, the configuration and working mechanism of the HSB are elucidated, and the formulas for calculating its mechanical parameters are derived. Then, three HSB specimens are designed and manufactured, each possessing different parameters for SMA cables but identical parameters for VE dampers. Next, cyclic loading tests are carried out to examine the hysteretic responses of these three HSBs. The focus is on revealing the influence of different quantities and pre-tension forces of SMA cables on the mechanical behavior of HSB, as well as examining the loss of pre-tension force in SMA cables during the testing process. The research findings demonstrate that the working mechanism of HSB is experimentally validated, and that training contributes to achieving more stable mechanical behavior in HSB. HSB exhibits excellent recoverability, with the hysteretic curves overlapping substantially in two identical loading tests, with a maximum decrease of only 8.6 % in various mechanical properties. The greater the quantity and pre-tension force of SMA cables, the higher the initial stiffness and activation force of HSB, while the transition stiffness and residual deformation are smaller. Trained HSB specimens show a noticeable reduction in pre-tension of SMA cables in the first cycle of subsequent cyclic loading, averaging around 28 %, which shall be carefully considered in the future applications of HSB.