Experimental Study and Mathematical Modeling of an Enhanced SMA Friction Self-restoring Damper (eSMA-FSRD)

Source abstract

Self-restoring dampers are reliable devices for enhancing the seismic resilience of structures. However, dampers that employ shape memory alloy (SMA) wires or bars as their core elements face two distinct limitations; SMA wires are prone to end-anchorage fracture, while SMA bars exhibit an indistinct transformation plateau. To address these limitations, this paper proposes an enhanced SMA friction self-restoring damper (eSMA-FSRD). Its basic configuration and working mechanism are introduced, the kinematic mapping and force-equilibrium equations of the leveraged force-transmission mechanism are established, and seven specimens are designed and tested under quasi-static loading, with the initial inclination angle of the dowel bars (θ), the preload (F0), the lubrication condition of the friction surfaces, and the number of SMA bolts (nb) as the variable parameters. The results show that all specimens exhibit typical flag-shaped hysteresis loops with excellent self-restoring capability. As θ increased from 29.7° to 45°, the peak load-carrying capacity increased by 72.6%, whereas the displacement stroke decreased by 43.4%. Applying F0 widened the hysteresis loop and enhanced the energy-dissipation capacity, at the cost of a slight increase in residual displacement. Increasing nb led to a nearly linear growth in the load-carrying capacity, stiffness, and energy-dissipation capacity, while the hysteretic shape remained essentially unchanged. The enhancement mode of the damper underwent a continuous transition from the displacement-enhanced to the load-carrying capacity-enhanced mode as θ increased. Finally, analytical expressions for the continuous nonlinear tangent stiffness were derived, and a refined restoring force model was established; the predicted peak load-carrying capacity deviated from the test results by less than 3.5%, and the model accurately captured the continuous nonlinear evolution of stiffness throughout loading. An energy-dissipation prediction model was further developed, with a mean error of about 8.6% in predicting the cumulative energy dissipation of the seven specimens. The proposed analytical model provides a theoretical basis for the engineering design and numerical analysis of the eSMA-FSRD.