Enhancing the seismic resilience of structures using a two-stage friction self-centering damper (TFSD)

This study investigates a two-stage friction self-centering damper (TFSD), comprising a friction damper (FD) and a self-centering friction damper (SCFD) connected in series. A predefined gap length for frictional sliding in the FD allows energy dissipation firstly, then the SCFD is activated when the deformation exceeding the gap to provide both energy dissipation and self-centering. Cyclic loading tests and numerical modeling were conducted on a specimen of TFSD. A prototype multi-story building structure was used to study the seismic responses influenced by TFSD design parameters, including the ratio of the first-stage sliding force to second-stage sliding force (α) and the gap ratio (γ), which is the ratio of lateral floor displacement corresponding to the gap length to the story height. The advantages of the TFSD braced frame (TFSDF) in controlling structural responses and resisting collapse were evaluated through comparison with the frame braced by buckling-restrained braces (BRBF) and SCFD braces (SCFDF). Experimental results indicate that the TFSD exhibits full hysteresis loops under low deformations, transitioning to flag-shaped loops after the inputs beyond the gap length. The numerical model of TFSD shows good agreement with the experimental results. The parametric analysis on the multi-story case shows that the structure achieves minimal peak inter-story drift ratio (θ_P) and peak floor acceleration (A_P) when α ranges from 0.3 to 0.7, and the residual inter-story drift is governed by γ. Compared to the SCFDF, the TFSDF shows lower peak responses under Design Based Earthquake (DBE) and Maximum Considered Earthquake (MCE) shaking levels, with θ_P and A_P reduced by up to 26 % under MCE shaking level. Moreover, the fragility analysis demonstrates that the TFSDF consistently outperforms both BRBF and SCFDF in collapse resistance across all damage states.