Seismic performance of a new S-shaped mild steel damper with varied yielding cross-sections

In this paper, a novel replaceable metallic energy dissipation device named S-shaped mild steel damper with varied yielding cross-sections (VYSSD) is proposed. The VYSSD mainly consists of consumption plate, outer limit plates and fixed bottom plate, in which the consumption plate is the energy dissipation element and can be easily replaced after earthquakes. Under action of external loads, section curvature of each segment of the consumption plate changes and the sections gradually enter yielding state to dissipate energy through flexural plasticity. A total of 18 VYSSD specimens were cyclically tested under quasi-static and fatigue loads to investigate the hysteretic behavior and seismic performance. The results show that the VYSSD has pump hysteretic loops, good low cycle fatigue performance and desirable displacement capacity. It is capable of avoiding plastic deformation concentration of traditional metallic dampers, and the failure mode is dominated by fatigue crack propagation. Moreover, a solid finite element model which can effectively simulate the hysteretic behavior and plasticity development of VYSSD was built, and the practical design formulas were suggested through parametric studies considering different geometric dimensions. Finally, a representative 20-story benchmark model was employed for seismic resilient application of the VYSSD. The structures with and without damper retrofitting were numerically modelled for conducting nonlinear dynamic analysis and seismic fragility analysis. The analyses illustrate that the VYSSD can significantly enhance the structural seismic performance, and exceedance probabilities of damage, demolition and collapse for the damper-fused structure are much lower than that of the original structure.