Brace-type metallic-friction hybrid dampers with fatigue-resistant metallic-damper subassemblies: Staged working mechanism and experimental evaluation

This study proposes a brace-type metallic-friction hybrid damper (HD) incorporating previously developed fatigue-resistant metallic-damper subassemblies. The HD integrates an H65 brass friction damper (FD) and a fatigue-resistant metallic damper (MD) into a brace-type assembly. The path-separation between FD sliding and MD gap activation enables the HD to realize a staged working mechanism. Cyclic loading tests of FD subassemblies were first conducted to investigate the effects of friction-pair hardness difference, Belleville washers and interface contact pressure on friction stability. Tests of HD specimens were then carried out to evaluate their staged hysteretic response, cyclic deformation capacity, and FD-MD contributions under the adopted quasi-static loading protocol. The results showed that the proposed FD developed stable hysteretic responses. Wear was mainly concentrated on the softer and replaceable brass friction pads. The proposed HD achieved the expected mechanism in which the FD provided energy dissipation throughout the loading history. The MD was activated at large displacements, thereby supplementing the peak resistance and secondary stiffness. The delayed gap activation and the retained LTZ-slip mechanism redistributed the cyclic deformation demand transmitted to the MD, allowing the integrated MD to remain functional while the HD underwent repeated large global displacement amplitudes. The contribution decomposition showed that, at the 1.5% drift ratio stage, the resistance contribution of the MD in each HD was approximately 44%–68%. At this stage, the FD accounted for more than 82% of the energy dissipation. At the 2.0% drift ratio stage, the MD resistance contribution increased to approximately 48%–76%. The FD remained operative after severe MD damage and fracture under the adopted test protocol.