Mechanical behaviors and seismic performance of a novel rotary amplification friction damper (RAFD): Experimental and analytical studies

Friction dampers are widely used energy dissipators for the seismic fortification of engineering structures, due to their efficiency, reliability, and cost-effectiveness. Since the friction force is proportional to the normal load applied on the sliding interfaces for given friction materials, increasing the applied normal load is always the only approach to enhance the energy dissipation capacity of friction dampers. However, a large applied normal load may result in serious wear problems at the interfaces, which in turn affects the functionality of the damper. To address the above issue, a novel rotary amplification friction damper (RAFD) is proposed in the present study, which can realize several times amplified friction force for a given normal load due to the adopted amplification system. The conceptual design and working mechanism of the proposed RAFD are first introduced. Subsequently, a damper prototype was manufactured and experimental studies were carried out to examine the behaviors of RAFD. Then, a nonlinear mechanical model considering the gap between the gear and rack is developed based on the experimental results. Finally, an analytical model of a single-degree-of-freedom (SDOF) system equipped with RAFD is established to investigate the control performance of RAFD in reducing the structural seismic responses and evaluate the influences of various parameters including gap and earthquake types (far-field and near-field ground motions). The analytical and experimental results demonstrate that the proposed RAFD showcases superior seismic control effectiveness compared to the traditional friction damper; the presence of a gap would reduce the control effectiveness of RAFD to some extent, while earthquake types have minimal impact.