Bistable track nonlinear energy sinks with nonlinear viscous damping for impulsive and seismic control of frame structures

Engineering structures are susceptible to natural and man-made hazards, threatening structural normal functionality and safety. Considerable attention has been paid to the research and development of structural control techniques. Tuned mass dampers (TMDs) are control devices practically applied. However, they only exert the optimum control efficiency in the vicinity of the structural frequency. In contrast, nonlinear energy sinks (NESs) have recently proved robust against potential frequency changes in structures and external excitations, but their control effectiveness is dependent on input energy levels. To this end, a bistable track NES (BTNES) with nonlinear viscous damping is proposed in the present study. The track profile of BTNES is designed as a polynomial combining negative quadratic and positive quartic terms, which correspond to linearly negative stiffness and nonlinearly positive stiffness when an auxiliary mass moves on the curved track. The governing equations of a two-storey frame structure with BTNES subjected to impulsive loads are first derived. The track profiles and damping coefficients of BTNES are optimized for different viscous damping exponents. Then the control performances of BTNES are systematically investigated under various impulsive velocities, structural frequencies, and near-fault and far-field earthquake ground motions. The BTNES performances are also compared to those of a linear TMD and a traditional track NES with only a quartic profile. The results indicate that BTNES with a large viscous damping coefficient has superior control performances in terms of effectiveness, robustness, and damper stroke, which highlights that BTNES has promising applications in protecting structural safety against multiple dynamic hazards.