Eddy-current nonlinear energy sink for seismic response mitigation: Numerical and experimental study

The nonlinear energy sink is an effective device for reducing unwanted vibration in structures, but it requires a supplementary damping source for seismic protection of civil structures. In this study, an eddy-current nonlinear energy sink (ENES) is proposed, which employs a permanent magnet to provide a controllable damping force. The mechanical behavior of the ENES was derived, and an analytical model was established to investigate the effect of supplementary damping. A shaking table test was conducted to validate the effectiveness of the ENES in reducing seismic responses. The results show that a square shape of the magnet with an appropriate distance to the conductor plate is preferred to generate a uniform magnetic field. As the primary structure has a considerable damping ratio under seismic events, an appropriate damping coefficient is vital for the ENES in reducing seismic responses. In addition, the supplementary damping improves the effectiveness of the ENES even when the seismic input levels vary. Further, the ENES also shows robustness against the frequency change of the primary structure, reducing the peak acceleration by about 20 % during the test. Therefore, for seismic protection of steel and concrete structures with a damping ratio over 1.0 %, the ENES with supplementary damping is recommended.