Vibration mitigation of stay cables using electromagnetic inertial mass dampers: Full-scale experiment and analysis

Abstract

Previous numerical study has shown tremendous improvements in increasing the modal damping of bridge stay cables using inerter-based dampers. This article presents an experimental and numerical study on the vibration mitigation of a 135 m long full-scale cable using a novel inerter-based damper termed electromagnetic inertial mass damper (EIMD). The effect of the inerance and damping coefficient of the EIMD on the dynamic characteristics of the cable-EIMD system were systematically investigated using total 133 sets of free vibration data. A numerical model of the cable-EIMD system was established using finite difference method for implementing complex eigenvalue analysis. The relation between the first modal damping ratio and the EIMD parameters was observed in the experiment, which matches well with the prediction by the complex eigenvalue analysis. When installed at 2.5% of cable length away from the anchorage, the EIMD has achieved the maximum first modal damping ratio up to 3.66%, which is 192.8% larger than the theoretical upper limit (1.25%) of a viscous damper (VD). We also observed that the inerter element of the EIMD amplified the damper vibration amplitude and caused approximate π/2 phase lag of damper response. Such unique mechanism remarkably increases the energy dissipation of the EIMD. The inerter element significantly reduces the optimal damping coefficient required for cable vibration mitigation compared to that of the VD. The vibration mitigation performance of the EIMD for higher modes is also validated via harmonic vibration test using sine sweep excitations. The EIMD is capable of achieving superior vibration mitigation performance for bridge stay cables if both the inertance and damping coefficient were set as their optimal values.