Suppression of multi-mode non-planar rain-wind-induced vibrations of stay cables: Scruton number threshold and optimal damper design

Suppressing cable vibrations should address energy dissipation by dampers and energy input from the air. In this study, a methodology framework is proposed to efficiently suppress wind-induced cable vibrations with dampers. In this framework, the Scruton number (Sc) threshold is clarified by identifying amplitude-dependent aerodynamic damping in on-site environments; on this basis, the damper is optimized by solving eigenfrequencies of the cable-damper system with a multi-objective genetic algorithm. This framework is applied to deal with the multi-mode non-planar rain-wind-induced vibrations (RWIV) of an ultra-long stay cable on the Sutong Bridge. Firstly, two typical RWIV events observed during one-year field monitoring are reported through the evolution analysis of decomposed modal responses. Then, a scheme of bi-directional viscous dampers combined with a high-damping rubber (HDR) damper, as optimized in location and size, is implemented to mitigate the vibrations. The results suggest a tentative threshold of Sc > 12.5 for both in-plane and out-of-plane modes within the frequency range of 1.9–3.6 Hz to prevent the RWIVs of the cable. The effectiveness of the optimized dampers in mitigating the RWIVs is demonstrated through on-site monitoring.