High-mode vortex-induced vibration of stay cables: monitoring, cause investigation, and mitigation

Herein is described a case study using long-term field monitoring data from a cable-stayed bridge to investigate the cause of high-mode vortex-induced vibration (VIV) observed in stay cables. Wind characteristics and dynamic responses of girders and stay cables were analyzed to investigate two possible vibration sources-interactions with girders and vortex shedding. To this end, a modal decomposition procedure that included automated peak picking and successive band-pass filtration was proposed. These novel steps revealed a relationship between the shedding frequencies of stay cables and corresponding critical wind velocities. The main cause of large amplitude VIVs was diagnosed using a novel damping identification procedure that consisted of automated modal decomposition, temporal correlation, and optimization-based curve fitting techniques. The damping identification results demonstrated how the modal VIV amplitudes of stay cables have a strong dependency on damping capacity. The effectiveness of Stockbridge dampers in mitigating high-mode cable VIVs was subsequently examined through field application and comparison analysis during a typhoon. The unique interaction between stay cable vibrations and the buffeting response of bridge girders observed during this period was additionally discussed.