Wind-Induced Stay Cable Vibrations: Measurement and Mitigation

In February 1998, stay cable oscillations were observed on the Cochrane Bridge, Mobile, Alabama in winds accompanied by rain. Rowan Williams Davies & Irwin Inc. (RWDI) was retained by A.G Lichtenstein & Associates to assist them in identifying the causes of the cable oscillations, to assess the potential of future wind-induced cable vibrations, and to design a damping system to mitigate the oscillations. RWDI performed on-site oscillation decay measurements for some of the stay cables. Inherent damping values for the cables were calculated from the decay traces. Using these damping values and a criterion based on Scruton number (mass damping parameter), the potential for rain/wind type oscillations for the stay cables was assessed. In addition, the cables susceptibility to other forms of wind-induced vibrations was reviewed. The program of work provided an opportunity to check the validity of criteria for wind-induced oscillations against field observations.