Rain-Wind-Induced In-Plane and Out-of-Plane Vibrations of Stay Cables

Abstract

A theoretical model of in-plane and out-of-plane rain-wind-induced vibrations (RWIVs) of stay cables is developed in this paper. The proposed scheme models the cable, akin to sectional models of a bridge deck, as a segmental rigid element with two degrees of freedom (DOF) (in plane and out of plane) and the rivulet as a single DOF oscillator. The interaction between the cable surface and the water rivulet is first analyzed by using a wetting theory, which suggests a combined application of linear and Coulomb damping forces between the rivulet and the cable. Based on the model, the response of the combined cable-rivulet system is numerically evaluated. The results show that the in-plane and out-of-plane DOF of the cable are coupled. For the equilibrium of the rivulet on the cable surface, the gravitational and aerodynamic forces on the rivulet have similar time-averaged values with opposite signs. The interaction between the cable surface and the rivulet leads to energy dissipation, which helps to stabilize the rivulet. Like galloping, RWIV appears to be triggered by a sudden drop in the mean aerodynamic force coefficient. However, it is not a divergent type of vibration because the rivulet oscillates on the cable surface and its equilibrium position changes with wind velocity. Finally, the turbulence effect on the RWIVs is investigated. As the longitudinal turbulence intensity approaches 15%, the RWIV abates concomitantly.