Evaluation of Aerodynamic Damping in Multimodal Rain-Wind-Induced and Vortex-Induced Stay Cable Vibrations

Stay cables of cable-stayed bridges can be susceptible to multiple types of vibrations due to wind excitation. Among those, vortex-induced vibration and rain-wind-induced vibration have been observed the most frequently. These two types of vibrations share a number of major characteristics, including that both are of the limit cycle kind and that each occurs over restricted reduced velocity ranges, although the reduced velocity ranges over which these two types of vibrations occur are different. Another common characteristic of these two types of vibrations is that they could have contributions from multiple modes of the cable, including modes in either the same or orthogonal planes, due to the excitation from sheared wind in the atmospheric boundary layer. This paper presents a study to identify the aerodynamic damping in such multimodal vortex-induced and rain-wind-induced full-scale stay-cable vibrations using the unscented Kalman Filter. The dependence of the aerodynamic damping on the representative reduced velocity is evaluated. A particular focus is placed on the coupled aerodynamic damping resulting from vibration in the participating modes.