Aerodynamic damping properties of two transmission towers estimated by combining several identification methods

Based on full-scale measurement data, we report on several aerodynamic damping properties of two transmission towers under conditions of strong winds. In estimating the damping ratio from data that contain many components of close frequencies of tower and conductor vibrations, we cannot estimate the damping ratio of each component if we use an estimation method available for only a single-degree-of-freedom system. Therefore, we combined several identification methods and are introducing a new method of estimating damping properties. This method is applicable to the response record of a multi-degree-of-freedom system such as the coupled structure of a transmission tower-and-conductors. Using the new estimation procedure, we were able to extract the component of every vibration mode of the towers from a measured time history and estimate the accurate damping ratios individually; and, our results revealed that the wind speed dependency of the aerodynamic damping property of the coupled tower-and-conductors system had wide differing characteristics depending on the vibration mode. Moreover, using a three-dimensional nonlinear analysis, we discuss, in detail, the effects of the progressive deformation of a transmission–conductor–plane due to an increase in wind speed on the development of the aerodynamic damping of the coupled tower-and-conductors system.