Understanding of bridge cable vibrations and the associate flow-field through the full-scale monitoring of vibrations and Wind

This dissertation investigates the conditions that promote rain-wind-induced vibrations of inclined cable on cable-stayed bridges. Rain-wind-induced vibrations are known as the most common type of cable vibrations and capable of severe vibrations. The recent increase in the number of cable stayed bridges continuously becoming longer and lighter have resulted in a high number of observations of cable vibrations. A theoretical background for the tool used in this work is presented in terms of cables vibrations mechanisms, aerodynamic damping and system identification techniques. A detailed literature review of reported observations of rain-wind-induced cable vibrations of fullscale bridges is shown. The database of observed events on bridges collects information about the conditions that likely develop the phenomenon, together with the means used to suppress or reduce the occurrence of cable vibrations.
The research starts from data collection of cables vibrations of the Øresund Bridge. A dedicated monitoring system was installed to record full-scale data together with wind field measurements and meteorological data, during cables vibrations.
Results from the monitoring system are reported such as cable vibrations amplitude, cables frequencies involved in the vibrations, wind directions, wind speeds and rainfall rates. Those indications are used to select full-scale cables vibrations for further analyses. In particular, aerodynamic damping is investigated by means of system identification procedures based on the Markov-Block-Hankel matrix.
From identified aerodynamic damping from full-scale data, back-calculated aerodynamic coefficients of Øresund Bridge cable were obtained.
Wind tunnel tests were performed on a scaled model of the actual cables both in dynamic and static tests to investigate aerodynamic coefficients, in parallel to their identification by means of back-calculation from full-scale data. Finally, conclusions on the role played by aerodynamic damping for the rain-wind-induced vibrations are given, combining the understanding from the state of the art and the results from full-scale monitoring events.
Special thanks to Rune Brincker to grant permission to use the material of his newly published book about system identification to form the chapter of this thesis. A special thanks also to Anela Bajeric for granting the permission to use her material about system identification review for the needs of this thesis.