Field Observation of Global and Local Dynamics of a Cable-Stayed Bridge

This work examines dynamic characteristics of a cable-stayed bridge, utilizing acceleration data from the bridge deck as well as the cables. A weather station installed on the bridge provides additional data for the interpretation of the observed wind and traffic induced vibrations. The measurement data are acquired on the Stavanger City Bridge. The bridge layout, combining steel and concrete girder segments supported by a tower and stay cables, makes it an interesting case for system identification analysis especially as all three parts of the bridge structured are monitored to some extent. Especially as cable vibration sensors are rarely included in long-term wind and structural health monitoring of the cable-stayed bridges. The data analysis investigates the characteristics of the suspended steel box and the supporting concrete girder, synchronization in response between the different structural components and the interaction between deck vibrations and cable vibrations. The paper explores the performance of system identification techniques for estimation of damping, which is challenging for damping levels as low as 0.05%, such as in the case of the stay cables. It is found that there is a strong interaction between the cables and the deck structure. Detailed identification of the cable properties showed a clear dependency between the total cable damping and the wind velocity, revealing the contribution of aerodynamic damping.