A power spectral approach to the analysis of the dynamic response of cable stayed bridges to spatially varying excitation

The response of cable stayed bridges to spatially varying loads is introduced by considering their response to seismic excitation. After reviewing different methods of representing the ground motion and calculating the response, a power spectral method was chosen as this enabled efficient calculation of the response whilst allowing the random nature of the loading to be taken into account. This approach is developed in detail and validated by comparison with a Monte Carlo simulation of the response of a simple footbridge to asynchronous seismic excitation. This comparison showed clearly the effects of asynchronous excitation and also that it is essential to take into account the random nature of the loading. Finally, the method was used in a study of the response of a cable stayed bridge to asynchronous seismic excitation, the results of which showed that the ground wave velocity influenced both the size and location of the maximum response. By using an evolutionary spectral approach account was also taken of the non stationary nature of seismic excitation which was found to have a significant effect on the bridge response. To validate the approach further, testing had to be carried out on either a real or model structure. The analysis technique considers the dynamic response to spatially varying random loads, properties which are shared by wind and traffic excitation. The thesis describes a project which was set up to monitor the dynamic response of Kessock Bridge in Scotland to wind excitation over a period of several months. The instrumentation and monitoring strategy are described in full together with comparisons between finite element modelling and a modal survey of the bridge. A large amount of data was collected during the monitoring period and only limited processing is presented in this thesis. Although this has not been sufficient to validate the theoretical approach, it does demonstrate the possible influence of spatial variations in the wind on the dynamic response of the bridge.