FE modelling and updating of unique fink truss footbridge

Recent improvement of mechanical characteristics of structural materials and fast development of the finite element (FE) based computational structural analysis are resulting in innovative solutions in footbridge design. When doing research into dynamic analysis of these structures, their dynamic properties are required and are usually obtained from an FE model. However, because of structural complexity, the FE modelling of footbridges is often prone to errors due to modelling uncertainty. The best and quite often the only way to evaluate the reliability of the FE modelling is to involve modal testing and FE model updating of footbridge structure with the aim to match test results. Using this approach, a complex and rather unique Fink truss structure of Royal Victoria Dock Bridge in London was analysed. Eleven measured modes of vibration were identified via an ambient vibration survey and then compared with their counterparts from an initial FE model developed by best engineering judgment. In this initial FE model the maximum difference between two paired natural frequencies was 29%. In a subsequent updating exercise it was found that uncertainties in main beam and crosshead geometry, as well as the inherent simplicity of the fully symmetric FE model, were the main source of the modelling error.