Identification of wave forces on a floating bridge from acceleration and wave elevation data using inverse methods and wave field reconstruction

Knowledge of the ambient loads are important for assessing the dynamic behavior of long-span bridges. However, the assumptions in the adopted load models used in the dynamic analysis leads to uncertainties in e.g. reliability assessments. To reduce the uncertainties, full-scale studies of the loads on existing structures can be performed. Recently developed methods for inverse identification can estimate the unknown forces on a structure using a limited set of dynamic response measurements and a numerical model of the structure. In this contribution, a pilot study of full-scale force identification is performed in a practical case study of the Bergsøysund bridge, a pontoon bridge with a floating span of 840 m. A state of the art filtering technique for input estimation is applied to identify the wave forces on the bridge using measured acceleration data. This article also presents a method for frequency-domain reconstruction of the wave forces, based on a parametric wave field model from measured wave elevation data. The obtained force estimates from the two approaches shows a reasonable agreement. The practical use of the identification techniques are reviewed from the viewpoint of this case study and sources of uncertainties are discussed