End-Shield Bridges for High-Speed Railway Full scale dynamic testing and numerical simulations

Sammanfattning: The increasing need for High-Speed Railway (HSR) to improve the infrastructure of the transport network and reduce the travelling time requires increasing research within this field. Bridges are main components of any railway network, including HSR networks, and the optimization of their design for this purpose would contribute to a faster and more cost effective development of the HSR network. The initial investment, and even the running and maintenance costs, of the bridges can be decreased by reaching a better and deeper understanding of the their dynamic behaviour under HSR operation. This can be achieved by developing more reliable analysis techniques that can predict the dynamic response of the bridges with high accuracy.This licentiate thesis aims to study the dynamic behaviour of end-shield railway bridges under the operation of high-speed trains. 2D beam analysis is used to study the effect of the distribution of the train’s axle load. Relatively accurate 3D FE-models are developed to study the effect of Soil-Structure Interaction (SSI) and predict the dynamic response of the bridges. A range of modelling alternatives are studied to develop the most accurate model. The project includes a full scale test of a simply supported Bridge with end-shields using load-controlled forced excitation. The results from the test is used to update and verify the theoretical models.A manual model updating process of the material properties of the 3D FE-model is performed using the frequency response functions (FRF) from the field measurements. A Simple 2D model is also developed, where a spring/dashpot system is implemented to simplify the Soil-Structure interaction, and updated to try to reproduce the field measured responses.The conclusions driven from the project emphasize the importance of including the effects of Soil-Structure Interaction in the dynamic analysis of end-shield bridges for an enhanced prediction of their dynamic behaviour regarding natural frequencies, mode shapes, damping, amplitudes of vibration of the bridge.The conclusions also show that the modelling of the surrounding soil and the careful assumption of the soil material parameters have significant effect on the dynamic response of the bridge. Even the boundary conditions, bedrock level and the ballast on the railway track have considerable effects on the response. The results of the full-scale testing along with the FE model show that the bridge’s concrete section behaves as uncracked section under the studied dynamic loading.