Dynamic Soil-Structure Interaction Analysis of High-Speed Railway Bridges : Efficient modeling techniques and Experimental testing

Abstract: The work reported in this thesis presents a general overview of the resonant response of high-speed railway bridges considering soil-structure interaction. The study aims to identify the effect of the surrounding and underlying soil on the global stiffness and damping of the structural system. This may lead to better assumptions and more efficient numerical models for design. A simple and accurate analytical model for computing the dynamic characteristics of the fundamental bending mode of single span beam bridges on viscoelastic supports was proposed. This model was used to study the effect of the dynamic stiffness of the foundation on the modal parameters of railway beam bridges. It was shown that the variation in the underlying soil profiles leads to a different dynamic response of the system. This effect depends on the ratio between the flexural stiffness of the bridge and the dynamic stiffness of the foundation-soil system but also on the ratio between the resonant frequency of the soil layer and the fundamental frequency of the bridge. In addition, an approximate formula to estimate maximum resonant acceleration of beams under passage of high-speed trains has been proposed.The effect of the surrounding soil conditions on the vertical dynamic response of portal frame bridges was also investigated both numerically and experimentally. To this end, different numerical models have been developed. A simplified and accurate model for the surrounding soil was also proposed in order to define a less complicated approach appropriate for practical design purposes. Controlled vibration tests have been performed on six full-scale portal frame bridges to determine the modal properties of the bridge-soil system and calibrate the numerical models. Both experimental and numerical results identified the substantial contribution of the surrounding soil on the global damping of short-span portal frame bridges while the effect decreases as the ratio between the deck stiffness and the abutment/soil stiffness decreases.