Dynamic Soil-structure Interaction of Portal Frame Bridge Walls for High-speed Railways

Abstract: In Sweden, high-speed railways is a subject for public debate. The first stage of a high-speed train network, Ostlänken between Stockholm and Linköping, is under investigation, and is planned to be trafficked in 2028. The high-speed railway is intended to hold traffic with speeds up to 320 km/h. At such speeds, the design requirements of the accelerations of the bridge superstructure become more stringent. Previous studies show that the interaction between the bridge and the backfill soil can reduce these accelerations. In this thesis, dynamic soil-structure interaction (SSI) of portal frame bridge walls has been studied. The SSI was represented by complex impedance functions that were calculated and analyzed for different parameters of a bridge-embankment interface. The impedance, representing dynamic stiffness and damping, were in this thesis calculated in the frequency domain with finite element (FE) software, by performing steady state analyses on 3D solid bridge-embankment models. To discretize the infinite extent of an embankment, the standard viscous boundary method was used, implemented by inserting infinite continuum elements at the boundary in the FE-software ABAQUS. The method showed successful with mitigating waves at the boundary. A parameter study was conducted, where the influence of geometries and material properties were shown through a comparison of impedance functions. Both embankments on a fixed boundary, representing bedrock, and embankments on circular ground soil plates of various thickness and stiffness, were compared. SSI showed to induce large amounts of dynamic stiffness and damping to a bridge structure. A stiffer embankment, as well as a stiffer ground soil, has shown large influence on the dynamic stiffness and is believed to reduce vibrations in a bridge deck. The study suggested that proper material modeling is important for both the soil and the concrete, to receive accuracy in the impedance functions. The work also indicates that a properly designed bridge wall geometry could be an important step towards developing the design of future high-speed railway bridges.