A Simplified 2D Modelling Approach for Soil-Structure Interaction in the Dynamic Analysis of End-Shield Bridges

This thesis investigates the dynamic response of end-shield railway bridges subjected to high-speed train loading, with a particular focus on the role of soil– structure interaction (SSI). The objective is to assess the performance of a simplified 2D modelling approach that can reliably estimate bridge accelerations under resonance conditions, while significantly reducing computational effort compared to full 3D finite element models. Eighteen existing railway bridges with varying span numbers, geometries, and foundation types were analysed. A reference 2D model incorporating impedance functions, validated against experimental data, served as the benchmark. The proposed simplified 2D model introduces the effect of surrounding soil with concentrated springs and dashpots at the abutments and columns foundations, and distributed springs and dashpots at the end-shields. Sensitivity analyses were conducted to evaluate the effects of soil stiffness, damping, and boundary conditions on the response of the bridge. The results show that the simplified model generally produces slightly higher accelerations and lower natural frequencies, yielding conservative but acceptable predictions. While shallow foundations at the abutments show minimal influence on the bridge response, the contribution of pile foundation becomes significant, especially in single-span bridges. The flexibility of column foundations gives a substantial contribution to the dynamic response of the bridge. Moreover, the sensitivity analysis confirms that the stiffness and damping properties of the backfill soil at the end-shields influence the modal damping and may affect the acceleration response, especially for single span bridges. The findings confirm that the simplified approach offers a practical and conservative tool for early-stage design and evaluation of end-shield bridges under dynamic loading.