Track-Bridge Interaction – Sensitivity Studies on the bridge across Bryngeån and TBI Analysis on the bridge across Sege å

Sammanfattning

As Sweden expands and modernizes its railway network, the design of durable and cost- efficient railway bridges becomes increasingly important. A central technical challenge in this context is track-bridge interaction (TBI), the mechanical interplay between the rail and bridge structure. This interaction affects how forces from traffic loads, temperature variations and braking are transferred within the system. It plays a decisive role in determining rail stresses, substructure loads and whether rail expansion joints are needed. A deeper understanding of TBI is critical for ensuring structural performance, material efficiency and long-term functionality, particularly as design standards evolve. This thesis investigates track-bridge interaction (TBI) in railway systems. The study focuses on how bridge geometry, boundary conditions and updated design standards influence additional stresses in the rail and the distribution of forces between the rail and the bridge components. Using finite element modeling, two case studies were examined: the existing Bryngeå bridge and the planned Sege å bridge. For Bryngeån, a detailed sensitivity analyses were conducted by systematically varying parameters such as support stiffness, embankment length and spring behavior between rail and deck. For Sege å, a TBI analysis was performed without further parameter studies. The sensitivity analysis showed that the vertical linear stiffness model for the rail-to-deck connection can be used without significant loss of accuracy compared to more complex bilinear alternatives. They also revealed that reducing the horizontal stiffness of the supports decreases both rail stresses and reaction forces, which could lead to more material-efficient bridge designs. Additionally, embankment lengths of 300 meters were sufficient to capture the additional stresses in the system. The analysis of Sege å further showed that nearly half of the total longitudinal forces are carried by the rail and transferred into the embankments. This demonstrates a load-sharing behavior that may justify the use of simplified Eurocode methods, even for bridges exceeding 40 meters in span. Based on the calculated rail stresses, the bridge across Sege å is expected to meet the requirements for additional axial forces according to both the current, SS-EN 1991-2:2003, and upcoming, prEN 1991-2:2021, Eurocode. Consequently, the bridge should be able to be constructed without a rail expansion joint. A collaborative workshop with industry and academic experts provided additional insights on the practical application of Eurocode and the potential for model simplifications. Overall, this thesis contributes to the understanding of how design assumptions and evolving standards affect TBI assessments and offers recommendations for more efficient, yet reliable, railway bridge design.