A numerical investigation of track-bridge interaction in railway bridges

Öztürk, Alper
In railway tracks, additional stresses occur in rails due to interaction between the rail and the bridge superstructure, which is a phenomenon known as track-bridge interaction (TBI). The additional rail stresses (ARSs) develop mainly as a result of temperature effect, vertical bending of bridge superstructure, braking/acceleration of trains traveling over the bridge. One of the major parameters affecting the TBI response is the behavior of interface elements simulating the coupling between the bridge superstructure and the rail. In TBI analysis this coupling is defined by the so-called longitudinal resistance-displacement curves (RDCs). The first part of the study focuses on the longitudinal aspect of TBI through numerical investigation. The numerical modeling approach was verified with available analytical solutions and data obtained from bridge monitoring. The primary interest was to illustrate how sensitive the TBI response is to changes in RDCs. The parametric study was extended to investigate the effect of expansion length and substructure stiffness. Analysis results reveal that for simply supported precast concrete girder bridges, using RDCs developed from ballastless railway track measurements can be an economical alternative to specified provisions. Substructure stiffness was determined to have a crucial effect on the ARSs especially under acceleration/braking loads. The second part of the study comprehensively investigates longitudinal TBI in railway bridges under seismic ground motion. The investigation focused on two prestressed concrete girder bridges located in a seismically active area of Türkiye. The study focused on the influence of various parameters on TBI, including service earthquake intensity measure, soil property, distance to fault, and deck expansion joint locations. A detailed numerical modeling approach utilized Nonlinear Time History Analysis (NTHA) to capture dynamic responses under recorded seismic ground motions. Results reveal that earthquake magnitude and distance to fault significantly affect ARSs. Expansion joints at pier locations impacted rail stress distribution, reducing maximum tensile stresses and increasing compressive stresses. Furthermore, using fixed boundary conditions at pier bases provides comparable results to soil spring modeling for the investigated bridges. Comparison of analysis results for utilization of unloaded and loaded RDCs highlights the importance of considering train-induced loads in seismic assessments. Finally, the same numerical approach was further utilized to explore the effect of scaling of the ground motion, distances to epicenter and rupture on TBI response, based on recent earthquakes happened in Kahramanmaraş, Türkiye. Five different ground motion sets were selected based on their intensity including Pazarcık (Mw=7.7) and Elbistan (Mw=7.6) earthquakes. Five stations were utilized for each event to assess how earthquake intensity measures can reveal limitations in TBI response in design. As seismic intensity increases, the analysis highlights the importance of displacements over ARSs in design limitations. Design recommendations were developed based on evaluation of this study.
Citation Formats
A. Öztürk, “A numerical investigation of track-bridge interaction in railway bridges,” Ph.D. - Doctoral Program, Middle East Technical University, 2024.