Modal evaluation of railway tracks by finite element techniques

Railway lines constitute a vital mode of transportation for any nation, and engineers are currently focusing on enhancing their effectiveness and efficiency, which poses a significant challenge. The railway track is one of the systems of numerous masses that allow each mass to take part in the free vibration response. It is crucial to determine the structural model’s attributes before performing the dynamic analysis. An investigation was conducted using free vibration analysis to determine the natural frequencies, periods, and mode shapes of the Ballasted and Ballastless Railway Track System. The present study employed entirely unified 3D solid elements developed in the finite element application ANSYS to emulate the modal behaviour of a standard Indian railway track model, both with and without ballast. Modal analysis considers several factors that affect the results, including the modulus of the various parts of the superstructure and substructure layers of the track. The quantity of natural modes obtained is determined by the upper frequency threshold established in the modal analysis. This range is selected to encompass all pertinent mode forms (longitudinal, vertical, torsional, etc.) and their associated natural frequencies that may experience resonance with predominant train excitation frequencies. The investigation aims to determine the natural frequency of the Ballasted and Ballastless Railway Track System corresponding to its mode shape under various conditions, including the presence or absence of ballast, different rail, sleeper, and subgrade types, and different damping ratios of the track system. The track’s slight frequency increase from 3.4428 Hz to 3.6506 Hz indicates enhanced torsional and vertical stiffness relative to longitudinal stiffness. Low frequencies suggest possible whole-track section resonance impacting ballast and subgrade integrity. Ballastless tracks provide elevated natural frequencies (up to 2% higher) owing to the rigid concrete slab, hence diminishing the likelihood of low-frequency resonance. A dense subgrade markedly elevates frequencies (e.g., from 6.4 Hz to 8.5 Hz in ballasted track, representing a 90% to 120% increase compared to loose sand), hence affirming subgrade stiffness as a crucial factor in track dynamic performance. This study’s findings offer valuable insights for railway and bridge engineers in identifying the most efficient design and maintenance strategies for ballasted and ballastless railway lines. This work can serve as a foundation for future dynamic and fatigue analyses of the railway track under dynamic vehicle loads.