Multibody dynamics analysis of vehicle–track interactions for railway substructure condition monitoring

Vibration-based structural health monitoring of railway tracks mainly focuses on the track superstructure, leaving the track substructure less monitored and leading to a lack of assessment of overall track support conditions. Accurate measurement of track substructure stiffness is crucial for assessing railway infrastructure and improving predictive maintenance decisions. The study presents a railway track model incorporating a realistic substructure stiffness profile to examine vehicle–track dynamic interactions and analyze axle box acceleration responses under varying track conditions using the multibody simulation software Simpack ® . The critical rail foot stresses are studied at different vehicle speeds using validated existing track design-based data. The results highlight the responsiveness of modal characteristic frequencies to changes in substructure stiffness, positioning them as potential indicators for structural health monitoring of track components. Among the vibration modes, the first two are sensitive to subgrade stiffness variations; however, the second mode's susceptibility to subgrade shear distortions limits its reliability as a monitoring tool. In contrast, the third mode, primarily influenced by ballast stiffness, proved highly accurate in detecting track structure changes. The superposition of the first and third modes successfully replicated the track stiffness profile, offering a reliable method to predict stiffness variations due to ballast or subgrade defects. This stiffness mapping enabled the determination of critical rail foot stresses across different vehicle speeds. The study concludes that the superposition of modal frequencies corresponding to axle box acceleration data can be valuable for assessing rail stress and railway track support conditions.