PSI - Issue 84

Giorgia Ghirelli et al. / Procedia Structural Integrity 84 (2026) 1047–1054

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indicating an upward shift in the monitored span due to the presence of the last carriage on the adjacent span. Prior to and after the train passage, not negligible displacements of varying magnitude are recorded that are probably associated to slight movements of the camera rather than actual bridge oscillation.

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(c) (d) Fig. 3. Vertical displacement time history: (a) frame-by-frame corner re-identification for all checkerboard corners; (b) averaged frame-by-frame corner re-identification; (c) averaged temporal tracking; (d) averaged hybrid tracking with periodic re-identification. The hybrid strategy is selected as the reference methodology for comparison with the FE model, as it provides the best balance between tracking robustness (typically ensured by re-identification) and computational efficiency (characteristic of tracking-based approaches). 5.2. Numerical FE analyses To support the vision-based measurements and provide a broader understanding of the structural response, a numerical finite element (FE) model of the bridge is developed. The model aims to reproduce the bridge dynamic behavior under train-induced excitation and to generate displacement time histories that can be directly compared with those obtained from video processing. The bridge is modeled using beam elements to represent the main structural components, including the parabolic arches, the transverse beams, the longitudinal girders, and the suspended deck slab. Support conditions are implemented according to the actual boundary configuration, combining fixed hinge bearings and movable hinge-sliding devices. The finite element model includes two adjacent spans to capture the interaction observed in the experimental results. The FE model is first used to compute the modal properties of the bridge, providing reference modal frequencies and the corresponding mode shapes. The comparison between the numerical and experimentally identified modal properties, not presented here for the sake of brevity, highlights the capability of the numerical model to reproduce the dynamic behaviour of the bridge.