Purpose <p>A laboratory-scale footbridge was developed as a reconfigurable test-bed for experimental investigations into structural dynamics. The system comprised two primary steel girders spliced near midspan, combined with composite deck panels fabricated using a sandwich plate system (SPS) consisting of two steel faceplates bonded by a polyurethane core. A clear understanding of its fundamental dynamic properties was essential to support subsequent research. </p> Methods <p>Accordingly, a preliminary finite element (FE) model was created, and experimental modal analysis was conducted to identify modal parameters both numerically and experimentally. The tests revealed vibration modes not reproduced by the initial FE model, demonstrating the need for model updating to achieve closer alignment with measured behaviour. To ensure appropriate parameter selection, component-level testing of the spliced beams and deck panels was performed. These analyses indicated that the effective stiffness of the primary beams required reduction due to the splice connection, while the deck stiffness needed to be increased to reflect the composite action of the sandwich configuration. This highlighted limitations in initial modelling assumptions regarding material representation and boundary conditions. </p> Results <p>Consequently, an optimisation-based FE model updating process was implemented, involving systematic adjustment of boundary restraints, material properties, and section parameters within a sensitivity-driven framework. The updated model achieved strong correlation with experimental results, with discrepancies in natural frequencies reduced to less than 8&#xa0;% and mode shapes exhibiting high agreement according to the modal assurance criterion (MAC).</p>