Revealing Bridge Modal Properties from Vehicle Measurements Using Contact-Point Response

Indirect (vehicle-based) bridge monitoring suffers from the difficulty of extracting structural information from vehicle responses. This study theoretically demonstrates that the contact-point response based on the vehicle scanning method (VSM) inherently excludes vehicle dynamics, enabling clearer extraction of bridge structural information from reconstructed signals. Within this theoretical framework, bridge frequencies can be identified directly, and spatial modal characteristics can be further obtained using a wave-based decomposition through the wavenumber Fourier transform and pass-band filtering. Numerical results demonstrate that the VSM remains applicable to truss bridge identification under different vehicle speeds and in the presence of pavement roughness. Although higher-order modes become progressively less distinct as the pavement effects increase, the fundamental mode remains consistently identifiable, indicating that dominant dynamic characteristics can still be extracted under realistic operating conditions. This contrast reflects an inherent limitation of vehicle-based measurements; at the same time, the shift from post-processing to formulation-level separation provides a more direct and physically consistent basis for modal identification.