A Novel Approach to Bearing Damage Identification in Flexural–Torsional Coupled Box Girder Bridges Using Vehicle–Bridge Interaction

This paper investigates the flexural-torsional coupling vibration characteristics of thin-walled box girder under vehicle loading in conjunction with bearing damage. First, an analytical model is established based on Vlasov’s thin-walled beam theory and a simplified single-degree-of-freedom vehicle model. Employing the Galerkin weighted residual method and Laplace transform, the closed-form solutions for coupled vehicle-bridge vibrations are derived in the vertical, lateral, and torsional directions. To capture warping effects and boundary conditions, a three-dimensional finite element model of the thin-walled box girder incorporating damaged bearingsis introduced. Furthermore, a novel secondary displacement moment indicator is proposed for baseline-free identification of bearing damage, drawing upon vehicle–bridge interaction measurements at contact points. Numerical results demonstrate that loss of bearing stiffness in the vertical direction amplifies the dynamic responses at regions near the damaged supports and induces observable shifts in the bridge’s low-order frequencies. The secondary displacement moment index remains highly sensitive to bearing damage even under varying vehicle speeds and road roughness conditions, showing strong potential for practical monitoring of bridge bearing integrity.