A differential strain-based approach for identifying prestress and moving forces in prestressed concrete bridges

Abstract Restressing force in prestressed concrete bridges (PCBs) is reduced due to ageing, and operational and environmental loading, and it can significantly impact on their load-carrying capacity. Existing dynamic methods are insensitive to the prestress force, and the identification accuracy is significantly affected by operational environments. This paper is to develop a novel differential strain-based time-domain inverse method for prestress force identification of PCBs under moving vehicles. Both prestress and moving forces are identified simultaneously from dual strain measurements on the bridge. A Vandermonde matrix-based convolution formula is constructed to ensure the accuracy of the least squares solution for ill-posed inverse problems. The proposed method is validated using numerical studies on a two-span continuously supported prestressed concrete T-beam and verified experimentally on a simply supported box girder bridge model. Field monitoring data, together with a calibrated finite element model of a three-span continuously supported PCB, is used to further verify the performance of the proposed method. To ensure accurate formulation of the prestressed bridge–vehicle system matrix for effective force identification, modal updating with Rayleigh damping is employed in the calibration process. The results demonstrate that the proposed method can simultaneously and accurately identify both prestress and moving forces, enabling reliable real-time structural condition assessment of the bridge.