Bridge Influence Line Extraction and Damage Identification Based on Dynamic Displacement Response

The displacement influence line (DIL) is an important index to evaluate the health of bridges. In practical engineering applications, due to the unknown nature of vehicle loads, it is usually difficult to directly extract and apply damage identification from the dynamic response of bridges. In order to solve this problem, this paper proposes a calculation framework combining multi-segment basis function approximation and adaptive piecewise iterative fitting, which is used to accurately extract the displacement influence line from the dynamic response of the bridge and realize damage identification. Specifically, the DIL is approximated by multi-segment basis functions, and the adaptive segmentation strategy is used for iterative calculation, so as to extract high-precision DIL with quasi-static characteristics. Furthermore, two damage identification indexes, displacement influence line deviation (DDIL) and displacement influence line deviation curvature (DCDIL), are constructed in this paper. The results of numerical examples show that the root mean square error (RMSE) of DIL extracted by this method is 0.0102 compared with the theoretical value, which verifies the accuracy of the extraction algorithm. In terms of damage identification, the damage location deviation of DDIL and DCDIL is controlled within 0.1m, and when the damage degree increases from 20 % to 30 %, the peak amplitude of DCDIL increases by at least 100 %, reflecting its significant sensitivity to the degree of damage. The research verifies the effectiveness and accuracy of the proposed method in extracting influence lines and damage identification in simply supported beam bridges with equal cross-section and continuous beam bridges with variable cross-section.