Distributed stiffness assessment of bridges based on macro-strain envelope curve under moving trainloads

Due to the limited gauge length of traditional strain gauges, the bridge strain influence line cannot be obtained from actual measurement, rendering the evaluation of the longitudinal stiffness distribution of bridges by monitoring results a difficult task. To address this issue, a distributed long-gauge strain sensing technology was used to evaluate the stiffness of high-speed railway bridges. Firstly, the distributed macro-strain influence line of bridges under train load was derived, followed by the clarification of the mechanical relationship between the longitudinal stiffness of railway bridges and the distributed macro-strain of the bridges. Then, a stiffness evaluation method was proposed based on the distributed macro-strain time history envelope curve. Secondly, the feasibility of the method was verified through finite element simulations. By establishing a refined dynamic macroscopic strain calculation model for railway bridges, the proposed method was explored for the accuracy and feasibility of bridge stiffness under different damage conditions. Finally, a real bridge verification test was conducted on a bridge on the Shanghai-Kunming Railway, and the test results showed how the thickness of the bottom plate would vary with the bridge span in the bridge design.