Optical frequency domain reflectometry sensing for damage detection in long-span bridges using influence surface

With the development of optical frequency-domain reflectometry (OFDR)-based distributed strain sensing technology and static influence line (IL) measurement concept, the special influence surface (IS) measurement, a function of sensing and force locations, has become technically feasible. This study investigated, for the first time, damage detection in long-span bridges using the special IS constructed on the basis of the OFDR-based distributed sensing. The damage detection performance of IS was validated through numerical and experimental case studies on a scaled physical Tsing Ma bridge (TMB) model. First, the special IS concept was elaborated. The scaled TMB model was then introduced as a representative long-span bridge. Subsequently, the IS characteristics of different bridge components of the scaled TMB were analyzed using the finite element model (FEM). Various IS-based indices, including strain IS (SIS) and displacement IS (DIS), were applied to hypothetical damage scenarios where the bottom and top chords were subjected to severe damage in the FEM. The extracted ISs successfully realized damage localization with relatively great sensitivities. For comparison, the modal parameters were also output for damage detection. In the experimental section, an OFDR-based distributed sensor was placed along the top chord of one middle grid in the scaled TMB model to construct the SIS. The SIS changes could accurately localize the single, double, and triple bottom-chord damages. The numerical and experimental results demonstrated the feasibility and effectiveness of the OFDR-constructed special SIS for damage detection, indicating that IS is a promising damage indicator for long-span bridges, promoting the development of distributed sensing techniques in structural health monitoring for real-bridge applications.