Damage Identification of Multi-Girder Steel-Concrete Composite Girder Bridges with Distributed Long-Gauge FBG Sensors Under Moving Load

In-service, multi-girder Steel-Concrete-Composite-Girder (SCCG) bridges may experience damage. The long-gauge Fiber-Bragg-Grating (FBG) sensor can measure macro-strain which is sensitive to damage and can be installed and distributed continuously which is impossible for traditional point-gauge strain sensors. However, it lacks application of these sensors for both model and actual SCCG bridges, especially for multi-girder SCCG bridge which has significant spatial characteristics and possible transverse load redistribution due to damages. In this study, the distributed long-gauge FBG sensors were applied to the damage identification for a multi-girder SCCG bridge. First, based on the concept of the Envelope of Macro-strain Influence Line (EMSIL), a damage indicator, RE, was proposed for the damage identification of the SCCG. To validate, experimental and numerical studies were conducted. It shows RE is sensitive to damages induced by the change of the sectional stiffness and the neutral axis position. Then, the redistribution of the bending moment due to damages was investigated for an SCCG bridge with three girders. It shows the usual damages in steel girder, transverse joint and crossbeam have little influence on the bending moment redistribution. Finally, the damage identification was conducted for individual damage in the steel girder and composite damages in both the steel girder and transverse joint (or crossbeam) of the three-girder SCCG bridge. Based on the EMSIL obtained from the quasi-static components of the macro-strain time-history under moving vehicle load using variational mode decomposition (VMD), the identification effect was satisfied using the introduced RE, which proves that RE can be utilized to identify the change of the sectional stiffness and the neutral axis position for multi-girder SCCG bridges.