Fiber Bragg grating-based long-gauge fiber optic sensor for monitoring of a 60 m full-scale prestressed concrete girder during lifting and loading

Fiber Bragg grating (FBG) sensors have many advantages in that they can be multiplexed and miniaturized, they can produce absolute measurements, and they are unaffected by electromagnetic interference. For these reasons, their application to civil engineering structures has been actively studied. In this study, FBG-based long-gauge fiber optic sensors (LGFOSs) were used to monitor a prestressed concrete (PSC) girder bridge. LGFOSs, which can measure the average strain over long lengths, were fastened to a PSC girder during the construction and loading processes. The test structure was a full-scale PSC girder with a 60 m-span, and its behavior was monitored during construction processes, such as lifting and transporting the girder, after prestressing. Then, a four-point bending test assuming service loading conditions was conducted, and the strains were measured during the test. By comparing to results measured from conventional electrical resistance strain gauges, the results measured from the LGFOSs were investigated. The LGFOSs effectively measured the strain histories during the lifting and transporting processes. From the loading test, the LGFOSs could also measure the strains effectively after cracking, unlike conventional sensors. Moreover, using the measured data before and after cracking, the deflection of the girder was estimated and subsequently compared to the results of a linear variable differential transformer (LVDT).