Deflection estimation of a full scale prestressed concrete girder using long-gauge fiber optic sensors

This paper investigates an applicability of long-gauge fiber optic sensors to prestressed concrete structures. A main motivation is to monitor the deflection of railway bridges without intervenes of the signal intensity fluctuations. A 25 m long and 1.8 m deep bulb-tee prestressed concrete girder was compositely fabricated with a 2 m wide and 22 cm thick reinforced concrete deck. Two pairs of 3 m long-gauge sensors were attached to the prestressed concrete girder with parallel topology. Using the geometric relationship between curvature and vertical deflection in a simple beam and the quadratic regression of curvatures at the discrete point, it is possible to extrapolate the deflection curve of the girder. The estimated deflection measured by the developed method is compared with the results using conventional strain gauges and LVDTs. It has been demonstrated that long-gauge fiber optic sensors could provide the same accuracy with conventional sensors.