Based On Fiber Bragg Grating Sensors Bridge Deflection Detection And Monitoring

Because of the bridge deflection represents the structural rigidity under the loadings. The load, the environment and the structural material variation may result in the change in the deflection, which is one of the most direct and effective parameters for bridge health condition assessment. Therefore, the measurement and monitoring of bridge deflection play an importance role in bridge health monioting system.Due to the fact that the operational bridge is in an adverse circumstance, this thesis uses the optical Fiber Bragg Grating (FBG) sensors to measure the real time strains and temperatures. Two kinds of methods to obtain the bridge deflection curves based on FBG sensors are presented and the methods have been verified by numerical simulated beams and laboratory tested beams.1. In detail elaborates the basic principle and characteristic of FBG for strain and temperature measurements have been described in details. As the temperature compensation of FBG is a key problem in its real application. One kind of FBG temperature self-compensating device is conceived in the thesis.2. A method of averaged segement curvature fitting to obtain the bridge deflection curve is proposed. The thesis presents the theory, algorithm, implementation process and programming. The method has been been verified by the beam model tested in the laboratory.3. A method of divided span curvature least-spqare fitting to obtain the bridge deflection curve is proposed. The corresponging theory, algorithm, implementation and LabVIEW-based programming are presented.The method has been verified by numerical simulated beams and laboratory tested beams.4. Under operational conditions, there are a lot factors that may influence the deflection of pre-stressed concrete bridge. In other words, the long-term bridge deflection includes the deformation caused by the loads, concrete shrinkage and creep, temperature, pre-stress lost, and self volumetric deformation. The thesis also discusses how to consider and eliminate the deflections due to these factors from the total deflection so that the actual bridge deflection due to loading can be obtained. In addition, a new method to monitor concret creep deformation is proposed.