Study and Application about Differential Fiber Bragg Grating Force-Testing Ring

Cable force testing techniques which based on fiber Bragg grating (FBG), namely, FRP smart tendon, FBG vibration sensor and FBG force-testing ring, etc, have been widely used in bridge cable long-term safety monitoring. Except for FRP smart tendon, the other two FBG-based cable force sensors have already possessed some mature engineering application examples. In view of the installation manner of force-testing ring which should be installed between anchor slab and anchor nut, the testing accuracy of FBG force-testing ring which doesn´t need to carry out spectral analysis is higher than the FBG vibration sensor. Due to the simple design thought that along the axial stress direction of elastic body to layout FBG, existing FBG force-testing rings usually need additional FBG to achieve sensor temperature compensation. However, differential FBG force-testing ring can eliminate the temperature influence in testing. The good linear relationship between sensor wavelength and load verified the rationality of differential structural design. The practicability and accuracy in actual engineering of differential FBG force-testing ring were revealed by a certain bridge cable force comparison testing results.