Development of Advanced Fiber Optic Sensors and Their Application to Health Monitoring of Civil Infrastructures

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Monitoring plays an important roll to keep various structures such as bridge, dam and tunnel in service condition and to prolong their life. Monitoring is also essential for safe construction with many uncertainties such as cut slope and underground excavation. In this study, an innovative monitoring system is assessed together with the development of strain and displacement transducer on the basis of fiber optic sensor. This newly proposed system is examined in laboratory and a construction site and it is found that this system can be applicable for various practical purposes. The followings are main conclusions obtained in this study.Fiber Optic Gauge (FOG) is developed as a strain gauge module based on Fiber Bragg Grating (FBG) sensor and the mechanical characteristics are clarified by the tensile and bending test together with the temperature sensitivity test. Clarification of the strain and temperature sensitivity extends the application of FOG to a wider range of temperature. Fib … More er Optic Displacement Device (FODD) is also developed on the basis of FBG sensor attached to vinyl chloride pipe. FBG sensors are installed in the several sections in the pipe with three sensors in each section. This installation of FBG sensors enables FODD to measure displacement and its direction. Interpolation of Spline and polynomial is applied to obtain continuous displacement. It is found that a good displacement measurement can be attained by a constant interval allocation of FBG sensors and application of Spline method particularly when displacement is not monotonous.It is also clarified the influence of the source voltage during the measurement and the local curvature of the data transmission optical fiber. Strain and displacement monitoring system is established on the basis of the various fundamental considerations. This proposed monitoring system is found to be applicable for a longer period of monitoring and for remote-controlled measurement as well. This monitoring system is expected to be applied for various structures for their safety control.However, the handling of fiber optics is very difficult compared to the ordinal resistive strain gauges, so that the proper packing method and the robustness to braking the primary optic fiber should be developed. Less