Health Monitoring Of Engineering Structures Using Fiber Bragg Grating Sensing Technology

Health monitoring of large engineering structures is helpful for knowing the behavior of the structures and can then take preventive measurements if some damages occur. Among all the high technologies of health monitoring, optic fiber sensing has its unique advantages. The Fiber Bragg Grating (FBG) sensing, has high sensitivity and stability, strong capacity against disturbance, representing the development direction of new light sensors. This paper uses the advantages of FBG sensing technology to solve two important and difficult problems: detection of seepage flow of high earth-rock dams and damages of composite structures, and the theoretical bases and key technologies for the development of FBG sensing technology in these two fields are provided. There are some creative results in this paper: Firstly,Scientific conception and theoretical, analytical methods of the FBG seepage sensing system for quantification and localization of seepage flow in high earth-rock dams is put forward. Using the FBG sensing system, the limitation of Distribute Temperature System (DTS) used in recent years can be broken free from the optimization of fiber sensor type carried out for the quantification and localization of seepage flow in high earth-rock dams. Finite element method analysis of seepage-temperature coupling fields is presented to solve the numerical analysis problem of the seepage flow in a high earth-rock dam. The distribution of temperature field, seepage field and the relationship between water velocity and FBG temperature are obtained. Secondly, the photo-electric multi-function seepage measurement system is presented. The electrical measurement subsystem and heating subsystem are studied to provide technologies for the seepage flow monitoring in high earth-rock dams and the dam foundations. The heating subsystem is made up mainly of PTC thermistors. It is safe and longstanding. The electrical measurement subsystem is made up of DS18B20 temperature sensors and microprocessor. Tests of a prototype of the system show very good characterization. Thirdly, a new kind method based on FBG sensing technology to measure the interface damages of steel-concrete composite slab of a bridge deck is presented. The FBG sensors suitable for measuring slippages and disengages are presented too. Model tests show that interface damages can be detected by using these FBG sensors and show the rule of damage development. So the mechanism of damages and development process can be discovered. During the composite structure model tests, FBG sensing system experiences three stages:dead loading test, fatigue test (up to 3×106 cycles) and destructive test. The FBG system works properly during the three stages. Abundant data are acquired which are helpful for the discovering of damage rule. Testing results are compared with those detected by strain gauges. The results show that FBG system is very reliable. Lastly, the FBG system management software is developed independently. FBG data can be saved, transfered, printed, processed, displayed using this software. In a word, the FBG sensing high-tech. is develop and combined with the traditional engineering fields. It is quite helpful to develop the technology of safety monitoring of engineering structures, and so has important scientific and practical significance.