Strain-temperature-displacement Monitoring Of High Speed Smeamless Switch Track By Fiber Bragg Grating

In the 350km/h high speed railway, China, on a continuous beam bridge, Leida bridge, a switch and its CRTS II slabs were the first time installed on it in the world. The influence of climate, geology and the dynamic impact by passing high speed trains cause high stress in the track, slab, and bridge, specially the variation of environment temperature makes the continuous beam of the bridge expansion or contraction. Therefore, In order to keep switch track working in a safe condition, temperature, strain, and the quantitative value of both creeping displacement must be monitored.Because the tracks are also used as a loop circuit of electric power for driving the trains, and under the open-air meteorological conditions, it is difficult to use the traditional electrical sensors. The operation principle of fiber Bragg grating (FBG) is to control the properties of light propagating in the fiber, different from the electrical sensors. FBG sensing technology is of high accuracy, good stability, moisture-proof and anti-electro-magnetic interference. This has led FBG becoming a strong competitor to measure the stain, temperature and displacement in constructions.This thesis presents a research project of the monitoring technology of FBG sensors on the high-speed switch track. The structure of FBG strain, temperature and displacement sensors, on-site installation and protection measures, analysis and treatment of the monitoring results, and the relevant conclusions are discussed in this thesis.The main research content and conclusion are as follow:1. The stress distribution of 60kg/m heavy track is analyzed by the FEA (Finite Element Analysis) method to identify the best position of rail strain monitoring. Considering the condition of application, a FBG gauge with strain especial shape is used. FEA method is also used to analyze the structure of the FBG gauge.2. The FBG strain gauge and naked FBG were respectively fixed on the track surface to test the strain sensing sensitivity. The tension and compression stress experiment of rail is done. The results show that the FBG strain gauge responded more than lpm reflective wavelength shift when a micro-strain loaded, better than the naked FBG, which responded only 1 pm reflective wavelength shift. And temperature compensation method of FBG strain sensor is illustrated.3. FBG temperature sensors and two different ranges of FBG displacement sensors are introduced, including the method of sensibilization of temperature sensor, and the operation principle, structure and installation of both displacement sensors.4. Gives the detail of calibration experiments of FBG strain, temperature, and displacement sensors, assembling process, on-site installation, and protection method of them.5. The monitoring results in over one year were analyzed. The monitoring results are accurate and reliable, and help to enhance the managing level of high-speed railway operation.