Application Research Of Fiber Bragg Grating Sensing Technology For Bridge Health Monitoring

The research on the application of fiber Bragg grating (FBG) sensors for bridgehealth monitoring is a recent research focus, owing to their excellent sensing capacity.Although FBG is a new sensing technology, the relative research was developed longbefore. Compared with the traditional electromagnetism technology, the FBG sensingtechnology has some disadvantages in the applications. This dissertation attempts tostudy the fresh problems brought from the new sensing technology, carry out theresearch on a novel FBG low-frequency-measurement accelerometer and design andestablish Bridge Health Monitoring (BHM) system based on FBG technology. As asummary, the research work in this dissertation contains the following:Firstly, some practical problems related to the temperature compensation whenusing FBG to monitor the strain, the lifetime prediction of FBG, multiplexing modesand design of BHM were analyzed.Secondly, different levels of tests were carried out. A series of tests wereconducted to compare the performance of the FBG strain sensors with the resistancestrain chips in terms of electromagnetic immunity, zero drift and repeatability. Theresults verified the attractive performances of the FBG strain sensors with respect tostabilization, reliability and veracity. After that, several kinds of FBG sensors wereused for the measurement of a concrete column. The results showed that the FBGsensors had its favorable workability and feasibility. Finally, a FBG sensing systemwas installed on the real Bridges. The success of these applicable researches on thelarge scale projects verified that the FBG sensing technologies have great potentialfor bridge health monitoring.Thirdly, a special low-frequency-measurement structure is developed to amplifythe vibration response and broaden the working frequency range. A L-shapedstructure is adopted to ward off the chirped phenomenon. Moreover, some dampingliquid is infused into the sensor to increase the working frequency range, and anoptimal design is obtained. A series of shaking table tests were then conducted toevaluate the sensitivity, linearity, transverse anti-jamming ability and amplitude-frequency characteristic of the prototype FBG accelerometer with differentdamping. The result shows that the design concept is feasible, and the sensitivity is upto 90pm/ms^-2 and the maximum working frequency is about 80% of the undampednatural frequency. Compared with the traditional accelerometer, the prototype FBGaccelerometer shows excellent workability.Fourthly, the static and dynamic performance tests of the strain FBG enhancedsensors were conducted. The results verified that the strain FBG enhanced sensorshave excellent performance.Finally, a BHM system was designed. The FBG monitoring system composed ofthe FBG thermometers, the strain FBG enhanced sensors and the above mentionedaccelerometers. The experiments were conducted using a structure model under theintact and damage states. The results showed that the designed monitoring system hadreasonable feasibility.