Research On Intelligent Bridge Structure Health Monitoring

With the increase of large-span bridges domestic and abroad, the demands for the lightweight bridge structures, the complexity of systems, safety and durability of bridges, are gradually raised. For these reasons, intelligent bridges will become the ideal bridge structures in future. The first step of "intelligent bridge", namely bridge structure health monitoring systems, has become the foremost research area concentrated on by researchers in the fields of engineering and academia. This dissertation introduces the theory of intelligent material structure, presents the concept of intelligent bridge structure, and studies bridge structure health monitoring system and bridge structure fiber bragg grating (FBG) technique, as well as the method of bridge structure monitoring evaluation. At last we apply these techniques to the cable-stayed bridge health monitoring in Wuhu Yangtse River Bridge successfully.The theory of intelligent material structure is introduced firstly, and the concept of intelligent bridge structure is presented. Based on the detailed explication of intelligent bridge structure composing and designing rules, we discuss information processing, intelligent types and design methods. We also point out that optical fiber sensor is the optimum sensor that fits for intelligent bridge structure, and intelligent bridge structure should take priority of embedded objects. Bridge structure health monitoring belongs to the first step of intelligent bridge structure, namely self-sense bridge structure. The design of intelligent bridge structure should follow two rules: function and benefit-cost analysis, which need many trials to carry on construction from the original design to the experimental test.According to the characteristics of intelligent bridge structure, the paper studies the composition, characteristics, design rules and principles, monitoring contents, sections and items about bridge structure health monitoring system. It summarized Bridge structure damage evaluation method at present and presents monitoring content and major composition of cable-stayed bridge health monitoring system. The system should make the best use of computer resources in the condition of the least artificial participation, consider its object, function, investment and key position, pay attention to realtime and long-term characteristics of monitoring. The paper also points out that software design should adopt virtual instrument technique, hardware design should be standardized, and the major monitoring content consists of the load and environment monitoring, geometrical deformation monitoring, and structure reaction of static load monitoring.According to the principle of FBG, the dissertation contrasts the three optical fiber sensor: intensity type, interference type and grating wavelength type, and conclude that FBG is better suited for bridge structure health monitoring. Through the research on the facture , structure principle, strain and temperature characteristics of fiber bragg grating, we find that the wavelength of FBG is proportional to the strain (temperature) and it can be applied to bridge structure health monitoring after calibration. Owing to the characteristics of bridge structure,we develop the pile packaged FBG embedded in concrete and construct FBG monitoring system with multiplex optical switches. Based on the FBG location technique and protection measure, 5 packaging FBG sensors and 5 bare FBG sensors are embedded successfully in the prestress concrete box girder, that the strain of concrete under the action of dead load is tested. Experimental result shows that the test value of FBG accords with the desired value very well and the absolute measurement of FBG is achieved. The strain of concrete under the action of static load is also tested, which shows that the test value of FBG accords with that of electric strain gauges very well and explains that the pile packaged FBG strain sensor which can be applied to bridge structure health monitoring is an ideal sensor element to solve the problem of the concrete inner deformation monitoring.According to the difficulties in the bridge evaluation of integral method, we put forward a local evaluation method that establishes a bridge structure safety evaluation index. On the foundation of structural linear elasticity, the relationship between load and reaction in the calculation of finite element for bridge structure is deduced and that using finite element calculation can establish bridge structure safety evaluation index is proved. In this way, the forepart bridge structure safety evaluation index can be calculated by theory, and the long-dated can be established by artificial neural network (ANN) and auto-monitoring data. Based on the research of ANN principle, ANN model for the relationship between temperature and cable tension force in the cable-stayed bridge is also established.According to the function of cable-stayed bridge health monitoring system in Wuhu Yangtse River Bridge, monitoring contents, measuring sites, software and hardware and data transmission techniques are researched, the running results of which system are obtained. Finally, we apply FBG monitoring technique to health monitoring system in Wuhu Yangtse River Bridge, then contrast the test value of FBGs with the test value of strain gauges. Experimental results show that FBG measuring has high performance on stability and reliability. Emulation model of temperature and cable tension force established by ANN is attempted. From the forecast of 23 groups of data, it can be seen that the forecast value accords with actual value very well, which proved the feasibility of using ANN to establish bridge structure safety index successfully.