Study On Key Problem Of Health Monitoring System For Long Span Cable-staged Bridge

Long-span cabled-staged bridges will be suffered from destroyed because of design & construction error, influence from the prevailing climate and environment, traffic and increasing loads gradually. If the bridges will not be monitored or identified as soon as possible, they will not be maintained and reinforced. Therefore it will affect bridge's safety and decrease bridge's lives. Unfortunately, the bridges will be damage and collapse suddenly.Based on the study on Wuhan Changjiang No.2 Bridge which is a long span cabled-staged bridge, this thesis starts from the key problems of long-term health monitoring system for large cable-staged bridge, including FEM theory, dynamic model updating methods, optima algorithm, structural simulation and forecast technology etc. Then, from setting up the bridge's theoretical model to bridge's health foundation, dynamic model updating method, modal parameters identification, structural load threshold, structural damage simulation are studied. The main research works and innovations of this paper are as following:Firstly, the key problems for long term monitoring of long span cabled staged bridge are put forward. The problems are concentrated on such as health baseline of bridge, FEM model updating, bridge's damage identification, design and construction error, monitor project installation, sensing availability & sensor life, structure degradation & disabled mode and bridge identification method.Secondly, the 3-D fine FEM model of Wuhan Changjiang No.2 Bridge is set up. Through drawing from design department, it is studied that the characteristic of large pre-stressed reinforced concreted cabled staged bridge. to such as components pre-tension cable, pre-tension rebar, rebar, reinforced concrete tower and beam, different element type, boundary condition. Finally, the FEM model of Wuhan Changjiang No.2 Bridge is set up by ANSYS. Thirdly, finite element model updating methods are summarized and advantage & disadvantage of the methods are discussed. Then, a new updating method based on sensibility is put forward for large cable-staged bridge. The classical FEM updating methods mainly adopt optimization for minimizing the error between analytical and experimental result, different updating objects(matrix updating & structural parameters updating ), optimization objects(minimized norm and rank) and different subjected condition. In recent years, some new updating methods such as sensibility method, NN method and GA method are studied.The forth, the modification procedure of FEM model of Wuhan Changjiang No.2 Bridge is studied. The 7 parameters such as pre-tension cable module, pre-tension rebar module, rebar module, tower module and density, beam module and density are initially selected as updated objects. Then, it is computed that the sensibilities of 7 parameters to the theoretical frequencies. The sensibilities of rebar module and tower density is less than other parameters, thus the 2 parameters are not considered as updated objects. The model updating is carried out using sensibility method and the correlated error between analytical and experimental mode frequencies is posed as an optimization object and structural parameters upper and lower values as constraint.The fifth, as a result of the above studies, it is computed for the beam deformation, the cross section strain under some static load cases according to the bridge load test criterion. The results are close to test results and it is demonstrated that the sensibility updating method is effective. In the meantime, threshold of bridge is put forward according to bridge design criterion. The computed threshold is used to alarm to online bridge's health monitor system.The sixth, prediction scheme is simulated for the cable-staged bridge suffered from damage and destroy.It is studied that the transit heavy vehicles such as 50T, 80T and 120T. As a result, it is not ignored that the heavy vehicles destroy the bridge.It is simulated that some different traffic flux per day such as 50 thousand vehicles, 100 thousand vehicles, 150 thousand vehicles and 200 thousand vehicles. The thesis computes the main cross section stress, cable tension, tower offsets, beam deformation, etc. It is discovered that the bridge threshold traffic flux is about 150 thousand vehicles per day and it offers scientific traffic control measure to the bridge manage department.It is simulated that the bridge is suffered from the lowest and uppermost surroundings temperature. The surroundings temperature is not major factor to bridge, but also the temperature gradient is. The more higher the gradient is, the more greater of stress.It is simulated that some cables is disabled. The all cable tensions will be distributed also and the all tensions are bigger than original forces. The more closer near the damage cables the cable is, the more bigger of the original of forces is.