Several Critical Problems Reasearch On Life Cycle Healthy Monitoring Method For Loangspan Cable- Stayed Bridge

The design of large span bridge is increasingly flexible, meanwhile, structure form and function is increasingly complicated. As a result, the bridge construction and maintenance is more difficult. The construction of long span bridge is a long and complicated process. With times transformation of structure system, the bridge is vulnerable affected by environment. Bridge under construction is weaker than the bridge after completion. The improper construction method could cause serious unreasonable girder liner type and force distribution. Moreover, the bridge aging rate is accelerated and the service capacity with bridge life is deteriorated. Therefore, safety accidents will occur with serious cases. In order to ensure the safety condition of bridge under its construction and operation, comprehensive monitoring and testing is needed. The construction control, loading test and operation monitoring are the three stages for bridge health information acquisition. The contents, methods, and techniques are the similar in these three stages. In order to share the equipments and information, these stages are combined to the unified life cycle monitoring system. From the point of information integrity and economic, the bridge life cycle healthy monitoring is reasonable. This monitoring system can track the important parameters of the bridge to explore the bridge's real condition and predict the future condition. The damage can be detected earlier, and maintenance can be done timely to prevent safety accident.Based on Yudaohe cable-stayed bridge, A deep study have been done on the structure damage detection and condition assessment using the Finite Element Method, dynamic model updating methods, modal parameters identification, optimal algorithm, and structural simulation. The main contents of this dissertation are described as follows:1. The monitoring method and analysis techniques of cable forces, stress, and deflection is studied. The construction of parallel strand cable is researched, and the mechanic model of construction is established. The initial tension of single strand is given. The temperature modification technique for FBG strain sensors is studied, and the modification formulation is given. The measurement value of cable forces, stress and deflection is consistent with the prediction value in the construction control of Yudaohe bride, and the bridge construction safety is assured.2. A structure damage detection method based on statistical characteristics of vibration signals is presented. Displacement responses under sine and white noise excitation are pursued firstly, and then the expression of displacement response statistical characteristics between different nodes is given. Because there is lots of structural stiffness information in the statistical characteristics, the feasibility of taking the statistical characteristics as a damage detection index has been proved in theory. Compared with the normal damage detection method, Spectrum Analysis with complicated calculation is avoided, and only regression analysis with simple calculation is needed. With another advantage of satisfactory noise immunity, this damage detection index is very suitable for on line structure healthy monitoring. Based on simulation for three normal types bridge (simple supported bridge, continue bridge and cable-stayed bridge), the identification efficiency of damage location, degree and extension has been proved.3.A structure damage early warning method based on girder deformations monitoring is presented. The girder deformations under the truck loads have been fitting with the vibration modals. The modal order for fitting is determined by the deformations contribution of various vibration modals. Taking the symmetry of normal bridges into account, the number and installation positions of the inclinometers have been presented for mid-span displacement. The inclinometer number cannot be less than twice of the odd modal order, and the symmetrical positions with the maximum angles on the odd vibration modals have been selected for installation. Displacement simulations for three type bridges under different class loads have calculated. The results show that the mid-span displacement can be efficiently fitting. The statistical characteristics of traffic are supposed unchanged in a period. So the change of main girder deformation is determined by the deterioration of structural stiffness. Statistic Analysis and Hypothesis Testing have been done to the main girder displacement data for damage promotion. Using different Hypothesis Testing methods for various bridges with different spans, simulation results show that statistic characteristic of mid-span displacement is sensitive to structure damages.4.A structure damage detection method based on line cable force monitoring is presented. As a typical cable supported structure, the cable forces of cable-stayed bridge contain lots of structure information. Therefore, the prerequisite for using cable forces to damage detection is sufficient. First, the main girder is equivalent to an elastic foundation beam, and only few cable forces near the load change under the concentrated load. The internal forces of the damage element are released, and cause the same effect of acting the concentrated forces on the node of damage element. So the conclusion that damage only caused few cable forces change nearby is given. With this conclusion, structural damage positions detection can be done based on the change of cable forces under the fixed truck load. Damage degree can be identified with Model Updating technique. The truck troop can be simplified to a uniform load with a concentrated load. The regression relationship between the cable forces can be found, and the regression relationship is determined by the areas of cable force influence lines. As the change of the influence line only appear nearby the damage element, so the damage position location identification can be finished with the cable forces regression ratios. The disadvantage that the rationality of cable forces is difficult to judge with the unknown truck load is avoided. Simulation has been done to prove the damage detection efficiency of cable forces regress ratios.5.A method of condition assessment of long span bridge based on management strategies is presented. Maintenance timing and scale are included in management strategies. The maintenance timing is determined by the worst condition of the main components, and the maintenance scale is determined by the weight average conditions of all components. In order to avoid individual subjectivity of calculating components weights by AHP method, the components construction costs is treated as the weights and different engineers can easily obtain the same result. An example of Yudaohe cable-stayed bridge is given to illustrate the procedures using this bridge condition assessment method.6. A bridge loading carrying capacity evaluation method with several rating levels is given to formulate a procedure from simple rough level to complex exact level. Section resistance, load effect and partier factors influence the bridge loading carrying capacity together. As the effective areas of reinforcement can be evaluated by inspection or monitoring information, so the section resistances can be modified. The truck rank is taken as a Filtered Poisson Process. With sited traffic investigation, the maximum distribution of load effects can be identified in a period. The load effect with 95% guaranteed rate is compared with its design value to formulate the modified factor. Partial factors are calculated from design reliability to target reliability. With more statistical properties information of the material strength, the modification from actual reliability to target reliability can be realized. The essential idea of this method is to exploit the potential capacity to avoid unnecessary waste with the promise of bridge safety.7. With the combination of bridge design, construction, inspection and maintenance codes, the principle of healthy monitoring system is considering the practical applicability, economical efficiency, and scientific research. The Yudaohe bridge healthy monitoring system is introduced. The contents include various sensors arrangement with corresponding acquisition equipments and basic functions of healthy monitoring software.