Local Damage Detection And Elimination Of Environmental Effects For Long-span Cable-stayed Bridge

The research focus of this dissertation is related to several key technique issues, which always occur and have to be solved during the routine structural testing and health monitoring for long-span cable-stayed bridge, including (1) load monitoring for the pin-pinhole contact in the cable-beam anchorage system with pin-hinge connection for cable-stayed bridge; (2) bond-slip detection and monitoring for the steel-concrete composite girder of the cable-stayed bridge; (3) elimination of environmental effect for cable-stayed bridge during its routine structural testing and health monitoring. The detail research constant are shown as following:(1) Load monitoring research for the pin-pinhole contact in the cable-beam anchorage system with pin-hinge connection for cable-stayed bridge.At first, a relationship model between the pin-pinhole contact area of the pin connection and external load applied on the connection was derived and built based on the contact mechanics, and a numerical simulation for the pin-pinhole interface contact verified the effectiveness of the proposed model. Based on this relationship model, three piezoceramci-based methods were proposed or developed to detect and monitor the load variation for the pin connection in real time. The effectiveness and feasibility of the proposed methods were verified by the experimental results for a pin connection test specimen in laboratory. It shows great potential for the real structural health or load monitoring combining the distinct advantages for the piezoceramics, such as the strong corrosion-resistant and less influence by the varying temperature and operational conditions.(2) Bond-slip detection research for the steel-concrete composite girder of the cable-stayed bridge:At first, a research was conducted to investigate how the occurrence of the bond-slip between steel and concrete materials for the steel-concrete composite structure will influence the electro-mechanical impedance (or admittance) signature of the host structure, the investigation demonstrated that the occurrence of the bond slip can be detected by monitoring and analyzing the admittance signals of the PZT-sensor, which was surface bonded onto the host structure. Then, a RMSD bond-slip detection index was proposed based on this conclusion, and the effectiveness of the proposed index was verified by the experiment for a steel-concrete composite specimen. In addition, the high-frequency excitation of the impedance-based technique also give the acquired admittance signal a potential to use for damage localization, which are very important for the practical applications.(3) Damage detection and elimination of environmental effect based on combination of successive displacement curvature:A new damage identification index, i.e., a liner combination of three successive displacement curvatures which were numerically obtained by a central difference approximation method, was proposed. Using simulation for a simply supported steel beam with environmental temperature change obtained from one year's temperature record in Beijing, validity and effectiveness of the proposed method was illustrated. Simulation result shows that the proposed method can eliminate the influence of environmental temperature. The damage detection and localization can be accurately identified without structural original data in healthy condition. It is also found that the method has noise robustness.(4) Damage detection and environmental effect elimination base on structural frequency cointegration:At first, cointegration method, which is used to deal with the non-stationary problem in econometrics, was introduced for the structural health monitoring, and a new damage detection method based on structural frequency cointegration was proposed to eliminate the influence of the environment variation. A cointegration relationship between two random frequencies sequences can be built, and its cointegration residual can be used as damage detection feature to eliminate the influence of the environmental effect. Then the validity and robustness of the proposed method were illustrated through a prestressed concrete beam and a simple supported steel bridge. In addition, the analysis for eight months datasets measured from Tianjin Yonghe cable-stayed bridge also verify the effectiveness for frequency-based cointegration method, which lay a solid foundation for the practical applications.