| Cable-stayed Bridge is the main bridge style for long-span bridge and stay cable is one of the most important components of the Cable-Stayed Bridge. However, stay cables are often suffered corrosion and fatigue damage and these factors threat the bridge safety in serve life. The structural health monitoring (SHM) system is becoming one of the most effective techniques for ensuring the health and safety of long-span bridge and structural safety assessment theory, as well as life-cycle design based on SHM are hot issues of civil engineering field in recent years. This dissertation focuses on systematically researching of traffic load modeling, traffic load effects modeling of stay cable, mechanical and fatigue properties of corroded cables and stay cable safety assessment methods of Cable-Stayed Bridge based on SHM by fully utilizing SHM data and actual stay cables.The main research contents of this dissertation are described as follow:Firstly, based on the geometric meaning of Hasofer-Lind reliability index which defined as the minimum distance from the origin to the limit-state surface in the standard normal space, the optimization model of reliability index is established and particles swarm optimization (PSO) is proposed to solve the optimization problem. Moreover, a structural reliability-based sensitivity analysis method namely relative convergence rate of random variables using PSO is proposed. In consideration of the fluctuation of convergence rate of a variable during the optimum process, an optimized strategy is proposed. The optimized group consists of the particles with the best fitness values. Finally, some numerical examples are studied entirely and illustrate the advantage and feasibility of the proposed method.Secondly, based on the vehicle load characteristic of highway bridge and field measured SHM data of Shandong Binzhou Yellow River Highway Bridge, the probabilistic distribution model of highway bridge gross vehicle load is established, and the different occurrence probabilities and different distribution parameters of light cars and heavy trucks are considered in the model. Based on the probabilistic distribution model of gross vehicle load and filtered compound Poisson Process of vehicle load under the loose traffic status, the extreme value distribution model of gross vehicle load is established. The fatigue load spectrum of highway bridge is also statistically studied in this dissertation. In addition, the Logistic Model is employed to predict the long-term traffic volume and the parameters of the Logistic Model are updated using the monitored traffic volume. The combination of the fatigue load spectrum and the traffic volume forecast using the updated Logistic Model provides a load model for estimation of fatigue damage evolution of bridges. Traffic load modeling of highway bridge is systematically studied and it is the foundation for bridge design and safety assessment in serve life.Thirdly, Fibre Reinforced Polymer Optical Fibre Bragg Grating (FRP-OFBG) cable a kind of fibre Bragg grating optical sensing technology-based smart cable is introduced. In addition, the application of the smart cables on a certain domestic bridge is demonstrated. The probability distribution and extreme value distribution of cable live load effects are established by using the field SHM data, and the Bayesian theory is proposed to update the live load effects based on SHM data. The equivalent fatigue stress range of cable is established. Furthermore, the characteristics of live load effects, extreme value of load effects and the fatigue cumulative damage for short cables and long cables are analyzed.Fourthly, the corrosion degree, mechanics and fatigue properties of corroded cables which are gotten from the dissection of actual stay cables and have been in used for 18 years are completely investigated by experiments. The corrosion degree and probability distribution of uniform corrosion and pitting corrosion are investigated. The effects of corrosion on elastic modulus, yield strength, ultimate strength, ultimate strain, elongation, reverse bend number and remaining fatigue life of wires are discussed. The constitutive relations of load and displacement are simulated by Monte Carlo simulation for corroded and uncorroded cables. The fatigue lives of corroded wires and cables are investigated by experiments and the effects of corrosion on fatigue properties of wire and cable are revealed. Fifthly, based on the wires strength experimental data and strength model of fiber bundle, the safety assessment methods of cable are investigated and the effects of corrosion, cable length and Daniels effects on cable strength are discussed. The mechanisms of cable strength reduction caused by corrosions are revealed.Sensitivity analysis of cable strength capacity is performed by using PSO relative convergence rate. Considering the probability distribution of wire fatigue life and linear fatigue cumulative damage theory, the cable fatigue life calculating model is established and effects of cable length, parameter of cable S-N curve, number of wires, variability of wire fatigue life and non-uniform stress of wires on cable fatigue life are discussed by Monte Carlo simulation. The effects of percent of wires broken in cable on cable fatigue life are studied. Based on results of corroded wire fatigue test and cable fatigue life calculating model, the cable S-N curves with different percent of wires broken are simulated, and compared with the results of cable fatigue test in order to illustrate the feasibility of the proposed cable fatigue life calculating model. As the foundation of cable safety assessment and life-cycle design, reliability assessment method of cable fatigue is established. The fatigue reliability decaying pattern of new cables and corroded cables with serve life are investigated. It can be seen that the corrosion is the controlled factor for cable fatigue limit-state and corrosion gives less effects on cable strength limit-state.Finally, as the targets of minimization of the expected life-cycle costs and maximization of expected life-cycle benefits, the economic model of bridge life-cycle design are developed. In view of the characteristics of the inspection costs and maintenance costs of cable are small, the inspection costs and maintenance costs of cable are ignored. The cable life-cycle design method is developed to satisfy the limit-state functions of cable strength and cable fatigue life, and considered the cable fatigue reliability index deterioration model in serve life. In order to minimize the life-cycle costs of cable, the optimal section area of cable is determined which provided a theoretical basis for cable design and replacement. Furthermore, the life-cycle design method for general bridge structure is established by using event tree model. The effects of resistance deterioration, discount rate, inspection accuracy, failure lost and initial cost on bridge life-cycle costs and reliability index are discussed by event tree model. |
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