Load Capacity Assessment Of Existing Bridge Based On Reliability Theory

During the long-term operation process of bridge, degradation of materials and structure damage with time will cause deterioration of the structural performance and decrease its load capacity gradually, that may affect normal use and reliability of structure and even lead to serious consequences. This thesis conducts research on load capacity assessment of existing reinforced concrete highway bridges based on random reliability theory.Firstly, the existing assessment methods of bridge, as well as structure reliability theory including component reliability and system reliability and reliability research status of concrete structure considering durability of materials are summarized and commented, which offer the theoretical foundation of the research.Secondly, considering the time variation of loads and resistance and the random of basic variable, the thesis builds the load effect and resistance effect models for structure reliability analysis. This part includes the following points:the probability model of vehicle effect is presented by considering assessment base period and modification factor of live load, and the time-variable probability model of component resistance is established by considering durability parameters of reinforced concrete and uncertainty of calculation modes.Thirdly, this thesis commends a practical combined failure criterion under both bending moment and shear force, and then establishes the performance functions in view of three most probable load capacity limit states, including flexural failure, shear failure and combined failure of bending and shear. On this basis, the thesis calculates time-variable reliability index and give flow chart of the reliability assessment of structure components.Fourthly, the thesis proposes the analysis method and flow chart of existing concrete bridge system reliability based on the idea of probability assessment system. According to time-variable reliability indexes of different limit state, a practical method to identify main failure status and main failure modes of bridge system is presented. Then, the thesis calculates system reliability combing with correlations of each failure mode and methods of series system and parallel system failure probabilityFifthly, taking a reinforced concrete continuous beam bridge as an engineering background, the thesis calculates the time-variable reliability index of each component by MATLAB based on the methods mentioned above, and then analyzes the most probable failure status of each section and main failure modes of bridge system, and finally evaluates the bridge system failure probability.