Research On Reliability And Remaining Service Life Of Existing Prestressed Concrete Bridge

Due to the aging of structural materials, increasing vehicle load, increasingly worse environment influence, and the maintenance cost shortage, a wide variety of structural damage and deficiency appear inevitable in considerable parts of prestressed concrete bridges after the prestressed concrete bridges have been completed and used in certain period, and the load bearing capacity deceases, performance deteriorates, durability is reduced. All these become the focus attention topic all over the world.The dissertation aims at the characteristics of existing prestressed concrete bridges structures, based on the research results in the past. The reliability and remaining service life prediction of existing prestressed concrete bridges are investigated for both the strength limit state and service limit state. The main work is as follows.1. Time invariant reliability analysis of existing prestressed concrete bridges.The strength and service limit state equations of reliability analysis are derived by strictly adhering to the load and capacity formulas and requirements set forth in Chinese highway bridge design specifications. Actions, geometrical parameters and material characteristics are all taken as random variables. Through integrating first order reliability method (FORM), the reliability indices at the strength limit state for flexural capacity and the service limit state for flexural cracking of a typical simply supported prestressed concrete beam widely used in Chinese highway are calculated.2. The deteriorate model of resistance analysis of existing prestressed concrete bridges.After discussing the deteriorate model of resistance of existing prestressed concrete bridges, summarizing the statistics parameters and strength resistance models in many parts of research references, special emphasis is placed on the chloride induced reinforcement corrosion penetration modeling in prestressed concrete bridges and the chloride concentration at the concrete surface, the threshold concentration for steel corrosion. The diffusion coefficient and the corrosion rate are considered based on Fick's second law of diffusion. The time-varying model of reinforcement strength and area is founded by means of dealing with deterioration of reinforcement strength and area due to corrosion, and the probabilistic model of resistance for the simply supported prestressed concrete beam is established both general corrosion and pitting corrosion.3. Time dependent reliability analysis of flexural capacity of existing prestressed concrete bridges.A probabilistic model of time resistance for the strength limit state for flexural capacity is established. After discussing the time dependent reliability analysis methods, the program coded by C++is used to calculate the time-variant reliability index of flexural capacity is established too, based on the time-variant characteristics of many existing prestressed concrete bridges and analysis the deficiency of time dependent reliability index, simulated the lifetime reliability index of existing prestressed concrete bridges.4. Time dependent reliability analysis of service limits state for existing prestressed concrete bridges.Prestressed concrete bridges are typically designed to ensure that the initial and final stress at service load conditions are within the allowable limit, while the strength flexural capacity of section is checked later. Usually the service limit state governs the design of prestressed bridge girders, and the research work in reliability of service limit state for existing prestressed bridge are so important. In first, the time dependent reliability analysis of service limit state function for cracking and deflection is established, then through integrating first order reliability method (FORM) and Monte Carlo methods, the program composition with C++is used to calculate the time-invariant reliability index and time dependent reliability index of flexural cracking and deflection for prestressed bridge. At last, the time dependent reliability for service limit state of existing prestressed bridges based on many kinds of resistance degradation functions are analyzed.5. The remaining service life forecast of existing prestressed concrete bridges based on time dependent reliability theoryThrough calibrate the design reliability index, definition the safety reliability index and calculate the time dependent reliability index of existing prestressed concrete bridges, the rules of the residual strength and service life in existing prestressed concrete bridges are received, based on this rule and the inspection of prefabricated prestressed concrete simply supported beams, the work of paper is proved and technique of forecast remaining service life at the lifetime in existing prestressed concrete bridges are come true.