| Chinese bridge construction climax makes a good chance for technology of concrete members prestressing with external tendons to be applied and developed. But, the study and application of this new technique are almost limited in existing bridge's strengthening. As far as existing information is concerned, mechanical behavior studies of new concrete beams prestressing with external tendons still lack very much. Based on testing data, design code and related documentation of many countries, the paper investigates the theory and method of load-carrying ability, deformation of main beam, stress of concrete and prestress losses of external prestressing concrete bridges comprehensively, in details, the following aspects are investigated.1. This paper reviews the developing history and present status, and explores the constitution of external prestressing systematically.2. In the paper, stress increment formulas are summarized, and dominating formulas for ultimate stress counting of unbonded prestressing tendons are analyzed carefully.3. On the basis of the analysis on achievements and amount of testing data, through the internal force equilibrium and deformation compatibility of cross section, a simple method based on the global deformation is derived to calculate the ultimate load-carrying capacity of external prestressing concrete beams.4. Based on the special problems of structural design of external prestressing simple supported beams, the dissertation discusses the calculation method of the prestress losses in external prestressing structures.5. According to variation principle, the paper deduces stress increment formulas of external tendons in regular services stage. At the same time, this paper establishes formulas of concrete stress and beam deformation, combining the mechanical property.6. The paper researches factors which influence endurance of external prestressing concrete bridges, and then presents measures and suggestions for enhancing it.
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