| Large-span P.C. bridges are widely used nowadays, but the ultimate bearing capacity of them is seldom calculated with three-dimension spatial nonlinearity analysis theory, which seriously restricts the safety evaluation of bridges of this type.The nonlinearity behavior analysis theory and ultimate bearing capacity calculating method for Large-span P.C. bridges are researched systematically in this paper, and some valuable results and innovations are brought forward, includes:(1) A large-span bridge structural ultimate bearing capacity analysis method considering dual nonlinearity based on degenerated three-dimension solid virtual laminated element theory is put forward, and based on which an nonlinearity finite element analysis program is programmed. And this program can be applied to the ultimate bearing capacity analysis of both large-span steel bridges and large-span concrete bridges.(2) The dependency and applicability of the analysis method and program are verified by several classic mechanical numerical examples and various model failure tests with different materials and support conditions.(3) Several detail treatments for some key problems in the ultimate bearing capacity calculation of large-span P.C. bridges are investigated, such as the accurate simulation of pre-stress effect, the proper consideration for the established internal force, the reasonable calculation of cracking load, the FEM iterative format considering initial stress, constructing analysis model rationally to promote calculating efficiency, etc.(4) In multiple load case, the ultimate bearing capacity of the secondary navigable span of Sutong Yangtse River Highway Bridge (which is a continuous rigid frame bridge) is analyzed with the above program, and the influence of various level of pre-stressing is also discussed. According to the calculated ultimate loads, failure characters, load- deformation curve, and safety coefficients, etc, the bridge is evaluated and some valuable conclusions are attained.
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