A Study Of Mechanical Characteristics And Ultimate Load-Carrying Capacity Of Long Span Self-anchored Suspension Bridge

The self-anchored suspension bridge, with its unique structure, beautiful appearance, good economic performance as well as the advantages of the strong adaptability to the terrain and geological conditions, is attracting increasingly more attention in engineering. It forms a longitudinal self-balancing system with the main cable anchored on the stiffened girder. Hence, the self-anchored suspension bridge is different in construction methods and mechanical characteristics from the land-anchored suspension bridge. Based on the study of the SanChaJi Xiangjiang Bridge, this dissertation attempts to analyze the mechanical -characteristics and the local-overall interactive buckling ultimate carrying capacity of the long span self-anchored suspension bridge. The main contents are as follows:(1) A spatial beam element is established for the calculation of self-anchored suspension bridge's ultimate carrying capacity with local-overall interactive buckling is considered. The displacements of any element are composed of the overall displacement and the local displacement. The overall displacement is calculated based on the plane-section assumption, and the local displacement is derived through a unit length of transverse segment in longitudinal direction of the stiffened girder. Based on the finite deformation theory and the U.L. formulation, the incremental equations and the element stiffness matrices of the self-anchored suspension bridge with local-overall interactive buckling are established. The calculation program is also developed.(2) The structural optimization theory is used in the determination of the finished state of the self-anchored suspension bridge. The tension-compression and bending strain energy of stiffened girder and pylons is chosen as the objective function. The hanger force is taken as design variables and the girder shape in finished state is selected as state variables. Combining the numerical analysis and the nonlinear finite element method, this dissertation proposes an iterative method for calculating the shape and unstressed length of the main cable of the self-anchored suspension bridge. The corresponding calculation program is also developed.(3) The parameters which produce effects on mechanical behaviors of the self-anchored suspension bridge were discussed, including the span arrangement, the ratio of sag to span, the main girder shape, the hanger spacing, the main girder bending stiffness and the axial stiffness of the main cable. Using the gradient value of objective function to the design variables, the sensitive coefficient of structural parameters is introduced. The sensitive coefficients of the bridge shape, structural stiffness, moment in main girder and pylon bottom are calculated. They can be a reference for structure design and construction control.(4) A model test with the scale 1:28 is carried out to validate the process of construction and calculation method. The designed finished state of the model test is obtained by controlling the process of construction using optimization theory. It indicates that the method of unstrained installation of hangers can be used in practice, and the construction efficiency is improved. The measured results agree well with the calculated values under live load, and the validity of calculation theory and program is verified.(5) The ultimate loads of SanChaJi Xiangjiang Bridge with the local-overall interactive buckling under different load conditions are analyzed. The factors that affect the ultimate loads such as the cross beam spacing, stiffness and local deformation of main girder are discussed.(6) The selection of structure system, optimal calculation of finished state, mechanic state in the construction stage, seismic response and control of SanChaJi Xiangjiang Bridge are analyzed in this dissertation. The results are provided as a reference for structure design.