| The plate-truss composite structure, in which the concrete deck plate and steel main truss co-act together, has come into use in a long span cable-stayed bridge for both highway and railway because of its many advantages. But no references are available about this kind of bridge. Bridge engineers and design department want to comprehensively understand its property of force bearing, and a simple and efficient analysis method is in urgent need for this kind of structure. After studying on these, this dissertation proposes a set of methods to analyze ultimate load carrying capacity (ULCC) of long span cable-stayed bridges with plate-truss composite beam.1. The spatial mechanics model of the cable-stayed bridge with a plate-truss composite beam for ULCC analysis, which can take the couple function of local and global deformation into accounts, is set up. The main beam is discreted into finite segment elements of plate-truss composite beam that involve tension (compression), bending, twisting, section distortion, wrapping deformation, secondary stress of truss, local bending and shear lag effect of deck plate. This kind of element can efficiently overcome the lack of existing analysis methods. It can analyze the local bending deformation of deck plate by introducing transverse finite strip elements of concrete deck plate, and the effect of uneven longitudinal deformation of concrete deck plate by introducing multiple parameter displacement function of shear lag warping deformation that is of high precision, comprehensive consideration and wide-ranging use. Based on the thoughts that the total displacement of particles is the sum of the displacements caused by global and local deformation, the displacement model and calculating formulae are formed.2. According to the principle of nonlinear continuum and the theory of geometric nonlinear finite element, the U.L. formulation incremental equilibrium equation for cable-stayed bridge with a plate-truss compositebeam is set up and the explicit calculating formulae of the elastic stiffness matrix, geometric stiffness matrix and the column matrix of nodal forces equivalent to elemental stresses of plate-truss composite beam are deduced.3. A elasto-plastic constituation relation of concrete deck plate is degenerated from Chen-Chen's isotropic strengthening elasto-plastic model with three parameters. The expressions of all nodal internal forces of used elements are obtained. The plasto-coefficient method of generalized internal force that reflects the influence of local deformation of plate-truss composite beam on plastic yielding is proposed. Based on this method, the elasto-plastic element stiffness matrix, which is used in the spatial ULCC analysis for cable-stayed bridge with plate-truss composite beam, is established.4. Virtual temperature load method to adjusting the tension force in the cable is proposed, and its computing procedure and iteration expression are given. The method unites the computing models before and after adjusting cables, makes the analysis process of ULCC of cable-stayed bridge from exerting dead loads a continuous loading calculating one, and conveniently takes the influence of all kinds of nonlinear factors into account.5. Firstly, elasto-plastic incremental equilibrium equation of each sub-element is separately established. Then, it is transformed by means of coordinate transformation matrix mentioned in this dissertation. Finally, based on the 'Set-in-Right-Position' rule, it is added to structural stiffness equation under global coordinate to form the structural U.L. formulation incremental equilibrium equation of the ULCC analysis of cable-stayed bridges with plate-truss composite beam.6. Based on the analysis model and methods mentioned above, a computing program for ULCC analysis of cable-stayed bridges with plate-truss composite beam is developed. According to the computing results obtained from classic calculating examples and existing experiment, the correctness of the mechanics methods,...
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