Semi-analytical Method For Bridge Structures With Box Cross Section

Thin-walled box girder structures are used widely in the upper structure of bridges for their lower self-gravity, better torsion and bending performance, and great spanning capacity. Therefore, the study for box-girder bridges is particularly important. In the thesis, a box girder structure is simplified equivalently and continuously into a thin-walled tube with a flange. Then a semi-discretization is made by some longitudinal node lines on this three-dimensional model, the unknown horizontal deformation functions defined on the longitudinal node lines and the unknown vertical deformation functions defined on box girder vertical cross-section are used as primary unknowns. Thus, the displacement field or the motion field of the box girder structure could be expressed by these primary unknowns. The static problems or dynamical problems are converted into boundary value problems or eigenvalue problems of ordinary differential equations by applying energy principle, and then, numerical solution of the equations will be obtained by ODE (Ordinary Differential Equation) Solver, which provides a new semi-analytical method for the analysis and calculation of box girder bridges. The main work can be listed as follows:1. The signification that the thin-walled box girder structure is a promising structure suiting to the need of bridge development is introduced so as to show the significance of analyzing the box girder structure with a three-dimensional continuously distributed mass and stiffness model by semi-analytical method based on ODE Solver both in theory and practice; some problems of building a computational model are discussed. for example, the assumption about stress and strain of thin-walled box girder structure, how to select primary unknowns to describe the displacement field or the motion field of the box girder structure,the problems of the coordination transformation of displacement function. The standardization of the governing equations and the usage of COLSYS are introduced.2. The free vibration analysis of a simple beam with box cross sections is performed by the semi-analytical method. Some reasonable and significant conclusions are presented through the computational results obtained from examples, and they imply that the simplified semi-analytical model is reasonable and feasible, and the semi-analytical method is feasible and effective.3. The free vibration analysis for a viaduct with thin-walled cross sections is also performed by the semi-analytical method based on Ordinary Differential Equation Solver;The influences of deformations of subgrade under high-pier and the interaction between overhanging beams on the natural vibration frequency of the viaduct are discussed.4. The calculation for influence fields of a large bridge is formulated by employing the semi-analytical method based on Ordinary Differential Equation Solver. The reaction and stress influence fields of a paired three-span cable-stay bridge are computed. Thus, the convenient and useful tools are provided for the analysis of bridge structures under moving loads.