Nonlinear Analysis Of The Structural Behavior For Super Long Span Concrete Arch Bridge With CFST Stiffened Skeleton

With its good mechanical performance, excellent span capacity, convenient construction technology, concrete arch bridge with concrete-filled steel tubes stiffened skeleton has conspicuous and competitive advantages in the high-speed railway long-span bridge construction. The mechanical characteristics of this structure has shown a kind of development situation which can be described as "higher stress&larger displacement" with increasing design span. Therefore, the traditional elastic analysis methods are not suitable any more. Nonlinear Analysis Method has been widely used in considering the effect of geometric nonlinearity on the ultimate bearing capacity of reinforced concrete structures. However, other nonlinear effects such as the material nonlinearity, temperature effect and time-dependent effect still need further research and nonlinear study of steel-concrete composite structure is not perfect yet.Combining with the construction of Beipanjiang Bridge with span of445m, which located near Guangzhao Hydropower Station, in Changsha-Kunming section of Shanghai-Kunming passenger dedicated railway, the Degenerated Beam Element Theory is applied to nonlinear finite element analysis of concrete arch bridge with concrete-filled steel tubes stiffened skeleton in this thesis. The main work is as follows:1. The fundamental principles of nonlinear finite element analysis based on the Degenerated Beam Element are described and some relative formulae are derived.2. The ultimate bearing capacity of the CFST reinforced composite columns under axial compression is calculated based on the finite element analysis software—CSBNLA. Then, based on the results, a simplified formula for calculating the axial compressive strength of the CFST reinforced composite columns is proposed according to the Limit Equilibrium Theory.3. Three different finite element simulation modeling methods for CFST reinforced composite structure are discussed and the one which can consider the structure section stiffness gradually combination in the construction process is adopted to establish the finite element analysis models of Beipanjiang Bridge by use of MIDAS Civil and CSBNLA. After the calculation results are verified, a static nonlinear finite element analysis of the whole process of Beipanjiang Bridge is carried out. In the meantime, the results as well as the different effect of nonlinearity on the structure responses are preliminarily studied and analyzed.4. The ultimate bearing capacity of the main arch ring of Beipanjiang Bridge during its service stage is also calculated by considering the influence of geometric nonlinearity, material nonlinearity, shrinkage and creep. The results show that the Degenerated Beam Element, using the sub-block (layer) integral technology, can easily consider the structure stiffness gradually combination in the construction process and expediently deseribe the nonlinear structure behaviors such as the crack and crush of concrete, shrinkage and creep effects and steel’s plastic flow after the yielding; it is significant enough to give more attention to the effect of nonlinearity on the geometrical configuration during construction and ultimate bearing capacity of the concrete arch bridge with CFST stiffened skeleton.