| The arch ribs of the concrete-filled steel tube arch bridge are mainly subjected to the axial force. The stability is getting more and more important with the increase of the span. The influences of geometrical nonlinearity and material nonlinearity on the structure stability have important significance due to the features of the concrete-filled steel tube arch bridge, such as the gradual variation of the structural system in construction, nonlinear behavior in loading, the correlation between construction and service stage. Firstly, the fundamental theories of nonlinear finite element and stability are described in this thesis. The nonlinear solutions are discussed. The evaluating index, unstable criteria and distinguishing unstable mode are also studied. Secondly, the key technique of the static analysis with long-span concrete-filled steel tube arch bridge using the general finite element program is presented in order to obtain reasonable inner force of construction and service stage. Finally, the reasonable calculation model is chosen to calculate the stability of Qingchuan Bridge in construction by means of the finite element program ANSYS based on the fundamental theories of nonlinear finite element method. The stability of the modes with the linear elasticity and the elastic-plasticity in construction are calculated and analyzed. The first-class stable safety coefficient, unstable mode and the second-class stable safety coefficient on various loads are obtained. The structure safety coefficient and the influence of the different non-linear modes on the stability are compared. It can be obtained that the initial deficiency and material nonlinearity are the primary factors that influence the second stable safety coefficient. Relatively, the geometrical nonlinearity has little influence on it. Above all, the present results can provide a practical reference for design and construction of the concrete-filled steel tube arch bridge.
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