Static And Dynamic Geometric Nonlinear Analysis Of Long-Span Cable-Stayed Bridge

The long-span cable-stayed bridge, a kind of flexible structure system with high redundant number, consists of three basic members: the tower, cables and girders. Because of its variant inner forces under dead load, nonlinear behavior and coupling between construction method and completed structure, the construction nonlinear analysis that considers those factors and character of free vibration become very important in the design of cable-stayed bridge.This thesis focuses on the geometric nonlinear static and dynamic analysis of long-span cable-stayed bridge. Firstly, the basic theory of geometric nonlinear analysis for long-span cable-stayed bridge is introduced. Then three principle factors that affect the geometric nonlinearity of cable-stayed bridges are described, which are large displacement, cable sag effects and combined effects of bending moment and axial force; and the finite element methods are introduced separately. In this thesis, using large-scale finite element program Bridge-Doctor and Midas, the geometric nonlinear static and dynamic analysis are made on Lidu Bridge .The linear and nonlinear analysis of all load cases in constructing stage and finished stage are made. According to the comparison between those results, conclusions are obtained as followed:(1) Cable sag effect, large displacement and the combined effect of moment and axial force have great effects on the moment of the main girder. The degree of influence is different in different construction phases, while cable sag effect is the greatest.(2) Closure construction of middle spans has more effect on nonlinearity than that of side spans. So the nonlinearity of these working conditions must not be ignored.(3) the cable sag effect, the combined effects of bending moment and axial force and the large displacements are all the main points of nonlinear behaviors of cable-stayed bridges under dead loads. So there will be inaccurate results if just the linear analysis is made.(4) Nonlinearity of system transformation (removing fixed constraints of tower beam) has great effect on the moment of the end of tower and the displacement of the top of tower. And large displacement has greater effect.(5) Linear analysis is enough to live loads, since the difference between linear and nonlinear analysis to the structure is relatively small under live loads.According the analysis of the free vibration character, rigidity in plane is much less than out plane. And the normal modals are vertical bending vibration of girder and longitudinal vibration of tower.