Static Nonlinear Analysis Of Long-Span Cable-Stayed Bridges In Construction Stage

This thesis focuses on geometric nonlinear static analysis of long-span cable-stayed bridges. Firstly, the basic theory of geometric nonlinear analysis for long-span cable-stayed bridge is introduced. Then three principle factors that affect geometric nonlinearity of cable-stayed bridges are described, which are large displacement, effect of cable sag and combined effects of moment and axial force; then the finite element methods are introduced separately. And then, the finite element model of Nanjing Third Bridge according to its scheme of cable-stayed bridge with single pylon is erected by ANSYS, a general finite element software. After that the thesis presents detailedly the dealing methods to simulate the real load-bearing condition of bridge structure and how to deal segmentary strengthing of cable, effects of cable sag and erecting and removing of element under construction phase. At last, the linear and nonlinear analysis to all load cases under construction stage are made. According to the comparison between those results, conclusions are drew as. followed:(1) Nonlinearity of large displacement and cable sag has thelargest effect on the moment of main girder, while the combined effect of moment and axial force has the least effect. What's more, the effect degree is different in different construction phases.(2) Closure construction of side spans and the remove of crane have very little effect on nonlinearity, so effects of nonlinearity can not be considered in these load cases.(3) Nonlinearity in construction stage of deck system has a bigger effect by 18.2% on part nodes of main girder but no more than 4% on the end of main girder. The maximum value 7.2% occurs in comparison between nonlinear results and linear results of horizontally displacements on top of tower, in which large displacement and sag effects are main factors.(4) Nonlinearity of system transformation(removing fixed constraints of tower beam) and remove of temporary pier has a great effect on the end of tower. In the comparison between the results, the effect of nonlinear factors in system transformation on the moment of end of tower reaches by 67.8%, and the effect of nonlinear factors in remove of temporary pier on the moment of end of tower reaches by 35%. Among these factors, large displacement has the largest effect on the moment of end of tower.(5) In comparison of vertical displacement of main girder, the difference in midspan of right span before system transformation(removing fixed constraints of tower beam) is the largest. The differential ratio of vertical displacement of main girder under the effects of large displacement and sag effects reaches by 17% around. Inother load cases, the largest differential ratio is 8.3%.