Geometric Nonlinearity Analysis Of Long-Span Cable-Stayed Bridge

The cable-stayed bridge, a kind of flexible structure with statical indetermination, consists of three basic members:tower, cables and girders. Because of its variant inner force under dead load, nonlinear behavior and coupling between construction method and completed structure, the construction nonlinear analysis that considers those factors become very important in the design of cable-stayed bridge.This thesis focuses on geometric nonlinear static 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 geometric nonlinearity of cable-stayed bridges are described, which are large displacement, cable sag effects and combined effects of bending moment and axial force; then the finite element methods are introduced separately. In this thesis, the feasibility of several nonlinear solution of geometric nonlinearity is discussed for the cable-stayed bridge and the relative calculations are operated to get the influence of each nonlinear factor, especially emphasize structure large displacement and cable sag effects. And then, Using large-scale finite element program Midas , the geometric nonlinear static analysis are made on Xuzhou Peace Road Bridge .The internal force and displacement of every phase are obtained and accumulated. Regarding the closure of the whole bridge as the initial internal force state, author draws the quantitative influence of every nonlinear factor on whole bridge after the deck pavement is finished.At last, the linear and nonlinear analysis of all load cases under construction stage and finished stage are made. According to the comparison between those results,conclusions are obtained as followed:(l)Cable sag effect has the largest effect on the moment of main girder and nonlinearity of large displacement has larger effect, while the combined effect ofmoment and axial force has the least effect.Further more, the effect degree is different in different construction phases.(2)Closure construction of side spans have very little effect on nonlinearity,so effects of nonlinearity can not be considered in these load cases.(3)Under dead load the cable sag effects is the main point of nonlinear behaviors of cable-stayed bridges, and the combined effects of bending moment and axial force an3 the large displacement are relatively small. So it is nor enough if we only execute linear analysis to a cable-stayed bridge.(4)Linear analysis is enough to live load since the difference between linear analysis and nonlinear analysis to the structure is relatively small under live load.