Geometrically Nonlinear Analysis Of Long Span Composite Girder Cable-stayed Bridge With Three Towers

Wuhan Erqi Yangtze River Bridge is the longest span composite girder cable-stayed bridge with three towers under construction. The main span is 616 m. Due to the cable-stayed bridge system with three towers, the flexibility of bridge is increased, and geometrically nonlinear problem is further highlighted. On the other hand, owing to the combined girder form for long-span composite girder cable-stayed bridge with three towers, material properties of steel and concrete is greatly different, which result in complex internal force change and distribution. Therefore, the geometrically nonlinear analysis is very necessary for composite girder cable-stayed bridge with three towers.Taking Erqi Yangtze River Bridge as an example, First the spatial nonlinear finite element model is established. Secondly, based on double girder nonlinear finite element model, cable sag, beam-column effect and large displacement effect were considered. The various influences of geometrically nonlinearity are studied on internal force and deflection in four cases. An accurate solution method of unstressed cable length and a cable force adjusting programme were proposed, which are applied in Erqi Yangtze River Bridge. These studies have important theoretical and practical significance to grasp internal force characteristics and further improve the calculation analysis level for longest span composite girder cable-stayed bridge. The main contents and conclusions of the research are listed as follows:(1) The spatial double girder nonlinear finite element model is established through link elements, shell and spatial beam elements by APDL parameterization technique.compared with single girder model, the spatial double girder nonlinear model was fully verified the effectiveness and correctness. The results show the spatial double girder nonlinear model can be used to the nonlinear analysis of long-span composite girder cable-stayed bridge with three towers, which has good precision.(2) Based on double girder nonlinear finite element model, the nonlinear analysis was developed under four cases, which including linear case, cable sag case, beam-column effect and large displacement case, all nonlinear case. The various nonlinear factors effect on internal force and deflection are studied. The results show all kinds of geometry nonlinear factors will affect the deformation and stress state of bridge. Cable sag is the most important factors. The geometric nonlinear effect considering all factors is larger than only considering a nonlinear factor. The nonlinear effect is different on internal force and displacement to different component. As far as the displacement of main girders and towers concerned, Cable sag effect is larger than beam-column effect and large displacement effect. For internal force of main girders and towers, cable sag effect is few than beam-column effect and large displacement effect, but for internal force of cables, three nonlinear factors effect is all few.(3) Determination of unstressed cable length is important to realize the initial configuration of long span cable-stayed bridge. Based on centenary theory, an accurate solution method of unstressed cable length is proposed; the end force of cable is used, characteristic parameter constraint equations is established when the cable tension known, its iterative is given when An accurate solution method of unstressed cable length is applied. The unstressed cable length of a long span cable stayed bridge is calculated, through contrasted with analytic solution and Ernst method, the results show the reliability of the method.(4) Based on nonlinear finite element methods, A cable force adjusting programme is proposed by means of ANSYS secondary development, the initial cable forces is iteratively calculated and repeatedly adjusted so that calculating cable force match with design cable under dead load. Simultaneously all kinds of geometric nonlinearity are considered. This cable force adjusting programme are applied to analyze the bridge-completing initial cable force of Erqi Yangtze River Bridge, The results show that the cable-force-adjusting programme is convenient and high efficient in analysis of cable-stayed bridges with three towers.