Geometric Nonlinear Analysis Of Long-span Composite Girder Cable-stayed Bridge With Three Pylons Under Construction Process

With the advantages of superior across performance, rapid construction progress, making full use of material, bridge becomes the one of the most competitive bridges in the long span bridge construction. However, owing to the increase of the span, the length of stay cable、main beam the flexibility and the structural deformation all increase, resulting in the change of the geometry cannot be ignored and the internal force and structure deformation have a nonlinear relationship with load. Specially, the bridge is in cantilever state all the time before structure system transformation during construction stage, the overall rigidity is smaller, the geometric deformation is larger, geometric nonlinear problem in construction stage seems particularly outstanding. Consequently, it’s necessary to carry out geometric nonlinearity analysis of the large span composite girder cable-stayed bridge in construction stage.At present, adopting geometric stiffness matrix to analyze beam-column effect, TL formulation method or UL formulation method to analyze large displacement effect and the equivalent modulus of elasticity method to analyze stay cable sag effect, the researchers at home and abroad have done some studies on the geometry nonlinear of the large span cable-stayed bridge during construction stage. However, with the increase of the span, the precision of this method decreases, and the disadvantage of the UL formation increment method is loading step must be small, which can be solved by CR formulation incremental method developed in recent yearsWuhan Erqi Yangzi River Bridge is a composite girder stayed-cable bridge with three pylons and double cable planes, consisting of90+160+616+616+160+90m. The main span reaches616m, the largest span of the same type bridge in the world.This paper takes this bridge as the background of research. Using elastic catenary cable element to analyze stay cable sag effect, geometric stiffness matrix to analyze beam-column effect and CR formulation incremental method to analyze large displacement effect, Simulating each working procedure of cantilever construction, the space structure nonlinear finite element model is established to research the regularity effect of the three geometric nonlinear factors on the deformation and internal force of the long span composited girder cable-stayed bridge with three pylons in the single cantilever and double cantilever state stage.The results show that:1) Geometric nonlinearity has a great influence on the deformation and internal force of the long span composited girder cable-stayed bridge with three pylons during cantilever construction stage. In the single cantilever and double cantilever state, the influence on the deflection of cantilever end reaches14.83%and12.22%respectively, the influence on the maximum internal force of main girder reaches6.43%and5.61%respectively.2) The influence of stay cable sag effect on the top deflection of main pylon in the finished stage applied to secondary dead load reaches12.01%. Compared with the beam-column and large deflection effect, stay cable sag effect is the biggest influence factor, accounts for72%of the top deflection of main pylon.3) The method, adopting elastic catenary cable element to analyze stay cable sag effect, geometric stiffness matrix to analyze beam-column effect and CR formulation incremental method to analyze large displacement effect, has a high precision.The paper provides important basis and guarantee for the rationality on cantilever construction of composited girder cable-stayed bridge.