Refined Finite Element Model And Geometric Nonlinear Analysis Of Long-span Composite Girder Cable-stayed Bridge

Cable-stayed bridge becomes the fastest developmental and the most competitive bridge in the modern bridges because of the spanning capacity, convenient construction, beautiful appearance and other advantages in recent years. Cable-stayed bridge is the highly statically indeterminate structure which consists of bridge towers, stay cables and girders. Structural analysis becomes more difficult because of the complex statically indeterminate structure form. There are always some errors between the model analysis results and the real structure measured results. However, the accurate degree of the calculation analysis will directly relate to the design and safety in the process of construction. Structure stiffness gets to diminish with the increase of bridge spans. And the structure tends to have large deformation under loads. Then the whole structure shows the obvious geometric nonlinearity due to the deformation. The geometric nonlinear analysis of the cable-stayed bridge is very important and necessary for understanding the safety and reliability of the structure under the given loads.Wuhan erqi changjiang river bridge which is building is recently the longest span composite girder cable-stayed bridge with three towers in the world. This paper takes this bridge as the engineering background, main work is as follows:1. Two spatial finite element models of Wuhan erqi changjiang river bridge were established based on ANSYS:singer-girder model and refined model with space shell, solid and bar element. The static calculation results of the two models under dead load were comparative analyzed. The results revealed that the vertical displacement of the concrete girder of the singer-girder model reached to 12.4cm because the prestressing tendons cannot be established. The value was 8.2cm larger than the result of the refined model. And the cable forces there were larger, the bending moment of the side tower bottom were smaller. These revealed that there were great errors with the calculation results of the singer-girder model. The space internal force distribution and deformation feature can be accurately reflected just with the refined model in this paper.2. The geometric nonlinear effects under dead load were analyzed. The bending deflection effect of stayed cable was considered with modified fixed elastic modulus by Ernst formula. The large displacement effect and the beam-column effect were considered by the calculation module of the ANSYS. The results revealed that these analysis methods were feasible. Any geometric nonlinear factor can affect the deformation and force state of the structure. They had the greatest impact on the bending moment of the tower and the vertical displacement of the main girder. The impact was up to 25% partly. The cable force and main girder stress were affected smally. The bending deflection effect of stayed cable had greater impact than other nonlinearity on the vertical displacement of the main girder.3. The nonlinear effects on the vertical displacement of the main girder at the mid of the main span and the bending moment of the side tower bottom under the most unfavorable processing condition of live load in the service stage were analyzed. The results revealed that the geometric nonlinear effects on the vertical displacement of the main girder under the dead and live load were all increasing. And the effects under live load were smaller relatively. The effects on the bending moment of the tower under dead load were decreasing in most area. But the effects under live load were increasing, and the increased proportion was up to 6.9%.The research results in this paper provide important reference for the design, construction and operation management of Wuhan erqi changjiang river bridge. The modeling idea and analysis method can be applied to the analysis of other big and complex structure.