Flexural And Torsional Finite Element Analysis Of Box Girder With Special Support

Thin-wall box girder has been widely used in bridge engineering because of its excellent space-structural characteristics. In recent years, with the limitation of environmental conditions, the skew crossing, the curve bridge, and complex loading of the bridge are usually adopted in urban bridge construction, while in high-level line, the skew and the curve bridge are also common. However, there are a few researches on shear lag effect of the complex bridge, especially on the flexure torsion system, so it is quite valuable in engineering application to analyze systematically the flexure torsion of skew supporting box girders.Based on the elementary beam theory, the research complements the impact of shear lag effect. According to thin-walled stem theory and finite element method, with the principle of minimum potential energy and functional variation method, the research builds two controlling basic differential equations of skew-supporting thin-wall box girder:one is the flexural deflection in the central coordinate system, and the other is the bending-torsion coupling in the torsion center coordinate system. With the definition of stiffness coefficient, the stiffness matrix of box beam element is deduced, taking into account of shear lag effect; according to the principle of virtual work, the equivalent nodal-load formula of element inter-loads is determined; in terms of transform and inverse-step transform rules, skew supporting constraints are solved. After gaining displacement solution, section stress is calculated. In terms of finite element analysis of bar system, the research compils the count program of one-dimension finite element in flexural torsion analysis of skew-crossing continuous box girder by using MATLAB. The statistics from one example and the results of the model show that the method applied in the research is simple and effective.The following findings can be concluded from the research:(1) Due to the influence of shear lag effect, calculative deflection of box girders is larger, compared with that of elementary beam theory; when box girder has various supporting forms and rib distances, their deflections at different loads increase by different margins; the deflection of simply supported box girder increases faster than that of cantilever box girder, and also increases more obviously in concentrated force; when simply supported box girder with a larger rib distance is in concentrated force, the increasing of its deflection is the most significant.(2) Influenced by bending-torsion coupling, the stress distribution at transverse section of a skew box girder is not symmetrical, although in the function of symmetrical load, especially in the function of eccentric load, the extent of stress non-homogeneity seems greater. Along the longitudinal direction, though bimoments are large in both eccentric load section and supporting section, they decrease rapidly. Besides, the distribution of shear lag moment is similar to that of bending moment.