| As a classic subject, shear lag effect of thin-wall box girder should not be ignored in the design and analysis of bridge structures.Based on the theory of thin-walled stem and bar system structure finite element method, a reasonable displacement model is posed. The parameters of the section are collected on the structure appropriately, and the axis of 3d spatial structure is simplified to one-dimensional beam element in the collection, it can realize automatically the function of shear lag effect in the structure analysis. Because the structure analysis, only requires the axial along the beams are discrete and each section only need a few degrees of freedom. Traditional finite element can get precision at the expense of increasing a large freedom.In comparison with traditional finite element, finite segment method as the way of discrete of structure is a kind of high efficient method.As a widely acknowledged method in engineering design, one dimensional analysis method for bar system structures supplements shear leg deformation ofζand definitely defines the generalized force shear lag moment Mζ. Mechanics concept becomes brief and distinct and the shear lag effect of thin-walled box girder can be analyzed as general bar system structure. Compared with traditional shell and entity element, this method has self-evident advantages of easy data input/output, short time for calculating and clear mechanics concepts; it can accordingly be easily mastered by engineers. The method can achieve higher calculation accuracy with extremely few discretization freedoms. The method with the semi-analytical of discrete structure provides a new and effective way to study shear lag effect of box girder.This paper will mainly study the several aspects as follows:1. Based on the comprehensive consideration of the traditional shear lag warping displacement modes and the amending modes of the equilibrium conditions included in the warp stress, the deflection formulas considering shear lag effect are given for both simply supported and cantilever box girders under concentrated and uniformly distributed load. According to numerical examples, the deflections of simply supported and cantilever box girders are respectively calculated. The deflection increase of box girders considering shear lag effect is analyzed.2. The generalized force corresponding to the shear lag displacementζin shear lag analysis of the box girder is clearly defined, namely the shear lag moment Mζ, and the formula of stress is derived by using generalized force (internal force).3. Considering the coupling sexual of the shear lag displacement and deflection and slope, the differential gowerning equations of thin-walled box girder with shear lag effect are established. The homogeneous solution of governing differential equation for the shear lag analysis is adopted as the displacement function for the unit. The formulas of the element stiffness matrix and the vectors of each element in the equivalent nodal forces are obtained by taking the constants of integration as conversion variables. So the shear lag analysis in complex box girder with varied cross-section becomes easy.4. Present shear lag study is mainly directed against single box girder of single room, the research of shear lag effect on twin-cell box girder is very little.This paper will choose twin-cell box girder as the research object, and finite segment method will be analyzed the shear lag effect of three spans continuous variable cross-section of box girder. |
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