The Analysis Of Shear Lag About Thin-walled Box Girder

Shear lag effect is a significant mechanics character of thin walled box girders. Several years recently in our country, many landscape cracks are found in more and more thin walled box girders, and this phenomena shows, to neglect the shear lag effect will cause the insecurity of design work of construction.This thesis particularly expatiates the conception of the shear lag effect about thin—walled box girder and its disadvantage to structure, makes a summary of a variety of theories and methods to solve the shear lag problem in engineering group. The applicability and limitation about above theories and methods are particularly comment in this thesis and it gives the research prospect. Energy variation principle is a good method to solve the shear lag effect. When analyzing the shear lag effect in thin walled box girder with constant section formerly, experts usually consider there are same longitudinal displacement functions at the top, foot and cantilever flanges, but this supposition is not usually true. This thesis give up the older supposition and assumes three different longitudinal displacement functions to analysis the shear lag effect. The differential equations, boundary conditions and the closed-form solutions of the equations are derived from the theory of minimum potential energy. The result is, when the top, foot and cantilever flange have same breadth, then flanges have the same longitudinal displacement functions. This result shows that the work of this thesis is the farther development of former study. Compared the calculation results with the results obtained from ANSYS and other methods, the method proposed in this thesis is proved to be both more effective and accurate. Finite beam segment method is an effective way to solve the shear lag problem of statically indeterminate structure, such as continuous girder with constant cross section etc. Based on the theoretical solutions and on the traditional finite beam segment method, a finite segment model which take three different longitudinal displacement functions into account is further developed and is applied to calculate the shear lag problem easily. This thesis particularly expatiate the forming process of stiffness matrix and the nodal force vector. The new developed method is convenient, and is more useful than former and has greater engineer value.