Analysis And Experimental Study On Shear Lag Effect Of Thin-walled Box Girder

The thin-walled box girder itself has the characteristics of torsion resistance and bending rigidity.As a cross-section,the box girder is used in more and more bridge structures.The elementary girder bending theory is based on the flat section assumption.The influence of shear deformation on the longitudinal displacement of the box girder is not considered.It is considered that the bending normal stress in the cross section is evenly distributed along the lateral direction when the box girder is bent.However,the shear lag effect occurs when the box girder is actually bent,and the normal stress at the junction between the top and bottom plates is larger than the normal stress at the far side,so that the normal stress value calculated by the original elementary girder bending theory is calculated.There is a big gap between the actual stress value and the actual stress value of the box girder.If the shear lag effect is not considered in the design,it will bring safety hazards to the bridge structure.In this paper,the variational method,finite element method and model test method are combined to explore the shear lag effect law of single-box single-chamber and single-box double-chamber box girder.The main work is as follows:Firstly,the expression of the longitudinal displacement of the box girder under bending is solved by the principle of minimum potential energy of the variational method,and then the expression of the bending stress of the top and bottom plates of the test girder considering the shear lag effect is obtained.Using the Midas civil and ABAQUS modeling calculations,the numerical solution of the shear lag coefficient of the test box girder is obtained.Carry out a model test and measure the stress of the box girder.Through the comparison of the variable decomposition,the numerical solution and the measured values,the investigation of the shear lag effect of the single-box single-chamber box girder is completed.Secondly,the form of the warp displacement function of the box girder is introduced,including quadratic,cubic,quadruple and cosine functions.Combining the shear flow calculation and the finite element calculation,and using the origin fitting method to obtain the expression(quadratic type)which best matches the warping displacement function of the single-box double-chamber box girder,the single-box double-chamber box is obtained by the variational method.The expression of the longitudinal displacement of the girder,and then the expression of the bending normal stress of the top and bottom of the single-box double-chamber test girder.Then,the study is based on the finite element method,the shell element model and the solid element model of the test girder are established by using the professional finite element analysis software ABAQUS.When the single-box double-chamber box-shaped girder is subjected to the vertical symmetrical load in the span,the corresponding shear lag coefficient of each of the three different loading modes is along the lateral distribution curve,and the single-box doublechamber box girder top and bottom plates are extracted from the girder end 60 cm.And the normal and longitudinal displacement of the section at 50 cm.Finally,a single-box double-chamber test steel girder with a length of 1.6m,a top plate width of 0.8m,a floor width of 0.6m,a height of 0.2m and a thickness of 8mm was actually produced.The longitudinal stress and lateral direction of the top and bottom plates at 60 cm and 50 cm from the end of the beam were measured.The stress value,combined with the generalized Hooke's law,obtains the actual normal stress value of the beam body,and compares the variable decomposition,numerical solution and measured value of the shear lag of the single-box doublechamber box girder to evaluate the accuracy of the variable decomposition.