| Recently,there are many methods to analyze the shear lag of box girder.The most important method is energy variation method,but it cannot be used to analyze the shear lag effect of continuous box girder bridge with variable section.With the vigorous development of science and technology We can build a finite element model with the help of a computer.However,the establishment of this finite element model is time-consuming and requires high computers.Due to the influence of various factors during the analysis,the results obtained are also different.Not very satisfying.When analyzing the shear lag effect of variable section continuous box girder,this paper selects the accessory deflection caused by the shear lag effect as the generalized displacement.Based on the redefinition of the generalized shear lag moment,the box shape caused by the shear lag The beam deformation is separated from the deformation of the elementary beam and analyzed as an independent deformation form.At the same time,the energy differential method is used to establish the control differential equation and boundary conditions for additional deflection,and on this basis,f(additional deflection of shear lag),f '(additional deflection angle of shear lag),M(generalized moment of shear lag),Q(generalized shear force of shear lag),and four initial parameters,and according to the box beam Based on the boundary conditions of the differential equation,the initial parametric solution of the differential equation is derived.Considering the shear deformation in the flange plate,it proves that the selection of the quadratic parabola of the shear lag warping displacement function is reasonable.Based on the ideas of finite element analysis and Method,a two-node element for the box beam shear lag effect is proposed,which has four degrees of freedom.According to the definition of the element stiffness matrix,the stiffness of the beam section element shear lag effect is derived based on the initial parameter solution.Matrix and equivalent nodes Vector,a program for static analysis of a plane rigid frame in reference structural mechanics,and a calculation program for analyzing the shear lag of a continuous box girder bridge with a variable cross-section is written in FORTRAN language.In addition,examples in the existing literature are used to write this article.The program is analyzed,and the analysis results are compared with literature solutions and finite element solutions,which proves the reliability of the program.This paper takes Hongshengli three-span continuous prestressed variable-section box girder bridge(40m + 70 m + 40m)as an engineering example.Under different load conditions,the ratio of the warping normal stress of each key section to the bending normal stress They are different,and the shear lag effect also has a significant effect on the deflection at the key section.Under the condition 1(the load is distributed uniformly in the middle span,and the concentrated load is distributed in 1/2 of the middle span),the middle span 1/2 The ratio of the normal warpage stress to the normal bending stress at the cross section is large,and under the influence of the shear lag effect,the deflection at the 1/2 cross section of the midspan is increased by 12.9%;under working condition two(left and right sides)The load is distributed uniformly across the span,and the concentrated load is distributed at the 1/2 cross section of the left edge),the ratio of the normal bending stress to the bending normal stress at the pier fulcrum section is larger,and under the influence of the shear lag effect,the edge The increase in deflection at the cross section of 1/2 has increased by 15.9%;under condition three(the left side span and the mid-span are arranged with uniformly distributed loads,and the left side span is arranged with the concentrated load at the 1/2 side),the left side span is 1 / 2,The ratio of the warping normal stress to the bending normal stress at the cross section is large,and under the influence of the shear lag effect,the left side spans 1/2 of the cross section.The deflection increased by 15.2%;under the condition 4(the entire bridge span structure only acts on the self-weight load),the ratio of the normal bending stress to the bending normal stress at the pier support section is larger,and it is affected by the shear lag effect.The deflection increase at the mid-span 1/2 section is 13.6%;under the condition of the fifth working condition(second stage dead load),the ratio of the normal bending stress to the bending normal stress at the pier fulcrum section is large.And under the influence of the shear lag effect,the deflection at the 1/2 span of the mid-span increases by 13.5%.Based on the analysis of the various working conditions above,the shear lag effect has a significant effect on the force of the bridge,so Must be carefully considered in actual engineering... |
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