Analysis Of Torsional Effect Of Continuous Beam Girder Under Lane Load

In recent years,thin-walled box girder has been widely used,and theoretical research on the torsion of box girder has been increasing.Three-dimensional finite element model has been widely used in it,but its time-consuming and labor-intensive,because the analysis is affected by various complex factors,the results are more complicated.It is difficult for people to analyze part of the influence on the structure,and there are still some limitations in the actual engineering application.The main research in this paper is the analysis of torsional effects of continuously variable cross-section box girder under lane load.On the basis of thin-walled members,the relational expressions of physical quantities under torsion are obtained through theoretical derivation.The first-order variation of the total potential energy formula of the box girder was solved to obtain the basic differential equation with constrained torsion.The differential equation was solved,and the boundary conditions were explicitly combined.The finite element method is used to analyze and obtain the stiffness matrix and equivalent node force of the box girder element under constrained torsion.Using FROTRAN language,based on the program Frem2,a program for calculating the torsion effect of box girder was prepared.The reliability of the self-programming program was determined by comparing the calculation results of existing examples in the literature.The engineering example selected in this paper is the Beijing-Hangzhou Ancient Canal Bridge.Three load cases are selected based on the actual situation to calculate the torsional effect using a self-programmed program,and the bending effect is calculated using a plane element finite element program.Defines the stress amplification factor,which is used to characterize the effect of torsion caused by eccentric load on stress.Combined with actual calculation examples,the following conclusions are obtained:(1)Under the effect of constrained torsion,the law of warping double moments is: the value of the concentrated torque is the largest at the action of the supporting torque and the support section,and it decays from the maximum value to both sides;There is a mutation in the position.The distribution law of torsion angle is: the maximum value is reached where there is a concentrated external force,and the support point is zero.(2)Under the same working conditions,the stress amplification factor is the largest when a single lane is acting;the stress amplification factor is the smallest under the four lanes.(3)In case one(maximum mid-span bending moment),the maximum value of the stress amplification factor appears at 1/4 and 3/4 of the middle span;under case two(maximum positive mid-span bending moment),the The maximum value appears at the first bearing;in case three(the bearing has the largest negative bending moment),the maximum value of the stress amplification factor appears at the middle span 3/4.(4)In the same cross section,where the top plate and the web intersect,the torsional effect caused by the eccentric load has the largest influence on the stress.(5)under the loads of different lanes under all load conditions,the maximum value of the stress amplification coefficient is 2.0787,which occurs under the single lane under the second condition(the maximum positive bending moment of the mid-span).(6)under the four-lane load that is most consistent with the actual situation,the stress amplification coefficient at the middle of the mid-span is about 1.09,and its maximum value is about 1.2~1.3,wherein: the first operating condition is 1.2179,the second operating condition is 1.3187,and the third operating condition is 1.2079.