Stress Analysis And Program Design For Torsion And Distortion Of Box Girder Bridge

Box section is widely used in various types of bridge because of itsgood mechanical properties. But cracking phenomenon occurs more andmore during the operational phase under the action of bending moment andtorsion. Box girder is a spatial structure subjected to complex forces. As thecalculation of distortion and torsion of the box girder is too complicated, itgenerally simplified into a plane problem and be solved by using simplifiedcalculation method. But the simplified calculation is not very accurate; itcan't well reflect the machanical properties of each part of the box girder.So it is nessesary to develop a program to calculate the torsion stress anddistortion stress, then the people can get a direct obersavation of the boxgirder acted by forces to provide a basis for design.The paper discusses torsion calculation theory and distortion analysismethods of box girder. In the calculation of torsion and distortion, eachelement has four degrees of freedom and a cubic function is used. Thenbased on variational principle we get an element stiffness matrix and aneffective load matrix which will be used in finite element calculation. Aprogram is built in FORTRAN for torsion and distortion calculation and thecomputational process is also elaborated in the paper. The informationabout box girder's section and material can input in program as files. Andthe value of stress can be output as files after running the program. Thus thetorsion and distortion calculation of box girder is transformed intoone-dimensional finite element calculation. This calculation method isrelatively simple, and the calculation process is clear, efficient andhigh-speed.The program is proved to be correct by calculating an example andcomparing the value from analytical method with the value from program.And the ratio of the box girder's torsion or distortion stress gotten from theprogram to bending stress is close to the results from related papers. Fromthe results we can conclude that the values of eccentricity magnificationfactors are different in the bridge with different sections and different spans.Considering the limitation of eccentricity magnification factor empiricalvalue, it is nessesary to do stress calculation during analysis to in case of that local stresses of box girder are too great in any part.