Analysis On Distortion Effect Of Thin-walled Box Girders

Box section is more and more used widely in bridge construction, this is not only the boxsection has big torsional and bending stiffness, but also the box beam structure owns smallweight and many other advantages. But when the box girder bearing the eccentric loads, Inaddition to cause torsional rigidity on section, also can produce torsional constraint on section,the latter is named distortion deformation. In the distortion deformation,the box sectionproduce the warping stress and warping stress has a large proportion in itself bending stress.So when the box girder is designed,the distortion effect must be taken into account and not beignored.the distortion equation of the box girder have two kinds of forms:one is represented withthe torsion angle of distortion (distortion angle),the other is represented with the deflection ofdistortion. This paper focuses on the detailed derivation of the distortion equation which isrepresented with the distortion angle. the work of this paper is the follows:First of all, in order to obtain the distortion loads of calculation,I break down theeccentric loads on the box girder. The distortion loads include vertical and horizontaldistortion loads. And I analysis the box girder in the oblique support (three legs) cases,in thiscase also can produce the distortion loads because of the weight of box girder. But this kind ofdistortion loads belong to the supporting force, requiring a separate analysis.Secondly, using the energy variational principle and the static equilibrium method toderive the distortion angle equation of the box girder of single room. Through making thedistortion angle equation compared with distortion deflection equation,obtaining theconversing relationship between the two.Box girder distortion equation and elastic basegirder have similar expression,so we can solve the the distortion angle of the box girderthrough solving the deflection of elastic base girder.Then working for the theoretical calculation and modeling analysis for a box girder ofsingle room under uniform eccentric load. Using the two different kinds of distortionequations for the example’s calculation, it can obtain two different kinds of results ofcalculation, then making use of the result of ANSYS analysis and comparing with the tworesults of former. It can conclude that the distortion differential equation of the staticequilibrium method is more accurate.Finally, studied the effect of setting diaphragm plates for distortion of box girder. Inconcentrated eccentric loads or uniform eccentric loads working, the effect of settingdiaphragm plates for distortion of box girder is different. In uniform eccentric loads,thediaphragm plates’ settings have obvious effect on reducing the distortion. When Setting certain number of diaphragm plates,it can decrease the effect of distortion effectively. But Inconcentrated eccentric loads,the diaphragm plates’ settings fo the other sections has smalleffect but the sections of the concentrated eccentric loads,it can achieve the desired resultsonly setting diaphragm plates for the sections of the concentrated eccentric loads.At present, the bridge designers have be aware of the importance of the distortion of boxgirder, gradually, the effects of the box girder’s distortion have be analyzed and improved. Inthis paper, through the analysis on distortion effect of a rectangular section’ box girder ofsingle room,also shows the necessity of analysis on distortion effect of thin-walled boxgirders.