Theoretical And Experimental Investigations On Shear Lag Effect Of Multiple-cell Box Girders

Box girder which have bending and torsion resistance high stiffness, highintegration of cross-section property and strong construction adaptability, etc. are widelyused in a variety of bridge structures. These bridges structures include simply supportedgirder bridges, continuum girder bridge, cantilever bridge, etc. This paper studies underthe Natural Science Foundation of China which are Space Mechanics and Finite SegmentMethod of Thin-Walled Multi-cell Box Girders and Shear Lag Effect of Thin-WalledMulti-cell Box Girders Supported by Cables framework. For twin-cell box girders andthree-cell box girders，key problems of shear lag calculation for box beam aresystematically studied by through theoretical analysis combined numerical simulationand experimental results，The mail work and achievements are as follows.（1）For a twin-cell box girder, from the difference of the shear lag warping betweendifferent cantilever plates, and combined with the axial force equilibrium condition ofthe whole section, a new shear-lag warping displacement function is defined for eachcantilever plate of the box girder. The governing differential equations of equilibrium forthe shear lag for the twin-cell box girder are established on the basis of the variationalprinciple. For a typical simply supported beam with a twin-cell box girder, using threedimensional numerical methods of the plate-shell element and the analytical solutionmethod proposed in this paper, respectively, the shear lag distributions under the uniformload and the concentrated force are obtained. It is shown that the new displacementpattern of the shear lag warping can reflect the difference of the shear lag warpingbetween different cantilever plates and the new analytical solutions are in goodagreement with the finite element results. The shear lag effect on the top and bottomplates near the middle webs is different from that near the side webs on the twin-cell boxgirders. For an example girder, the stresses near the middle webs are larger than thosenear the side webs.（2）For a twin-cell box girder、three-cell box girder, considering the difference ofshear lag warping between each Span changes. For a typical simply supported beam oftwin-cell box girder、three-cell box girder, according to space shell numerical methodsand the analytical solution method in this paper, the shear lag distribution law of crosssection under the action of uniform load and concentrated force has been studied. Theresult shows that the span changes can reflect the difference of shear lag warpingbetween each cantilever plate and the results obtained the analytical solutions which arein good agreement with the finite element results. Cross-width ratio of small shear lageffect of a large, cross-width ratio of shear lag effect of a small.the stress of web site in top and bottom plate are greater than the stress of the edge of the web site.（3）Through analysis on the distribution law of the shear flow of the box girderunder vertical bending, the new method to define the warping displacement function ofshear lag is presented on the basis of the mechanism that the effect of the shear lag of thethin-wall box girder is caused by shear deformation of flange-slabs. The governingdifferential equations of equilibrium considering the shear lag for twin-cell box girderare established on the basis of the variation principle. For a typical simply supportedbeam with a three-cell box girder, using methods of the analytical solution methodproposed in this paper. It is shown that the new displacement pattern of the shear lagwarping can reflect the difference of the shear lag warping between different cantileverplates and the new analytical solutions are in good agreement with the finite elementresults.（4）For research on plexiglass model of twin-cell box girder、three-cell box girderloaded test and conducted a comparative analysis of three aspects of the analyticalsolution method、numerical experiments and space shell numerical methods. The resultshows that the shear lag warping of the displacement pattern can reflect the difference ofshear lag warping between each cantilever plate and the results obtained the analyticalsolutions which are in good agreement with the finite element results. And the numericalsize and variation are basically close about analytical solution method、numericalexperiments and space shell numerical methods the analytical solution method and spaceshell numerical methods，which showed that the test has good accuracy，also reflects theshear lag effect of the analytical solution method is feasible and has high accuracy.