Analysis On Transverse Internal Force Of Concrete Box Girders

The concrete box girder structure is extensively used in modern bridge engineering due to its many advantages.Obvious longitudinal cracks occurs on the part of the box girders in the operational phases.It is mainly caused by the large values of box girder cross section hollow rate and distance between webs as well as the thin wall,which will generate large transverse internal forces under load.Therefore,the calculation of transverse internal forces for such kind of box girders has become an issue concerned by the fields of academic and engineering around the world.Based on the summary and improvements of traditional frame theory,according to the primary problems existed in the relevant research,this paper studied deeply on the transverse internal forces of single-cell box girder with inclined webs mainly from the following several aspects.(1)Comparative analyses have been carried to compare different computing theory of transverse internal forces and some improvements have been proposed.An improved frame analysis theory for box girders under asymmetric load is established based on the generated “TYL” method.This method combines the distortional theory of box girders and the frame analysis theory adequately.The fundamental formulas of calculating transverse internal forces are established based on the deformation coordination between the displacements of distortion and frame.The results obtained by this method have been compared with the ones obtained by ANSYS shell element,which prove the applicability and accuracy of this method.The essential difference between the frame method in this paper and the generated “TYL” frame method is the different definition on the frame displacement.Through the comparison the research shows that the results obtained by the improved method is evidently better than the ones obtained by generated “TYL” method.(2)When calculating the transverse internal forces of box girders,the frame method only considering the rigid support can’t objectively reflect the actual mechanical property.Although the method proposed by this paper have enough accuracy,it is too complicated to apply in the engineering due to the consideration of the effect of distortion.Therefore,the transverse correction coefficient is proposed to correct the results obtained by frame method only considering rigid supports.The influences of the variations of load position,the beam depth,the web-inclined degree and the cantilever length on the transverse internal forces and the correction coefficient were analyzed through a numerical example.The reasonable values of the transverse correction coefficient on the calculating cross-section of the box girder are proposed by the results obtained by the method both of this method and finite element through an engineering project.(3)Based on the research on the transverse internal forces in the decks of some established concrete continuous box girder bridges in our country,the research shows that the current bridge specification can’t satisfy the safety requirements when calculating the transverse internal forces of large span prestressed concrete box girders.The relevant coefficient in the current bridge specification should be increased to realize the safe design of large span prestressed concrete box girder bridges.