Study On Shear Lag And Pre-stressed Effect Of Curved Box Beam

Curved box-girder is widely used for modern highway bridges, railway bridges,interchanges and viaducts. Due to geometric complexity of curved box-girder,cross-section warping and shear lag effect will occur during the service life besidesconventional structural behaviors (i.e. extension, flexure, torsion, etc). The safety ofbridge would be doubted without consideration of the cross-section warping and shearlag effect in design. Shear lag effect is not considered in the actual design but justdiscussed academically for the reason of the insufficient research in our country. Inthis paper, a shell finite element model of single-box and single-cell box-girder basedon the shell finite element method is proposed and a model test is carried out to verifythe shear lag as well as the nonlinear bearing behavior of curved box-girder further.The main content is as following: Considering the structural behaviors of curved box-girder and the analyticdemands of shear lag effect, 8-nodes plane shell element is used to build spatial finiteelement model and a corresponding spatial finite element analytic program isdeveloped by FORTRAN language. A typical example validates that the resultcalculated by the program is in well agreement with the example's, which shows thatthe program is reliable and applied;Through analysis, the generant reason of shear lagphenomenon is tried to be explained further. In order to distinguish the nonuniformdistribution of direct stress on top plate caused by torsion and shear lag effect,suggestion has been brought forward on the definition of shear lag coefficient withconsideration of the nonuniform distribution of force on internal-external web platesof curved box girder. For the purpose of studying influence of prestress on shear lageffect, the property of prestress bar in the curved box-girder is analyzed based onspace vector theory and the influence of prestress on the shear lag of curved boxgirders was explored at elastic stage based on the equivalent load method;A separatedreinforced concrete finite element model is established by ANSYS, which is used toanalyze the non-linear characteristic of the test specimens;Potential problems ofexperiment and theory are analyzed based on the comparison between prestressconcrete model experimental results and academic results.Academic calculation and experimental investigation indicate that:(1) Shear lageffect is mainly caused by the non-uniform variation of longitudinal shear stress. (2)Shear lag coefficient will be reduced at the mid-span section of curved box-girder andincreased near the beam end. (3) The ANSYS non-linear finite element analysisresults is in well agreement with the test results, which proves that the method ofmodel building is feasible.