The Analysis Of Space Stress And Shear Lag Effect Of Prestressed Concrete Thin-walled Box Girder Bridge

Having analysis theory of prestressed concrete continuous box girders as a center mainly, the design feature and main analytical method of box girders, concrete strength theory and the analytical method of shear lag effect of nonprismatic connected-girde are introduced in the paper. Moreover, the three-dimensional solid model of the box-girder is built by ANSYS with the powerful modeling and analysis function. In several load conditions, compare respective normal stress and major principal stress of crest slab, web and bottom slab of box-girder of the space model with that of the plane model in the same load conditions, and take a test verification for a real bridge. Analyze distribution of longitudinal stress and shear lag coefficient along cross section in two load conditions, contrasting change regularity of shear lag coefficient before prestressed with that after prestressed, and researching shear magnifying coefficient of the model under the live load.By comparing and analysing two kinds of models, several conclusions are drawnFirst, Longitudinal stress obtained in space model is bigger than that in plane model which make design controled by longitudinal stress safer. The principal tensile stress of the plane model is small.Second, prestressing effect has a biggish effect on internal force of long-span structure.Third, the box-girder has a obvious transversal stress effect. Under the weight and prestressing force, the tensile stress difference of crest slab and bottom slab of box-girder in the vicinity of the main pier is too big. The maximum value is about 4.0 Mpa, which should be paid attention.Fourth, the space model can better fit the actual structural stiffness, strength, which can reflect the true structure of the stress state.Fifth, shear lag effect of which can be increased by uneven prestress. shear lag coefficient of crest slab has a bigger dispersion degree than that of bottom slab. And prestress layout can change variation tendency of longitudinal stress in lateral direction, causing shear lag to be alternate.And last, approximtaion shear magnifying coefficient 1.05 used in calculation of bridge is less than normal obviously. So the author thinks that calculation of a bridge should consider the shear magnifying coefficient under the live load based on its width and span.