Study On Mechanical Behavior Of Curved Steel-Concrete Composite Box Girder Considering Slip And Shear Lag

The steel-concrete composite girder is a combined structure in which steel girder and concrete slab are combined by providing shear joints to form the entirety.Because of giving full play to the advantages of steel and concrete structures,in recent years,composite girder structures have been widely used in bridge construction,especially in urban overpasses and viaducts.However,the research on the mechanical behavior of curved composite box girder lags behind the engineering practice,and the related design codes are not perfect.Aiming at the mechanical response of curved steelconcrete composite box girder under static load,based on the previous research,this paper proposes a theoretical model of mechanical analysis of curved composite box girder considering interface slip and shear lag effect.The main research contents are as follows:In order to establish the theoretical model of the mechanical analysis of the curved composite box girder,based on the warping torsion theory,the curved steel-concrete composite box girder is simplified as an elastic rod concentrated on the girder centroid.Considering the torsional warping of the section,combined with the slip and shear lag effect of combined box girder,the relationship between the strain and the basic deformation of the combined box girder is derived.Then,based on the principle of minimum potential energy,the theoretical model for mechanical analysis expressed by control differential equations and boundary conditions are established.When solving the differential equation,the solving steps of Galerkin method are introduced,and the approximate expressions of the mechanical parameters such as vertical deflection,tangential slip and axial normal stress of curved composite box girder are obtained.Taking a simply supported curved composite box girder as an example,a threedimensional finite element model is established by using the finite element software to analyze the axial stress distribution of the mid-span section under concentrated load and uniform load.The theoretical calculation results and the finite element numerical simulation results are compared to verify the correctness and applicability of the theoretical model.At the same time,the axial stresses without considering slip and shear lag are analyzed,and the respective stress contributions of these two effects are discussed,so that the follow-up researchers have a deeper understanding of the stress characteristics of the curved composite box girder.Finally,the influence of various parameters on mechanical behavior of curved composite box girder are analyzed.The effects of span-radius ratio,slip stiffness,width-span ratio and wing-width ratio on the vertical deflection,tangential slip and shear lag coefficient of the mid-span section of the simply supported curved box girder are studied,which provides the theoretical basis for the design of similar structures.The results show that the vertical deflection and tangential slip of the curved composite girder can be approximated calculated by the straight composite girder of the same span length when the span-radius ratio does not exceed 0.73.The increase of the slip stiffness reduces the mid-span deflection and the beam-end slip in curve,and this paper predicts the optimal slip stiffness based on the variation curve of the mid-span deflection with the slip stiffness.The shear lag coefficient of curved composite box girder is quite different from that of linear composite box girder.The width-span ratio and the wingwidth ratio are the main factors affecting the shear lag coefficient of curved composite box girder.