Theoretical And Experimental Research On Shear Lag Of Curved Box Girder With Corrugated Steel Webs

The corrugated steel web composite box girder is a kind of bridge steel-concrete composite structure appearing in the 1970 s.Its main feature is that the corrugated steel web is used to replace the concrete web,which can effectively reduce the dead weight of the beam and avoid the occurrence of oblique cracks in the concrete web.However,similar to other thin-walled box girder structures,the uneven distribution of shear stress in the upper and lower wing plates will also lead to shear lag.In this paper,the shear lag effect of curved box girder with corrugated steel webs is studied by combining theoretical analysis,model test and finite element simulation.The main results are as follows:(1)In view of the uneven distribution of shear stress in the flange of box girder,three different longitudinal displacement difference functions are set up for the top and bottom slabs and cantilever slabs of box girder respectively.The elastic control differential equation of linear box girder with corrugated steel webs is established by using energy variational principle.The control differential equation of box girder is solved by MATLAB programming combined with natural boundary conditions.Based on the stress solution formula derived from this theory,the distribution law of longitudinal normal stress along the beam width of straight box girder with corrugated steel webs under concentrated and uniformly distributed loads is given.Under the action of different load forms,the calculation theory in this paper can accurately reflect the mechanical and deformation characteristics of box girder structure;under the action of symmetrical load,the normal stress distribution of the cross section of box girder is symmetrical.(2)On the basis of thin-walled curved bar theory,the elastic control differential equation of composite curved box girder with corrugated steel webs is established,and the stress solution considering the coupling of bending,torsion and shear lag of box girder is derived according to functional definition.Combining with the boundary constraint conditions of box girder,the stress values of curved box girder with corrugated steel webs under different loads are calculated by the theoretical solution program in this paper.The shear lag effect of curved box girder with corrugated steel webs is calculated and analyzed by choosing different shear lag warping displacement functions.The results show that the distribution of normal stress on the cross section of curved box girders with corrugated steel webs is asymmetric due to the torsional deformation due to the curvature radius.The quadratic parabola is chosen as the shear lag warping displacement function,which is compared with the cubic parabola and cosine function for the waveform.The shear lag effect of curved box girder with steel webs is more accurate than that of curved box girder with corrugated steel webs.The shear lag effect of curved box girder with corrugated steel webs under concentrated load is more prominent than that under uniform load.(3)Three curved box girders with corrugated steel webs are designed and manufactured.The distribution of deflection and shear lag along the transverse section of the box girders in the elastic stage is studied.The results show that the theoretical analytical solutions of the deflection and stress of the test girders are in good agreement with the experimental values and the finite element values,which further verifies the correctness of the theoretical calculation and the finite element model.For curved box girders with corrugated steel webs,the torsional warping stress and distortion stress can not be neglected when the shear lag effect of box girders is analyzed.Because of the curvature radius of curved box girders,the torsional and distortion effects of box girders in symmetrical bending can not be offset.(4)Based on the theory of energy variational method,the influence of section geometry parameters and web type on shear lag coefficient of box girder is studied.The results show that the main parameters affecting the shear lag coefficient of continuous curved box girders are width-span ratio B/L and roof thickness t,while curvature radius R and height-width ratio H/B have relatively small effects on the shear lag coefficient.Under concentrated force,the maximum shear lag coefficient of mid-span section and support increases with the increase of width-span ratio or height-width ratio,but it increases more significantly with the change of width-span ratio,and increases only slightly with the change of height-width ratio.With the increase of roof thickness or curvature radius,the shear lag coefficient of box girder decreases gradually,but the thickness of roof decreases with the increase of box girder.The effect of shear lag is more obvious,while the radius of curvature is weaker.Under concentrated load,the shear lag effect of the roof of continuous curved box girder with corrugated steel webs at the mid-span section is weaker than that of concrete box girder,but opposite at the bottom plate.