Study On Shear Lag Effect Of Single Box Double Chamber Corrugated Steel Web Composite Box Girder With Variable Thickness Roof

With the rapid development of China ’s bridge industry,corrugated steel web composite girder bridge,as a typical bridge in bridge engineering,has been widely used in engineering practice because of its light weight,high efficiency and convenient construction.At present,domestic and foreign scholars have rich research results on this kind of composite box girder,but there are few studies on the shear lag effect of the actual section of the composite box girder with corrugated steel webs in the project,that is,the shear lag effect of the multi-segment linear change rule of the roof thickness.This paper draws on the research results of the shear lag effect of the composite box girder with corrugated steel webs in the relevant literature,and uses the method of theoretical derivation and finite element simulation to study the shear lag effect of the single-box double-chamber composite box girder with variable thickness roof.The main research contents are as follows:(1)In view of the variable thickness roof single box double chamber corrugated steel web composite box girder,by introducing the shear lag warping displacement function based on the quadratic parabola,considering the roof and floor thickness along the cross-sectional direction of multi-segment linear variation,the additional axial displacement of the box girder is solved.The analytical solution of the stress and deflection of the box girder considering shear lag and shear deformation is solved by the energy variational method.The shear lag coefficient and deflection calculation formula of the box girder under concentrated load and uniform load are derived.The correctness of the theoretical formula is verified by an example.(2)The finite element software was used to model the actual dimensions of the Dongyang interchange bridge and to compare the results of this paper,the results of the top and bottom plate calculation by equal thickness and the finite element values;the shear lag effects in the cross-sectional direction and longitudinal direction of the box girder under different loads were analyzed.The results show that: the theoretical values of this paper are in better agreement with the finite element values than those calculated by equal thickness;the shear lag effect is most obvious at the web position in the cross-sectional direction,and decreases gradually from the web position to both sides,and the shear lag effect at the middle web is larger than that at the side web;the shear lag effect under concentrated load is smaller in the longitudinal direction,and the closer the concentrated load position is to the support,the more obvious the shear lag effect is.The shear lag effect under concentrated load is smaller in the longitudinal direction,and the closer the location of concentrated load is to the support,the more obvious it is;the shear lag effect under uniform load shows parabolic law in the longitudinal direction.(3)The influence of box girder structure size,corrugated steel web size and diaphragm number on shear lag effect of box girder is analyzed.It is concluded that the width-span ratio is the main influencing factor affecting the shear lag effect of the box girder.With the increase of the local thickness change rate of the box girder roof,the shear lag effect decreases,and the change trend in the cross-sectional direction is more gentle.It is verified that the increase of local thickness has an inhibitory effect on the shear lag effect of the box girder.The wave height and straight plate length of the corrugated steel web will affect the wrinkle effect of the corrugated steel web and then affect the deflection of the box girder.The number of diaphragms has a weak effect on the shear lag effect of the box girder,but when the number of diaphragms is less than 2,the number of diaphragms is negatively correlated with the mid-span deflection of the box girder.(4)The shear lag effect of continuous beam is theoretically derived and the correctness of the calculation formula is verified by finite element software;the distribution law of shear lag effect in the cross-sectional direction and longitudinal bridge direction of box girder is analyzed;the shear lag effect of continuous beam under different width-to-span ratios is studied and the empirical formula of effective distribution width related to the width-to-span ratio is established.The results show that: the overall error between the theoretical results and the finite element results is small;the shear lag effect in the longitudinal direction of the box girder under uniform load shows a parabolic pattern from the side bearing to the reverse bending point,and the shear lag coefficient from the reverse bending point to the middle bearing shows a monotonic curve pattern;the reasonableness of the empirical formula related to the width-to-span ratio is verified by comparing with the calculated values of the highway bridge code,and the effective distribution width under uniform load is closer to the code value.The empirical formula of width is closer to the specification value.