Analysis And Experimental Study On Shear Lag Effect Of Concrete Box Girder With Butterfly Webs

The butterfly web box girder structure is characterised by its light weight,low maintenance cost,short construction period and good ventilation performance.Its web is butterfly shaped and prefabricated assembly is used for construction,which can greatly improve construction efficiency.Domestic research on butterfly web box girder structures is scarce and does not cover the shear hysteresis effect.In this paper,a 1:8scaled-down model of the butterfly web box girder and an Abaqus finite element model were established using the Mustard River Bridge as a reference,and loads were applied to both separately to extract load-displacement curves and stress distribution curves,and the relevant parameters of the structure were varied to study the shear hysteresis effect using the advantages of finite element analysis.On the basis of the experiments and finite elements,the cross-sectional stiffness of the box girder was calculated by equating the section at the hollow web to a rectangular open web according to the principle of equivalent section.After the cross-sectional equivalence,the theoretical equation for the shear hysteresis effect of the butterfly web box girder is derived based on the energy variation principle,and the theoretical values obtained are compared with the experimental and finite element values.The definition of effective width in the relevant domestic and international codes is referred to,and the effective widths under each country’s standards are calculated and compared with the test beam model.The effect of the shear hysteresis effect on structural deformation,ultimate load carrying capacity and bending shear stress is analysed according to the effective width.The main findings and conclusions are as follows.(1)Under load,the butterfly web box girder(simply supported)basically shows positive shear hysteresis effect distribution,and the shear hysteresis effect at the hollow web in the span and at the bearing position is larger.(2)The effect of each factor on the shear hysteresis effect is analysed by varying the span diameter,flange width,plate thickness and structural form of the box girder.(2)The effect of each factor on the shear hysteresis effect is analysed by varying the parameters of slab thickness,span diameter and structural form.The shear hysteresis effect of the bending shear section of a butterfly web box girder(continuous)under uniform load is greater than that of the bending shear section under concentrated load.(3)Based on the equivalent section method and the energy variation method,the formulae for calculating the shear hysteresis effect of butterfly web box girder are derived,and through comparative analysis it can be seen that the results of the energy variation method for calculating the shear hysteresis effect of butterfly web box girder are closer to the experimental values,which can provide reference for the calculation of the shear hysteresis effect of the structure.(4)According to the definition of effective width,comparing the experimental and finite element results with the values of effective width of box girder in the codes of various countries,it can be seen that the effective width of butterfly web box girder calculated by using the domestic code is more reasonable.On this basis,the effect of shear hysteresis on structural deformation,ultimate bending capacity and bending shear stress is analysed,and it is found that the effect of shear hysteresis on structural deflection is mainly concentrated in the bending shear section;the ultimate load carrying capacity of the box girder calculated using the Japanese code is closer to the test value;the contribution of shear hysteresis bending shear stress to the overall bending shear stress of the web is small,and the structural bending shear stress can be calculated according to the primary beam theory The shear hysteresis buckling shear stress is a small contribution to the overall bending shear stress of the web.