Analysis On Shear Lag Effect Of Double Cell Box Girders PC Continuous Rigid Frame Bridge

Box section was given priority to the form of the cross-section for large-span bridge, especially for Large-span PC Continuous Rigid Frame bridge.Because there is uneven shear deformation in the flange plate of the box girder, the distribution of normal stress was distributed in a curve along the cross-section. This phenomenon is called shear lag effect Ignoring the shear lag effect will result in unsafe design.In order to probe into shear lag effect of Large-span PC Continuous Rigid-frame Box Girder Bridge,this article use the main bridge of Continuous Rigid frame of the Wei River extra large bridge for relying on the project,using Finite Element procedure for PC Continuous Rigid Frame bridge calculation of the section normal stress analysis.This paper mainly studies include:First,this paper introduces the development of large-span PC Continuous Rigid Frame Bridge and current research ways of shear lag effect.On this basis,this paper focuses on the energy variational method to solve box girder shear lag effect and gives the solution process of shear lag effect in several common bridges.Second,this paper basing on Wei River Bridge,through the establishment of finite truss element model as a whole by Bridge Doctor and MIDAS,comparison analyze the normal stress of the control sections,and through the establishment of finite element model as a whole by ANSYS, calculate the normal stress and shear lag coefficient of the control sections in various working conditions and give the distribution of the normal stress of box girder under shear lag effect. Through calculate,these conclusions have been found as following:The distribution of normal stress has negative shear lag effect in the top of double cell girders of continuous rigid frame bridge under the symmetric load.The shear lag coefficient of the junction of the middle web and the roof of the box girder section is smallest. The shear lag coefficient of the the roof of the box girder section is biggest. The distribution of normal stress has positive shear lag effect in the bottom of double cell girders of continuous rigid frame bridge under the symmetric load.The shear lag coefficient of the junction of the web and the bottom of the box girder section is biggest. The shear lag coefficient of the the roof of the box girder section is smallest.At last,this paper analyze the influence factors of shear lag effect in box girder,including geometric parameters such as width span ratio,width height ratio and length of cantilever and load types and ways such as concentrated load and distributed load.Through calculate and analysis, these conclusions are found as following:The width span ratio and width height ratio of the box girder are important factors of shear lag effect.They have a positive relation with the shear lag coefficient.The length of cantilever of the box girder has little effect on the shear lag coefficient.The load types and ways of the box girder also are important factors of shear lag effect. When the concentrated load is loaded in the free section of the cantilever box girder,all sections of the cantilever box girder only have positive shear lag effect. When the distributed load is loaded in the cantilever box girder,all sections of the cantilever box girder have alternative positive and negative shear lag effect.