Numerical Study On Shear Lag Effect Of Steel-concrete Composite Box Girder

Throughout the development status of domestic and foreign bridge,the kinds of bridgealways emerge in an endless stream,especially the long-span bridges crossing the mountains,rivers and lakes,basically have adopted the better anti torsion ability of box section,theappearing of steel-concrete composite box girder brought the application of bridge structure form to an innovative leap.Although the steel-concrete composite structures in bridge engineering application can effectively reduce the beam height,reduce the mid-span deflection,improve the bearing capacity of the structure,but with the popularization and application of long span and wide deck composite box girder,shear lag effect has been a topic that engineering designers and builders can not avoid.At present,the domestic and foreign research on the shear lag problem is mainly concentrated in the concrete box girder bridge and the steel box girder bridge,but the research on the shear lag problem of steel-concrete composite box girder bridge is still not perfect.In this paper,the shear lag effect of steel-concrete composite box girder is studied systematically.The main research contents and results are as follows:(1)The basic assumptions and basic equations of energy variational method for solving the shear lag effect are introduced in this paper.Based on the energy variational principle,the actual section normal stress formula of the simply supported box girder,cantilever box girder and continuous box girder has been demonstrated in the whole process,providing a reference for solving the beam shear lag effects under different conditions of the follow-up box.(2)The influence of width span ratio,aspect ratio,width thickness ratio,flange width of composite box beam geometry factors are focused on the shear lag effect.Under the symmetrical loads and the variations of each factor,this paper analyzes the distribution of bridge panel shear lag coefficient and explains reasons of the rules generated in detail.(3)The effects of different loading modes and diaphragm settings on the shear lag effect of composite box girder are discussed.When the load is moved from the center of the cross section to the beam rib,the influence of the shear lag of the bridge panel undergoes a transformation process from the "negative shear lag effect" to the "positive shear lag effect".In addition,the areas of shear lag effect along the longitudinaldirection of the bridge is limited,and the effect is larger only in the near field of the load section.In spite of the different loading modes,the influence of the diaphragms on the shear lag effect of the bridge deck is not the same,overall,the setting of the diaphragms is advantageous to improve the force of the bridge deck.(4)Based on the CB05 non navigable part of continuous composite box girder of Hong Kong-Zhu Hai-Macao bridge,The MIDAS/FEA finite element software is used to calculate and analyze the shear lag effect of the bridge deck in the construction stage and the stage of the bridge.In this paper,the stress state change of composite box girder bridge and the difference of shear lag effect at different control sections are summarized,and the security evaluation of the structure is also carried out.