Analysis And Research On Shear Lag Effect Of Twin-cell Box Girder

With the development of infrastructure in China,especially in the construction of highways,bridge structures have also been rapid development as an important component of highway.At the same time,the traffic flow also puts forward higher requirements for the width of bridge deck.Single box twin-cell girder and single box multi-cells girder begin to emerge.Twin-cell box girder has been widely used in various bridges because of its light weight,large torsional rigidity,high ductility,suitable for piping layout and adapting to modern construction methods.However,due to the difference of the web shear flow for twin-cell box girder,the stress distribution law of the twin-cell box girder flange is different from the traditional single box girder.Therefore,in this thesis,the problem of shear lag of twin-cell box girder is studied by theoretical research and numerical simulation.The main research contents are as follows:(1)This paper introduces systematically the concept and development of shear lag,sums up the existing theories and methods of shear lag analysis,and puts forward the main contents.(2)Based on the energy variational method,interface slip effect of steel-concrete composite girder and shear deformation of steel webs are taken into account,and different shear lag warping displacement functions are defined for concrete roof,floor and cantilever slabs.The governing differential equations and their closed solutions for shear lag effects of twin-cell composite box girder are derived.The analytical solution of the warping displacement function,slip function,deflection,stress and shear lag coefficient for simply supported composite box girder under uniform load and concentrated load and the ends of cantilever box beam under concentrated force are obtained.(3)The solid element model of single box twin-cell composite girder is established by the finite element software ANSYS,and the distributions of deflection,slip,stress and shear lag coefficient of composite box girders under uniformly distributed loads are obtained.The results based on the energy variational method and results for analytical solution are compared,and the analytical solution is in good agreement with the finite element method,and the deviation is within acceptable range,so the correctness and applicability of the method are verified.(4)The basic principle of equivalent load for prestressed tendon is simply introduced.Based on the energy variational method,the shear deformation of concrete webs and the strain energy of steel bars are taken into account,and the governing differential equations and boundary conditions of cantilever box girder with variable cross section are derived and obtained.Using the finite difference method,the expressions of stiffness matrix,load matrix and generalized displacement array expressed in differential form are derived respectively.According to the matrix,the stress,deflection and shear lag coefficient expressed in differential form are obtained.(5)Based on the Minjiang River Bridge,the calculation and analysis of the Minjiang River Bridge based on the bar system within linear elastisity are carried out by Midas/Civil.The elementary beam theory solution for the stress of section for box girder is obtained.Spatial finite element analysis of Midas/FEA for the partial structure is used to obtain the sectional stress value considering shear lag effect.Compared with the actual stress values,the shear lag effect in construction stage of Minjiang River Bridge is analyzed.