Experimental Study And Theoretical Analysis On Shear Lag Of Curved Box Girder Under Dynamic Loads

In the bridge structures,thin-walled box girder is a common structure type,shear lag is the typical mechanic behavior for thin-walled box girder,many researches have revealed that shear lag will not only cause local stress concentration and cracks but also impairs the bending stiffness of the beam,which leads to the increasing of vertical deflection and affects the safety and durability of bridges.At present,there is good solution for shear lag effects under static loads,under dynamic vehicle loads and vertical seismic excitation,curved box girder considered curvature will not only create couple deformation of bending,torsion and shear lag but also create warping and distortion,which makes research difficult.Besides,dynamic shear lag effect includes not only spatial mechanic characteristics of structures but also amplify coefficients,hence,it is very necessary to study shear lag effect of curved box girder under dynamic loads.In present work,theoretic analysis,finite element and experiment method are adopted to study shear lag effect of thin-walled box girder under dynamic loads,the follows are included.1,The spatial mechanic characteristics of thin-walled box girder and its research status and method are systematic summarized and concluded,which can provide reference for scholars to further study shear lag effect of thin-walled box girder.2,Shear lag warping displacement modes is introduced in flange parabola series,cosine function,exponential function and catenary are respectively assumed.Vibration governed differential equations of curved box girder and its responding boundary conditions are deduced by energy variation method and Hamilton principle,by assuming displacement field functions,the explicit solution to the first set bending frequency of curved box girder is carried out with Galerkin method,and the is obtained.Cubic parabola or catenary are proved to be the logical shear lag warping displacement mode.Under uniform distributed dynamic loads,there is resonance phenomenon when the dynamic loads frequency range between 92-93 Hz and the stress variation is great,the stressamplification coefficients of cross section are the same and present consistency,dynamic loads don't change the shear lag coefficients on upper flange of curved box girder but can change its stress,the differences of shear lag effect of curved box girder between static loads and dynamic loads are small;3,In order to study typical cross sections' shear lag effect of primary beam under seismic excitation,a organic glass reduced scale model(1:20)of continuous curved box girder with 3 spans is made,and the vibration table test is conducted.Then compared the experiment with finite element analysis of ANSYS,they basically agree with each other.On the basis of reliable finite element model verified by experiment,the influence of non-radial support on shear lag effect of continuous curved box girder is analyzed by finite element method.The results indicate that for continuous curved box girder,shear lag effect of inner support cross section is most prominent under seismic excitation,the next is mid-span cross section at middle span,and the shear lag effect of mid-span cross section at side span is minimum;non radial support angle and direction have a great influence on shear lag effect,shear lag effect of continuous curved box girder is sensitive to the change of support angle and other external geometrical parameters.4,Form function matrix is created by introducing high order displacement interpolation function in the node.Based on virtual work principle and dynamic finite element theory,the spatial element stiffness matrix and density matrix of thin-walled box girder with 11 degrees of freedom in each node are deduced.The tension-compression,bending,torsion,warping,distortion and shear lag effect are comprehensively considered in deducing stiffness matrix.The dynamic response of thin-walled curved box girder under El-centro seismic waves is solved with Newmark-? method.The spatial shell element model of thin-walled curved box girder is established,they agree well with each other.There is no need to transform coordinate because the flow cylindrical coordinate system is adopted,the convergent result is got when dividing beam into several elements along longitudinal direction.