Research On Shear Lag Effect Of Thin-walled Box Girder Under Dynamic Load

The research on shear lag effect was originally limited to metal structures in the aeronautical field.Since the 1960 s,many bridge structures had been found partial cracking and instability in the beginning of design,even existed more serious damage,which all due to the neglect of shear lag effect.As an important factor affecting the safety of bridge,shear-lag effect has gradually attracted scholars’ attention.With the development of recent decades,research on shear-lag effect has obtained some achievements,which can effectively solve part of the problems on practical bridge structure’s design and using phase,while still lack comprehensiveness and pertinence.With the development of transportation industry in our country,new problem related to shear-lag effect has been found continuously in some new-built bridges,research on shear-lag effect under dynamic loads and other abnormal phenomenon such as negative shear lag effect are still scarce,the related provision in recent specifications has not yet formed a complete system on effective flange width,therefore,it is of great theoretical,meanwhile,practical significance to study and solve the problem of shear lag effect.In the view of advantages and widespread use of box-section beam,taking box-section beam as the main research object,combined with energy variation method and numerical analysis method,based on the principle of minimum potential energy,this paper mainly study the shear lag effect of box beam under different conditions.In this paper,the calculation method of thin-walled box’s girder shear-lag effect under different influences is established through theoretical derivation,which mainly focus on the shear-lag effect of thin-walled box girder under dynamic loads.The review introduces the research theories and main research methods of the bridge shear lag effect at the current stage,the current domestic and foreign codes on the effective flange width of box girder are listed;With the method of minimum potential energy principle calculus of variation,based on the cubic parabolic form of the warp displacement mode,this paper establishes differential equation of elastic theory regarding the shear deformation,furthermore,the nalytical solutions of shear-lag coefficient in terms of the simply supported beam and cantilever beam under concentrated loads and uniform loads are obtained;According to homogeneous differential equation of free vibration,combined with the vertical displacement differential equation and boundary conditions,which based on the principle of minimum potential energy,thin-walled box girder’s bending moment analytical solution of undamped free vibration is deduced,box girder section’s normal stress analytical solution under transient dynamic load is established,meanwhile,thin-walled box girder’s shear lag effect of different width to span ratios is also studied in this paper;Based on the study of free vibration,this paper analyzes the forced vibration of simply supported box girder,the shear-lag coefficient of thin-walled box girder is redefined based on the deflection,the simply supported thin-walled box girder’s analytical solution of the shear lag coefficient is established,then,author compares the shear lag effect of thin-walled box girder in terms of different size factors,combining shear lag coefficient according both stress and deflection;Recent regulation of box girder’s effective flange width is summarized,combined with relevant domestic and foreign codes and method author’s calculation method,this paper analyzes and compares the shear lag effect of long-span straight box girder while using the finite element analysis,then obtains influence law of shear-lag effect on the behavior of bridge structure,deduces some reasonable methods for calculating the shear lag coefficient and effective flange width,which are of reference significance for similar bridges’ research on shear lag effect and preliminary design.