Study On Shear Lag Effect Of New Type Corrugated Web Steel-concrete Composite Small Box Girder Bridge

With the continuous development of composite girder bridge with corrugated steel webs and the improvement of design and technology,a new type of improved composite box girder appears.The main difference is that the traditional concrete floor is replaced by steel floor.Compared with the traditional composite structure with corrugated steel webs,this new composite structure with corrugated steel webs has lighter weight,makes full use of the tensile properties of steel,and is also greatly convenient for construction,which has been applied in construction.There are many mechanical researches on traditional composite box girder with corrugated steel webs,but few researches on this new structure.In this paper,the shear lag effect of this new structure is studied.The main contents are as follows:(1)Firstly,the relevant information about the research on composite box girder with corrugated steel webs at home and abroad is collected to understand its main mechanical characteristics,especially the definition,research methods and research status of shear lag effect.(2)By establishing the shear lag warping displacement function,considering the modification of different wing displacement and the additional axial displacement correction term due to the normal stress imbalance of the section,the shear lag effect of the simply supported corrugated steel web composite box girder is derived based on the energy variational method.Then,the maximum difference function of the flange angle under different external load cases is derived by using different boundary conditions.Through the difference function,the deflection,normal stress and shear lag coefficient of each flange are derived.In the theoretical derivation,it is found that the shear lag effect and the shear deformation of the web will affect the deflection,but the shear deformation of the web has no effect on the normal stress.The shear lag effect of box girder is different under different load forms,but the load has no effect on the shear lag coefficient under the same load form.(3)Taking a project as an example,the deflection,stress and shear lag coefficient of simply supported box girder are calculated by using the formula derived in the second chapter.Using the finite element software to establish the model in the example,extract the deflection and stress values of the model,and compare the results of the two methods,we can see that the data are in good agreement.Through the analysis of the two methods,it can be seen that the shear lag effect appears in the section stress distribution under the load.When the resultant force of uniform load and concentrated load is the same,the shear lag coefficient of mid span section is larger under concentrated load.The influence range of shear lag effect caused by concentrated load in the middle of the longitudinal bridge is very small,and the shear lag effect in the middle of the span is the largest.The shear lag effect appears in the whole span under uniform load,and increases from the middle of the span to the fulcrum.When comparing the effective distribution width of roof concrete with the code and the theoretical value in this paper,the difference of midspan section under concentrated load is large.(4)By changing the size of each component of the box girder,the influence of different factors on the shear lag effect of simply supported composite box girder with corrugated steel webs is analyzed.Considering the convenience of transportation and construction in the design of modern urban bridge,small box girder structure is adopted,so the deflection,stress and shear lag effect of simple supported multi box single room small box girder in different construction sequence are analyzed by using finite element software,and a more reasonable construction sequence is obtained.