Study On Shear Lag Effect In Side-box Girder Of Concrete Cable-stayed Bridge

Nonuniform stress phenomenon from shear lag effect always bring adverse influence tothe design of box girder, especially those with a wider flange plate. If not seriouslyconsidering shear lag effect in practical engineering, there may be some disastrousconsequences. Side-box girder cross section because of its light weight, convenientconstruction and the like are increasingly applied in the design of main girder of cable-stayedbridge. According to the stress characteristics of the cable-stayed bridge, the main beam bearcompression and bending load together. With the increasing of bridges’ width and thedecreasing of span to width ratio, nonuniform stress phenomenon and shear lag effect of wideand thin side-box girder cross section become more and more obvious, therefore, it is verynecessary to study shear lag effect on this kind of section structure.Based on systematically summarizing the current research of shear lag effect on theoryand method, this paper analyzed the shear lag effect of side-box cross section with analogousbar method, obtained the normal stress calculation formula which considering shear lag effectand the shear lag coefficient calculation formula at mid-span of simply supported beam orfixed end of cantilever that subjected to concentrated load or uniform load. In view of thestress characteristics of the main girder which mainly bear compression and bending load ofcable-stayed bridge and according to the deformation characteristics under load action withconsidering the shear lag effect, it is assumed that different longitudinal displacement functionto flange plate with different widths, the shear lag control differential equation and theformula to solve the common boundary conditions by using the energy variational methodbased on the principle of minimum potential energy are derived. After, calculation result fromthe finite element software ANSYS at an engineering example was applied to check theformulas obtained from the two methods above. Through comparative analysis, it verifiedcorrectness of the calculation formulas derived above. Analytical method has simplecalculation steps, so it is easy to solve the shear lag coefficient by a spreadsheet orprogramming. What’s more, it can match the design requirements and improve the workefficiency in the bridge preliminary design stage. Finally, analysis was made in detail forcorrelative influence parameter of side-box girder shear lag effect in order to grasp its law. This paper has certain theory significance and practical significance to study the shear lageffect of side-box girder section.