Experimental Study On Shear Lag Effect In Simply Supported Concrete Box Girder

Box girders are widely used in the bridge engineering due to the advantages of box girder.Box beam is characterized by reasonable in structure,economical in cost,strong in anti-bending and anti-twisting,however,the shear lag effect is extremely prominent.In the seventies of last century,numerous box girder bridges were damaged due to the stress concentration which is caused by the ignorance of shear lag effect in design.After that,shear lag effect is gradually brought to the forefront by international scholars.In previous studies,the unknown displacement function is assumed to solve the shear lag problem in box girder while the bending moment and shear force on the effect of shear lag and strain distribution along plate thickness direction are usually ignored,the related study records according to the actual engineering model of box girders records are also rarely found.In this paper,based on the strain of typical sections in simply supported full-scale section concrete box girder under symmetrical concentrated loads,research works are as follows.By reasonable design of the loading plan on box beam model,choose typical cross-sections of setting,bending-shear,pure bending and concentrated force acting to test strains on the up and down surfaces by the commonly used strain slice.Also use the innovated device to test the strain inside the concrete roof and calculate the main strain through sub strains.The shear lag coefficient is applied to analysis the shear lag effect of typical cross-sections,study the influence of shear and moment on the shear lag effect,analysis the relationship between the shear lag effect and loads level,explore the shear lag effect in different flange plate thicknesses,and by contrasting the shear lag effect between the surface,reinforcement and inside the concrete,the reliability of the innovated device on testing the concrete internal strain is proved.Experiment results show that the lag effect is mainly caused by shear and there is little relationship between shear lag effect and moment,no obvious change occurs in shear lag effect as load increases,the shear lag effect in different flange plate thickness did not show obvious regularity,and the shear lag effect of internal concreteis similar to that of the surface and the reinforcement.