Theoretic Analysis And Experimental Research About Shear Lag Effect Of Variable Cross-Section Continuous Box Girder Bridge

Shear lag issues were studied by scholars long before, while only the shear lag problems for aviation structures were studied at that time. In the 1970s~1980s, many scholars worldwide paid attention to shear lag issues because several bridges were damaged due to neglecting shear lag effect.. Some research results about shear lag problems were attained and part of engineering issues were solved during the twenty years. With the development of highway engineering, some new problems about shear lag effect appear continuously. These problems need farther research.In the dissertation, aimed at the variable depth box girder used frequently in bridge engineering, the shear lag effect is studied about its distribution and variety during the status of cantilever construction, using plane and space finite element method (FEM). The influence of longitudinal and transverse prestressing force, and effect by difference in temperature are analysed compared. The precision of effective flange width adopted in the new highway bridge design standard (JTG D62-2004) is validated by case studies.The conclusions are as follows:(l)The space FEM can accurately reflect the stress of the practical structure. The shear lag effect of box girder bridges can't be neglected.(2) Longitudinal and transverse prestressing force can weaken shear lag effect, while transverse prestressing force will increase girder's bending stress. It must be considered during construction.(3)While analyzing shear lag effect using plane frame FEM, the effective flange width provision in the standard (JTG D62-2004) is reasonalble and safe.