Research On The Parameters Of Shear Lag Effect In Cantilever Box Girder Bridge

Box-grider beam has been widely used in a variety of bridge systems duing to its advantages—strong torsional performance, light weight, large capacity and convenient construction.However, the impact of its shear lag effect has to be considered. Duing to the effect of shear lag, there is very great difference between the actual stress of box-section and the calculated stress according to the general beam theory.If the phenomenon is ignored,it can result in the insecurity in the structural design. Therefore, designer should take necessary measures to avoid or reduce the adverse effects arising from this phenomenon. But there is not a unified theory about the effect of shear lag factor at present, the specific stipulations about the analysis and the calculation of shear lag did not have been made both at home and abroad on the existing box design specifications. So the further study should be taken on this issue.In this paper, the shear lag effect on the basis of the principle of minimum potential energy is studyed using variational method, and the effect of shear lag factor is explored. The main study contents include:(1) Based on energy variational principle, the governing_differential equations of the shear lag effect is deducted in the the application of the minimum potential energy theory. And then the variable decomposition of the shear lag effect is studyed in both cases of the constant section and the variable cross-section, the solution of shear lag effect is as well as researched in the hyperstatic structure.(2) Analyze the various parameters of shear lag effect to identify the main factors,such as the imposed of prestressing load, box girder cross-section geometric parameters and load types and ways. With the help of finite element method, space finite element model and plane truss model are respectively established. Some conclutions can be shown that the width span ratio of the box-girder bridge is the main factor of the shear lag effect,in addition, imposing the load of prestressed also effectively reduces the shear lag effect,at the same time, different forms of load may cause different effects of shear lag.(3) According to the measured data from the construction of Weijiazhou Bridge, some analysis can be derived from about shear lag effect in the cantilever box-girder bridge, the above conclusions through models is furtherly demonstrated.