Prestressed Concrete Cantilever Box Girders Considering Shear Lag Time-varying Effects Analysis

Shear lag can not only cause uneven distribution of stress of section along the flanges, but also cause additional deflection of beam. Creep and shrinkage will increase the deflection of beam and cause stress redistribution between concrete and steel in section. It will also cause redistribution of internal force of continuous girders which undergoes the transform of structural systerm. Cantilever Construction Methord is widely used in thin walled PC box girder with large span, so it has theoretical significance and engineering value to construction control and the calculation of internal force and deformation of bridges of studying the coupling effect of shear lag and creep.On the base of concluding the calculating methods of shear lag and creep, this paper solves the generalized displacement function at loading time by using the energy variational method according to boundary condition, and derives formula of shear lag considering the effect of steel.On the base of time-dependent relationship of stress and strain of concrete and equilibrium of force and compatibility of deformation at any time, a novel approach to analyze long-term behavior of PC cantilever box girders considering the effect of shear lag, shrinkage & creep, relaxation, ratio of steel is presented, and the formulae are established which provides a sound approach to further study of the time-dependent behavior of PC box girders.All the deduced formulae are developed by Fortran Language, comparison between the presented method and the result of experiment shows that the new method is feasible. We can get different result by changing the value of some parameters, so we can know how they influence the coupling effect of shear lag and creep.