Simply Supported Box Girder, Prestressed Concrete Creep Effects Take Into Account The Shear Lag Analysis

The long-term deflection of prestressed concrete box girders due to creep is an important index in design, and shear lag is another important index which should be considered. In this paper, it's the first time to study the synthetic effect of shear lag, ratio of prestressed steel and non-prestressed steel, to time-dependent behavior of PC box girders based on energy law and variation's principle, and the formulae are established which presents a novel train of thought to further study the long-term behavior of PC box girders considering the effect of shear lag and steel.First of all, after the dead load and prestress are treated as extra load and energy law is used, the formulae to calculate effect of shear lag considering effect of prestressed steel and non-prestressed steel are deduced, which can directly and obviously to analyze the effect of steel to time-dependent deflection, stress and strains of concrete and steel, thus to promote the precision of analysis. Study shows that the steel reduces the effect of shear lag.Second, When the 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 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.Finally, All the deduced formulae are developed by Fortran Language, which is used to calculate the example. Comparison among the new method, finite element based software Midas & Dr. Bridge shows that the theoretical values obtained by new method are liable and reasonable, and the new approach is easy to be used to check the results from software.