Calculation of Short-Term and Long-Term Behavior of Prestressed Concrete Box Girders Considering Effect of Shear Lag

A set of formulae to calculate short-term behavior of simply supported prestressed concrete box girders under dead load and prestress are established based on energy method, in which shear lag and effect of prestressed steel and non-prestressed steel are taken into account. As the time-dependent relationship between stress and strain of concrete, equilibrium of sectional forces and compatibility equation are introduced, a novel approach to analyze long-term behavior of prestressed concrete box girders is presented, and the theoretical formulae considering the synthetic effect of creep and shrinkage of concrete, relaxation of prestressed steel, shear lag and restriction of steels are deduced, which can be used directly to calculate time-dependent deflection of box girder, stresses and strains of concrete and steel at any location at any time. Comparison of theoretical values shows that that the long-term deflection increases by shear lag while distribution of transverse concrete stresses become even by concrete creep and shrinkage.