Creep Analysis of Prestressed Concrete Structures Using Creep-Transformed Section Properties

I n the analysis of prestressed members the presence of more than one layer of prestressed or non-prestressed steel complicates the computation of prestress loss and deformation. 1--3 This is particularly true in the case of a combination of prestressed and non-prestressed reinforcement in one or more layers, or in the case of composite beams. In these cases the analysis is greatly simplified by using the so-called creep-transformed section properties in a quasi-elastic stress analysis. The proposed approach makes use of well-known methods of stress analysis and is, in principle, similar to the elastic stress analysis of a member consisting of two materials in which one component (concrete) changes its temperature while the temperature of the other (reinforcement) remains constant. The easiest way to determine the temperature-induced stresses in the two component materials is to apply the forces corresponding to the free temperature strain of the one component, to the transformed section which takes account of the different material properties of the two components. In this proposed time-dependent analysis of reinforced or prestressed concrete members, the strain due to free shrinkage and creep corresponds to the temperature strain, and because of the time-dependent nature of the problem at hand, the creep-transformed cross section properties include the effect of concrete creep.