Simplified analysis of creep and shrinkage in prestressed concrete beams

Abstract

This paper summarises the results of an analytical and numerical study of creep and shrinkage in prestressed concrete beams, in which a simplified analysis was used to evaluate long-term flexural deformations and loss of prestress. Simple, approximate, closed-form equations were derived for the long-term curvature and loss of prestress in a prestressed section, due separately to creep and shrinkage. Numerical calculations show that the quantity and location of the prestressing steel and reinforcing steel in the section, together with the magnitude of the sustained moment, are prime factors affecting deformations and prestress loss. Although reinforcement in the section tends to have an attenuating, or "braking", effect on long-term creep deformations, and hence deflections, there are situations where it actually magnifies them. The clauses in AS 3600 that cover long-term losses and deflections do not adequately allow for these various effects.