Creep and shrinkage in prestressed concrete beams: An experimental study

The existing creep and shrinkage models used for predicting long-term behavior of prestressed concrete (PSC) beams are originally developed for cylinders under axial compression. This experimental study investigates the creep behavior in axial and flexural compression and attempts to verify the suitability of the standard models for application in PSC beams. The study is carried out by monitoring the strains and the prestress losses in four PSC beams having the same cross-section, subject to prestress loading alone, and the strains in two axially loaded cylinders, under ambient environmental conditions for a duration of 365 days. The effects of drying, stress gradient across the depth, bonding of prestressing steel, and high reinforcement have been considered. The experimental results have been compared with the predictions by six standard models (AASHTO, ACI 209R-92, GL 2000, B3, MC2010, and Eurocode model). For the PSC beams, the predictions from standard models are based on a numerical three-dimensional finite element model that accounts for the stress variation with time due to prestress loss and the effect of reinforcement. The results show that creep behavior in flexural compression is different from that in axial compression and most of the standard models over-estimate the strains in PSC beams considered in the present study. The study also provides an overview of the relative accuracies of the standard models and has practical relevance in the design of PSC bridges and estimation of prestress loss.