Experimental study on long-term behavior of PSC beams

The present study reports the experimental investigations of the long-term strains in two PSC beams, one bonded and one unbonded, having the same cross-section and concrete mix, subject to the same prestress and environmental conditions. In addition, control specimens in the form of one unloaded prism specimen of the same cross-section, and two standard cylinders, one loaded axially and the other unloaded, were also monitored for the same time duration of 250 days. Electrical strain gauges and fiber optic sensors were used for strain measurement, and the results show that they agree well with each other. The ACI 209 model is found to have the least error in the prediction of axially loaded cylinder creep and shrinkage strains. However, all the prediction models (assuming constant stress) are found, in general, to overestimate the creep and shrinkage strains, and the overall loss in prestress in the two PSC beams. When the loss in prestress is incorporated, using a 3D finite element numerical model, the prediction is found to improve significantly in all the models, and particularly in the case of the GL 2000 and MC2010 models. Alternatively, improved predictions can be obtained by using the compliance from cylinder creep data and the shrinkage strains from a control specimen (having the same volume-to-surface ratio) for predicting the strains in PSC beams; this is found to yield good results.