Prediction of prestress losses in RC beams externally strengthened with prestressed CFRP sheets/plates

This paper presents an analytical model for predicting the short and long-term prestress losses in reinforced concrete (RC) beams strengthened with prestressed carbon fiber reinforced polymer (CFRP) sheets/plates. The long-term prestress loss model is developed by treating the strengthened beam as two sub-elements: an RC beam and a prestressed CFRP sheet/plate, connected through an adhesive bonding layer. Through force equilibrium and displacement compatibility of the two sub-elements, the influences of concrete shrinkage, concrete creep as well the interlayer slip between the RC beam and the CFRP sheet/plate on the prestress losses of CFRP are modeled using an incremental model. For a post-tensioned system with strong end anchorages, closed-form solutions for the prestress losses due to creep and shrinkage of concrete are obtained. The reliability of the proposed analytical model is validated through comparisons with previous test results reported by the authors and others research groups. The maximum difference between the experimentally observed values and the predicted values for the long-term prestress losses was found to be only 2.2% of the initial prestress of the CFRP.