Flexural Strength of Reinforced Concrete Beams Strengthened with Prestressed Carbon Fiber-Reinforced Polymer Sheets - Part II

In an accompanying paper in the same issue of this journal, the development of a prototype mechanical device for prestressing carbon fiber-reinforced polymer (CFRP) sheets was described. To investigate the feasibility of using this device, seven reinforced concrete (RC) beams were strengthened with prestressed CFRP sheets. This paper describes theoretical and experimental results related to prestressing levels that can lead to debonding of the sheets immediately after transfer and during flexural testing. An investigation regarding the increase in the flexural capacity that results from prestressing and anchoring the CFRP sheets at the beam ends with U-wraps is also discussed. Analytical and experimental results suggest that values of the tensile strength of concrete are likely to be higher than suggested by ACI. The predominant premature failure mode in RC beams prestressed with CFRP sheets is by concrete cover separation unless the CFRP sheets are effectively anchored with U-wraps. For the prestressed sheets anchored with U-wraps, concrete cover separation was averted and the predicted theoretical capacity was achieved. Results also showed that the addition of prestressed and non-prestressed sheets increased the cracking load by nearly 3 to 6 times, respectively compared with the control beam. The yield and ultimate loads were increased by nearly 25%, but displacement ductility capacity of the system was reduced by nearly 5 times.