Behavior of RC Beams Strengthened with Externally Post-Tensioning CFRP Strips

Synopsis: Experimental study has been performed in order to investigate the behavior of RC beams strengthened with externally post-tensioning CFRP (Carbon Fiber Reinforced Polymer) strips. A total of 11 specimens have been manufactured of which specimens strengthened with bonded or unbonded CFRP strips considering the level of post-tensioning as experimental variable, and a specimen with simply bonded CFRP strips. The following phenomena have been observed through the experimental results. The specimen with simply bonded CFRP strips failed below 50% of its tensile strength due to premature debonding. On the other hand, all the specimens strengthened with post-tensioning CFRP strips showed sufficient strengthening performance up to the ultimate rupture load of the CFRP strips. Also, it was observed that the cracking loads and yield loads of the strengthened beams were increased proportionally to the posttensioning level, but the ultimate loads were nearly equal regardless of the posttensioning level and bonded or unbonded system. In addition, the yield loads and cracking loads of the beams with bonded post-tensioning systems were increased about 20% compared with those of the unbonded post-tensioning systems. However, the beams strengthened with unbonded post-tensioning CFRP strips showed ductile behaviour with large deflections resulting from the reduced member stiffness.