Effect of basic design parameters on IC debonding of CFRP-strengthened shallow RC beams

Abstract

Bonding of fiber-reinforced polymer (FRP) plates to the tension face is an effective technique for strengthening reinforced concrete (RC) beams. However, an important design issue is the sudden and premature failure by intermediate crack (IC) debonding of the externally bonded FRP plates from the concrete surface of the strengthened beams. The objective of this paper is to examine the effect of basic design parameters on the IC debonding of the FRP-strengthened RC beams and to assess the accuracy of prediction models of IC debonding in international codes and guidelines. A total of 13 RC beams were constructed and tested for this purpose. The test variables include steel reinforcement ratio, compressive strength of concrete, depth of the beam, and the width of the FRP reinforcement. None of the test variables caused a change in the IC debonding failure mode, except for the strengthened beam with FRP area covering its full width. Among studied variables, only the compressive strength of concrete had a significant effect on the debonding strain of the FRP plates. The results of this experimental work were compared with IC debonding prediction models—currently in effect—of international codes and guidelines. Among these codes, ACI 440.2R-08 and the Italian guide CNR DT200 showed the most accurate and consistent prediction of the IC debonding strain.