Intermediate crack (IC) induced debonding is the predominant failure mode in FRP-strengthened RC beams, while the development length of FRP laminate is enough and the shear strength of the beam is adequate. 9 CFRP-strengthened reinforced concrete (RC) beams were tested to investigate the mechanism of IC induced debonding. Based on the investigation of strain distribution in CFRP laminate and the experimental phenomena of the strengthened beam, the debonding process and its mechanism become clearly. The full debonding process can be separated into three stages: initial debonding stage, stable debonding stage, and the final debonding failure. The fundamental reason of IC induced debonding was the formation of plastic hinge region in the strengthened RC beam due to the longitudinal rebar yielding. The plastic deformation induced higher interfacial shear stress and peeling stress, resulting in the principal tension stress acting on the concrete substrate became higher. When it exceeded the tension stress of concrete, the CFRP laminate would debond from the concrete substrate of the beam.
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