MECHANISM OF COVER DELAMINATION OR FRP DEBONDING OF CFRP STRENGTHENED RC BEAMS AT DIFFERENT STAGE

The existing experimental results and failure modes indicate that cover delamination or FRP debonding from RC beams strengthened with CFRP will limit the overall effectiveness of the bonded FRP system, and result in premature failure in addition to the conventional modes of failure observed in unstrengthened RC beams. The main objective of this study is to assess the effects of flexural cracks in the midspan tension zone of the plated beams on interfacial stresses. Based on experimental results and crack patterns of RC beams strengthened with externally bonded CFRP sheets, the distribution of interfacial stresses of CFRP strengthened un-cracked and pre-cracked RC beams is discussed. It is shown that cracks or cracking in substrate along the CFRP-strengthened RC beams causes the shear stress concentrations, which are believed to be responsible for the premature failure observed in CFRP-strengthened beams. Finally, on the basis of failure modes of aging structures, general design recommendations for CFRP anchorage are proposed for preventing or delaying premature failures of CFRP-strengthened beams.