Role of bond in RC beams strengthened with steel and FRP plates

This paper discusses the problem of predicting the stiffness, load capacity , and failure modes of RC members strengthened in bending with bonded steel or carbon-fiber-reinforced plastic thin plates. A critical issue of this s trengthening technique is that, when the plate debonds, the load capacity s uddenly drops and the failure mode is typically brittle. Because of the con crete cracking diffusion and the yielding of the steel rebars, a significan t amplification of the bond stresses takes place at the beam-plate interfac e. Delamination occurs when the bond strength is reached locally. To proper ly describe and realistically predict the behavior of the strengthened beam s, a displacement-based fiber beam model is used. Bond slip between the bea m and the plate is included by assuming separate displacement fields in the beam and in the strengthening plate. The proposed model is used to confirm and investigate distinct failure modes observed in experimental investigat ions. The discussion is limited to shallow beams, where shear deformations are neglected.