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 strengthening technique is that, when the plate debonds, the load capacity suddenly drops and the failure mode is typically brittle. Because of the concrete cracking diffusion and the yielding of the steel rebars, a significant amplification of the bond stresses takes place at the beam-plate interface. Delamination occurs when the bond strength is reached locally. To properly describe and realistically predict the behavior of the strengthened beams, a displacement-based fiber beam model is used. Bond slip between the beam 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 investigations. The discussion is limited to shallow beams, where shear deformations are neglected.