RC beams flexurally strengthened with CFRP sheets combined with FRC layer for mitigating debonding failures

A hybrid strengthening system, comprising a carbon fiber reinforced polymer (CFRP) sheet combined with fiber reinforced concrete (FRC) layer is proposed in this study as a mitigatory solution to brittle debonding problems. Five reinforced concrete (RC) beams, comprising both control cases and those strengthened with the hybrid CFRP-FRC system at various FRP reinforcement ratios, were fabricated and tested to assess the system's effectiveness. A comprehensive finite element (FE) model was also developed to complement the experimental campaign and extend it into a parametric investigation on the effects of FRP reinforcement ratio (ρf), fiber percentage in FRC (vf), and FRC layer thickness (tFRC). Compared with beams strengthened with FRP alone, using the FRC layer increased the ultimate load (Pult.) of FRP-strengthened beams by 29–59%, depending on ρf and vf. The ductility of the hybrid FRP-FRC strengthened beams also increased by more than twice compared to the beams strengthened with only FRP. For the FRP reinforcement ratio (ρf) of 0.18%, use of an FRC layer with vf = 2% yields the highest increase in Pult. and ductility for the hybrid system. Ultimately, the brittle FRP debonding failure was successfully eliminated using the FRC layer, leading to desirable FRP rupture. Built with capabilities to capture material nonlinearity, contact, and debonding phenomena, the FE model predictions excellently matched those of the test results in terms of the beam's capacity, failure modes as well as load-deflection and load-strain responses.