Bond efficiency of EBR and EBROG methods in different flexural failure mechanisms of FRP strengthened RC beams

In recent years, using FRP sheets for strengthening and rehabilitation of reinforced concrete beams has been considered as an effective, convenient and practical method. Preventing surface debonding phenomenon is one of the issues facing the use of FRP sheets as external flexural and shear reinforcement of concrete beams. Premature debonding is caused by the lack of appropriate bonding between concrete surface and composite sheet. Externally Bonded Reinforcement (EBR) is a common method for mounting the sheet that uses conventional surface preparation. In addition, in recent years, Grooving method (GM) in its special form of Externally Bonded Reinforcement On Grooves (EBROG) has been proposed as an alternative to conventional method of surface preparation in EBR method. Although the capability of GM in preventing the premature debonding of FRP sheets from concrete substrate has been discussed in the literature, however, its efficiency compared to EBR technique in different flexural failure modes has not been investigated. In this paper, 12 reinforced concrete (RC) beams with dimension of 1000 × 140 × 120 mm were strengthened with FRP sheets and were tested. Specimens with different tensile steel and FRP reinforcement ratios were designed in a way under which the EBR and EBROG methods can be compared in two failure mechanisms of concrete crushing and FRP sheet rupture after tensile steel yielding. The results clearly showed that using the method of grooving compared with surface preparation method leads to increased ultimate load carrying capacity and ductility, and absorbing the energy in the beams by preventing the premature debonding mechanism. The results also showed that the efficiency of grooving method compared to conventional surface preparation is more highlighted in the beams with FRP rupture mechanism.