Improved hybrid bonding technique for attaching FRP to reinforced concrete beams

The use of externally bonded fibre reinforced polymer (EB-FRP) composites is becoming popular for the repair of understrengthened or damaged reinforced concrete members. However, the EB-FRP strengthened members often fail owing to fibre reinforced polymer (FRP) debonding, reducing the strength utilisation ratio of FRP and leading to catastrophic structural failure. To solve the problem, an improved hybrid bonded FRP (IHB-FRP) technique is developed in this paper. The pull-out test was conducted to select an appropriate mechanical fastener for the technique and IHB-FRP strengthened reinforced concrete beams were tested under three-point bending to examine the effectiveness of the technique. Experimental results show that the selected fastener is suitable for the IHB-FRP technique and the IHB-FRP strengthened beam fails owing to FRP rupture even for seven plies of FRP strips. Finally, the required tightening force in the fastener is estimated to ensure the effectiveness of the IHB-FRP technique.