Ultimate strength of reinforced concrete beams retrofitted with hybrid bonded fiber-reinforced polymer

The external bonding of fiber-reinforced polymer (FRP) to reinforced concrete members has become a popular method of retrofitting/strengthening concrete structures in recent years. This technology allows the high tensile strength of FRP to be transmitted to the concrete structure through surface adhesion. Surface adhesion that relies on the tensile strength of concrete is known to be weak and unreliable. It results in a poor degree of bonding between the FRP and the concrete members and often induces premature debonding at the bond interface. Such premature debonding has greatly reduced the usage rate of the FRP material's tensile capacity. One feasible, and probably the only fundamental, solution to this problem is to ensure that the FRP "takes root" in the concrete substrate. The authors have accordingly developed a new technology-hybrid bonded FRP (HB-FRP)-that combines adhesive bonding with a new means of mechanical fastening. A pilot test demonstrated that the bond strength of this new technology was 7.5 times that of a conventional adhesive bond, thus successfully resolving the problem of intermediate crack-induced debonding (IC-debonding) for which "no efficient method is available yet to avoid.." This paper presents the results of an experimental study on the quantification of the ultimate bond strength of HB-FRP retrofitted concrete beams, from which a theoretical model is developed for the design of their members. Copyright © 2010, American Concrete Institute. All rights reserved.