Experimental & finite element study of hybrid bonding of FRP to RC structures

Abstract

Externally bonding fiber reinforced polymer (EB-FRP) materials to concrete surfaces significantly strengthens existing flexural reinforced concrete (RC) structures. However, the poor bond strength between the FRP and the concrete normally causes the premature delamination of the FRP plates or sheets from the concrete surface, which notably reduces the likelihood of fully utilizing the tensile capacity of FRP reinforcement. Various techniques have been developed to enhance the bond strength and hence tackle premature failure, such as installing anchorage at the plate end, mechanically fastening instead of adhesively bonding the FRP to the concrete (MFFRP), and the use of near surface mounted (NSM) FRP. These techniques have demonstrated distinct advantages in improving the bond strength of FRP to concrete, but are unable to completely avoid premature failure. There is thus a need to improve the poor bond link between FRP and concrete. A novel technique that combines EB-FRP and MF-FRP – and is therefore termed hybrid bonded FRP, or HB-FRP – has been proposed by the author’s supervisor. The HB-FRP system uses a simply developed mechanical fastener to constrain the relative movement of adhesively bonded FRP to concrete. In this study, flexural tests are carried out on HB-FRP strengthened one-way slabs to investigate the effectiveness of the new technique. The results show that HB-FRP is able to increase the load-carrying capacity of the flexural member several fold. Further investigation by the conducting of a pull shear test on HB-FRP reinforced concrete prism has established that the strength of the bond between the FRP and the concrete is nearly doubled following the addition of a single mechanical fastener to an EB-FRP concrete prism. The HB-FRP shear concrete joint is then numerically analyzed by using the finite element (FE) method. The FE model developed in this study produces predictions that are very close to the experimental results, and is thus considered sufficient to simulate the structural behavior of HB-FRP concrete joints.