Repair and retrofitting of external RC beam-to-column joints using the hybrid NSM + EBR method

•One of the shortcomings of RC structures that designed based on old versions of design code (before 1980 s or 1970 s) is the lack of transverse reinforcement in the joint panel zone that make them susceptible to seismic loads. Experiences of damage to the panel zone in the previous ground motions prove that retrofitting the joints in the damaged structures is an appropriate method to ascertain that the reinforced concrete structures achieve full capacity under the following loadings.•The main objective of this study was to investigate the effect of the hybrid retrofitting method (NSM + EBR) on improving the performance of the damaged joint and their ability to recover the lost capacity, stiffness, ductility, and damping of the joint.•The attained experimental results from testing 8 samples of external beam-to-column joint at a scale of 2:3 with seismic (S) and non-seismic design (NS), which were repaired and retrofitted with FRP bar and sheets using two NSM and hybrid (NSM + EBR) methods, was presented.•According to the results of this study, it can be concluded that the hybrid methods were able to recover the lost capacities of joints, and even reach their capacities to levels higher than the seismic control specimens. In this study, the repair and retrofitting of external reinforced-concrete (RC) beam-to-column joints using FRP composites is investigated by performing experimental tests. The seismic design detailing for the panel zone is not considered in the design of the tested joints. The test program was performed in three stages. At the first stage, the specimens were loaded until reaching different levels of damage. Subsequently, the damaged specimens were repaired and retrofitted by the NSM and hybrid EBR + NSM methods using FRP composites. Finally, the retrofitted joints were loaded cyclically until their failure. This study is intended to investigate the influence of the utilized retrofitting methods on improving load carrying capacity, stiffness, and ductility of damaged RC joints. For this purpose, eight RC beam-to-column joints, including seven non-seismically designed (NS) and one seismically designed joint (S), were cast and tested. The attained experimental results for the load-carrying capacity, stiffness reduction, and the cumulative dissipated energy of NS specimens were compared with the S specimen. The results showed the proposed hybrid retrofitting methods can recover the lost capacities of joints and even increase their capacities