عنوان مقاله [English]
Reinforced concrete structures are strengthened in different ways. Near surface method (NSM) and FRP confinements are some of these ways. Studies show that the use of FRP for the confinement of columns increases both the load carrying capacity and ductility. Former studies in the field of using FRP bars by applying NSM method show that these bars increase the columns flexural capacity. Despite increasing bending capacity by NSM-FRP bars, this method of strengthening leads to decreasing ductility and energy dissipation capacity of the columns. Besides the aforementioned shortcomings of this method, the lack of complete usage of load-carrying capacity of FRP bar is another deficiency of the aforementioned method in which this deficiency is removed by compounding this method with CFRP confinement. In the experimental part of the study, five specimens of square reinforced concrete column strengthened by the methods of NSM-GFRP and NSM-GFRP in combination with CFRP confinement, the effect of
concrete covering on the load-bearing capacity, initial stiffness, ductility and energy dissipation capacity were assessed. Also, hysteresis curves and Load-versus-drift ratio envelope curves were compared with each other. The specimens, under cyclic uniaxial flexure with constant axial load, were tested until failure. The results show that the use of both strengthening methods increases the columns carrying capacity. However, the NSM-GFRP method decreases energy dissipation capacity and ductility of the columns. Contrary to this method, the CFRP confinements in combination with the NSM-GFRP would increase the ductility and energy dissipation capacity, indicating that this is one of the useful methods for strengthening of the structure. Also, the results show that with the increase of the concrete cover from 20 to 40 mm, load-bearing capacity, ductility, and energy dissipation capacity would be reduced in both strengthening methods. With the increase of concrete cover from 20 mm to 40 mm, carrying capacity, ductility, and energy dissipation capacities of 10, 3, and 18\% for specimens strengthened by NSM-GFRP method, and of 25, 40, 33 \% for specimens strengthened with the combination method of NSM-GFRP and CFRP confinement would reduce, respectively. Thus, the effect of concrete cover on combinatory reinforcing method is higher.