Investigation on shear behavior of reinforced concrete deep beams without shear reinforcement strengthened with fiber reinforced polymers

Shear failure is an undesirable type of failure in terms of structural safety. Particularly, reinforced concrete (RC) deep beams without shear reinforcement are vulnurable to shear failure. In order to improve the shear behavior of such beams, externally bonded (EB) fiber reinforced polymer (FRP) as a strengthening technique is being applied to the outer part of the beams. However, investigations on the shear behavior of deep beams without shear reinforcement strengthened with FRP materials are insufficient in the literature. Therefore, a comprehensive experimental study was carried out on RC deep beams without shear reinforcements strengthened with fully wrapped FRP strips. The experimental parameters were chosen as the shear span-to-effective depth ratio (av/d), the number of carbon layers, the span length between carbon strips, and the type of FRP. A total of sixteen deep beams, four of which were reference beams, were fabricated and tested under three point bending load until failure. According to the experimental results, the gain percentage both in the shear and deflection capacities of strengthened deep beams increased with the av/d. Additionally, the failure modes and crack patterns of strengthened deep beams were different from those of the reference beams. Moreover, all test parameters affected the ductility behavior of deep beams having av/d of 1.5 and 2 positively. A comparative study was also conducted employing the methods commonly used in the literature and the methods based on the strut and tie model. It was observed that the methods based on strut and tie model provided superior estimates over the models commonly used in the literature.