Shear strengthening of deficient RC deep beams using NSM FRP system: Experimental and numerical investigation

Abstract It is essential to retrofit deep beams with shear inadequacies because these beams, although they have the same shear and flexural reinforcements as ordinary beams, are more susceptible to shear failure. Hence, it is of great significance to overcome the shear weaknesses in deep beams. This research paper aims to experimentally examine the effectiveness of near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) for retrofitting reinforced concrete (RC) deep beams subjected to shear forces. The study involved three different types of specimens. The first specimen was constructed with concrete throughout its span and included shear stirrups. The second specimen was divided into two halves, with one half lacking shear reinforcements and the other half having them. The third specimen had steel web reinforcement in one half of the span, while the other half was strengthened using NSM CFRP U-wrap strips and externally bonded horizontal CFRP strips. The proposed strengthening method significantly increased the shear strength of the deep beams, surpassing that provided by steel web reinforcement alone. Furthermore, the NSM CFRP strengthened specimen exhibited a change in failure mode from shear to flexural failure. In comparison to the control beam without stirrups, the beams strengthened with NSM CFRP U-wrap strips demonstrated an impressive 82% improvement in shear strength, while the beam with shear reinforcement showed a 23 % enhancement in load capacity. The proposed strengthened scheme is capable of enhancing the structural performance and load-carrying capacity effectively. A finite element model was generated utilizing ABAQUS software to simulate the behavior of the tested deep beams and verified against the experimental outcomes. The numerical models successfully predicted the behavior of the RC deep beams strengthened with NSM CFRP when compared to the experimental data.