Influence of curtailed reinforcement ratio on performance of one-way reinforced concrete slab with cut-off opening strengthened with NSM steel bars

Abstract

The primary focus of this work is the behavior of reinforced concrete (RC) slabs, including cut-off apertures supplemented by near surface mounted (NSM) steel rebars with novel scheme. Previous studies have shown that the failure of RC slabs strengthened using NSM is mostly due to debonding at concrete-NSM bar interface; therefore, this study focuses on using a hooked-end NSM bars (HENB) for these slabs around openings. The primary goal of this work is to address the absence of comprehensive research in the literature about the impact of various curtailed reinforcement ratios and the efficacy of end-anchored NSM steel bars. A 4-point flexure test was used to evaluate ten specimens of reinforced concrete (RC) slabs. Every slab is the same length (1000 mm), breadth (300 mm), and thickness (150 mm). The slabs on the tension side were reinforced with deformed steel bars. In order to achieve maximum bending and zero shear, the holes were bored in the middle of the slab span. Three ratios of tensile reinforcing bars have been cut: 20%, 40%, and 60%. NSM bars came in two varieties: straight NSM bars (SNB) and hooked-end NSM bars (HENB). The results demonstrated that using HENB reduced debonding and early failure at the ends of NSM bars which led to a change in the collapse pattern to a more relatively ductile type. As the ratio of curtailed bars increased from 20% to 60%, the cracking capability of slabs decreased by 29.4% and 74.79%, respectively, as compared to solid slabs. Using HENB significantly increased the slabs' cracking load, ultimate capacity, stiffness, deflection, and energy absorption when compared to the same unstrengthened slab. Finally, 3D finite element (FE) modeling software was used to develop a numerical model for every tested sample. The FE results were in agreement with the empirical findings, as evidenced by the average discrepancy ratios of 3.76% between the FE and experimental ultimate loads of the slabs.