Fatigue Performance of One-Way RC Slabs Strengthened in Flexure with NSM Steel and FRP Bars

Abstract Many reinforced concrete (RC) members, such as bridge slabs, are periodically subjected to repeated loads and therefore require strengthening to extend their service life. The near-surface mounted (NSM) technique has recently emerged as one of the most effective methods for flexural strengthening. This study investigates the fatigue behaviour and flexural load-carrying capacity of one-way RC slabs strengthened with NSM steel, CFRP, GFRP, and BFRP bars. A total of ten slabs were tested: five under static loading and five under cyclic loading. The fatigue group was subjected to one million cycles at 50% of the ultimate static load of their respective controls, followed by static loading to failure. Performance parameters examined included crack development, failure modes, ultimate load, mid-span deflection, residual strength, ductility, energy absorption, and deformability. The results demonstrated that NSM strengthening significantly improved slab performance. The slabs were strengthened using carbon fibre-reinforced polymer (CFRP), glass fibre-reinforced polymer (GFRP), basalt fibre-reinforced polymer (BFRP), and steel bars, designated as FCR, FGR, FBR, and SR, respectively. The maximum load-carrying capacities increased by 122.5%, 49.1%, 61.35%, and 21.77%, respectively, compared to their corresponding control slabs. Residual bearing capacity also improved, with CFRP- and BFRP-strengthened slabs (FCR and FBR) achieving 11.26% and 8.17% gains over their static counterparts. These findings confirm the effectiveness of the NSM technique in enhancing fatigue resistance and post-fatigue serviceability of RC slabs, with CFRP bars providing the greatest strength improvement among FRP options, while steel bars offered a balanced combination of strength and ductility.