Shear performance of continuous deep beams reinforced with steel, GFRP bars, stirrups, and novel grating systems: an experimental study

This study presents a novel use of commercially manufactured glass fiber-reinforced polymer (GFRP) gratings as internal shear reinforcement in continuous reinforced concrete deep beams, a concept not previously applied in structural systems. The approach involves embedding prefabricated GFRP grating panels within concrete to enhance durability, corrosion resistance, and shear performance. An experimental program was conducted on six full-scale, two-span deep beams under monotonic loading. Specimens included beams reinforced with conventional steel bars and stirrups, GFRP longitudinal bars with steel stirrups, and hybrid systems combining GFRP bars with one to three layers of GFRP gratings. The evaluation focused on ultimate shear capacity, crack development, failure modes, maximum diagonal crack width, support reactions, and strain distribution. Beams with three grating layers achieved a 75.7% increase in shear strength over the reference, reduced diagonal crack width by 28%, and enhanced post-cracking toughness by 38%. Strain measurements confirmed effective engagement of the grating’s vertical ribs in resisting diagonal tension, with up to 199% strain increase after cracking. Comparisons with strut-and-tie models (ACI 318–19, CSA S806, and Eurocode 2) showed conservative strength predictions due to neglecting grating effects. A modified strut-and-tie model was developed to account for grating contributions, showing strong agreement with test results, with an overall average of 1.08. These findings provide preliminary evidence that GFRP gratings may be a durable and efficient alternative to steel stirrups in shear-critical concrete applications, warranting further investigation.