Punching Shear Behavior of GFRP-Reinforced Concrete Slabs with Openings at Varying Distances from the Column Face

Glass fiber–reinforced polymer (GFRP) reinforcement has been increasingly used in concrete structures due to its corrosion resistance and high strength-to-weight ratio. However, its relatively low modulus of elasticity and reduced shear resistance can influence the punching shear behavior of slab–column connections. Punching shear failure in RC flat plates is associated with the development of high shear stresses in the vicinity of the column, which may be further intensified in the presence of unbalanced moments and slab openings. Such openings are commonly required for utility ducts and are often located near columns. This study presents experimental results from six full-scale GFRP-RC slab–column edge connections, including one control specimen without an opening and five specimens with a constant-size opening located at distances ranging from 0 to 4 d from the column face, where d is the effective slab depth. The objective is to evaluate the effect of the opening distance from the column on punching shear capacity. Furthermore, a supplementary finite-element study was conducted to examine square openings with varying sizes and distances from the column front face, for GFRP reinforcement ratios of 0.9% and 1.8%. The experimental results indicated that punching shear capacity decreased as the openings moved toward the column face. Specimens with openings at 4 d exhibited 9% lower capacity than the control specimen. Finite-element analysis showed that larger openings led to greater reductions in punching shear capacity, while the opening effect became negligible at approximately 5 d from the column front face for the opening configurations investigated. Moreover, Canadian standards and American codes for GFRP-RC structures underestimated the capacity of the tested specimens.