Punching shear strength of reinforced concrete slabs strengthened with glass fiber-reinforced polymer laminates

Fiber reinforced polymer (FRP) is mainly used to improve the flexural capacity as well as to provide the confinement for concrete members because of its superior tensile strength. This article reports on a study undertaken to determine the punching shear strength of concrete slabs strengthened with glass fiber-reinforced polymer (GFRP) laminates, and to study the effects of concrete compressive strength, steel reinforcement ratio, and GFRP laminates on punching shear strength. The parameters of the 18 specimens studied are concrete compressive strength, steel reinforcement ratio, and the number of GFRP laminate layers. The behavior of the concrete slabs reinforced with GFRP laminates in addition to steel reinforcement is compared to that of slabs with steel reinforcement alone. The results show that applying GFRP laminates markedly increases the punching shear capacity of slab-column connections. The GFRP laminates' enhancement of the ultimate punching shear capacity is more effective for the slabs with low concrete compressive strength and reinforcement ratio. Based on these results, the authors present a design procedure to calculate the ultimate punching shear strength of slab-column connections strengthened by the GFRP laminates. The authors conclude that good correlations between predicted and experimental results have been achieved.