Enhancing the Punching Shear Capacity of Two-way Concrete Slab Reinforced with GFRP Bars without Vertical Hook Shear Reinforcement
Emmanuel K. Banini *
Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana.
Charles K. Kankam
Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana.
Vincent K. Akortia
Department of Civil Engineering, Ho Technical University, Ho, Ghana.
Eugene Akomeah
Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana.
*Author to whom correspondence should be addressed.
Abstract
The pursuit of durable, ductile concrete has intensified because steel reinforcement suffers corrosion and durability problems. Glass fiber–reinforced polymer (GFRP) bars offer high strength-to-weight, corrosion resistance, and nonmagnetic properties, yet their low elastic modulus and sudden failure can result in large deflections, wide cracks and sudden collapse of GFRP reinforced concrete. This experimental study examined punching shear capacity and behaviour of two-way slabs reinforced with GFRP bars without shear reinforcement. It assessed whether hybrid reinforcement of GFRP bars in tensile zone and steel in compression zones of a flat slab improves punching shear capacity and failure mode relative to behaviour of GFRP or conventional steel-reinforced slabs only. A total of 26 full flat slab specimens with varied reinforcement ratios were cast and concentrically loaded representing interior columns of slab-column connection; parameters including load–deflection, first-crack load, crack patterns, ultimate capacity, punching shear resistance, and energy absorption were evaluated. Experimental failure loads or punching loads were compared with predicted failure loads using American, British and Canadian design codes as well as one proposed model existing in literature. The results revealed that American (ACI 318-19) code gave a better but conservative prediction of VExpr/VPred of 1.25 (experimental to predicted failure loads ratio) compared with the British (BS 8110) code, Canadian code and the model in literature all of which overestimated the punching capacity of the flat slabs. The study concludes that tensile reinforcement ratio and concrete strength have significant effect on punching capacity of the flat slab while compression reinforcement and hybrid reinforcement with conventional steel in compression zones have insignificant or unclear effect on punching shear capacity of the slab specimens. It is proposed that punching shear equation of ACI 318-19 design code be modified to include the contribution of tensile reinforcement to the punching shear capacity of flat slabs.
Keywords: Glass Fibre–Reinforced Polymer (GFRP) bars, hybrid GFRP-steel reinforcement, two-way concrete slabs, structural behaviour of flat slab, punching shear capacity