Performance evaluation of normal- and high-strength concrete column specimens reinforced longitudinally with different ratios of GFRP bars

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Glass fibre-reinforced polymer (GFRP) bars, as reinforcement in concrete structures, have several desirable properties over conventional steel bars, such as high tensile strength, low density and resistance to corrosion. However, there are still some concerns about using GFRP bars as longitudinal reinforcement in concrete columns primarily due to their low compressive strength and low modulus of elasticity. It is evident that the compressive behaviour of GFRP bars as longitudinal reinforcement in normal strength concrete (NSC) and high strength concrete (HSC) columns has not been extensively investigated to formulate adequate design guidelines. In this study, 12 reinforced concrete column specimens were tested under concentric compression loading. All the tested column specimens were 600 mm in height and 154 mm in diameter. The column specimens were divided into two groups as per the compressive strength of the concrete used in casting the column specimens, which were 45 MPa and 90 MPa. Each group consisted of six column specimens, one plain concrete column specimen and five column specimens reinforced transversely with 6 mm steel helices spaced at 40 mm pitch (transverse reinforcement ratio ρt = 2.2 %). Out of those five column specimens, one had no longitudinal reinforcement (ρ = 0), one was reinforced longitudinally with steel bars (ρ = 2.4) and the rest were reinforced longitudinally with GFRP bars (ρ = 2.7, 3.2, and 4.3 %). From testing results, it was observed that steel and GFRP bar reinforced NSC column specimens exhibited two peak axial loads, with a higher second peak axial load than the first peak axial load, whereas steel and GFRP bar reinforced HSC column specimens exhibited one peak axial load only. It was also observed that the contribution of the longitudinal steel bars was about two times the contribution of GFRP bars in both NSC and HSC column specimens. Finally, the ductility of GFRP bar reinforced NSC column specimens was greater than the steel bar reinforced NSC counterpart, whereas this trend was the opposite in the column specimens cast with HSC.

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