Strength and Deformability Aspects of Circular Concrete Members Reinforced with Hybrid Carbon-FRP and Glass-FRP under Flexure

Abstract

Although the flexural behavior of fiber-reinforced-polymer (FRP) reinforced-concrete (RC) members has been the focus of many studies in recent years, no research work has examined such behavior in FRP-RC members with circular cross sections. This paper reports on a study in which the flexural strength and deformability of circular concrete members with hybrid reinforcement—carbon-FRP (CFRP) bars and glass-FRP (GFRP) spirals—were assessed experimentally and analytically. Three large-scale RC specimens with a total length of 6,000 mm and 500 mm in diameter were constructed and tested under four-point bending. Three CFRP longitudinal-reinforcement ratios (0.8%, 1.2%, and 1.8%) were considered. GFRP spirals were used to eliminate shear cracks and achieve the full flexural capacity. A steel-reinforced concrete specimen with a reinforcement ratio of 1.2% and steel spirals was fabricated as a reference. Test results indicate that the CFRP-RC specimens failed gradually at a high degree of deformability before concrete crushing. Moreover, the flexural strength of the CFRP-RC specimen with a reinforcement ratio of 1.2% was almost 3.3 times greater than the counterpart steel specimen (with a similar reinforcement ratio) at steel yielding. The ductility and deformability of the test specimens were estimated using different approaches. The estimated deformability factor was significantly higher than that required by the North American FRP-design standards. Detailed design procedures using a computer program are proposed for estimating the flexural capacity of circular CFRP-RC members. The experimental and analytical results are discussed and compared.