Flexural strength and serviceability evaluation of concrete beams reinforced with deformed GFRP bars

This paper presents a study to investigate serviceability, strength, and deformability of normal- and high strength concrete beams reinforced with deformed glass-fiber-reinforced-polymer (GFRP) bars under flexural loading. Understanding the flexural behavior of concrete beams reinforced with deformed GFRP bars with normal- and high-strength concrete would contribute to the existing literature and would provide information critical to the further use of deformed GFRP bars as internal reinforcement for concrete structures. Eight beams with a cross-sectional width and height of 200 mm and 300 mm, respectively, and a clear span of 2700 mm were tested under two-point flexural loading until failure. Four beams were made with 35 MPa normal-strength concrete (NSC); the other four with 65 MPa high-strength concrete (HSC). The bottom/tensile reinforcement of each beam consisted of two GFRP bars. Four different GFRP bar sizes (12 mm, 16 mm, 20 mm, and 25 mm in diameter) were used with reinforcement ratios ranging from 0.38% to 1.63%. Seven beams failed in concrete compression and the eighth beam failed in tension when the FRP ruptured. The test results showed that increasing the FRP reinforcement ratio had a greater effect on the service moment than the resistance moment. The effects of bar spacing on the behavior of wide beams were also investigated, revealing that the service moment increased when the bar spacing decreased, while the resistance moment increased when the concrete strength increased. In addition, the deformability concept produced significantly higher ductility indices than the energy based concept. Neither method evidenced a clear trend in the ductility indices of the tested beams. A new approach was proposed to determine the ductility index of concrete beams with FRP bars based on beam curvature. This approach demonstrated a clear trend with the tested beams: the high-strength concrete beams had higher ductility indices than the normal-strength concrete beams.