Flexural Behavior of Concrete Hollow-Core Beams Reinforced with GFRP Bars: Experimental and Analytical Investigation

This study investigated the flexural behavior of hollow concrete beams reinforced with GFRP bars with longitudinal openings of different sizes and shapes. A total of seven beams were tested, including two solid GFRP-RC beams, four hollow GFRP-RC beams with longitudinal holes accounting for between 6 and 15% of the total cross-sectional area, and one hollow conventional steel-RC beam with a longitudinal hole of 9% of the total area. The beams were tested in flexure, and the results in terms of cracking and the ultimate loads, strains in steel and concrete, and failure modes were reported. The circular cavity performed slightly better than the square cavity, with a 3.8% higher cracking load and 4.5% higher ultimate load for the same area and location. In addition, an analytical study of the flexural capacity of the hollow beams was developed. It was found that the proposed analytical model predicted the cracking and ultimate load of the tested hollow GFRP-RC beams with good agreement. Finally, a detailed parametric study was conducted to investigate the effects of several key factors, including the size and location of the holes, as well as the concrete grade and the reinforcement ratio. The results indicated that the position of the holes had a significant effect on the behavior of the hollow GFRP-RC beams. The parametric study showed that the compressive strength of the concrete was the most influential factor on the flexural capacity of the beams, while the GFRP reinforcement ratio had a minor effect on the cracking load.