Effect of Transverse Reinforcement Ratios and Configurations on the Behavior of Hollow Circular Concrete Columns Reinforced with GFRP under Concentric Loading

Hollow concrete columns (HCCs) are an effective structural system for piles, electric poles, and bridge piers due to their low self-weight in conjunction with the high strength offered and reduced material use. This study investigated the behavior of concentrically loaded circular HCCs reinforced with glass fiber–reinforced polymer (GFRP) bars and spirals. Eleven hollow circular columns with outer/inner diameters of 305 and 113 mm and two solid specimens as controls were fabricated. All had a height of 1,500 mm. The investigated parameters included transverse GFRP reinforcement ratio in terms of the on-center spiral spacing and spiral diameter, configuration (spiral and hoops), and the influence of hollowness. The theoretical ultimate load-carrying capacity and the confined concrete strength of the tested hollow GFRP-reinforced concrete columns were evaluated and predicted using the available design equations and confinement models in the FRP design codes, standards, and literature. The test results indicate that either decreasing the spacing of the spiral/discrete hoops or increasing the spiral diameter could increase the ultimate carrying capacity as well as improve the confinement efficiency and ductility of HCCs.