Experimental and Theoretical Development of Load–Moment Interaction Diagrams of Circular Hollow GFRP-Reinforced Concrete Bridge Columns

The use of hollow concrete columns (HCCs) as piers and piles for bridge applications is widespread due to their higher load-carrying capacity, stiffness, and strength-to-mass ratio compared to the solid section. This study aimed to examine the behavior of HCCs reinforced with glass fiber–reinforced polymer (GFRP) bars and spirals under different loading conditions, analyze the impact of various parameters on their load-carrying capacity, and expand the research database with numerous load–moment interaction diagrams. Ten large-scale GFRP-HCCs, which had a height of 1,500 mm and inner/outer diameters of 113/305 mm, were tested under different levels of eccentricity (concentric, 8%, 16%, 33%, and 66%). A parametric study was conducted to examine the effects of the hollow ratio, longitudinal reinforcement ratio, bar compressive strength, longitudinal reinforcement type, and concrete compressive strength on HCC behavior. The study highlighted the importance of considering the compressive strength of the longitudinal GFRP bars because neglecting it underestimated the axial load and bending moment capacities of the HCCs. The results revealed that initial eccentricity had a greater impact on bending moment than second-order effects.