Study on Concrete Confined Effectiveness with FRP Bars

Corrosion of steel reinforcement is a major cause of deterioration in reinforced concrete (RC) structures exposed to aggressive environments. Although fiber-reinforced polymer (FRP) reinforcement provides excellent corrosion resistance, its confinement effectiveness in RC columns has not been fully understood. This study experimentally investigated the axial compressive behavior of rectangular RC short columns reinforced with steel, carbon fiber-reinforced polymer (CFRP), and glass fiber-reinforced polymer (GFRP) bars. Ten specimens with different reinforcement types and stirrup configurations were tested under monotonic axial compression to evaluate compressive strength, axial strain response, deformation behavior, failure mechanisms, and confinement performance. The results indicated that the contribution of FRP reinforcement depended on the reinforcement configuration and confinement mechanism. Specimens reinforced with CFRP longitudinal bars exhibited higher axial capacity than the steel-reinforced control specimen within the tested configurations; however, the influence of the longitudinal reinforcement ratio should also be considered. GFRP stirrups exhibited confinement behavior comparable to CFRP stirrups, whereas CFRP stirrups experienced premature fracture at bent corner regions, which reduced their confinement effectiveness and deformation capacity. Reducing stirrup spacing from 150 mm to 75 mm provided limited improvement in compressive strength because of premature stirrup failure and insufficient development of confinement effects. Existing confinement models tended to overestimate the post-peak response of FRP-reinforced columns. These preliminary findings provide experimental insights into the confinement behavior of FRP-reinforced concrete columns and contribute to the development of improved analytical models.