Axial and Flexural Behavior of High-Strength Concrete Square Columns Laterally Reinforced with a New System of CFRP Tube Ties

Conventional fiber-reinforced polymer (FRP) bar ties in square FRP-reinforced concrete (FRP-RC) columns provide low strength and ductility. This is due to the lower ultimate tensile strength at the bent sections (corner) than at the straight sections of the conventional FRP bar ties. To overcome this problem, a new system of carbon-FRP (CFRP) tube ties was developed and its applicability was investigated in high-strength concrete (HSC) square columns. Hence, this study experimentally investigated the axial and flexural behaviors of the HSC specimens reinforced longitudinally with glass-FRP (GFRP) bars and laterally with CFRP tube ties (CFRP-TTs). The effect of CFRP-TTs on the behavior of GFRP bar-reinforced HSC specimens was investigated in terms of strength development and failure pattern under different loading conditions (concentric, 25- and 50-mm eccentric axial loadings, and four-point bending). The experimental results of the GFRP bar-reinforced HSC specimens laterally reinforced with CFRP-TTs (Group GC specimens) were compared with the steel bar-reinforced HSC specimens laterally reinforced with steel ties (Group SS specimens). The test results showed that the better confinement offered by the CFRP-TTs in the Group GC specimens resulted in higher axial load and bending moment capacity than in Group SS specimens under concentric, 25-mm eccentric axial loading, and four-point bending conditions