Experimental Study on FRP–Reinforced Concrete–Steel Double-Skin Tubular Columns under Eccentric Compression Loads

Fiber-reinforced polymer (FRP) reinforced concrete-steel double-skin tubular columns (DSTCs) consist of an exterior glass FRP tube, an interior steel tube, and reinforced concrete in between. They have attracted the attention of researchers owing to their high ductility, lightweightedness, resistance to corrosion, and ease of construction. However, studies regarding FRP-reinforced concrete-steel DSTCs under eccentric loading are fewer compared with those regarding unreinforced DSTCs. To investigate the behavior of composite columns under eccentric compression, 12 circular cross-section columns with a height of 700 mm and an outer diameter of 210 mm were tested. They included two axial compression columns and 10 eccentric compression columns. The main parameters considered were the eccentricity, void ratio, longitudinal reinforcement ratio, and concrete strength. The results showed that the arrangement of steel bars inside the hybrid DSTCs could improve the eccentric carrying capacity and ductility of the composite columns. Furthermore, this study showed that the eccentric carrying capacity and initial stiffness decreased as the eccentricity and void ratio increased, whereas they increased with the longitudinal reinforcement ratio and concrete strength. The growth rate of the carrying capacity decreased when the longitudinal reinforcement ratio increased to 3.66%. When the void ratio exceeded 0.5 and the eccentricity ratio was 0.4, the ductility and carrying capacity decreased. Finally, a simplified model was proposed to predict the axial load–moment curves of reinforced DSTCs. The theoretical predictions were in good agreement with the experimental results of this study.