Axial Compressive Behavior of FRP-Concrete-Steel Double-Skin Tubular Columns Made of Normal- and High-Strength Concrete

This paper presents the results of an experimental study that was undertaken to investigate the effects of key parameters on the compressive behavior of fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs). A total of 24 normal-strength and high-strength concrete-filled DSTCs were manufactured and tested under axial compression. The key parameters examined included the concrete strength; thickness of FRP tube; diameter, strength, and thickness of inner steel tube; and presence (absence) of concrete filling inside it. The results indicate that both normal- and high-strength concretes in a DSTC system is confined effectively by FRP and steel tubes, resulting in a highly ductile compressive behavior. The results also indicate that increasing the inner steel tube diameter leads to an increase in the ultimate axial stress and strain of concrete in DSTCs. It is observed that the concrete filling of the inner steel tubes results in a slight decrease in the ultimate axial strain and a slight increase in ultimate stress of DSTCs. No clear influence of the strength of inner steel tube is observed on the ultimate condition of concrete in DSTCs. It is found that, for a given nominal confinement ratio, an increase in the concrete strength results in a decrease in the ultimate axial strain of DSTCs.