Axial compressive behavior of hybrid CFRP-concrete-steel double-skin tubular columns

This paper investigates the axial compressive behavior of hybrid carbon fiber reinforced polymer (CFRP)-concrete-steel double-skin tubular columns (DSTCs) under core cross-section loading. A total of 18 DSTCs are tested, comprising 9 stub columns and 9 long columns. The thickness and fiber winding direction of the CFRP tube, hollow ratio, and slenderness ratio are compared. The impact of these factors is examined on failure modes, ultimate strength, and ductility of DSTCs. The tested results indicate that the failure modes of DSTCs are correlated with the fiber winding direction of the CFRP tube. Concrete confined by CFRP tubes with a fiber winding direction at 90 degrees degrees demonstrates minimal damage. The ultimate load of DSTCs is enhanced by increasing the thickness of CFRP tubes, whereas it is negatively influenced by both the hollow ratio and slenderness ratio. The ductility of DSTCs improves as the thickness of CFRP tubes and the hollow ratio increase. Additionally, the established FEA is utilized for stress analysis as well as parametric study of DSTC columns. The results show that the thickness of CFRP tubes, the modulus of elasticity in the circumferential direction of CFRP tubes, the slenderness ratio, and the hollow ratio have a greater effect on the axial compressive performance of DSTC long columns. The strength of concrete, the strength and thickness of steel tubes have less influence on the axial compressive performance of DSTC long columns. Typical FRP-confined concrete models are utilized to validate the axial ultimate strength. A new stability coefficient is recommended to improve the precision.