Effects of thin-walled inner steel tubes on the compressive behavior of concrete filled double skinned steel tubular columns

Concrete-filled double skin steel tubular columns with higher hollow ratios (HHR-CFDST) have gained significant attention in recent times as essential components in offshore wind turbine structures. As these structures continue to grow, an effective strategy to reduce steel consumption is to increase the diameter-to-thickness ratios of the steel tubes. However, there is a lack of studies exploring the performance of HHR-CFDST columns with thin-walled inner steel tubes. To address this, four HHR-CFDST columns with varying ratios of the inner tubes and one double-skin hollow steel tubular column were produced and tested under axial compression. The study investigated failure modes, local buckling behaviors, and ductility characteristics. The local buckling performance index of specimens with different ratios varied by up to 16.90 %. Additionally, a finite element model was used to analyze the stress distributions of the concrete when peak loads were reached, revealing a maximum variation of 45.4 % in stress values among specimens with different ratios. A multi-parameter impact analysis was then conducted to establish a reasonable limit (250) for the ratio of the inner steel tube in engineering design. Finally, the findings from this investigation were integrated into existing ultimate strength formulas outlined in established specifications.