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This paper introduces a novel cross-sectional design for concrete-filled steel tubular (CFST) columns termed "concrete-filled double square steel tube" (CFDSST). The CFDSST columns incorporate an inner square steel tube positioned diagonally at 45° relative to the outer square steel tube, which serves as a stiffener for the outer tube. A three-dimensional finite element simulation model is presented to accurately predict the behavior of axially loaded CFDSST short columns. This model considers the influence of concrete confinement by the steel tubes. Experimental data are employed to validate the accuracy of the finite element model. The validated model is then utilized to assess the performance of the proposed columns, considering various geometric and material properties. The results highlight the substantial enhancement in structural performance achieved by the innovative CFDSST column configuration compared to conventional square CFST columns. The integration of the inner CFST components enhances both buckling resistance and the confinement mechanism of the column. This contributes to the increased load-bearing capacity, ductility, and residual strength of the columns. Notably, the steel tube thickness, the yield strength, and the concrete compressive strength greatly affect the performance of the column. Lastly, a simplified design model is formulated to predict the compressive capacity of the CFDSST stub columns, providing accurate outcomes validated by numerical analysis. • A new configuration of CFST columns is introduced. • Finite-element simulation model for CFDSST stub columns is developed. • The behavior of CFDSST stub columns is parametrically studied. • The proposed finite-element simulation and design models provide accurate predictions. [ABSTRACT FROM AUTHOR]

Concrete-filled double skin steel tubular columns with large hollow ratios (LHR-CFDST), as quintessential elements within offshore wind turbine structures, have received significant attention in contemporary times. As the scale of this type of structure continues to expand, an effective strategy to reduce steel consumption involves elevating the diameter-to-thickness (D/t) ratios of the steel tubes. Presently, there is a dearth of studies that explore the performance of LHR-CFDST columns in the case of thin-walled inner steel tubes. Four LHR-CFDST columns with varying D/t ratios of the inner tubes and one double-skin hollow steel tubular column were produced and tested under axial compression. The study encompassed an investigation into failure modes, local buckling behaviors, and ductility characteristics. The local buckling performance index of specimens with varying D/t ratios differed by up to 16.9%. Furthermore, the verified finite element model was subsequently employed for mechanistic analyses pertaining to the sandwiched concrete's stress distributions, and so on. When the peak loads were attained, the maximum variation in the stress values of the concrete of the specimens with different D/t ratios reached 50.4%. Subsequently, a multi-parameter impact analysis was applied to give a reasonable limit on the D/t ratio (225) of the inner steel tube for engineering design. Finally, the prevailing ultimate strength formulas outlined in established specifications were adapted by integrating the characteristics uncovered through this investigation. • Thin-walled inner tubes have a significant effect on CFDST with large hollow ratios • Inner tube's D/t ratio is positively correlated with the local buckling • Stress distribution and contact stresses in concrete are inextricably linked to the inner tube's D/t ratio • Multi-parameter impact analysis gives a reasonable limit of the D/t ratio for design • The equation considering the effect of buckling predict the CFDST columns with thin-walled inner tubes more accurately [ABSTRACT FROM AUTHOR]