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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]

Steel tubes with large diameter-thickness ratios are widely used in tubular steel towers of wind turbines. These steel tubes are susceptible to local buckling under compression-bending load, thus leading to a failure of the overall structures. In this paper, a new structural form of steel tubes with longitudinal stiffeners was proposed. Six specimens were tested to study the effects of stiffeners forms and diameter-thickness ratios of steel tubes. Finite element models were compared and validated by test results and used to further study the structural mechanisms. Lastly, the ultimate strength of specimens was evaluated by existing design guidelines preliminarily. According to the results, by setting stiffeners, especially the T-type stiffeners under the same consumption of the steel, the local buckling was prevented and the plastic deformability of the steel tubes was increased, resulting in the great enhancement of ultimate strength and ductility. The limits of quantity and width-thickness ratio of stiffeners to obtain a more stable and significant improvement effect were suggested through parametric analysis. The current methods agree well with the test results of unstiffened steel tubes but might be inaccurate for stiffened steel tubes. • Six specimens with different stiffener types and diameter-thickness ratios were tested under compression-bending load. • The finite element models were compared and validated by test results and used to further study the structural mechanisms. • The effects of stiffeners on the compression-bending behavior of steel tubes were revealed. • The limits of quantity and width-thickness ratio of stiffeners to obtain a significant effect were suggested. • The applicability and accuracy of the calculating methods in existing design guidelines were preliminarily evaluated. [ABSTRACT FROM AUTHOR]