Performance of L-shaped columns comprising concrete-filled steel tubes under axial compression

This study examines the performance of a new type of composite column: L-shaped columns comprising concrete-filled steel tubes connected by double-vertical steel plates (LCFST-D). The fundamental structural behaviour of the LCFST-D columns is discussed. Seven LCFST-D columns were tested under axial compression. In the experiments, the variables were the height and the width of the vertical steel plates. The experimental results were used to assess the load-deformation relationship, strain distribution, and strength index. The tests demonstrated that the axial-compressive performance of the LCFST-D columns was favourable and showed that the mono-columns worked more cooperatively in the LCFST-D column structural form. Next, 3D nonlinear element models were used to analyse the mechanical properties and axial compressive behaviour of the LCFST-D columns. The results of the finite-element analysis were in good agreement with the experimental results. Based on the finite-element model, parametric studies were conducted to investigate the effects of the thickness and width of the vertical steel plates; the slenderness ratio, size and thickness of the steel tube; and the steel and concrete strengths. A method is proposed to calculate the slenderness ratio. This method considers the material properties of the steel and concrete and the sectional shape. Based on the confined effects of the concrete-filled steel tube, a method is proposed to calculate the axial-compressive bearing capacity of an LCFST-D column. The calculation results are in good agreement with the finite-element and experimental results, and the error is <10%.