Investigation on special-shaped concrete-filled steel tubular column under pure torsion

This paper discussed the torsional performance of special-shaped concrete-filled steel tubes (SCFST) columns. A pseudo-static test research of nine specimens was carried out under pure torsion. The investigated factors include section shape, stiffening form, width-to-thickness ratio of column limbs and steel tube thickness. The failure modes, hysteresis curves, skeleton curves, energy dissipation capacity, and stress distribution were analyzed to investigate the torsional performance of specimens. The overall failure modes of different section forms are ductile damage. There are a number of 45°oblique buckling in the steel tube, and the steel plates at the top and bottom of the column are transversely torn. At the concave corner, the weld of multi-cell and the welded point of the tensile steel bar were cracked from the top to bottom. Besides, the concrete is mainly crossed by torsional oblique cracks. The hysteresis curves of the SCFST columns are plump shape without pinching phenomenon, representing good energy dissipation capacity. The effect of stiffened methods is the most significant for the torsional performance. The ductility and bearing capacity of multi-cell specimens are better than those of tensile-bar stiffened specimens. Based on the same torsion ratio of concrete and steel tube and ignoring the effect on the tensile bars, calculation methods for initial torsional stiffness and torsional bearing capacity were proposed. Comparison results show that the calculation method has good performance in terms of the accuracy and efficiency.