Investigation on special-shaped concrete-filled steel tubular column under combined compression and torsion

Abstract

This paper discussed the combined compressive and torsional performance of special-shaped concrete-filled steel tubes (SCFST) columns. A pseudo-static test research of eight specimens including two kinds of stiffening forms was carried out under compression and torsion. The investigated factors include section shape, stiffening form, stiffening position and axial compression ratio. From the test, specimens presented the characteristics of compression-torsion failure. The steel tube experienced buckling deformation and separated from the concrete at the middle and bottom of the column. The welds of some specimens cracked from the top to the bottom at the concave corner during the stage of decreasing load capacity. This resulted in localized crushing and the generation of torsional oblique cracks in the concrete. The hysteresis curves of the SCFST columns were relatively full in spindle shape without obvious pinching phenomenon, representing a good energy dissipation capacity. The ductility of the multi-cell CFST (MCFST) column is slightly better than that of the tensile-bar stiffened CFST (BCFST) column. There is a positive correlation between the torsion bearing capacity and parameters, such as the column limb width-thickness ratio, steel tube thickness and yield strength. When the axial compression ratio is less than 0.5, the axial compression can improve the torsion bearing capacity; when the axial compression ratio exceeds 0.5, the existence of axial compression will weaken the torsional capacity. The finite element model was established for parameters analysis, and calculation method for the T/Tu-N/Nu bearing capacity correlation curve was proposed, and the calculation results are more conservative and have certain safety reserve.