Performance and design of oval-ended elliptical CFT columns under combined axial compression-torsion

Previously, a series of studies focusing on the response of the oval-ended elliptical concrete-filled steel tubular (OECFT) columns under various single load conditions were performed due to its novel superiorities in flow smoothness, architectural aesthetics and structural efficiency. Nonetheless, the properties of the OECFT column imposed with combined forces have never been addressed. In attempt to fill this gap, this paper aims to present a numerical analysis via ABAQUS solver to explore the torsional behaviour of the axially-loaded OECFT column. Following that, the finite element (FE) modelling was verified by the existing experimental data, and then the comprehensive parametric research on the type of column was conducted. Detailed responses of the OECFT column subjected to combined axial compression-torsion, in aspect of the typical torque ratio (T/T-u) - angle (theta) curve, failure patterns, contact action and characteristic relationship of relative ultimate torque value (T-u/T-u0) versus axial compression ratio (N/N-u0), were respectively investigated. The numerical simulation revealed that the torsional resistance of the type of column increased with the increase of the steel strength, concrete strength and steel ratio, while a decrease was obtained with the increase of the aspect ratio. Accompanied by the changes in axial compression ratio, material strength and steel ratio, obvious influences on the T-u/T-uo-N/N-uo curve were obtained. Finally, a design provision to assess the torsional strength of the OECFT column under combined axial compression-torsion was proposed and was validated in compliance with the aforementioned analyses. (C) 2020 Elsevier Ltd. All rights reserved.