Novel concrete-filled steel square tubular columns stiffened with semi-circles: Concept and behaviour

Abstract

A novel concrete-filled steel tubular (CFST) column with semi-circular stiffeners welded in the inner side of the square tube is proposed in this study. The semi-circular stiffeners are developed based on the confinement mechanism in square CFST columns and aim to strengthen the confinement effect on concrete in the whole cross-section area, therefore improving the overall structural performance of the composite columns. The section is also flexible to use different grades of concrete in the core and cell regions. Experimental investigation on axial compressive behaviour of the semi-circle stiffened concrete-filled steel tubular (SCS-CFST) columns was carried out. High strength steel Q690 and two concrete grades C40 and C90 were adopted for the test specimens. Various parameters including steel tube thickness, cross-section slenderness, combination of different concrete grades as well as semi-circular stiffener size were investigated. Results showed that the semi-circular stiffeners were effective resist local buckling of the square tubes. SCS-CFST columns, particularly for those with C40 infilled in the core region and C90 infilled in the cell regions, presented significantly enhanced compressive strength and ductility compared to the corresponding normal unstiffened CFST columns. The applicability of existing design equations in European, American and Chinese standards was evaluated for the novel SCS-CFST columns. A new design approach that could more accurately consider the confinement effect in different regions was proposed and exhibited good performance.