Eccentric behaviour of square CFST columns strengthened using square steel tube and high-performance concrete jackets

Abstract

The eccentric behaviour of concrete-filled steel tube (CFST) square columns strengthened with square steel tubes and high-performance concrete (HPC) jackets is investigated. Four types of HPC are used for concrete jackets: ordinary concrete (OC), self-stressing concrete (SSC), steel-fibre-reinforced concrete (SFC), and steel-fibre-reinforced self-stressing concrete (SFSSC). The experimental variables include eccentricities, width-to-thickness ratios, strengths of the concrete jacket, initial stresses and volume percentages of the steel fibre. The eccentric behaviours of columns with various types of concrete jackets are carefully addressed through the failure mode, load-lateral deflection curve, load versus strain behaviour, capacity analysis and ductility. Among the three volume percentages of steel fibre (0.6%, 0.9%, 1.2%) investigated in this study, 0.9% is the most suitable for improving the behaviour of retrofitted columns. The columns strengthened with the SFSSC jacket exhibit higher load-bearing capacities than the other three types of HPC jackets with good ductility. Considering the self-stressing and steel fibre effects, the stress–strain curves of various HPC jackets are presented. Subsequently, a finite-element (FE) model for the retrofitted column is established and verified along with the loads carried by each component. A detailed analysis of the load-lateral deflection curve and the interaction and stresses of the four components is performed in three stages. Finally, the load-bearing capacities of the retrofitted columns under eccentric loads calculated fusing the EC4, GB50936 and AISC 360 codes are compared.