Axial compressive behaviour of steel fibre reinforced self-stressing and self-compacting concrete-filled steel tube columns

Abstract

This study attempted to explore the effects of initial self-stress in concrete and steel fibre on the compressive behaviour of concrete-filled steel tube (CFST) columns. A total of 36 CFST columns with a radial self-stress ranging between 3.31 MPa and 6.66 MPa and a steel fibre volume percentage of 0, 0.6% and 1.2% were tested under axial compression. The steel tube thickness of 2.5 mm, 3.5 mm and 4.25 mm was used to achieve different confining stiffness to the expansion of concrete core. The concrete strength grade of C40, C50 and C60 was used to obtain different expansion deformations. The failure mode, axial load-axial shortening curve, ultimate load and ductility of CFST columns were investigated. Experimental results showed that all specimens exhibited shear failure, and neither self-stress nor steel fibre had obvious influence on the failure mode. Self-stress in concrete enhanced the ultimate load of the CFST columns by 9.8%–27.6%, but decreased their deformability significantly. Adding steel fibres could enhance the ultimate load and slightly improve the post-peak behaviour and ductility of CFST columns with self-stress. Based on the results of this study and literature, an optimum self-stress level (the ratio of radial self-stress and concrete strength) of 0.10 is proposed. Finally, formulas are proposed to predict the load carrying capacity of FSS-SCCFST columns under axial compression, and the predictions agree well with the test results.