Uni-axial compression test of concrete-filled-steel-tube columns with external confinement

Abstract

A series of experiments on ring-confined concrete-filled-steel-tube (CFST) columns were carried out to investigate the enhanced uni-axial behaviour of CFST columns in terms of Poisson's ratio, uni-axial strength and elastic stiffness. External confinement in the form of steel rings was advocated to restrict the lateral dilation of CFST columns in order to maintain an intact steel-concrete interface bonding arising from the difference in the Poisson ratios of steel and concrete. To study the effectiveness of the external ring confinement, uni-axial loading tests were carried out on 5 CFST column specimens with and without rings. All the specimens were tested under uni-axial compression in a 5,000 kN testing machine. From the test results obtained, it is evident that: (1) The external rings could improve the uni-axial strength and stiffness of the CFST columns; (2) The Poisson's ratio of ring-confined CFST columns is smaller than that of the unconfined CFST columns; (3) The Poisson's ratio of the ring-confined CFST columns are all smaller than or close to 0.2, which is the commonly accepted Poisson's ratio of concrete. Therefore, the addition of external ring confinement could successfully restore the intact steel-concrete interface bonding in CFST columns.