Efficiency on uni-axial compressive strength improvement by using externally confined concrete-filled steel tube columns

Abstract

Concrete-filled steel tube (CFST) columns have become one of the most popular structural forms of column construction in tall buildings. It is particularly efficient for columns constructed of high-strength concrete because the steel tube can provide a uniform and continuous confinement that significantly improves the ductility. The CFST columns are therefore characterised by higher strength, ductility and large energy absorption before failure. However, a major problem of CFST columns is the imperfect steel–concrete interface bonding that occurs at the elastic stage, which adversely affects the confining effect and decreases the strength and elastic modulus. To resolve the problem, external steel rings are proposed to restrict the dilation of steel tube under axial compression. The authors have conducted a series of pilot tests on uni-axial compression behaviour of some CFST columns with the proposed external confinements. From the results, it was found that the strength and stiffness can be significantly improved by 10–20%. The authors have also compared the strength of these columns with the reinforced concrete (RC) columns counterparts with the same concrete and steel volume. It is evident that the strength of CFST columns is much higher than the RC columns, which indicates that the use of CFST columns can utilise less construction materials and create a more environmentally friendly construction method.