Uniaxial behaviour of confined high-strength concrete-filled-steel-tube columns

Abstract

High-strength concrete (HSC) columns are usually provided with heavy confining steel within the potential plastic hinge region to restore flexural ductility. However, as the effectiveness of confining steel decreases with the concrete strength, the required confining steel content for high-strength concrete columns becomes very large, which causes steel congestion in the proximity of beam–column joints. A better method is to adopt a concrete-filled-steel-tube (CFST) column, which uses a hollow steel tube to confine high-strength concrete. Compared with ordinary reinforcement, concrete-filled-steel-tube columns provide a more uniform confining pressure to the concrete core and reduce steel congestion. Nonetheless, a major shortcoming of concrete-filled-steel-tube columns is that the imperfect interface bonding occurs at the elastic stage as steel dilates more than concrete in compression. This adversely affects the confinement of the steel tube and decreases the elastic strength and modulus. To resolve the problem, it is proposed in this study to use external steel confinement in the forms of rings and ties to restrict the dilation of the steel tube. For verification, a series of uniaxial compression tests on externally confined concrete-filled-steel-tube columns was performed. Theoretical models for predicting the uniaxial load-carrying capacity of ring-confined concrete-filled-steel-tube columns were also developed.