Behaviour of Self-Compacting Concrete Columns Reinforced Longitudinally with Steel Tubes

Performance of concrete columns has been significantly improved by using composite material systems such as encased sections and concrete filled steel tubes. Different combinations of encased sections and steel sections have been widely studied. Steel sections and concrete have been used to construct composite columns with different cross-sections. The composite columns are usually constructed of normal vibrated concrete. Recently, self-compacting concrete (SCC) is also used in the construction of the composite columns. The synergies between steel and SCC in composite columns provide better performance in terms of high strength, stiffness, ductility, as well as fire and seismic resistance. This study proposes two innovative concepts: a new method to determine the stress-strain behaviour of SCC under direct uniaxial tension and a new method of reinforcing SCC columns by using longitudinal small-diameter steel tubes instead of reinforcing steel bars. For the stress-strain behaviour of SCC under direct uniaxial tension, special steel claws were designed, built and installed at both ends of 100 × 100 × 500 mm SCC specimens. These claws were used to transfer the applied tensile forces to the specimens. The crosssection of the specimens was reduced in the middle to ensure that failure would occur in the middle of the specimen. The test results showed that there was no slippage or fracture at the ends of any of the tested specimens. Also, the failure occurred in the middle of specimens, as expected. The direct tensile testing method developed in this study was also used for different types of concrete including normal strength concrete (NSC), high-strength concrete (HSC) and steel fibre reinforced high-strength concrete (SFHSC). The developed method provided rational and reliable results for the direct tensile strength of the SCC, NSC, HSC and SFHSC using a simple and effective testing technique.