مهدی نعمت زاده افروزی

This paper is going to present an experimental study into the effect of bond shear stress at the interface between the concrete core and steel tube on the compressive behaviour of circular steel tube confined concrete (STCC) stub columns with active and passive confinement. Active and passive STCC columns are produced in four groups including circumferential-grooved, lubricated, talc-coated and normal specimens. All STCC specimens are loaded under compression test until the failure and various parameters such as compressive strength, modulus of elasticity, axial, lateral and volumetric strain, ductility, energy absorption, stress–strain curve and failure mode are investigated. The results indicate that the reduction or elimination of the interface shear stress in specimens with active confinement leads to an increase in the peak strength and strain as well as a reduction in the ductility, ultimate strength and ultimate strain, with an insignificant effect on the initial modulus of elasticity. The observed behaviour in passive specimens includes a reduction in the ultimate strength, ultimate strain, initial modulus of elasticity and ductility and a negligible change in the peak compressive strength. Also, the findings show that prestressing STCC columns with the present method significantly improves the compressive behaviour.