THE APPLICATION OF CIRCULAR STEEL TUBE FOR CONCRETE CORE CONFINEMENT AND ADDITIONAL AXIAL SUPPORT IN REINFORCED CONCRETE COLUMN

Abstract

Circular hoops, rectilinear hoops with crossties, and spirals are widely used in reinforced concrete columns as transverse reinforcement to prevent shear failure and provide confinement. Besides transverse reinforcement, many researchers have used square or circular steel tubes to provide confinement to concrete. This paper compares experimentally the application of circular steel tubes and spirals in providing confinement to concrete. Five types of compressive test specimens were tested under axial compression, comprising one type of column confined by rectilinear hoops, one type of column confined by a circular steel tube, two types of columns confined by a combination of circular steel tube and rectilinear hoops, and one type of column confined by a combination of spirals and rectilinear hoops. The result showed that circular steel tubes confined the concrete core well and provided additional axial support. The compressive test specimens using circular steel tubes had 40.74% higher axial load-carrying capacity, exhibited more ductile behavior, and had less damage than compressive test specimens using spirals. It proved that circular steel tubes were more effective in providing confinement to concrete than spirals. Rectilinear hoops with a spacing of one-fourth and one-half of the column cross-section increased the maximum axial load by 57.78% and 20.89%, respectively.  The effect of the arching action on the concrete between the rectilinear hoops and the circular steel tubes could be neglected so that there was no ineffectively confined area, and the outer concrete was assumed to be fully effectively confined by the rectilinear hoops.