Experimental study on steel-reinforced concrete-filled steel tubular columns under the fire

This paper aims to experimentally study the fire performance of steel-reinforced concrete-filled steel tubular (SRCFST) columns without fire protection. Eight SRCFST specimens with cruciform section profiled steel were tested under the ISO-834 standard fire. The various test parameters including cross-section type of steel tube (circular or square), the load ratio and load eccentricity were considered and discussed. The temperature distribution, failure modes, axial and lateral deformation, fire resistance of the specimens obtained by test were investigated in detail. The results show that the cruciform section profiled steel provided great confinement effect to core concrete, and can efficiently suppress the generation and development of cracks in concrete. The specimens with diverse load ratio or loading method present various tendency of axial deformation versus time curves, i.e. five stages for axially loading specimens with common load ratio (n = 0.4) and three stages for specimens with high load ratio (n > 0.4) or specimens under eccentric compression. The critical temperature of SRCFST specimens is much lower than that of steel structures and CFST columns at same parameters, and the fire resistance of SRCFST columns has significant improvement compared with CFST columns. Moreover, available design method for SRCFST columns and CFST columns were compared with test results to evaluate the applicability for SRCFST specimens.