Axial compressive performances of thin-walled steel tube confined steel-reinforced concrete columns after fire exposure

Abstract

The thin-walled steel tube confined steel-reinforced concrete (STCSRC) column can efficiently utilise the confinement effect of steel tube on concrete. The local buckling of external thin-walled steel tubes can be delayed or avoided owing to their discontinuity at beam–column joints, thus, the structural performances of thin-walled STCSRC columns are improved. To date, the behaviour of thin-walled STCSRC columns after fire exposure under axial load has not been reported. Experimental and theoretical studies of axially-loaded circular thin-walled STCSRC stub columns were conducted in this paper, exploring mechanical performance indexes and mechanisms after fire exposure. A total of eighteen thin-walled STCSRC stub columns were designed, considering the parameters of the steel tube to concrete area ratio, heating time, and strength of the concrete. To better comprehend the behaviours of thin-walled STCSRC stub columns after fire exposure, detailed discussions in terms of the temperature distribution, failure modes, load–axial strain response, stresses of steel tubes, and load proportion of each component are presented. The heating test results reveal that the maximum temperature is lower and the time to reach the peak temperature is longer when measuring points are closer to the centre of the cross-section. The thin-walled STCSRC stub column after fire exposure presents shear failure under axial compression. The longer the heating time, the earlier the shear slippage line appears. Compared with the specimen at room temperature, the residual compressive resistance and stiffness reduce with increasing heating time. The ductility of the thin-walled STCSRC stub column improves when increasing the heating time. In addition, the diameter of the cross-section, H-shaped steel to concrete area ratio, and concrete strength have beneficial effects on residual axial load capacities and stiffnesses. Moreover, simplified calculation methods were assessed to predict the residual axial load capacities and stiffnesses of thin-walled STCSRC stub columns.