Experimental and Analytical Study on Ultimate Load Capacity of RC Columns in the Subway Stations Under High-Temperature Gas Fume Effects

In fires, reinforced concrete (RC) columns in the subway stations were seriously threatened by high-temperature gas fumes. In this paper, an axial compressive simulation test that involved eight RC columns was undertaken to investigate the effect of high-temperature gas fume on RC columns. Two of them were control specimens with different cross sections. The others were exposed to high-temperature gas fumes. The specimens were heated to 300, 400, and 500 °C. The effects of high-temperature degree on ultimate load capacity and failure mode were investigated. As the applied load was increased, the crack gradually spread to the unheated area. Meanwhile, the initial stiffness and energy dissipation capacity were also summarized. The test results show that the ultimate load capacity and initial stiffness of RC columns decreased sharply with the increase in temperature. Compared to unexposed RC columns with circle cross section, the ultimate load capacity of specimens exposed to high temperature decreased by 47.9, 56.0 and 67.9%. The initial stiffness of RC columns with circle cross section exposed to 500 °C was 13 times lower than those of unexposed RC columns. The energy ductility of RC columns increased with the flue gas temperature. Furthermore, an analytical model was established to predict the residual axial load-carrying capacity of RC columns. It was demonstrated that the analytical model is correct and the predicted results are consistent with experimental results.