The coupling interaction in the rankine method for concrete filled steel tube columns under high temperatures

The Rankine approach has been extended to predict fire resistance of steel, reinforced concrete and concrete filled steel tube (CFS) columns. The conventional Rankine method ignores the coupling interaction and leads to a lower bound prediction compared with actual failure loads, especially for CFS columns. This paper develops a rational and straightforward approach to predict the fire resistance of CFS columns considering the shear bond effect. The method hinges on concept of modified buckling coefficient, and applicable to both axially and eccentrically loaded columns. It shows that the proposed approach predicts the failure load more accurately compared with the traditional Rankine approach. Four case studies comprised of 118 CFS columns from different labs are analyzed to verify the proposed approach. Material deterioration at elevated temperature with regard to the strength and stability of columns is also quantified.