Investigation on fire resistance of steel-reinforced concrete-filled steel tubular columns subjected to non-uniform fire

The fire performance of steel-reinforced concrete-filled steel tubular (SRCFST) columns under non-uniform fire exposure is analytically and experimentally examined. Four SRCFST columns are methodically tested under 3-, 2-opposite-, 2-adjacent-, and 1-face heating to achieve the failure modes, temperature evolution in time, axial and lateral deformations, and fire resistance. Finite element (FE) analysis models were used to verify and assess the test results. The obtained results reveal that profiled steel benefits the integrity and fire resistance of SRCFST columns. The temperature distribution of the cross-section is substantially affected by uneven temperature distribution, resulting in shifting the stiffness center toward the unexposed side at the elevated temperature. The parametric studies are also conducted over various influential factors to analyze their effects on the fire resistance of SRCFST columns subjected to non-uniform fire. A modified calculation methodology based on the extended Rankine approach is developed to predict the fire resistance of SRCFST columns under various fire conditions, covering uniform fire, 3-, 2-opposite-, 2- adjacent-, and 1-face heating. Based on the quantitative comparisons between the experimentally observed data and the numerically predicted results, the simplified method generally yields accurate predictions on the ultimate load capacity of SRCFST columns under non-uniform fire.