Post-fire behaviour of slender reinforced concrete columns confined by circular steel tubes

The post-fire behaviour of slender reinforced concrete columns confined by circular steel tubes is investigated experimentally and numerically in this paper. Experiments were performed firstly to explore the fundamental behaviour of steel tube confined reinforced concrete (STCRC) slender columns after exposure to the ISO 834 standard fire, including the cooling phase. Temperature distributions, load versus lateral displacement curves, strains in the steel tube and failure modes were obtained and discussed. Next, a 3D finite element model was developed with the program ABAQUS using a sequentially coupled thermal-stress analysis. After validation of the FE model, parametric studies were carried out to identify the influence of key parameters on the load-bearing capacity and buckling reduction factor of slender STCRC columns. The considered parameters were the heating time, cross-sectional dimension, slenderness ratio, material strength, steel tube to concrete area ratio and reinforcement ratio. Finally, a simplified design method was proposed for predicting load-bearing capacity of STCRC slender columns after exposure to standard fires.