Comparisons of the fire performance between square concrete-filled steel tubular columns and square tubed-reinforced-concrete columns

Tubed-reinforced-concrete (TRC) column is an innovated type of composite column that resembles concrete-filled steel tubular (CFST) columns in appearance. Different from CFST columns, the steel tube of a TRC column is terminated at the beam to column connections and the steel tube mainly provides confinement to concrete. In fire conditions, TRC columns may behave very differently as compared to CFST columns. Till now, very few studies have been conducted on the fire behaviour of TRC columns. This paper intends to compare the fire performance of these two kinds of composite columns, which would be helpful to understand the behaviour of TRC columns in fire. Two configurations of CFST columns were investigated, one with rebars and one without. A finite element model was developed using ABAQUS and validated against test results. The effects of load ratios, sectional dimensions, slenderness ratios and load eccentricity ratios on the axial and lateral deformations, load redistributions, fire resistance and failure modes of TRC and CFST columns were analysed. During heating, the axial load is redistributed from the steel tube to the inner section in CFST columns while this load redistribution mainly occurs between concrete and reinforcing bars for TRC columns. The fire resistances of these three kinds of composite are mainly affected by load ratio, sectional dimension and slenderness ratio. The bar-reinforced CFST columns perform best in fire under concentric loading and their fire resistance are around 20% better than those of the TRC columns. As for eccentric loading conditions, the fire performance of TRC columns is the best.