Fire performance of eccentrically-loaded square and rectangular tubed-reinforced-concrete columns

Tubed-reinforced-concrete (TRC) columns are gaining increasing popularity in engineering constructions, however, research on their fire performance is still limited and mainly focused on concentrically-loaded columns. In this study, extensive numerical analysis was carried out to investigate the performance of square and rectangular TRC columns under eccentric loading and exposed to ISO 834 standard fire. A sequentially-coupled thermo-mechanical finite element analysis (FEA) model was developed in ABAQUS and validated well against fire testing results. The high-temperature overall deformations, internal bending moments and cross-sectional load redistributions of square TRC columns with different load eccentricities were analysed. Parametric studies were conducted to investigate the influences of load eccentricity ratio, sectional aspect ratio, bending direction, fire protection thickness, sectional dimension, load ratio and slenderness ratio on the fire resistance of square and rectangular TRC columns. Load eccentricity was found to have a greater effect on the fire resistances of columns of lower slenderness than those of columns of higher slenderness. Rectangular TRC columns of sectional aspect ratios no larger than 2 could generally achieve identical buckling resistance as that of the equivalent square sections. The influences of sectional aspect ratio and bending direction on the column fire resistance were insignificant. A design method was then proposed for both the ambient-temperature and high-temperature designs of eccentrically-loaded square and rectangular TRC columns. The fire design method could cover both protected and unprotected TRC columns. The design method has been thoroughly validated against detailed FEA modelling and yields excellent agreements with the modelling results.