Experimental investigation of concrete-filled square hollow section columns subjected to non-uniform exposure

An experimental study was carried out to investigate the fire performance of concrete-filled square hollow section (SHS) columns subjected to non-uniform exposure. Six full-scale concrete-filled SHS columns were tested to failure and their thermal distribution, axial deformation, lateral deflection and failure mode were measured. The effects of the number of sides exposed to fire, load ratio and the load eccentricity on the fire resistance were discussed. The results indicate that the number of sides exposed to fire has significant influence on the thermal distribution. For concrete-filled SHS columns subjected to a 1-sided exposure and 3-sided exposure, the thermal distribution is uniaxial symmetric and the lowest temperature area is closer to the side unexposed to fire rather than in the cross-sectional center. The fire resistance of the concrete-filled SHS columns increases considerably with the decreasing number of sides exposed to fire and decreasing load ratio, while load eccentricity has moderate influence. A sequentially coupled thermal-stress FE model was developed to reproduce the tested columns. The experimental results were compared with existing design provisions for concrete-filled SHS columns in uniform fire, indicating that current provisions may overestimate fire resistance of columns in non-uniform fire.