Structural fire performance of restrained composite columns made of concrete-filled square and circular hollow sections

Most of the previous studies on concretefilled steel hollow section columns at high temperatures addressed the effect of depth-tothickness ratio, column slenderness, initial applied load level, load eccentricity, and local buckling of concrete-filled steel tubes on the fire resistance of these columns. For this reason, it important and required to study the influence of the axial and rotational restraint on the buckling behavior of these types of columns subjected to fire. The results of a series of fire resistance tests on these types of columns inserted in a steel frame are presented and discussed in this paper. The primary test parameters taken into account were column slenderness, type of section geometry, and axial and rotational restraint level imposed by a surrounding steel frame to the columns. The specimens were then uniformly exposed to the ISO 834 standard fire curve, and the critical time (fire resistance), failure temperature distribution and respective failure modes were assessed. Finally, the results of this research study showed most of all that the fire resistance of identical semi-rigid ended columns may be not significantly affected by the stiffness of the surrounding structure but, on the contrary, their post-buckling behavior may be affected.