Fire resistance performance analysis of square tubed-reinforced-concrete columns with unequal end restraints

To investigate the fire resistance performance of tubed-reinforced-concrete (TRC) columns with unequal end restraints and develop relevant fire-resistance design methods, finite element analysis (FEA) was conducted in this paper on the fire behavior of square TRC columns under unequal end restraints. The influences of axial restraint ratio, rotational restraint ratio, cross-sectional size, load ratio, and slenderness ratio on the deformation, axial force and bending moment, buckling length, and fire resistance of the column exposed to the fire were analyzed. It was found that the increase of rotational restraint at either end of the column can lead to an increase in fire resistance and a decrease in buckling length ratio at failure. The beneficial effect of rotational restraint is especially significant when the restraint ratio ranges from 0 to 0. 5. Based on parametric analyzing reslults, simplified equations were proposed to determine the buckling length ratio and axial force of TRC columns at different heating times and with various unequal end restraints. A practical method was finally developed for the fire resistance design of square TRC columns under unequal end restraints, which was in the same form as the previously-proposed methods of pin-ended columns and columns with equal end restraints. These design methods can be used to predict the axial force and buckling length at failure and fire resistance of square TRC columns with unequal end restraints accurately and are recommended for the fire performance design of square TRC columns with combined axial restraints and unequal rotational restraints in non-sway plane frames. © 2023 Science Press. All rights reserved.