Consider a column 3600 mm (12 ft.) long with square cross section
of 300 mm (12 in.), as the reference column. Four longitudinal
reinforcing bars with a diameter 19 mm (0.75 in.) are used
(q = 1.13%). The bars are tied with 8 mm (0.3 in.) ties. The main
reinforcing bars have a specified yield strength of 420 MPa
(61 ksi). The compressive strength of the concrete is 35 MPa
(5000 psi), and the concrete cover thickness is 30 mm (1.18 in.).
The studied columns with different cross-section sizes, shown in
Table 2, have the identical load ratio, slenderness ratio, and
approximately the same reinforcement ratio (1.13–1.27%). The fire
duration (tr) and load capacity (Pr) of the reference column in fire
condition are taken as the reference values.