A conversion relationship between the load ratio used in fire-resistance calculation and that used in structural design at normal temperature is analyzed for axially loaded concrete columns.To meet the target fire-resistance reliability indexes for fire endurances related to Grade 1 and Grade 2 fire resistance ratings

respectively

the minimum sectional dimensions for four-face heated axially loaded concrete columns are proposed.The results show that:（a） the design load ratio at room temperature is about 2

5

times of that for fire-resistance calculation

and an approximate value of 2.5 is feasible to common concrete columns;（b） in the case that the load ratio is less than 0.2 and the fire-resistance reliability index is not less than

the target index

columns with a section of 300 mm×300 mm given in current code can meet the Grade 2 fire resistance requirement;and（c） load ratio and fire resistance rating are main factors that influence the minimum sectional dimensions of axially loaded concrete columns.