Fire resistance behavior of large-space single-span portal frame structures is influenced by steel components temperature rise and fire-resistance critical temperature of whole structure.Based on statistic analysis of temperature rise data of non-protected large-space structure steel components

we got a temperature rise fitting formula of steel component considering fire source power

building volume

cross-section shape coefficient of steel component.Combining with the statistic analysis of the whole structural fire-resistant critical temperatures data of single span steel portal frames

we got an another whole structural fire-resistance critical temperature fitting formula considering loading rate

column high and coefficient K.Through the analysis of influence of above factors on the temperature gradient of steel components and fire-resistant critical temperature change rate

we obtained objective weights of different factors

and used them for some specific cases.Results show that loading rate is the most important factor with a maximum weight about 0.4.Fire source power is the second important factor.When the building volume

cross-section shape coefficient and coefficient K are small

their weight values are great

their weight values decrease with increases of themselves.This study offers a support to fire risk assessment of non-protected portal frame structural buildings and give a reference to fire-resistance design and fire control management.