Creep effect on buckling of axially restrained steel columns in real fires

At present, Harmathy creep model is used in most fire resistance analysis, which explicitly consider creep. Harmathy creep model only predicts creep strains with acceptable accuracy for the case of constant stresses, but becomes invalid for the case of variable stresses. For the case of axially restrained steel columns subjected to fire, the fire induced stresses vary considerably and rapidly with time and temperature. In this paper, the effect of creep on the buckling behavior of axially restrained steel columns in real fires has been investigated. A creep model in ANSYS, which is capable of predicting creep strain regardless of any coupling between time and either stress or temperature of steel, is used to predict creep strains. The results for buckling temperatures and axial deformations, predicted with and without considering creep in numerical simulations, are compared. Both fast and slow fires are considered. The study found that for axially restrained steel columns in slow fires, considering creep gives higher buckling temperatures than those not considering creep; and for axially restrained steel columns in fast fires, considering creep might give higher or lower buckling temperatures than those not considering creep.

► Creep effect on buckling of axially restrained steel columns in real fires is studied.
► A validated creep model is used to predict creep strains.
► Considering creep gives higher buckling temperatures in slow fires.
► Considering creep might give higher or lower buckling temperatures in fast fires.