A simple approach for modeling fire-resistance of steel columns with locally damaged fire protection

In order to analyze the behavior of steel columns in a fire with partial damage to their fire protection, two simple models are presented. One of the models based on the differential equation of equilibrium may be used to predict the ultimate load bearing capacity of steel columns hinged at two ends and the other may be employed to predict the critical temperature of axially restrained steel columns. The imperfections including initial flexure of steel columns and load eccentricity are taken into account in the models. The edge fiber yielding at the mid-span of a column is taken as the failure criteria for the fire-resistance of the column. A numerical application is carried out to demonstrate the effect of the damage to fire protection on the ultimate load bearing capacity and critical temperature of steel columns in a fire. The results show that the load bearing capacity is reduced at a given temperature with increasing damaged length of fire protection. The axially restrained stiffness and load ratio have a significant influence on the critical temperature of steel columns. By employing the computer models, the approach proposed in the paper has been validated and good agreement has been found.