Basis and application of a simple interaction formula for steel columns under fire conditions

The Rankine method has been applied to steel columns and frames subjected to increasing loads but maintained at ambient temperature. An original derivation of the formula, which is general and based on the virtual work principle, is provided in this paper. The Rankine formula is extended to fire conditions by taking the temperature effects on steel material into consideration. Test results show that the Rankine formula yields close but slightly unsafe predictions for axially loaded columns. On the other hand, Rankine predictions for eccentrically loaded columns are very unconservative. In view of this, the present paper presents a logical approach to modify the Rankine approach so that the predictions for both axially and eccentrically loaded columns are conservative and accurate at the same time.