Strength and stability of steel frames in fire: Rankine approach

A simple analytical approach based on the Rankine principle has been developed to determine the ultimate resistance of steel frames in fire. The proposed Rankine approach gives an approximation of the frames' fire resistance through a simple interaction between two idealized structural behaviors-strength and stability. Here, the strength and stability of the structures are evaluated using the rigid-plastic and the elastic buckling analyses, both incorporating the thermal effects. The proposed approach is first verified using a finite-element model. The verification studies include the effects of column and frame slenderness ratios, beam-column stiffness ratio, steel grades, initial sway imperfections, and initial residual stresses. These studies indicate that frame slenderness ratio is an important parameter governing the behavior of simple frames in fire, and the performance of the proposed approach is related to it. The Rankine approach is then applied to a series of 18 test frames from the literature. It is shown that the proposed approach can provide predictions with sufficient accuracy for simple frames in fire.