Buckling analysis of braced and unbraced steel frames exposed to fire

This paper presents a buckling analysis of steel frames, taking into account the effect of temperature, in order to evaluate the buckling lengths of the columns in a fire situation. The results obtained for the buckling lengths are compared with those suggested in the fire part of the Eurocode 3 (Part 1.2) for the design of columns in braced frames in a fire situation. Part 1.2 of the Eurocode 3 does not provide rules regarding the buckling lengths for unbraced frames used in fire design, so this study offers a proposal for the buckling lengths of columns in unbraced steel structures. The results of the calculated mechanical resistance of the frames (using simple calculation models) and the evaluated buckling lengths are compared with the results obtained with advanced calculation models for a number of different cases in a fire situation.

► The elastic critical load of a steel frame varies with temperature.
► Members that control the buckling of a steel frame may change during a fire.
► Buckling lengths decreases as temperature rises.
► In braced steel frames buckling lengths tends towards the values in Eurocode 3.
► In unbraced steel frames buckling lengths tends to the values proposed in the paper.