Buckling length of a steel column for fire design

The Eurocode 3 part 1-2 gives some simple rules to determine the buckling length lfilfi of a steel column for fire design. In the case of a braced frame in which each storey comprises a separate fire compartment with sufficient fire resistance, Eurocode 3 suggests that the buckling length may be taken as lfi=0.5Llfi=0.5L in an intermediate storey and as lfi=0.7Llfi=0.7L in the top storey, where LL is the system length in the relevant storey.Stability analyses for the evaluation of the buckling length and critical load of columns in braced frames show that the Eurocode 3 rule may be rather inaccurate in many practical situations. The authors propose alternative formulas to determine the buckling length at elevated temperatures, as an improvement of the actual rule of the Eurocode 3 part 1.2.