The behaviors of steel columns, beams and beam-columns, exhibiting local, flexural, torsional, flexural-torsional and distortional buckling and their interactions at elevated temperatures.These have been studied by means of experimental and numerical analysis.The analytical formulas for the buckling resistances in the fire design situation have been presented.This new proposal, different from the actual proposal formulas of Eurocode 3 Part 1.2 has been modified in the work by comparison with the results from the experimental and numerical tests performed on submitted to temperatures varying from room temperature to 600℃.The numerical simulations have been based on the measured geometrical dimensions of the cross-section, the longitudinal imperfection, i.e.the out of straightness of the beams, the residual stresses and the yield strength.The Eurocode simple model promotes ultimate loads that depend mainly on the non-dimensional slenderness of the members.The analytical results provided by the Eurocode 3 Part 1.2 for a certain range of the slenderness, appear to be unsafe when compared with the numerical and experimental results.It is shown that the new proposal formulas are safer than the Eurocode 3 Part 1.2 formulas.The new proposal formulas have been planted to the buckling capacity of cold-formed steel members with uniform and non-uniform elevated temperatures developed by Dolamune, Kankanamge, N.and Mahendran, M.and also used for direct strength method.This paper is divided into two parts, one is referred to the hot-rolled steel members and the other is referred to the cold-formed steel members with uniform and non-uniform elevated temperatures.