“…X sections were also investigated at ambient temperature in [23][24][25], while laterally restrained I-sections that buckle due to torsional and flexural-torsional deformation were studied in [26]. In addition, a consistent approach of the Ayrton-Perry formulation, on which the European buckling curves are based [1,2], was proposed for torsional buckling by Chapman et al [27] and later extended to the general case of beam-columns buckling in [28]. In conclusion, based on the literature review, it is clear that despite the great interest about the instability phenomena of steel structures in fire, there is a paucity of studies devoted to investigate torsional and flexural-torsional buckling at elevated temperatures of hot-rolled and welded steel sections.…”