Local buckling in laterally restrained steel beam-columns in case of fire

The behaviour of laterally restrained steel beam-columns with slender cross-sections (Class 4) where local buckling occurs under fire situation is numerically investigated. Although recommendations are given in Eurocode to address the local buckling for the case of fire, few studies address its influence at elevated temperatures, and more particularly its influence on the load bearing capacity of laterally restrained beam-columns, which represents an unknown safety level for the Eurocode procedures. As a primary objective of this study, the level of accuracy and safety of simplified methods of Eurocode 3 is studied based on extensive numerical investigation of several member lengths, different bending moment distributions and load ratios for various cross-sections and considering different heating temperatures. Local and global geometrical imperfections as well as residual stresses have been included in the numerical simulations. It is concluded that the Eurocode procedures lack consistency and the capacity of laterally restrained beams-columns is overestimated in many cases due to local buckling. Therefore, modifications to the current design methodology are proposed in this study leading to better estimation of the overall capacity of the laterally restrained beam-columns in case of fire, and finally, improved safety and consistency is achieved.