The thesis starts off with a basic description of fire engineering and the behaviour of structural steel during exposure to high temperatures. This is followed by the third chapter, in which the necessary data for the thermal analysis is presented. In the fourth chapter we take a look at the procedure and results of the simplified and advanced method of thermal analysis. The final chapter shows the difference that the chosen method makes to a column’s ability to bear an axial compression force and the effect of using lateral restraints on the design moment resistance of steel elements during exposure to fire. In addition to the column, in the mechanical analysis, a beam with a cross-section IPE 300 is also considered, in which the influence of the lateral buckling on the standard bending fire resistance is examined.