The problem of analysing complex steel structures in relation to analytical and numerical tests of a single structure element has been presented. The aim was to demonstrate the compliance of the chosen methods for determining the strength parameters of a cantilever beam and to select the best cross-section for the optimization of the structure. The beam deflection and the value of the maximum reduced stresses (according to Huber von Mises’ hypothesis) have been determined numerically and analytically. Numerical analysis, on the basis of the finite element method, as well as the optimization, have been performed in the ANSYS environment. Based on the static analysis of the structure, optimization of the beam mass has been made by changing its cross-section dimensions, taking into account the specific optimization criteria, pointed in the work. As a result of optimization, solutions satisfying the required criteria have been selected. The weight of the structure has been reduced by half compared to the initial values of the designed structure. The permissible stresses have not been exceeded.