The paper deals with the numerical modelling of a complex, steel shell structure. The part under analysis is the upper segment of a steel pylon, which consists of several cylindrical shells and one conical segment. Particular parts of the structure are welded together. Geometrical and loading data calculations were performed for the particular material for both an ideally elastic case and an elasto-plastic case. The conclusion that the structural member analysed required strengthening were drawn on the basis of these results. The structural modification was proposed and additional calculations for this modified structure were also performed. Introduced additional shell elements locked the mechanism of plastic flow. The proposed modification can be treated as a possible strengthening concept. The whole analysis was performed by means of the ABAQUS system but some stages of calculations were also verified by the COSMOS/M system.