This study investigates experimentally the buckling behavior of steel columns having rolled sections of I shape when strengthened against buckling. The area and the moment of inertia of column cross section was increased over limited length of the column. This was carried out by welding two plates between the free edges of the flanges parallel to the web. Bolting or welding rolled sections to column cross section is another method. The column in this case would have discontinuous variation in its cross section. A total number of 8 columns were subjected to concentric axial load until failure. The variables considered are: 1) the ratio of the new moment of inertia to the original one, 2) the ratio of the length where cross section is changed to column total length, 3) the type and details of joining system; i.e. bolts or welds and 4) the end restraining conditions. The enhancement gained in the buckling load value due to the strengthening technique implemented was between 181% and 318%. Analytical solution was used to calculate the critical load values of the cases considered. The obtained results from both the experiments and the analytical solutions were compared and discussed. The efficiency of this strengthening method in changing and controlling the buckling behavior of already existing columns is assessed.