<p>Given the necessity of strengthening concrete columns that may suffer from accidental disasters, aging, or human-induced damage, this study presents an experimental investigation of the pre-damaged reinforced concrete (RC) columns jacketed using square corrugated steel sheets under axial compression. The influence of corrugated steel thickness, corner connection type of the jackets (welding vs. bolting), as well as pre-damage level, are investigated based on ten short RC columns. The strain and stress development in the corrugated steel jacket are analyzed in detail, revealing the confinement effect in the square section and load-carrying contribution of different parts. Although severer damage leads to the loss in the ultimate load-bearing capacity of original RC section, the transverse expansion is effectively restrained by the passive confinement provided by the corrugated steel jacket, which indirectly reduces the lost strength. As a result, the corrugated steel jacket can contribute to increasing the ultimate bearing capacity of the damaged RC specimens by 34.6% to 67.3%. The counteraction of the strength loss and improvement by confinement are quantified by incorporating strength degradation coefficient and confinement factor. A strength degradation model, as well as the ultimate load-bearing capacity model, are developed for designing such a jacketed concrete column.</p>