In order to restore the strength of failed reinforced concrete columns, the cracked shell was replaced by new materials of repair: plain concrete, fiber-reinforcement concrete and cement- mortar alternatively. Three groups of reinforced concrete squared tied columns were tested concentrically. The columns were short-columns reinforced with 2% longitudinal steel reinforcement ratio. Behavior of repaired columns have been presented by measuring concrete surface strain with axial load up to cracking load. Effects of both concrete compressive strength of materials of repair and preloading on the restoring column strength have been established. Test results have ,also, shown that the strength of failed column can be restored by replacing the cracked shell with new shell having high compressive strength. the strength of columns repaired by these materials can reach up to 136% of their original strength depending on both the compressive strength and the condition of preloading.Furthermore ,axial strength of repaired columns was derived by modifying the equation given by ACI-Code for calculating design axial load strength of reinforced concrete column..