This paper presents the development of some numerical models based on the results of laboratory tests performed on axially loaded RC columns strengthened with steel angles and strips. These numerical models consider the nonlinearity of the building materials and the effects of the contact interfaces between different materials. The results of the finite element models accurately describe the general behaviour of the strengthened columns. This study allows engineers to assess the relative importance of the mechanisms acting on the strengthened RC columns. Constructive recommendations are also provided in this paper.