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Retrofit and strengthening of columns can be an effective solution to improve the capacity of reinforced concrete (RC) structures when the structural details and strength are insufficient to resist extreme loads. When concrete jacketing is used by enlarging the existing RC column cross section, the main concern is the performance loss between new and old concrete due to potential interface slip. There are three major options to improve slip resistance at the interface including surface roughening, dowels, or both. In this study, these methods are evaluated and parameters are proposed to model the load transfer along the interface between the existing and new concrete. The response of reinforced concrete jacketed columns is simulated using the proposed numerical models. The effectiveness and need for surface roughening, dowels, or their combination are investigated. A slip coefficient is proposed to model the friction between new and old concrete materials based on comparison of the experimental data and numerical simulations.