The strengthening of reinforced concrete (RC) structures with external steel shear walls was investigated in this study. The proposed technique allows the strengthening of in-service RC structures in parallel to reducing the construction costs and leading to faster and more workable solutions. The experimental program includes three-dimensional RC models, which exhibited some of the structural deficiencies commonly encountered in existing RC structures. The related tests were conducted under the imposed reversed cyclic lateral sway. Accordingly, performance of the proposed strengthening technique is found to be adequate for improving the seismic capacity of existing RC structures. Additionally, base shear capacity and stiffness of the strengthened model were significantly improved. (C) 2011 Elsevier Ltd. All rights reserved.