3 rd International Balkans Conference on Challenges of Civil Engineering, 3-BCCCE, 19-21 May 2016, Epoka University, Tirana, Albania 42 Repairing and Seismic Strengthening of Damaged Reinforced Concrete Structures with External Steel Shear Walls Yavuz Selim Tama 1 , Hasan Kaplan 1 , Tarkan Görgülü 2 , Zeki Ay 2 1 Department of Civil Engineering, Pamukkale University, Turkey 2 Department of Civil Engineering, Süleyman Demirel University, Turkey ABSTRACT In this study, a new strengthening technique for earthquake-damaged reinforced concrete (RC) structures was experimentally investigated. Within the scope of the study, three- dimensional, two-storey RC model was constructed. During the production of this model, some of the common structural inadequacies in existing RC structures were taken into consideration. For this purpose, initially a reference model was exposed to lateral loads up to 1.7 % drift. Then, the damaged structure was repaired with epoxy injection. Finally, the repaired model was strengthened with External Steel Shear Walls (ESSW) and subsequently tested under the same load pattern. Chevron braced system is selected as ESSW. The results show that existing RC structures damaged under earthquake effects can be strengthened rapidly by proposed strengthening technique and the lateral load capacity and stiffness of these structures can be increased significantly. Keywords: Earthquake, Repairing and strengthening, External steel shear wall, Chevron braced system. INTRODUCTION Several techniques were developed for strengthening of the existing buildings 1-5. Increasing the lateral load capacity and stiffness of the structures are the common aims of those techniques, which contribute to the performance of the structure by limiting the lateral drifts. Seismic strengthening of structures is mainly based on two strengthening schemes: Element- Based and System-Based. The former, bases on the strengthening of the structural elements, which are expected, undergo a brittle failure. The latter involves introduction of new structural elements to the system, such as reinforced concrete shear walls to improve the overall structural performance. Element-based techniques may not always be sufficient to increase the seismic performance of the strengthened structure 3. In this case, it is better to introduce system-based strengthening methods, which improve base shear capacity as well as lateral stiffness. These methods usually compensate for the local deficiencies, which reduce the structural performance before strengthening, by decreasing the displacement demand. The use of RC infill walls has a wide range of applications for the strengthening of earthquake-damaged structures. Its efficiency was proved by numerous experimental studies 6-14 showing that strengthening with RC infill increases the lateral load capacity and stiffness while it reduces lateral drifts. In previous studies, the effect of connection capacity between existing and new concrete 9 and the effect of wall openings 8 were investigated. According to these studies, properties of reinforced concrete frames (column reinforcement ratio, column