Vienna Congress on Recent Advances in Earthquake Engineering and Structural Dynamics 2013 (VEESD 2013) C. Adam, R. Heuer, W. Lenhardt & C. Schranz (eds) 28-30 August 2013, Vienna, Austria Paper No. 479 Abstract. In seismic areas, many existing reinforced concrete (RC) buildings are vulnerable to dynamic actions and they need to be retrofitted for resisting seismic loads. In order to enhance earthquake resistance, shear walls are generally used in reinforced concrete (RC) framed buildings, and steel bracing is the most used in steel buildings. In the past two decades, a number of reports have also indicated the effective use of steel bracing in RC frames. Therefore, steel bracing systems can be used as a strengthening or retrofitting technique in both RC and steel buildings. Steel bracing of RC buildings started as a retrofitting measure to increase the lateral load resisting capacity of existing buildings. In order to explore the lateral load resisting capacity of such a frame, nonlinear static analysis is needed. Nonlinear static analysis (pushover analysis) under constant gravity loads and monotonically increasing lateral forces during an earthquake until a target displacement is reached is generally carried out as an effective tool for performance based design. The major outcome of a pushover analysis is the capacity curve which shows the base shear vs. the roof displacement relationship and represents the overall performance of the building. The use of steel bracing for the strengthening and or stiffening, steel braces are anchored firmly to boundary beams and columns and modeled as truss elements and increase earthquake resistance. In this paper, nonlinear static analysis of an existing RC building having 3-story with 7 bays in X-direction, 3 bays in Y-direction retrofitted with buckling restraint braces has been performed using SAP 2000. The performance of the retrofitted building is studied in terms of base shear forces and energy dissipations. Inter- story drift demands of the bare frame and strengthened frame with steel braces have also been discussed. Results indicate that, steel bracing system can significantly increase the structural stiffness and reduce the maximum inter-story drift of the frame. Keywords: Nonlinear static analysis; Strengthening; RC structures; Buckling restrained braced frames 1 INTRODUCTION An extensive number of existing RC buildings in seismically prone regions of Turkey are considered to be inadequate by current seismic code requirements. These structures would have deficiencies in lateral strength and/or ductility. Several strengthening techniques of those structures have been investigated both experimentally and analytically for enhancing the overall lateral stiffness against seismic motions. Use of steel bracing for strengthening RC frames has some major advantages and drawbacks. Employing concentric bracing to the RC frames increase overall lateral stiffness and decrease lateral drift. However, the bending moments and shear forces in columns to which they are connected decrease, whereas the axial compression increases. In such cases, reinforced concrete columns are expected to be stronger enough in compression. Eccentric bracing also reduces the lateral stiffness of the system and improve the energy dissipation capacity (Viswanath et al., 2010). Goel and Lee (1990) conducted an experimental research on seismic rehabilitation of RC frames using steel systems. They indicated that proposed technique significantly improved the strength and the stiffness of RC frames. Maheri and Sahebi (1995) investigated the use of steel bracing in RC frames. They concluded that with the proper connection between the brace and the frame, the steel bracing could be alternative to shear walls in concrete framed buildings. Pincheira and Jirsa (1995), Nateghi (1995), Ghobarah and Abouelfath (2001) studied seismic rehabilitation of RC frames analytically employing Non-linear static analysis of strengthened existing RC frame building using steel braces B. Doran 1 , B. Akbaş 2 , E. Şenol 1 , O. Şeker 3 1 Department of Civil Engineering, Yıldız Technical University, 34220 Esenler, Istanbul, Turkey 2 Department of Earthquake and Structural Engineering, Gebze Institute of Technology, Kocaeli, Turkey 3 Illinois Institute of Technology, Department of Civil, Architectural and Environmental Engineering, Chicago, IL, USA