Retrofitting of Reinforced Concrete Frames using Steel Bracing

Steel braced frame is one of the structural systems used to resist earthquake loads in multi-storied buildings. Many existing reinforced concrete buildings need to retrofit to overcome the deficiencies to resist seismic loads. The use of steel bracing systems for strengthening or retrofitting seismically inadequate reinforced concrete frames is a viable solution for enhancing earthquake resistance. Bracing system reduces bending moments and shear forces in the columns. The lateral load is transferred to the foundation through axial action. Total weight of the existing structure will not change significantly after the application of the bracings. Steel bracing is economical, easy to erect, occupies less space and has flexibility to design for meeting the required strength and stiffness. The bracing system improves not only the lateral stiffness and strength capacity but also the displacement capacity of the structure. In the present study, the seismic performance of reinforced concrete (RC) buildings rehabilitated using concentric steel bracing is investigated. The bracing is provided for peripheral columns. A ten storey building is analyzed for seismic zone III as per IS 1893-2002 using ETABS 2015 Software. The models are retrofitted with various steel bracing systems on periphery columns storey-wise and analyzed for seismic forces. The building is analyzed for models with Diagonal bracing, ‘V’ type bracing, Inverted ‘V’ type bracing, Combined ‘V’ type bracing, ‘X’ type bracing, ‘K’ type bracing and compared with an un-braced frame. The effectiveness of various types of steel bracing in rehabilitating a ten storey building is examined. The effect of the distribution of the steel bracing along the height of the RC frame on the seismic performance of the rehabilitated building is studied. The main parameters in this study to compare the seismic analysis of buildings are lateral displacement, storey drift, axial forces in the columns, Base shear. The percentage reduction in lateral displacement is found out. It is found that the ‘X’ type of steel bracing significantly contributes to the structural stiffness and reduces the maximum storey drifts of the frames. The bracing systems improve not only the lateral stiffness but also the displacement capacity of the structure.