SEISMIC RESPONSE OF RC FRAMES RETROFITTED WITH STEEL BRACES OR WALLS

The seismic performance of various retrofit schemes for nonductile reinforced concrete (RC) frames is investigated using inelastic static and dynamic response analyses of three prototype buildings. The structures considered for study contain typical reinforcing details of older frames and represent low- and medium-rise construction in regions of high seismicity in the United States. Retrofit schemes included the installation of posttensioned bracing, structural steel bracing, or infill walls of reinforced concrete. Dynamic analyses were conducted for five ground motions representative of major earthquakes on firm and soft soil conditions. Response of the original and retrofitted buildings is evaluated in terms of maximum displacements, interstory drifts, and predicted member behavior. The results show that there is no unique solution and that several different retrofit schemes can be designed to provide adequate performance. However, satisfactory performance was obtained only for schemes that controlled lateral drifts to levels that would not result in significant damage to existing gravity-load-carrying elements.