Rehabilitation of nonductile reinforced concrete buildings using steel systems

Many of the existing reinforced concrete (RC) structures performed poorly during recent earthquakes. Most of these structures were designed for gravity loads only with inadequate lateral load resistance. Several of the construction details in existing gravity load designed buildings do not conform to current code requirements for seismic design and may lead to nonductile inelastic behaviour.; The objective of this research program is to investigate the use of steel systems for the rehabilitation of existing nonductile RC buildings. The study is limited to low-and mediumrise frame buildings. A beam-column element capable of representing the behaviour of nonductile RC frame members is developed. The model is capable of representing the strength decay of nonductile RC members and the effects of the axial force on the yield moment and the deformation capacities of the member at peak strength. A procedure for evaluating the damage to nonductile RC structures following an earthquake is developed. The damage procedure depends on calculating the deterioration of the building stiffness and lateral load carrying capacity due to the application of the earthquake loading. The building stiffness and lateral load carrying capacity before and after the application of the earthquake loading were determined by conducting a pushover analysis.; Two nonductile RC buildings, three- and nine-stories, representing low-and mediumrise existing nonductile structures, were analyzed using various ground motion records. The seismic behaviour of the nonductile buildings when rehabilitated using various structural steel systems was determined. The investigated steel systems include the addition of concentric X-bracing, eccentric bracing and attached steel frames. The effectiveness of the various steel systems in rehabilitating the three- and nine-story buildings were examined.; The effect of the distribution of the steel bracing along the height and along the bays of the RC frames on the seismic performance of the rehabilitated building was studied. A simplified approach was proposed for selecting the proper brace distribution. The seismic performance of the nonductile three-story budding when using well designed eccentric bracing rehabilitation was compared with the performance of the building when using concentric bracing. The relationship between the deformation capacity of the rehabilitated building and the link deformation angle was evaluated. The distribution of the link strength along the building height was investigated. The seismic performance of the rehabilitated nine-story building was evaluated when using both flexible and stiff steel frames.