Rehabilitation of RC frame joints using local steel bracing

Reinforced concrete (RC) structural frames that were built prior to the 1970s generally do not meet current design code requirements and may behave in a non-ductile manner. The lateral load carrying capacity of these structures is often insufficient due to non-ductile reinforcement detailing, which includes insufficient or no beam-column joint transverse reinforcement and inadequate anchorage for the beam's bottom reinforcement. Experience shows that such frames are prone to earthquake damage and often suffer shear and bond slip non-ductile modes of failure. Recent earthquakes have demonstrated that the beam-column joint safety is an important factor in keeping the integrity of the entire structure. Concentric steel bracing systems have been used for the rehabilitation of non-ductile RC buildings in a number of countries. However, the application of eccentric (local) steel bracing in the rehabilitation of RC structures still lags behind due to the limited research and information on the design, modelling and behaviour of such a combined concrete-steel system. In this paper a new beam-column joint rehabilitation technique using local steel brace members is proposed. Two full-scale specimens representing a standard joint and a rehabilitated joint were made and tested under reversed cyclic load. Their behaviour was compared to that of a non-rehabilitated specimen. It is shown that the rehabilitation technique was successful in enhancing the overall performance of the deficient joint and upgrading it towards a close to current standard performance.