Seismic Retrofit of Multi-Story RC Buildings by Encasement Technique

Existing reinforced concrete buildings designed either considering gravity-only loads or following outdated provisions are deemed seismically deficient, especially if they are built in a seismogenic region. Consequently, many researchers have studied the possibility of strengthening these seismically weak structures to enhance their performance and mitigate losses in the event of intense seismic activity. However, most of the available retrofitting techniques in practice hinder the functionality of the vulnerable building and interrupt the inner workings during the upgrading process. Therefore, this research proposes an efficient nondisruptive seismic retrofitting technique to externally strengthen seismically deficient reinforced concrete moment frame structures. The primary goal of this research was to develop a strategy where the entire retrofitting process is completed outside the building. The proposed encasement technique comprises a rigid peripheral framing system that confines the existing structure under seismic excitation to increase the stiffness and enhance the global seismic behavior. The efficiency of the new system was verified by an exhaustive nonlinear three dimensional dynamic simulation of selected multi-story reinforced structures, which was conducted using CSI ETABS. A performance-based assessment showed the capability of this system to rehabilitate existing weak structures as it showed an improved and satisfactory performance, notably in the case of low-rise buildings.