Displacement-based seismic retrofit of reinforced concrete buildings through low-damage exoskeletons

Recent earthquakes that occurred in the last decades pointed out once again the extreme vulnerability of the existing building stock constructed before the enforcement of modern seismic codes. As a result, an unprecedented research effort has been undertaken to develop both local as well as global cost-effective retrofit strategies to enhance the resilience of the built environment. Specifically, global interventions are growing in interest considering the opportunity to be implemented from outside the building with negligible/limited owner's disruption, with respect to local strategies where inhabitants’ relocation and disruption may be required, potentially leading to a “no-action” policy. This work focuses on the implementation of global intervention consisting of external low-damage frame exoskeleton systems based on the PREcast Seismic Structural System (PRESSS) technology. Such technology, developed in the 1990's, replaces and enhances the development of the “plastic hinge” expected in the members of traditional (i.e., monolithic) systems with a peculiar “Rocking & Dissipative” mechanism, allowing for both the energy dissipation as well as the self-centring capabilities of the system. The main goal of this work is to propose an analytical Displacement-Based Retrofit procedure to design such a retrofit intervention within a performance-based framework. Furthermore, non-linear static (i.e., monotonic, and cyclic) and non-linear dynamic time-history analyses have been performed for validating the proposed procedure. Finally, to demonstrate the enhanced capabilities of the low-damage technology, a comparative analysis with a monolithic exoskeleton counterpart is presented. This includes conducting cyclic non-linear static and non-linear dynamic analyses to showcase the self-centring capabilities of the low-damage system.