Seismic risk assessment of a new RC-framed skin technology for integrated retrofitting interventions on existing buildings

A RC-framed-skin technology for the integrated seismic and thermal retrofitting interventions on existing buildings, recently proposed by some of the authors, is thoroughly investigated. By means of numerical analyses, its effectiveness and suitability within the framework of seismic risk class assessment is proved. The system is composed of a RC-framed structure with an external reinforced plaster layer that does not offer a structural contribution to the capacity of the system in ultimate conditions, but which can be effective by increasing the lateral stiffness in serviceability conditions. The system is realized from the outside of the existing building so guaranteeing limited invasiveness of the intervention and preventing the interruption of the building use by their occupants. An existing RC building, representative of a typical example of the Italian building stock, is analyzed as a case study, and its seismic risk class upgrade, obtained by the proposed strengthening intervention, is assessed by non-linear static analysis. The numerical models are developed within the OpenSees framework. The Expected Annual Loss (EAL) parameter, together with the Life Safety Index (LS-I), are chosen as synthetic measures that include both aspects related to Ultimate Limit state (ULS) and Serviceability Limit State (SLS) conditions. The risk class accounting for or disregarding the contribution of the external reinforced plaster are finally compared.