## 1 Introduction  
The seismic inadequacy of masonry and reinforced concrete (RC) existing building stock has been tragically highlighted by the strong earthquakes occurred in the last decade in South Europe. Actually, a number of these buildings, not designed according to seismic standards (they are commonly named gravity load designed, GLD, buildings), collapsed or were severely damaged causing the loss of human lives and significant economic losses. Moreover, most of these existing buildings have reached their nominal service life, exhibiting a significant decay of structural performance due to degradation phenomena, often not properly handled by an adequate maintenance program. Therefore, the need of efficient and cost-effective seismic retrofitting methods has become a priority for the society and for the scientific community in order to fulfill modern standards such as the Eurocodes (e.g., [1, 2]).  
In the last twenty years a number of systems have been proposed, developed, and experimentally tested for RC buildings retrofitting; see [3] for a thorough review carried out by subdividing the seismic upgrading techniques in two categories, i.e., local and global approaches depending on the level at which they operate: on single element or on the structure as a whole. Among others, in [4] externally anchored precast wall panels have been used for the seismic retrofitting of RC frame, with a significant reduction of the construction period and a limited invasiveness.  
More recently, a number of technological systems developed for energy and seismic renovation intervention have been proposed, see [5] for a comprehensive state of the art of interventions techniques for RC-framed buildings. These integrated solutions are typically based on realization of an external seismic-resistant system. In this way, the interruption of the use of the building during the intervention is also avoided, which represents significant cost and social saving. Concerning intervention techniques for existing RC buildings, in [6] an innovative technique for the simultaneous seismic-energy retrofitting of old buildings has been proposed, by combining inorganic textile-based composites with thermal insulation. A technological double skin exoskeleton with dissipative elements has been proposed in [7], while a new RC infilled frames connected to the existing ones has been studied in [8]. An integrated solution based on an earthquake resistant exoskeleton constituted by steel braced frames has been proposed in [9]. Similarly, in [10] the idea of external steel exoskeletons has been investigated for multiple retrofitting alternatives. Finally, Cross Laminated Timber (CLT) panels have been also suggested for the external integrated energy-seismic retrofitting of existing RC buildings. As an example, in [11] the possibility of replacing existing masonry infill walls in RC frame buildings with CLT panels has been investigated. It is worth underling the high potential of such an intervention technique (e.g., low cost and invasiveness, low time of realization, and low carbon material use), even if the related theoretical study and experimental testing are still at a preliminary stage.  
In this paper, the seismic performances of the new RC-framed skin for retrofit intervention on existing buildings developed within the TIMESAFE project [12] are analyzed by discussing the results of a number of nonlinear static (pushover) analyses carried out on both existing and retrofitted RC buildings.  
The main features of the proposed RC-framed skin, briefly summarized in the next section, are thoroughly described in [13] where also its feasibility and sustainability are investigated by means of a holistic Life Cycle Assessment for environmental impact and Life Cycle Cost for an economic evaluation.