## 1 Introduction  
In recent years, the European Union's interest in multidisciplinary improvements to the building heritage of its member countries has materialized through substantial funding for activities aimed at enhancing both the energy efficiency and seismic resilience of public and private buildings [1; 2]. In Italy, the building stock consists of historical or post-World War II constructions designed without seismic regulations, making the development of retrofitting techniques a matter of strong strategic interest. The retrofitting of existing concrete buildings aims to reduce the risks associated with failure and damage. Traditional retrofitting strategies aim to increase structural strength to reduce ductility demand. However, in the last two decades, new conceptual approaches have gained prominence, falling into two categories: increasing available ductility and reducing demand. The latter can be achieved by reducing input energy through base isolation or increasing energy dissipation via additional dissipative devices. These devices, like dissipative bracings or external dissipative structures (e.g., dissipating frames) [3], introduce a nonlinear component to the retrofitted structure, altering its behavior and eliciting nonlinear responses. Various conditions, such as interference with building utilization during the retrofit, can influence the choice of the retrofitting strategy. In some cases, the use of dissipative braces can be disadvantageous, primarily in terms of architectural and functional impacts. As detailed in this paper, these problems can be overcome by creating additional dissipative structures directly connected to existing buildings. Implementing external dissipative structures involves constructing new foundations and placing dissipative devices outside the existing building, often within specially dimensioned framed constructions. Some applications have recently been developed, discussed, and realized [4; 5; 6]. Both solutions, dissipative bracing and dissipative frames, imply that the retrofitted structure will include a nonlinear component that can modify the behavior of the structure itself and usually require the evaluation of a nonlinear response. Based on international codes and the scientific literature, the following considerations are made:  
None of the existing codes, with the partial exception of FEMA, defines design criteria for additional dissipative systems. FEMA 274 [7] and FEMA 356 [8] highlight the variability in design methods, depending on the type of existing dissipative devices. These devices can be broadly grouped into two major categories: displacement-dependent devices (yielding metallic and friction dampers) and velocity-dependent devices (viscoelastic solids or viscous fluids). Although a wide range of devices has been proposed in the literature, research aims to limit the residual damage induced by seismic events. The inadequacy of conventional structures for repair is a critical issue observed after severe earthquakes [9]. Additional dissipative structures offer significant benefits, including stiffness redistribution, damping, and the attraction of base shear in new foundations. Consequently, these interventions can significantly enhance seismic performance without increasing, in many cases, the base shear and floor accelerations. Dissipative structures can be equipped with various types of dissipative devices, such as generic hysteretic or viscous dampers, buckling-restrained braces [10], and shear link devices [11]. This paper describes an effective and easy-to-use displacement-based design procedure for the seismic upgrade of existing buildings (\(S\)) with additional dissipative structures (ADSs) for seismic enhancement. The procedure is derived from [PERSON] et al. [12] and is based on the capacity spectrum method [13]. It defines the retrofitted building's capacity by considering contributions from the existing structure and the ADS to achieve a desired performance level based on the target displacement.