The seismic vulnerability of the existing building stock in Italy represents a structural and social issue of primary importance. It is estimated that around half of the reinforced concrete buildings across the country were constructed before 1981, the year in which mandatory seismic design regulations came into force. In addition, many of these buildings show clear signs of deterioration and reinforcement corrosion, worsened by having exceeded their intended service life. These conditions demand targeted and effective interventions to strengthen structures and reduce seismic risk. However, it is increasingly crucial to develop innovative strengthening systems that prioritize sustainable criteria and are based on a multidisciplinary design approach. In this context, the SPEAD (Steel Plate Energy Absorption Device) can be considered as an innovative, sustainable and low-impact technology for the seismic upgrading of reinforced concrete structures. The system, designed as a local strengthening solution for beam-column joints, makes it possible to specifically increase the strength and ductility of beams and columns while minimising the impact on the built environment and building occupants. The non-invasive nature of the device allows it to be installed exclusively from the outside, making it particularly suitable for buildings in use, where the interruption of activities would cause significant economic and social disruption. In addition to optimising the overall seismic response of the structure, the device can dissipate seismic energy through hysteretic steel mechanisms, helping to reduce damage in the most vulnerable areas and facilitating post-event repair operations, thus extending the life of the building. This study presents a 3D nonlinear numerical analysis of reinforced concrete beam-column joints, evaluated both in the absence and in the presence of the SPEAD device. The finite element model was calibrated based on an extensive experimental study conducted at the Structural Laboratory of the University of Basilicata, which focused on the full-scale behaviour of reinforced concrete beam-column joints subjected to cyclic tests. The preliminary results obtained are very promising, highlighting a significant improvement in joint performance in terms of strength, ductility, and reduction of cracking in the joint panel, key factors in limiting structural damage and enhancing the durability, reparability, and overall safety of the building.