Non-invasive seismic retrofit of reinforced concrete structures: the SPEAD technique

The seismic vulnerability of the existing building stock in Italy constitutes a critical structural and social issue. It is estimated that approximately half of the reinforced concrete buildings nationwide were constructed prior to 1981, the year when mandatory seismic design regulations were introduced. Consequently, a significant portion of the existing building stock exhibits design deficiencies and durability problems. These conditions necessitate targeted and effective interventions aimed at structural strengthening and seismic risk reduction. Moreover, there is an increasing need to develop innovative and sustainable solutions aligned with European directives, based on multi-criteria and integrated design approaches. Within this framework, the SPEAD (Steel Plate Energy Absorption Device) system emerges as an innovative, sustainable, and low-impact technology for the seismic retrofit of reinforced concrete structures. Designed as a local strengthening solution for beam-column joints, the system enhances seismic capacity while minimizing impact on the building and its occupants. Its external and non-invasive installation makes it particularly suitable for buildings in use, avoiding interruptions that could cause significant economic and social impact. Furthermore, the device, entirely made up of steel, dissipates seismic energy through the hysteretic material behaviour, reduces cracking in the joint panel, and facilitates post-seismic repairs, thereby contributing to prolonging the structure’s service life. This study presents a nonlinear 3D numerical analysis of reinforced concrete beam-column joints, calibrated using full-scale cyclic test data. Preliminary results demonstrate a significant improvement in joint performance in terms of strength, reduction of concrete cracking, and decreased reinforcement slip, key factors for damage mitigation and enhanced durability and safety.