Design of a base-isolated artificial ground accounting for 3D seismic input: the case study of Castelluccio di Norcia

Seismic isolation is a technique that reduces the impact of earthquake forces on structures by increasing their natural vibration period and enhancing their damping capacity. While typical isolation systems are primarily designed for horizontal ground motions, the vertical component is often neglected unless specific regulations mandate its consideration. However, in near-fault zones, vertical ground motions can exceed horizontal ones, potentially affecting seismically isolated structures. This study examines the influence of vertical seismic forces on isolated buildings in near-fault zones, focusing on the reconstruction of Castelluccio di Norcia, a historic Italian village severely damaged during the 2016 Central Italy earthquake. The reconstruction involves an "Isolated Artificial Ground" system, a stepped reinforced concrete platform upon which buildings rest, separated from the ground by curved surface slider devices. To evaluate its dynamic response under various seismic events, a finite element model was developed and time-history analyses were conducted. Findings show that while vertical seismic component has minimal impact on horizontal displacements, it causes significant fluctuations in shear forces due to axial load variations and it influences also the frequency content of horizontal accelerations recorded on the platform. These results contribute to a better understanding of vertical seismic effects in near-fault scenarios and their implications for seismic isolation design.