Effects of vertical seismic component on base isolation systems: The case study of Castelluccio di Norcia

Seismic isolation mitigates earthquake-induced forces by increasing structural natural vibration period and damping effects. While traditional isolation systems primarily address horizontal ground motions, the vertical component is often neglected unless required by regulations. However, in near-fault regions, vertical ground motions can be more intense than horizontal ones, potentially affecting isolated structures. This study examines the impact of vertical seismic components on seismically isolated structures in near-fault zones, focusing on the reconstruction of Castelluccio di Norcia, a historic village devastated by the 2016 Central Italy earthquake. The reconstruction uses an "isolated artificial ground" approach, where buildings are supported on a stepped reinforced concrete plate with Concave Curved Surface Sliders. A Finite Element Model (FEM) was developed to analyze the dynamic response under various earthquakes using time-history analyses. Results show that vertical seismic components have a minimal impact on horizontal displacements but cause significant fluctuations in shear forces due to variations in axial loads. These findings enhance understanding of vertical seismic actions in near-fault scenarios and their implications for isolation design.