SEISMIC RETROFIT OF “PLINIO IL GIOVANE” SCHOOL BUILDING: MAJOR APPLICATION OF BASE ISOLATION USING HIGH DAMPING RUBBER BEARINGS

Seismic retrofitting of critical structures, such as schools, military facilities, and essential infrastructure, is crucial in earthquake engineering. These buildings need to meet higher performance standards than typical structures, aiming to withstand design-level seismic events (Life Safety Limit State, LSLS) and ensure functionality immediately after an earthquake. This involves not only protecting the structural components but also minimizing damage to internal equipment. For strategic buildings, maintaining operational capability post-event is essential. In seismic zones, traditional retrofit methods like roof and floor anchoring, wall bracing, and diaphragm strengthening often fall short and are invasive, altering the building's architecture and functionality. Seismic base isolation presents a non-invasive, highly effective alternative by reducing seismic demands with anti-seismic devices that offer high horizontal flexibility. The "Plinio Il Giovane" school in Città di Castello, Italy, constructed in the 1970s, serves as a case study. The building has a non-symmetrical L-shaped floor plan with three above-ground floors for educational use and is built with brick-cement floors and a reinforced concrete and brick roof. Città di Castello is in a high seismic hazard area with peak ground accelerations of 0.30g for a 712-year return period (LSLS) and 0.36g for a 1462-year return period (Collapse Limit State, CLS). For this project, Freyssinet provided 94 ISOSISM® HDRB-S 500x108 High Damping Rubber Bearings (HDRBs) and 42 elastomeric sliders (types CE 300x69 and CE 400x75). These devices enable the building to withstand 100% of the design seismic action, effectively eliminating its seismic vulnerability. The paper details the dynamic behavior of these isolators through experimental tests, and outlines the construction phases and technical details of the isolation process. Keywords: base isolation, high damping rubber bearings, masonry building, seismic retrofit