PSI - Issue 78

Elisabetta Bersanetti et al. / Procedia Structural Integrity 78 (2026) 372–378

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distributed homogeneously throughout the building, especially in the upper levels. General critical issues are associated with the high interstory height, the considerable masses particularly located at the top level and the absence, in various areas, of spine walls, resulting in high transverse deformability. The safety level calculated with respect to seismic actions is around 35 – 40%, both for in-plane and out-of-plane masonry response. A similar level of safety was also found for SLO (Operational Limit State) verifications. 3. Intervention Design – Objectives 3.1. Introduction For the building complex under consideration, the primary objective is to achieve both static and seismic retrofitting of the entire structure. In addition to structural goals, two further specific requirements must be balanced: • the protection of the heritage-listed asset, particularly its distinctive features such as volumetric proportions, façades, and monumental spaces; • the minimization of interference with ongoing activities inside the building, which, in practical terms, cannot be relocated during the execution of the works. It should also be noted that, due to the strategic function of the building, the design must minimize damage even in the event of moderate seismic activity. 3.2. Design solution Since the identified deficiencies are widespread and related to typical construction characteristics (low density of spine walls, high interstory heights, significant presence of openings), a traditional strengthening approach aiming for 80% seismic compliance would have required extensive masonry consolidation, making it necessary to relocate the agencies currently operating within the building. This consideration, along with the factors described above (such as the building occupying an entire urban block, the basement being architecturally insignificant and extending over the full footprint, and limited static deficiencies), led to the proposal of implementing base seismic isolation. Seismic isolation works by significantly reducing the seismic forces transmitted to the structure through decoupling the building’s motion from that of the ground. This is achieved by defining a horizontal cutting plane and inserting devices at t he interface between the superstructure (above the cutting plane) and the substructure (below it). These devices may vary in type (elastomeric bearings, flat or curved sliding bearings), but their essential property is that they are much flexible in the horizontal d irection and stiff and resistant to vertical loads. This results in a significant increase in the structure’s vibration perio d, and consequently a reduction in the seismic forces transmitted. Choosing the elevation of the cutting plane in the masonry was a particularly complex and labor-intensive task and the results was to identify it approximately 80 cm above the underside of the floor slab between the ground floor and basement. This slab itself is located about 70 – 100 cm above the exterior street level. This height allows minimizing alterations to the existing façade openings, as the openings in the basement are irregular and can be reconstructed in the lower part without compromising the architectural appearance. As for the specific design of the isolation devices, the choices were oriented toward ensuring an immediate response even to moderate seismic events, considering that the seismic acceleration expected for the Livorno area is not particularly severe by national standards. Another critical design constraint is the spacing of the isolation devices, which must align with the above masonry walls to avoid vertical deformation or decompression. For this reason and to preserve the architectural heritage, the decision was made to match the highly regular spacing of the existing openings on the façades, under the external ground.