Seismic base isolation of the ciborium of the high altar in the church of Santa Maria Maggiore in Spello, Italy

This work concerns the seismic isolation of one of the masterpieces of Renaissance sculpture in Umbria: the ciborium of the main altar in the Church of Santa Maria Maggiore in Spello, Italy. The intervention strategy was defined following a critical evaluation of the base isolation solution, supported by experimental tests aimed at the dynamic characterization of the sculpture. An in-depth understanding of the original construction techniques, materials, structural details, and their state of conservation was crucially important. The studies and analyses conducted revealed that seismic isolation is probably the only viable solution capable of both drastically reducing seismic risk and avoiding invasive interventions. In fact, by concentrating the intervention mainly at the foundation level—right beneath the monument itself—the sculpture remained unaffected by significant alterations. The execution of the work presented considerable challenges and was conducted with a “zero tolerance” policy for any even minimal movement or deformation of the sculptural group. Thanks to careful planning and the high level of technical expertise of the contractor, the desired result was successfully achieved: throughout all stages, no movement or deformation occurred in the ciborium or the altar. Both elements were kept in place during the excavation and construction of the isolation layer, with dismantling limited exclusively to the flooring.