The dome of “Badia di Sant’Agata” in Catania: an example of self-supporting structure and seismic protection device

Completed in 1767, the dome of the “Badia di Sant’Agata” is the first of the four big domes built in Catania after the disastrous earthquake occurred in 1693. The present study was triggered by the latest restoration works, which allowed a detailed investigation of the architectural elements and the building construction inside the entire domed complex (drum, dome, lantern). The in-situ analysis was completed by the examination of the available archival documents and diagnostic tests, and by processing a 3D laser scanning survey to determinate the dome profile and the masonry thickness at different levels. This analysis has provided two interesting outcomes: (i) the dome was built without any supporting falsework, by laying 22 coaxial courses of “giuggiulena” (a local limestone) ashlars; (ii) the ashlar fabric lays at the impost on a ring made of rubble stones bound with abundant mortar, probably to realize an ante litteram seismic protection device. The acquired data have permitted to accurately define the geometric and constructive features of the domed complex, and to implement a numerical structural model, based on a discrete element approach. Nonlinear static analyses have been conducted to assess the seismic vulnerability of the structure, confirming the positive contribution of the impost ring to reduce seismic actions.