The design of the dome of the Sanctuary of Vicoforte (Piedmont, Italy) among idea, geometry and construction practices: researches on the shape and the size of the largest oval dome in the world

The largest oval masonry dome that nowadays exists in Europe, the Sanctuary of Vicoforte in Piedmont, is constantly monitored in order to control the deformation of the building. But what is the real shape of the dome? To understand the exceptionality of this cultural heritage, the science of representation adopted tools, conventions, codes and signs focused on the analysis of issues that are historical and contemporary, structural and functional, symbolic and formal. The common definition of "oval" given to the dome (sometimes called "elliptical") is somewhat approximate. The shape is actually more complex. In the past, several schemes have been proposed , whose validity is verified for only a few horizontal and vertical sections. Analysis of the complex three-dimensional geometry are needed in order to compare archival drawings with the most recent studies and results of the recent survey. The paper will highlight how the use of three-dimensional modeling could allow a renewed reading of the dome’s geometry, with the aim of providing schemes of interpretation to support the analysis of construction and structural behavior. The originality consists in the process of three-dimensional analysis aimed at defining the true shape of domes that are commonly called "oval" or "elliptical", but that actually have more complex configurations due to construction techniques. The study will regard the following themes: the critical analysis of some design drawings for the sanctuary of Vicoforte and reading of its territorial relevance, the analysis of different geometric models historically proposed for the dome of Vicoforte compared to the modern three-dimensional survey, the analysis of the design drawings, that describe the ribs of the dome used for its construction, to obtain a 3D model of the dome.