Displacement Analysis of Wooden Trusses through Digital Survey and Visual Programming Tools. The Basilica of San Petronio in Bologna

Non-invasive diagnostic techniques for structural assessing heritage architectures are of utmost importance to guarantee their physical preservation. New structural investigation methods are being implemented using innovative digital tools since traditional numerical structural analyses usually require an in-depth knowledge of material properties that could be reached mainly through many destructive tests, which have high costs and could damage the architectural figurativeness of protected buildings. This issue is crucial when dealing with old timber trusses. Specialist literature often oversimplifies their behavior, basing its theories mainly on methods of investigation and calculation belonging to the 19thcentury structural analysis. This approach neglects factors of primary relevance that undermine traditional models and make the behavior of wooden trusses quantitatively challenging to understand, such as transformations that occurred over the centuries and the considerable dispersion of the mechanical resistance values of materials. For these reasons, a new method of investigation has been developed, aimed at deepening the knowledge of wooden roofs. This method follows a different path from standard knowledge methods both from the technical and methodological points of view. This quick and non-invasive method has been set up as a support tool to analyze the hypothetical displacements of these covering systems, based exclusively on the exploitation of TLS (Terrestrial Laser Scanning) point cloud geometric information through visual programming generative algorithms. This approach purposely avoids taking into account material properties and joint typology. The focus of this paper is the most recent phase of a broader research project that has studied several wooden roof structures in the area of Bologna, Italy, belonging to a set of remarkable historical churches and theaters, all dating back to the 16th and 18th centuries. This latest step extends the survey to the roofing system of the Basilica of San Petronio in Bologna, which has a span of approximately 19 m. The workflow application allowed highlighting the deformations that the Basilica’s trusses have undergone over time, improving the comprehension of their behavior, and highlighting the critical issues of the whole covering system. Such analyses suggested some hypotheses for future investigations on specific building macro-elements and could advise interventions for their preservation.