Il comportamento strutturale nel corso dei secoli

The contribution aims to demonstrate the need of a methodological and interdisciplinary experience to analyze and assess the stability of monumental buildings. It is needed a correlation of archival and iconographical documentation with an accurate and exact geometrical survey and a numerical analysis. Sequential 3D analyses of the structural complex corresponding to subsequent historical construction and repairing stages (six phases in total) have been performed in the static and dynamic range to investigate the origin of the surveyed crack pattern. The reliability of the model was assessed delineating the areas where high tensile stresses concentrated, with peak values close to the strength of masonry, compared to monitored main damages both nowadays and reported in historical documents and treatises. The FE modelling strategy is based on the concepts of homogenized material. In particular the masonry structures have been modeled by means of three-dimensional solid brick elements, while frame elements have been used to model the chains, the timber and iron truss. The numerical results have been presented for each phase of the dome history. Contour maps of principal stresses have been shown looking both the intrados surface of the domes from inside the Chapel and across of the walls. The model was able to delineate the areas where high stresses concentrated, thus resulting in a powerful tool to interpret the historical phases, to have a clear knowledge of its vicissitudes and to check the dome behaviour under both static and seismic loads. The main results show that the potential structural problem of the dome is related to the peak tensile stress (compared to a reasonable tensile strength of ancient tuff masonry), that for seismic load conditions are about two times the static values. Whereas compressive stress values, also under seismic loads are compatible with the ancient tuff masonry strength. Different phases highlight clear differences in terms of tensile stresses, while differences are almost negligible in the case of compressive stresses. Seismic analysis shows also that the stress fields in the dome are very similar for both historical Irpinia Earthquake (1980) and Italian code spectrums. Looking at the outcomes of various numerical phases, it is clearly seen that the dome underwent effective consolidations: the chain positions were accurately identified, and the need to reduce weights was rightly specified. It is remarked the skill and cleverness of the ancient technicians who designed proper and accurate interventions, leading to reduced tensile stresses today up to about 40%.