STRUCTURAL STUDY OF ARCHS THROUGH THEORETICAL AND EXPERIMENTAL METHODS: THE CASE HISTORY OF S. MARIA DELLE GRAZIE CHURCH ON THE SHORES OF COMO LAKE (ITALY)

The interpretation of the structural behavior of a historic building requires the implementation of a model aimed to reduce the structural and material complexity of the artifact to something we can manage so predicting its evolution. It is possible to create physical models, scaled or at real dimensions, which directly or indirectly represent reality. Currently, FEM models are mainly used; the powerful computational methods allow us to have a representation of reality so realistic as to lead us to believe that it is of course correct. The models implemented with informatic programs have, among other things, the advantage of being able to reach the "failure" without really breaking them, and therefore they are reusable indefinitely. But the model is in any case the reduction of a complex phenomenon to our theoretical scheme (therefore based on our current ability to understand the phenomenon itself) and it is important to be clear about the fact that it can be representative of the real only based on the correctness of the hypotheses posed (sometimes it can be instead very unrepresentative). For this reason, the NDTs play a very important role in a process that necessarily has to proceed step by step from the model to the real, from the hypotheses to the demonstration of their correctness. This paper refers to the structural case of the large diaphragm arches of a Renaissance church, that can be considered simple, apparently, but, in reality, is statically indeterminate. It presents the method in which the structural interpretation was carried out through a continuous dialogue between the theoretical results of different featured models and the experimental results (of course affected by uncertainties and errors) of different NDT techniques. Only in this way it is possible to define an appropriate scheme to represent the mechanical behavior of the historical structure and evaluate its structural safety with the current parameters.