Use of physical models in the structural analysis of spatial structures: an application to masonry arches and vaults.

The use of unreinforced masonry spatial structures, in particular arches and vaults, represents a typical solution in historical buildings. The Italian architectural heritage is heavily characterized by the use of thesekind of structures, which are particularly sensitive to seismic action. In recent years, the use of in-scale models to investigate the structural behaviour of vaults has largely increased in scientific research. Actually, physical models allow examining the complex three-dimensional failure mechanism derived by pseudo-static response of the structures due to large displacement of the supports, simulating seismic behaviour of the building components. The experimental campaign carried out in this thesis is based on the investigation on 1:5 in-scale models of round arches and barrel vaults with mortar joints, to investigate their different structural behaviour under settlement of the abutments derived from two different brick patterns: radial arrangement, with bed joints orthogonal to the head arch plane, and vertical arrangement, with bed joints parallel to the head arch plane. The first phase of the research is devoted to investigating and test the materials adopted to build the models, concerning different mortar mixes, different in-scale bricks and their production methodology. Preliminary tests are carried out on in-scale models of a circular arch with two different masonry apparatus, subjected to opening displacement until collapse, i.e., simulating movement of one abutment in the direction of the arch thrust. These tests aim at acquiring basic knowledge about the construction process and the behaviour of the structure, in terms of ultimate displacement and failure mechanism, as well as to develop a suitable acquisition strategy consistent with the destructive nature of the tests. With these premises, the second phase of the experimental campaign is carried out in the ModLab of Politecnico di Torino, where a new experimental set-up for the vault models is designed and built. Two tests for each brick arrangement are carried out on the barrel vault models, for a total of four trials. The vault models are tested with shear settlement, involving the movement of one of the abutments normally to the head arches plane. The acquisition process involves image and high-resolution video recorded during the tests, while a constant monitoring of a portion of the structures is conducted with Digital Image Correlation (DIC) cameras. Close-range photogrammetry and structured light technology are used to acquire point clouds of the models in specific steps of the tests. The data acquired with geomatic techniques are processed and related together obtaining metric three-dimensional dense clouds of each recorded step of the tests. Combining the information from each source the macroscopic behaviour of the vault during the abutment settlement has been reconstructed and, in part, related with the microscopic behaviour of a significative portion of the structure, analysed through DIC, in one test. For each test, crack patterns, rotations, ultimate displacements and failure mechanisms are recorded. Comparison of the obtained results has highlighted quite different behaviour between the vaults built with the two brick arrangements, in terms of different typical crack phenomena leading to different, local or global, failures of the vault. The results of the research could be used, in future work, in the validation of numerical models