Hooping as an Ancient Remedy for Conservation of Large Masonry Domes

The insertion of metal tie rods all around masonry domes, in order to hoop them and to absorb their horizontal thrusts, is the most ancient traditional strengthening technique for these fascinating structures. In this paper some general consideration on this primeval remedy are presented, starting from the historical and structural analysis of the large XVI century octagonal dome of Madonna dell’Umiltà in Pistoia (Italy). Several hooping systems had been inserted around this dome in different periods and with different techniques, in order to reinforce this weak masonry structure and their tensile stresses have been measured by means of dynamic tests. The results have shown the large differences in the tensile stresses among the different ties, allowing to understand the real contribution of each hooping systems. These data were then used to calibrate a finite element model which, allowed to retrace and quantify from a structural point of view the passage through the centuries of this daring construction and of the efforts made to preserve it up to now. In the paper, the final results are new suggestions on the most efficient way to ensure, once again with hooping ties, the preservation of this monument for the future, starting from empiricism.