Hooping as an Ancient Remedy for Conservation of Large Masonry Domes

摘要

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. This article presents some general considerations for this primeval remedy, starting from the historical and structural analysis of the large 16th-century octagonal dome of Madonna dell'Umilta 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 an understanding of the real contribution of each hooping systems. These data were then used to calibrate a finite element model, which allowed researchers to retrace and quantify from a structural point of view the passage through the centuries of this daring construction and to understand the efforts made to preserve it up to now. The final results presented here 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.