Tie-rods within vaulted masonry structures as a sign of history: the case of Santa Casa Lauretana in Tresivio.

Tie-rods are a widespread traditional solution for the reinforcement of arched structures, and a valuable source both for history of construction and for tracing each building's history. As such, they pose the issue of a respectful conservation as working structural elements. This requires not only a historical approach but also an understanding of the structural behaviour of the tie-arch unit. In this research, the paradigmatic case-study of Santa Casa is analysed. The variety of solutions -constructive typologies and historical phases- found within it are confronted with historical and recent manuals, searching for the reasons leading to its particularities. The consecutive strengthening interventions are analysed, looking for the expected structural problems linked to the different approaches.