Measurement of the tensile force in the hoop tie-rods of an historical dome.

The knowledge of the effective tensile load in structural tie-rods is of great interest, since their role is of crucial importance for the stability of the elements they connect. In many cases, tie-rods are ancient artefacts and have uncertain history, for example for what concerns the way they have been placed or the effective material strength. Tie-rods usually strengthen arches and vaults, but, in the special case here considered, these elements are embracing a dome of the 5th century. The authors experimentally measured the tensile load in these tie-rods, which belong to two ages, ancient and relatively recent. The work is especially devoted to the discussion of the importance of knowing the working condition of these tie-rods with the aim of estimating the stability of the entire dome, which has been critical since its construction. Moreover, the measures highlight a surprising result when the behaviour of recent tie-rods is compared with the behaviour of the ancients.