Experimental correlations between destructive and non-destructive tests on ancient timber elements

The refurbishment of ancient timber structures requires an acquaintance of the residual structural capacity of members in order to design reliable repairing interventions. Such information cannot be obtained by means of destructive tests on sacrificial elements extracted from the existing structures, while non-destructive tests (NDT) are currently performed in situ on timber elements. In this article, a methodology based on resistographic NDTs is analysed. In particular, an experimental campaign of NDTs on ancient chestnut elements has been carried out for determining a correlation between NDT results and mechanical wood properties, previously obtained by means of destructive tests. Then, a numerical formulation between resistographic tests carried out along the direction parallel to the grain and the longitudinal ultimate compressive stress has been proposed. In addition, since in situ NDTs can be performed only along direction transversal to the growth rings, a correlation between longitudinal and transversal NDTs has been obtained. Finally, in order to validate the proposed procedures, a series of analogous tests have been carried out also on new spruce elements.