Characterization of decay in the wooden roof of the S. Agata church of Ragusa Ibla (southeastern Sicily) by means of sonic tomography and Resistograph® penetration tests

Abstract

We describe the results of a sonic tomography survey and penetration tests carried out inside the S. Agata church of Ragusa Ibla, in southeastern Sicily (Italy). The purpose of this work was to evaluate the extent of decay in some of the ancient wooden trusses of the nave's roof, in view of possible strengthening interventions. Sonic tomography is entirely non-invasive and is suitable to investigate large portions of a structure, although in a qualitative way, while penetration tests are little invasive, point measurements that enable high-resolution detection of wood decay and cracks. We combined the two techniques to investigate the internal condition of 4 trusses that looked most deteriorated at a preliminary visual inspection. Results showed that decays occur mainly next to the walls, due to rainwater infiltration, and on the side of the timbers facing the rear of the nave; in general, chords have worse mechanical properties than rafters.