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

This article describes 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 purposeof this work was to evaluate the extent of decay in some of the ancient wooden trusses ofthe nave’s roof, in view of possible strengthening interventions. Sonic tomography is entirelynoninvasive and is suitable to investigate large portions of a structure, although qualitatively,whereas penetration tests are slighlty invasive as point measurements that enablehigh-resolution detection of wood decay and cracks. This study combined the two techniquesto investigate the internal condition of four trusses that looked most deteriorated at a preliminaryvisual inspection. Results showed that decays occur mainly next to the walls, dueto rainwater infiltration, and on the side of the timbers facing the rear of the nave, possiblyfor the higher level of moisture caused by lack of ventilation from that direction. In general,chords have worse mechanical properties than rafters.