In-situ assessment of structural timber using selected wave-based NDT methods

This paper reports on a research, carried out in collaboration between the University of Trento DIMS and the CNR Institute IVALSA. The research was aimed at evaluating the potentiality of a multi-sensor approach, based on the use of different wave-based NDT methods, for on-site assessment of structural timber. Experiments were carried out on softwood samples, both in laboratory, on a dismantled beam, and on site, on the timbers of the porch's roof in St. Lorenzo church (Tenno, Italy). For the mechanical characterization of structural timber, combination of stress-wave velocity measurement and density prediction models from PLS analysis of FT-NIR. spectra is proposed. Preliminary model generated for a single sample of Scots Pine showed a good correlation between predicted and measured values of local density. IR thermography and stress-wave time of flight tomography were used in combination, with the intention to couple information of subsurface and internal heterogeneities, respectively. Areas of abnormal velocity values in tomograms were examined taking account of external indicators in the thermography maps. The techniques adopted are suitable to investigate large portions of the timber elements. This made it possible to limit the number of local NIR spectroscopy analysis to investigate chemical and physical local changes, and assess the nature of the detected heterogeneities.