Coupling local semi-destructive techniques and non destructive imaging for the characterization of traditional timber structures: a case study

In case of preservation of historic structures, quality assessment allows for the maximum retention of original material and for the choice of the most appropriate intervention. The presence and extend of decay and damages in the interior of timber components is generally estimated by inspection of drilling cores and by drilling resistance measurements. Both reveal only local information. In the reported case study, non-destructive wave-based methods have been coupled with local tests, for the structural health assessment of a timber construction in St. Lorenzo church (Tenno, Italy). Samples extracted from the beams in the porch allowed the determination of wood species, moisture content and density, while NDT imaging techniques were used to map inhomogeneities and to locate the areas at the highest risk for damage. In particular, IR thermovision was used to detect moist areas along the members. Visual examination of defects and damage on the timber surface was coupled with acoustic tomography, to detect internal areas of low velocities, corresponding to decayed portions of material. Higher resolution information of decay extent was obtained, in selected points, from the analysis of resistance drilling profiles. Causes and severity of decay were evaluated on decayed portions of material with the near infrared (NIR) spectroscopy. The multi-sensor approach adopted, provided multi-scale, multi-resolution correlated information, which allowed the assessment, with low invasiveness and good reliability, of level and nature of damage and risk, for the definition of the most appropriate intervention.