Validation by micro-computed tomography of an assessment method to measure the residual strength of anobiids infested timber
J L Parracha, M F Pereira, A Maurício, P Faria, L Nunes
In this article a quantitative correlation study of pine timber structural elements, which have been subject to attack by anobiids, is presented. The main objective of the study was to establish a valid empirical correlation between the lost material percentage (consumed by beetles) and original/residual apparent density. Since the beetles’ attack produces a diffuse damage with a set of tunnels in random directions and sizes, this makes quantification more difficult. Micro-computed tomography (μ-XCT) was used to enable better assessment of material degradation state by quantifying the loss of density as this parameter is highly correlated with mechanical properties of timbers and thus central for the assessment. The results showed an experimental high correlation (r2=0.60) between original apparent density and lost material percentage and an even higher correlation (r2=0.83) between residual apparent density and lost material percentage. The results confirm the applicability of μ-XCT to define the relevant parameters for anobiid damage being this knowledge of fundamental importance for future validation of relevant non-destructive and semi-destructive techniques. After the μ-XCT study, screw withdrawal and shear parallel to the grain tests have been made in pine degraded timber. Screw withdrawal force and shear strength values were related with density loss (r2=0.82 for screw withdrawal; r2=0.78 for shear strength parallel to grain). A novel assessment method for evaluating the impact of anobiid damage on timber degraded structural elements based in four major steps is proposed enabling a more quantitative assessment of the structural soundness of the remaining timber.
Keywords: anobiids infestation, micro-computed tomography, density loss, damage assessment, in situ screw withdrawal