Automatic assessment of insect degradation depth in structural solid wood elements by drilling resistance measurements

The assessment of insect degradation on the surface of timber elements is a key point in evaluating the safety of wooden buildings. The depth and the degree of the insect attack are necessary data to determine the resistant section of the load-bearing elements. To the aim, the resistance drilling is applied as non-destructive technique in the on-site inspection. Here, a routine is proposed and verified to automatically process the resistance data and to identify the presence of insect decay. Twelve wooden beams disassembled from an old timber structure were used as experimental material: five to optimize the routine and seven to verify the output after the optimization. In total, 78 % of the measurements showed an error of less than 5 mm and 86 % less than 10 mm when compared to the determination made by an expert operator on the same drilling profiles. Comparing the non-destructive measurements with the cross-sections cut from the beams, the profiles seemed very informative when the degradation was caused by cerambycids, but less so with anobiid attacks.