Detection of Incipient Decay of Wood with Non- and Minor-Destructive Testing Methods

For inspections of timber structures it is important to find defects, damages and material heterogeneities in the interior of wooden construction components. Undetected decay (especially interior rot) can result in a sudden failure of the construction. In the usual structural safety analysis of timber structures, damages and their extent are estimated by visual inspection of drilling cores and by the determination of the drilling resistance. Both reveal information only about this single point of measurement. Often repeated sampling (numerous drilling cores) becomes necessary, which still may be insufficient to assess larger buildings. The destruction from drilling cores must be considered, it´s not suitable for statically highly stressed parts (which should all be covered). In heritage-protected buildings, drilling cores and the drilling resistance method are rather limited. With the visual inspection of the drilling cores without further magnifying devices, decay can only be detected in the advanced stage. Incipient fungal attack, which already has a significant influence on the elasto-mechanical properties, can´t be detected. The drilling resistance method and drilling cores are compared with the ultrasonic echo technique with regard to their suitability for structural health monitoring of timber constructions. The low reliability of assessing the drilling cores by visual inspection for incipient fungal attack shall be improved by further non-destructive tests of the drilling cores. The applications of non- and minor-destructive test methods are considered, particularly their use in cultural timber structures.