New approaches to practical evaluation method of bio-degradation of wooden construction - Non-destructive detection of defects using radar technique
Y Fujii, Y Komatsu, Y Yanase, S Okumura, Y Imamura, M Tarumi, H Takiuchi, A Inai
There have been a number of researches and developments on the techniques and apparatus for the nondestructive evaluation of the biological deterioration in wood and wooden constructions, such as decay or insect attack in house, public buildings or in historically important architectures. As for the detection of the decay in wood, techniques using sound in audible or in ultrasonic frequency ranges, stress waves, heat wave and X- ray have been investigated, where the changes in the physical properties expressed in the wave form were related to decay. The change in the velocity, the attenuation or the frequency spectrum of these physical energy waves can be associated with the decrease of the specific gravity or the structural change due to decay. Some mechanical properties such as the boring resistance and the elastic properties of wood surface could be an indicator of decay. The dielectric property of wood and its relation to decay is also useful. Miller et al. (1989) applied a radar technique to diagnosing of standing trees. However the techniques previously developed are not always feasible. One of the possible reasons is that these physical or mechanical properties change not only on decay but also on other factors, such as the water content or the grain direction in wood. In addition, sometimes the techniques are less practical, strictly not non- destructive or too expensive. In practical maintenance operation of wooden constructions, visual inspection together with sampling method plays an important roll, however a specialized training is needed for the operator to get the skill of the diagnosing. In this study, to establish a practical evaluation method of bio- degradation in wooden construction, scanning using a newly developed portable radar apparatus was investigated. By comparing the results with other methods, a more practical method to evaluate the bio-degradation in wood was proposed.