Since 1987, regulations for wood-based construction in Japan have been gradually reformed, and many wooden residences such as three-story houses and three-story apartment buildings, as well as large-scale wooden structures such as Izumo Dome and Ohdate Jukai Dome, have been constructed. Furthermore, the revision of the Building Standard Law of Japan in 2000 allows for the construction of high-rise wooden buildings when the fire safety of their structural wooden beams and columns has been verified. These innovations have been made possible by advancements in fire science and rigorous full-scale fire testing. This review examines the relationships between wood-based construction and fire science after World War II and recent progress in the development of fire-resistant wooden structures.

View full abstract

The objective of this study was to examine the evaluation of modulus of elasticity (MOE) in mature wood using microfibril angle at an early stage of growth. Several wood qualities, such as latewood tracheid length, microfibril angle of S2 layer in latewood tracheid (MFA), and static bending property were examined in 45-year-old sugi (Cryptomeria japonica) trees originated from seedlings. From the results of the radial variation of the MFA and latewood tracheid length, the boundary between juvenile wood and mature wood was determined to be around 21st to 24th annual rings from the pith. MFA showed a significant negative correlation with MOE and specific MOE, r=-0.747 and r=-0.889, respectively. In addition, the MFA value at the 3rd annual ring showed a significant negative correlation with MOE and specific MOE, r=-0.556 and r=-0.623, respectively. These results indicate that MOE value in mature wood can be evaluated using MFA values at an early stage of growth in sugi wood originated from seedlings.

View full abstract

The longitudinal changes in the basic density of disks (mean Bd) of todomatsu (Abies sachalinensis) were investigated using plus-tree clones and breeding-material clones. The relationship between Pilodyn penetration of a standing tree and mean Bd was also investigated. The patterns of longitudinal change of mean Bd differed among clones and could be classified into several types. The mean Bd of the region 1-3 m above ground could be used as an alternate value to the mean Bd, and including breast height was appropriate for a genetic comparison. A significant negative correlation between Pilodyn penetration of a standing tree with and without bark and mean Bd was obtained in both individuals and clones. Pilodyn penetration with bark was more useful than that without bark because it was easier. Therefore, it would be possible to evaluate the mean Bd in todomatsu based on the measurement of Pilodyn penetration with bark of standing trees at breast height. This method will allow us the non-destructive evaluation, and will be available as a good indicator of the wood quality of both individuals and clones.

View full abstract

The heartwood of Dalbergia latifolia was extracted succesively with n-hexane, EtOAc and MeOH solvent. The extracts were then examined for the bioactivity against termites and various fungi, including non-wood decay fungi. The quantity and quality of bioactive components of the extracts were also analyzed. The n-hexane extract was proved to be the most active fraction against termites (mortality and antifeedant) and wood decay fungi. As the main compounds of the extract, latifolin, dalbergiphenol and 4-methoxydalbergione were isolated and identified as the bioactive components, and they all belonged to the neoflavanoids. Of the three isolated compounds, the relative content level of latifolin was the highest, followed by 4-methoxydalbergione, and dalbergiphenol, respectively. With regard to bioactivity, latifolin showed relatively high termiticidal, termite-antifeedant and antifungal activity against Kawaratake (Trametes versicolor). Dalbergiphenol exhibited moderate termite-antifeedant activity and relatively high antifungal activity against Oouzuratake (Fomitopusis palustris), Rhizopus oryzae and Cladosporium cladosporioides. 4-Methoxydalbergione showed moderately termite-antifeedant activity and antifungal activity against Kawaratake. By comparing the structure of these compounds, the specific performance in bioactivity corresponded to the existence of hydroxyl in the ortho position in B ring and to the quinonoid structure in A ring. Thus, it was suggested that the major defensive actions against various organisms in D. latifolia was partly due to variation of the heartwood extracts and the changing partial structure of neoflavonoids.

View full abstract

The load-bearing ratio of working stress to allowable stress on beams of three wooden houses, which were built in an area of average snowfall, was investigated. Their load-bearing ratio of maximum flexure to flexure limit was also surveyed. Then the condition of stress or maximum flexure at each duration of load at the maximum load-bearing ratio was examined. It was found that : 1) It was supposed that safety margins were sufficient because the load-bearing ratio was less than 20% on average in 70% of all beams. However some exceptional beams exceeding 80% of the maximum load-bearing ratio were found. 2) There is a tendency of determining the maximum load-bearing ratio by “the maximum flexure” of roof beams. This is because a short depth of roof beams does not have an uncomfortable effect on living, and thus was chosen by the designer in order to take into consideration its economical advantage. 3) Some beams possessing less safety margin possibly existed if a shear wall without the support of a 1^st-floor column is located at mid-span. The safety margin of those beams is decreased with increasing shear strength of the shear wall.

View full abstract

House interior materials are exposed to irradiation by sunlight transmitted through window-sash. Thus, it is important to be aware that the window glass changes the specific distribution of the sunlight as well as reduces the irradiance. Wood discolors either by photo-darkening or photo-breaching, and discoloration is affected by the irradiation wavelength and the kind of wood. As part of the studies of the evaluation method of the photo-stability for house interior materials, indoor exposure tests for various wood-based materials were carried out, using three types of window-sash glass and wood-based materials. These tests clarified that the type of window-sash glass influences not only on the degree of discoloration but also the pattern of discoloration of light-colored softwood such as Pinus radiata. Moreover, this result corresponds to those of accelerated photo-stability tests using special glass filters.

View full abstract