• Journal of the Korean Wood Science and Technology
• /
• v.42 no.1
• /
• pp.78-87
• /
• 2014

It was examined the key criterion of the time of property revelation as Uljin-Geumgangsong wood. For this purpose, we investigated in physical properties in pine wood (Pinus densiflora Sieb. et Zucc.) and representative Uljin-Geumgangsong wood (Pinus densiflora forma erecta Uyeki). The results are as follows; Air-dry density of Uljin-Geumgangsong wood have higher values over about 20 percent than that of pine wood. And also heartwood rate of Uljin-Geumgansong wood have higher values above 70 percent. The number of vertical resin canals per $1mm^2$ in Uljin-Geumgangsong wood was 40 percent greater than in pine wood. As the average diameters of axial resin canals were 67.8 mm and 67.3~69.9 mm in pine wood and in Uljin-Geumgangsong wood, respectively, there was no significant difference among wood species. There tends to be an increase in diameters as annual rings increase. The number of horizontal resin canals in Uljin-Geumgangsong-1 was approximately 55 percent greater than in pine wood and Uljin-Geumgangsong-2. The number of resin canals in pine wood and Uljin-Geumgangson-2 decreased while it increased in Uljin-Geumgangsong-1 as annual rings increased. No significant difference was found in the number of rays among wood species and between earlywood and latewood of same wood species. As annual rings increased the number of rays decreased in both pine wood and Uljin-Geumgangsong. The heights of rays were greater in pine wood than Uljin-Geumgangsong and no difference was found between earlywood and latewood. In conclusion, rings of tree for the time of property revelation as Uljin-Geumgangsong wood is assumed about more than 150 years.

• Journal of the Korean Wood Science and Technology
• /
• v.46 no.5
• /
• pp.486-496
• /
• 2018

This study was conducted to confirm an effect of span length on bending properties of larch dimensional lumber in the four point bending test. The size of specimen in this study was 38 (width) ${\times}$ 89 (depth) ${\times}$ 3,600 (length) $mm^3$, and average air-dry density and moisture content of the specimens was $543.5kg/m^3$ and 10.5%, respectively. Visually graded No. 1 dimensional lumbers of 248 were divided by two groups to compare modulus of rupture (MOR) and modulus of elasticity (MOE). One group was tested in the four point bending test with span length of 1,650 mm, and other was tested with span length of 3,000 mm. While MOE was not different according to span length in 5% significance level, MOR was different in accordance with span lengths and was in inverse proportion to change of span length. Fifth percentiles of MOR in span length of 1,650 and 3,000 mm were 28.65 and 25.70 MPa, respectively. It was confirmed that the difference between MORs in each case increased as normalized rank increased. This is because of size effect in Weibull weakest link failure theory. Therefore, KS F 2150, in which there is only regulation about span to depth ratio of 15 or more, is needed to be revised to contain a method considering size effect for MOR. From the method, various results of bending test with different size of lumber could be used to determine design value of lumber.