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To clarify the mechanical behaviour differences between earlywood and latewood, separated the early- wood and the latewood specimens loaded to the rupture with tensile load parallel to the grain. The separated test specimens for tensile test were prepared from douglas fir (Pseudotsuga menziesii) and stress-strain relation was evaluated by optical measurement system using the Digital Image Correlation (DIC), which can visualize strain during the tensile test. The results are summarized as follows: The estimated strain data by universal testing machine show good accordance with that estimated by DIC. There was a difference in the fracture pattern of the earlywood and the latewood of douglas fir that the surface of ruptured earlywood typically simple while that of was somewhat complicate. The longitudinal tensile strength of earlywood specimens of douglas fir at wood height from ground 12.8 m, 9.8 m, 6.7 m and 0.9 m were 51 MPa, 69 MPa, 110 MPa and 114 MPa, while those of latewood were 208 MPa, 234 MPa, 247 MPa and 198 MPa. Elastic modulus in the longitudinal tensile of earlywood speci- mens of douglas fir at wood height from ground 12.8 m, 9.8 m, 6.7 m and 0.9 m were 5458 MPa, 7202 MPa, 9705 MPa and 8761 MPa, while those of latewood were 13747 MPa, 19405 MPa, 17365 MPa and 14044 MPa.

Wood is widely used as a housing material because of its environmental superiority, good mechanical properties, fine appearance, and high thermal insulation properties. However, wood is a sound reflecting material with a relatively low sound absorption capability. It is recognized that the sound absorption capability of wood is influenced by air permeability that varies by the sound incident surface structure. Wood is a porous material which has numerous cylindrical pores in the fiber direction. However, the permeability of wood is relatively low because there are very few continuous pores in wood. The pores in wood are classified into three types: through, blind, and closed. Among these pores, only the through pore has continuous vessel elements that readily permit fluid flow. Furthermore, the formation of pit–aspirations in softwoods or tylosis in hardwoods restricts the air or liquid flow in wood. Improving the permeability of wood has been an interest of many wood researchers because highly permeable solid wood can be treated easily by a functional treatment that allows the good dimensional stability, fire proofing, and other traits. It is generally recognized that wood treatability increases with permeability. Several treatments, such as steaming, extraction with solvents, and degradation with enzymes or microorganisms, have been attempted to increase the permeability of wood. However these treatments did not have a sufficient effect on increasing permeability, and a useful method has not yet been developed. In a previous paper, Kang et al. (2008 a) reported that the delignification treatment by Wise’s method improved wood permeability in the fiber direction, and that the sound absorption capability on the cross sectional surface of Larix kaemferi increased, as compared with the control wood. Also, it was found that the sound absorption capability of a mushroom bed log of Mongolian oak degraded by fungus over four years was 2–3 times higher than that of control wood (Kang et al., 2008 b). On the other hand, steam explosion is used in the field of pulp and fiberboard manufacturing or the wood– based biomass industry and is exposure to violent pressure and temperature changes via steam. For this treatment, the target material is mounted in a closed chamber, and then superheated steam is introduced from a boiler. The superheated steam heats the chamber and target material to a high temperature and pressure, which is maintained for a moment and then discharged abruptly by a blasting device. By this process, high–pressure Changes in Permeability and Sound Absorption Capability of Yellow Poplar Wood by Steam Explosion Treatment

A skin timber is a type of wooden structural member that is circular or square in cross section and that has an inner hole that is approximately 90% the width of the external measurement. It can be the best choice for building large–scale wooden structures of the sort that have been in increasing demand in Korea recently. In the United States and Canada, single–family houses and some apartment houses are generally of a wood– frame construction. According to a survey (KFRI, 2007), however, Korean people tend to prefer the post–and– beam type of house with exposed structural members because of the sentimental appeal of traditional Korean– style houses. According to the report, ‘The research on the future of Korean–style wooden building,’ conducted by the Korea Forest Research Institute (2007), both suppliers and consumers (63.3% of suppliers and 98.3% of consumers) prefer the post–and–beam construction with exposed very large–scale structural members to building with light wood frames, as with the 2–by–4 method of construction and pre–fabricated methods. One potential solution is the use of skin timbers. The structural members used in the post–and–beam method of construction are required to have high structural performance of connection. It is the bearing strength of the members that determines the structural performance of connection. Therefore, in this study, we performed experiments on with non–bored and bored small clear samples in order to determine the bearing strength of the bored specimens compared with the non–bored specimens and to determine the difference in performance between them as a function of the load direction. Once large–scale skin timber is made, a similar evaluation of bearing strength should be carried out on the full–size samples. We are developing the skin timber such as Fig. 1.