ISO published the international standard ISO 13910 concerning the testing and evaluation method for full-size structural timber strength in 2005, and this will influence the standard of Japan in the future. However, some irrational points are seen here, such as in the testing method for shearing strength and the rule for deriving the characteristic value. In the establishment of the Japanese official standard, it is necessary to make it suitable for our country, referring to the method proposed by Japan Housing and Wood Technology Center, based on a consideration of the specifications for the testing equipment in Japan and adjustment methods for effective use for the data accumulated domestically.

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We used a Pilodyn for estimating basic density in the green condition for the purpose of classifying logs of Cryptomeria japonica D. Don based on their density. The relationships between Pilodyn penetration depth in the radial direction (Pr) and basic density of blocks with pin penetration were examined in a wide basic density range of hardwoods and softwoods (199-779 kg/m³), and C. japonica (221-474 kg/m³). There were significant negative correlations in hardwoods (r = - 0.92, P<0.001), softwoods (r = - 0.86, P<0.001) and C. japonica (r = - 0.82, P<0.001). Thus, the basic density of the block could be estimated based on the penetration depth. Curvilinear regressions gave the best fits in hardwoods, softwoods and C. japonica and the estimated basic densities from the curvilinear regressions for the same Pr were close to each other. In C. japonica, Pr varied between sample groups with similar basic densities, and Pr was smaller in the group with greater earlywood width in spite of similar densities. We examined the applicability of the Pilodyn to estimating average density of C. japonica green logs. There was a significant correlation between Pr and the disk-averaged basic density (r = - 0.84, P<0.001). The 95% confidence limits of the disk-averaged basic density estimated from Pr were ±47 kg/m³ when Pr was measured once, in each of two directions. The variations of the disk-averaged basic density within logs were smaller than the confidence limits except for those at the ground level. It was concluded that the Pilodyn could be used for classifying logs of C. japonica based on their density, although it is necessary to consider that the density variation from pith to bark could be varied by tree age, inherited characters and growth conditions.

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To investigate the fine structure of wood in the non-equilibrium moisture condition, X-ray diffraction (XRD) analysis was conducted during moisture content changes in Japanese red pine specimens. The XRD analysis used a novel measurement system consisting of an X-ray diffraction analyzer with a differential scanning calorimeter (DSC) and a humidifier attached. Moreover, thermogravimetric (TG) measurements were also carried out under the same condition as XRD to estimate the moisture content (MC) during XRD measurement. It was confirmed from TG measurements that MC changed exactly as the humidity changed. However, the value of heat flow of adsorption/desorption of moisture still changed even after MC finished its increase/decrease. Both the (200) peak due to cellulose crystal and the halo peak due to non-crystalline regions shifted to a higher angle with increasing moisture content, and shifted to a lower angle with decreasing MC. Moreover, there was a delay in the (200) peak shift in the desorption process compared with the change of MC. Furthermore, a similar delay in the relative crystallinity change was also observed. These results suggest that the fine structure does not follow RH changes regardless of the agreement between the changes of MC and of RH.

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Strain distribution analysis of half-lapped “gooseneck” splice joints (Kama-tsugi) was carried out using digital image correlation. The effect of the shear plane length on the tensile strength of the joint and strain distribution of the tenon was examined. The dimension of the tenon was changed by altering the shear plane length (L) relative to the fixed width (d) of the compression plane and the fixed rise (H) of the shear plane. Results were as follows ;
(1)The tensile strength leveled off in joints whose dimension factors (L/d) were greater than eight.
(2)Large tensile strain perpendicular to the grain was observed near the re-entrant corners of the tenon. From this value of the tensile strain, it was found that local failure occurred prior to reaching the ultimate strength. The estimated area for the local failure was almost constant and was not affected by the shear length.
(3)Shear strain concentrated near the re-entrant corners of the tenon and gradually decreased toward the head of the tenon. The degree of shear strain concentration in its linear elastic region was calculated as the ratio of maximum shear strain to the average shear strain. The value of the degree was 3.7 in the tenon with the standard dimension factor of ten (L/d =10). The degree increased as the dimension factor (L/d) increased up to the dimension factor of fourteen (L/d =14).
(4)The tensile strength of the tenon was estimated by using the degree of strain concentration. The degree of strain concentration was introduced to account for the shear stress concentration at the maximum load. A good agreement was found between the estimated strength and the measured strength.

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In order to estimate changes of carbon absorption by trees, a method for calculating annual increases of oven-dried weight of individual trunks from width and mean density of annual rings was established. Discs at 1 m intervals above 0.2 m high from 24 sugi (Cryptomeria japonica D. Don) trees were collected after measuring green weight of 1 m long logs. Radial strips including the pith were cut from the discs for soft x-ray densitometry and the other parts of the discs were used for measuring oven-dried weight of the discs. Cross-sections 2 mm thick processed from the strips were exposed to soft x-rays followed by densitometry for measuring width and mean density of each annual ring. The weights calculated from the area and mean density of each annual ring and log length were significantly correlated with the oven-dried weights of the logs. Therefore, the densitometry was applicable for calculating the oven-dried weight of trees. It is believed that ring width and mean density can be used to estimate the annual increase of oven-dried weight of the tree trunks. The annual increase of the oven-dried weight calculated as accumulation of weight of each annual ring was influenced by the ring width, because it changed with variation of area of annual rings. Density variation seemed to affect the fluctuation of weight gain and its effects was considered to be smaller than the ring width.

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In this series of studies, a manufacturing technology was developed which uses wood flakes or shavings for binder-less insulation panels used in buildings. This paper describes the use of sugi (Cryptomeria japonica D. Don) bark chips in our panels for the purpose of expanding the choice of potential raw materials. Bark chip panels ranging in density from 100 to 180 kg/m³ were manufactured using bark chips of three different sizes. Thermal conductivity and drop impact resistance were tested and compared to our conventional panels made with wood flakes or shavings. The best panel performance which balances superior thermal insulation properties and superior drop impact resistance was obtained for panels with a density of 140 kg/m³ (optimum panel density), irrespective of the bark chip size. The bark chip panels at that density showed better thermal insulation properties (a thermal conductivity of 0.07 W/mK) and better drop impact resistance than the sugi wood flake panels with the same density. When compared to the wood shaving panels, however, the thermal insulation properties of the bark chip panels were found to be inferior in terms of higher thermal conductivity, because the thermal conductivity of the wood shaving panels was lower (0.06 W/mK) due to the lower optimum panel density of around 100 kg/m³ to maintain drop impact resistance.

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