We investigated the effects of climate factors on tree-ring structure of Cryptomeria japonica in central Japan. We collected cores from 33 plantation trees in the Takayama evergreen coniferous forest site at Gifu University and measured annual ring width (RW), annual mean density (RD), earlywood width (EW), latewood width (LW), earlywood density (ED) and latewood density (LD) by X-ray densitometry. We also calculated annual ring weight growth (RWG) by multiplying RW and RD. We developed seven residual chronologies of the parameters of tree-ring structure by a dendroecological method. Pearson's correlation analysis was applied to assess relationships among the chronologies, and relationships between the chronologies and climatic factors. EW showed significant positive correlations with RW and RWG. Moreover, EW showed significant positive correlation with the temperature current from March to April. These results indicate that EW is the most dominant factor which regulates RW and RWG of C. japonica. It is suggested that EW increases by the temperature rise of early spring before reactivation of cambium activity, and subsequently RW and RWG will increase.

There are two formulas for the allowable resistance of nailed joints. One is based on the European Yield Theory (EYT) and the other contains the head diameter of the nail as a parameter. In addition, there are a few cases where the behavior of the load rising after yield is considered theoretically. In this paper, we estimated yield and maximum load of nailed joints with MDF. The yield load was estimated by the EYT formula considering the moment generated by nail head rotation. The maximum load was estimated by the existing formula of screw joints considering a “rope effect”.

As a result, the estimation accuracy was increased by the improved EYT formula, taking into consideration the moment generated by nail head rotation. It was also shown that the rope effect of nailed joints can be estimated by the formula for screw joints. On the other hand, it was suggested that the bearing strength of the range between the plastic hinge and the tip of the nail might affect the gap of yield strength between the calculated and the experimental values. It was also suggested that, at the maximum load, nail withdrawal strength might be underestimated and nail-head pull-through strength be overestimated compared to actual values.

In this study, the surface-strain distribution behavior of sugi (Cryptomeria japonica) square timber under high-temperature drying was determined. The surface-strain distribution was measured using the mark-tracking method, which is an image analysis technique. Boxed-heart and pithless timbers with a cross-sectional dimension of 132 mm × 132 mm were dried under three types of drying condition. In each condition, the values of surface strain at the center of the timber were higher than those at the edge. This tendency was remarkable in the case of high-temperature drying of boxed-heart timber. The surface drying set, which was measured after drying, showed a positive correlation to the surface strain. This indicated that the surface strain could be used to rough estimation of the amount of the drying set under kiln drying. By measuring the surface-strain distribution using the image analysis technique, the temporal change in the surface strain during the high-temperature drying was clarified in detail.

In the present study, new high-performance strapped adhesive plates comprising of hinoki cypress (Chamaecyparis obtusa) and bamboo (Phyllostachys heterocycla) were investigated. Such plates are expected to find applications in making furniture or house wall construction. Two test set-up were performed, single-strap joint and double-strap joint. In the single-strap joint set-up, one bamboo plate was glued to one side of two abutting hinoki plates. Two thickness bamboo plate variables were tested, using 4 and 2 mm. On the other hand, in the double-strap joint set-up, two identical size bamboo plates were glued to both side of the two abutting plates. Two thickness bamboo plate variables were also tested, 4 and 2 mm. In all set-up, the hinoki plates were not bonded to each other. The joints were subjected to tensile strength tests until peeling, and the results were compared. In addition, the stress and strain were calculated using an elastic and orthotropic finite element method (FEM). It was found that the tensile load at rupture for a double-strap joint was not affected by the thickness of the bamboo plates. On the other hand, for a single-strap joint the thickness of the bamboo plates affects the tensile load at rupture. When the single-strap joint with thin bamboo plate was ruptured, the tensile load was larger than that of the more rigid thick bamboo plate. It was found that the stress around the adhesive layer of the joint with lower rigidity plate is smaller by flexibly deforming the bonded part under tensile loadings.

In this study, we used the life cycle assessment method to calculate greenhouse gas (GHG) emissions associated with lumber products by 10 sawmills in Mie Prefecture, Japan. These sawmills produced an average of 153 kg CO₂e m^-3 per year (range, 54-473 kg CO₂e m^-3). Average GHG emissions weighted by annual sawmill production was 258 kg CO₂e m^-3. We detected significant variation in GHG emissions among sawmills. Influential factors included the presence/absence of molding production and kiln-drying, as well as the type of heat source used for kiln-drying. Fossil fuels generally increased the amount of sawmill emissions; however, even when fossil fuels were used in kiln-drying, sawmills were able to reduce GHG emissions by adapting the drying process to the summer months.

Near-infrared spectroscopy enables identification of previously inseparable wood species by the observation of their anatomical features by optical microscopy and through the detection of subtle differences of chemical components between wood species. This research verified whether the combination of Near-Infrared spectroscopy, multivariate analysis and feature selection method can discriminate the anatomically similar and important softwood species used as building materials, Chamaecyparis obtusa and Thujopsis spp., and Tsuga sieboldii and Tsuga heterophylla. In addition, classification of old C. obtusa and T. dolabrata specimens collected from traditional buildings was conducted based on the statistical model trained by their new samples. In the case of new specimens, classification accuracy reached almost 90% in Cupressaceae and Tsuga, respectively. Moreover, feature selection succeeded in the quantitative demonstration of important wavelength regions for their discrimination. On the other hand, classification accuracy of old specimens had deteriorated to some degree because of the transition of chemical components during their degradation. However, relatively high classification accuracy was kept because the important variable regions chosen by the model are robust to the aging process by chance.