Sugi (Cryptomeria japonica) and todomatsu (Abies sachalinensis) are leading species for Japanese forestry. In those two species, “wetwood”, a phenomenon of water accumulation in heartwood, has often been found and the presence brings problems in wood utilization. Wetwood can also be observed in other species and the frequency of encountering wetwood seems to be species (or generic) specific. In this review, the phenomenon and appearance of wetwood are discussed as well as its definition. The green moisture content of wood is also reviewed and discussed, as it is an essential means to describe wetwood.

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Utilization of joint stochastic nature of timber strength properties such as elasticity and bending strength often produces good results. For example, the mechanical grading method provided an advanced system of allowable stresses. Statistical and visual expression methods are necessary for analyzing bivariate non-normal distributed data such as bivariate strength properties of timber. A probability ellipse is a graphical method for representing a bivariate distribution with specified inner probability. However it is not suitable for non-normal distributions. This report presents a method for drawing a skewed probability ellipse with marginal non-normal distributions. This method converts a conventional probability ellipse into a quantile-based non-normal ellipse using iso-probabilistic transformations based on marginal distributions. We have verified the following performances of the method by numerical experiments using some groups of accumulated data of tests in bending. The performances included accuracy of inner probability, uniformity of probability for de-correlated vectorial angle, and comparability among some data groups. These results confirmed that the method showed good performances.

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This report presents a method for drawing a non-normal probability ellipse with constant probability density (dNNE). In other words, dNNE is a probability density contour for which inner probability is specified. The aim of this study is to develop modeling and visualization techniques for bivariate non-normal distributed data such as elasticity and strength of timber. We have mathematically examined probability density contours of bivariate distributions and inner probabilities of the contours, and a numerical calculation method for drawing dNNE was obtained. A procedure for evaluating the probability of a data region enclosed by a closed curve was introduced into this method. We have verified the following performances of the method by numerical experiments using some groups of accumulated timber strength data in bending. The performances included suitability of probability density contours, accuracy of inner probabilities, and visual expressiveness for bivariate data. These results confirmed that the method showed good performances.

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In this study, we prepared benzylated wood meal by a mechanochemical processing method, and investigated the effects of processing time and amount of reagents. Wood meal of sugi (Cryptomeria japonica D.Don) heartwood, benzyl chloride, and 40% sodium hydroxide aqueous were measured, and processed in a high-speed vibration rod mill for up to three hours at room temperature. Pre-treatment of mercerization was not done to the initial wood meal. The weight percent gain (WPG) of the processed wood meal was calculated based on the yield after washing. WPG of the benzylated wood meal was affected by the additional amount of both 40% sodium hydroxide aqueous and benzyl chloride, and the processing time. The maximum WPG was 68.8% at the processing condition of wood meal 5.0g, 40% sodium hydroxide aqueous 7.5g, benzyl chloride 14.0g, and the processing time of 180min. According to FT-IR analysis of the benzylated wood meals, the hydroxy groups (3450cm^-1) were increasingly replaced with benzyl groups (699cm^-1, 740cm^-1), as the WPG of wood meal increased. These results showed that the benzylation of wood meal was progressed by the mechanochemical processing method.

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Although the existence of a size effect for timber strength has been internationally acknowledged, no size effect factor has yet been adopted as a domestic standard for structural timber, when intended for structural members used in domestic post and beam structures. Fundamental knowledge concerning the size effect must be clarified to secure structural safety, when large cross-sectional timber is used, e.g. in public buildings. The effect of the depth or width of the timber on bending strength was examined to clarify the size effect of sugi (Japanese cedar) timber in bending strength, using a method of cutting the timber with a side- and/or end-matched pattern from a log. The bending strength was compared among 3 kinds of depth, 300, 170 and 105mm with a fixed 140mm width for the effect of timber depth, and among 2 kinds of width, 150 and 105mm with a fixed 150mm depth for the effect of timber width, under a bending test condition of a standard span-depth ratio. Consequently, the average bending strength rose with decreasing timber depth, and the size effect parameter value calculated in accordance with the size effect factor was 0.25-0.35. Conversely, no effect of timber width on bending strength was found.

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It is necessary to estimate acoustic decline caused by rot to maintain wood sound barriers for the long term. We tried to estimate the life of the wood sound barriers by conducting a fungus cellar test to perform accelerated deterioration of small specimens with specifications equivalent to real wood sound barriers as well as measuring sound transmission losses using a small anechoic box. The sound transmission losses of untreated specimens were all less than the standard value provided by the sound barrier regulation for Japanese expressways 24 months after the accelerated deterioration test started. Conversely, the sound transmission losses of specimens treated with preservatives still exceeded the standard value mentioned above 42 months after the test started. Because the rate of deterioration of wood specimens in the fungus cellar test is considered about 6 times that in an outdoor condition, the service life of preservative-treated wood sound barriers can be estimated as at least 20 years.

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