Observations were made of within annual ring and pith-to-bark variations of the microfibril angle of the S₂ layer (MF angle) of tracheid walls in 106-year-old plantation trees of Japanese larch (Larix kaempferi Carr.). The MF angle was measured by the iodine method. The MF angle within the annual ring decreased from the beginning to the end region of earlywood, whereas in latewood there was less variation than in earlywood, regardless of cambial age. The decrease in MF angle in earlywood is gradual in rings of younger cambial age, whereas it is abrupt in rings of older cambial age, regardless of the rate of radial growth. The pith-to-bark variations of MF angle were found to be constant in earlywood. On the other hand, the MF angle of latewood decreased abruptly in the younger stage followed by a stable smaller angle in the older stage after the 15th to 30th rings. There was no significant correlation between ring width and MF angle of latewood in mature wood (after the 30th ring).

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This paper deals with testing the stress and strength of a laminated composite plate containing bamboo and hinoki wood, after being subjected to static bending moments. The resulting material properties of the hinoki and bamboo composite were determined by tension tests parallel to perpendicular to and at an angle of 45 degrees to the fiber direction. Stress and strain were calculated using an elastic and orthotropic finite-element method (FEM). The greatest stress was incurred on the hinoki surface of the laminated composite plate. The effects of variations in thickness of the hinoki element relative to the bamboo on stress distributions were examined. It was found that every stress component increased as the proportion of bamboo element thickness decreased. In addition, surface strain distributions under static bending moments were measured using strain gauges. Reasonable correlation was found between the numerical and experimental results. Bending strength tests were performed. It was observed that the bending strength of the laminated composite plate increased with an increase in the proportion of bamboo element thickness.

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The quality of squared lumber without pith and sawing yields were investigated on large diameter sugi logs with a top end diameter of 30 cm or more, the supply of which is expected to increase imminently. A strong positive correlation was observed between the moisture content of heartwood and that of squared lumber, and between the Young's modulus of logs and that of lumber. It was found to be reasonable to sort logs based on the moisture content of the heartwood and Young's modulus of logs to improve the production efficiency for reliable lumber. The size of the rough sawn lumber had to be increased for finishing accuracy; taking into account shrinkage and warp after kiln-drying. Current rough sawn size is often determined uniformly with target size. However, since warp and shrinkage due to drying vary depending on sawing pattern, there is the possibility of high sawing yield by setting the adaptable rough sawn size depending on the sawing pattern. There is potential to produce squared lumber with the required quality and with a high sawing yield by sorting logs suitably and setting the adaptable rough sawn size depending on the sawing pattern.

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Our previous study showed that airborne dust mass was less in sawing high moisture content lumber than dried lumber. Based on this finding, we developed the technique of reducing airborne dust generated from circular sawing by applying water to work pieces before sawing. Boards of air-dried sugi (Cryptomeria japonica) were soaked in water for 1 or 3 days, or had their top surfaces wetted using a roller containing water before circular sawing. The mass concentration of airborne dust (of 10 µm or less diameter) generated from circular sawing was measured with a low volume air sampler at a point 1550 mm above the floor and at 600 mm from the axis of the circular saw toward an operator. Soaking for 1 day decreased the mass concentration to about one-half of that in sawing air-dried lumber and to about one-third of that for 3 days of soaking. Soaking in water is effective for reducing airborne dust mass concentration. Wetting lumber surfaces decreased the mass concentration to about one-half. In this case, the sawdust generated was attached to the top surface (wetted surface) of work pieces, and thus the mass concentration was reduced. These findings suggested that the mass concentration of airborne dust generated from circular sawing could be reduced by soaking work pieces into water or by wetting the top surface of work pieces using a water-soaked roller.

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To study the effect of degradation of structural wooden panels on the performance of nailed joints, plywood and medium density fiberboards (MDFs) were decayed forcibly by Fomitopsis palustris (brown-rot fungi) or Trametes versicolor (white-rot fungi) and strength tests of nailed timber joints with wooden panels were conducted. As a result, plywood was considerably deteriorated, and mass-loss when decayed by F. palustris was greater than with T. versicolor, but MDFs were hardly decayed by either fungus. Lateral nail resistance of wooden panels and shear strength of nailed timber joints were decreased by decay of wooden panels as side members and lumber as main members, but high moisture content seemed to greatly affect strength degradation of each member in the early stage of decay. Yield and ultimate shear strengths of degraded nailed timber joints could be estimated properly based on European yield theory by using measured strength values of lumber and wooden panels and in consideration of mass-loss and moisture content of wooden panels. However, nail-head-pull-through strength of MDFs was estimated as low because of its modified density and the reduction coefficient for high moisture content established by the current standard for structural design of timber structures in Japan.

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