While the use of high-temperature setting method, for kiln drying green square timbers with pith at high-temperature and low-humidity conditions at the initial drying stage, has spread in Japan, there is no established optimal kiln-drying schedule for various softwood species of larger-sized rectangular timbers used for beams and girders. Therefore, we tried to determine an adequate high-temperature setting method for reducing both surface- and internal checks through analyzing the effects of temperature conditions and size of the timbers. The results suggested that moisture content after high-temperature setting treatment might affect the occurrences of internal checks in akamatsu(Pinus densiflora) and sugi (Cryptomeria japonica) timbers. The monitoring of moisture content during high-temperature setting treatment should be useful for reducing internal checks. As for differences in occurrence of surface checks among species, surface checks in akamatsu timbers were wider than in Japanese larch (Larix kaempferi) or sugi timbers. Larger timber size caused more frequent occurrences of surface checks in akamatsu and sugi but not in karamatsu.

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The purpose of this research was to clarify the effect of coloring on the impression of Japanese cypress for interior material. For this research, four types of interior decoration models that varied in color pattern were made using interior decorative panels of Japanese cypress and natural painting. The impressions of these interior decoration models were evaluated by the SD (Semantic Differential) method at Okayama prefecture. The main results were as follows: Regardless gender and region, a similar tendency was observed in the evaluation of impression of each interior decoration model. As the brightness was lowered by coloring, clear, light, and feminine impression of uncolored Japanese cypress turned into profound, heavy and masculine impression. As a result of factor analysis, it was found that the factors “color pattern” and “personal preference” affected the evaluation tendency of subjects. Because the correlation between the factors of “color pattern” and “personal preference” was low, it was thought that the coloring of Japanese cypress has a greater effect on its visual impressions such as clear and light than subjective impressions such as preferable and calm. It was also found that for subjects of an older generation, their past experience affects their preference.

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For the purpose of increasing the store of data regarding shear load factors for horizontal diaphragms sheathed with particleboard (PB) of Japanese conventional wooden houses, racking tests were conducted for two types of floors differing in joist intervals and for two types of attic horizontal diaphragms differing in nail type and edge distance. A floor sheathed with JIS 18M type 15 mm thick PB under in-line nailing with a N50 nail, an interval of 150 mm and edge distance of 12 mm was found to possess a shear load factor of 2.3 for a joist interval of 455 mm. Shortening the joist interval from 455 to 303 mm increased the yield load 1.27 times and the ultimate load 1.35 times because of using approximately 1.4 times the amount nails, and this resulted in increase of the shear load factor from 2.3 to 2.9. An attic horizontal diaphragm sheathed with JIS 18M type 12 mm thick PB under perimeter nailing with a N50 nail, interval of 150 mm and edge distance of 12 mm was found to possess a shear load factor of 2.8. Changing the specification of nailing from N50 to CN50 and the edge distance from 12 to 25 mm increased the yield load 1.14 times and the ultimate load 1.26 times, which resulted in an increase of the shear load factor from 2.8 to 3.6.

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Two types of mixed-species three-ply CLTs (Cross-Laminated Timbers) composed of hinoki-sugi-hinoki and akamatsu-sugi-akamatsu were manufactured in this study. The relationships between modulus of dynamic elasticity using frequency (E_fr) of logs or lamina graded visually for knots, and modulus of elasticity (MOE) of edge-glued laminae were investigated. Moreover, mixed-species three-ply CLTs were examined by static bending tests to clarify the bending properties. The results are summarized as follows: Positive correlations were recognized between E_fr of logs and MOE of edge-glued laminae for each species. When comparing average values of MOE of edge-glued laminae graded visually for knots, it was recognized that for sugi and akamatsu, MOEs of edge-glued laminae with none or fewer knots were significantly larger than those with few knots and loose knots. MOEs for mixed-species three-ply CLTs were clearly greater than those for sugi-only three-ply CLTs. When comparing mixed-species three-ply CLTs with hinoki or akamatsu single species three-ply CLTs, air-dry densities for mixed-species three-ply CLTs were significantly lower. However, differences of MOEs between mixed-species three-ply CLTs and hinoki or akamatsu single species three-ply CLTs were hardly recognized.

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