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スギ若齢木からの平割材における曲げ弾性係数の材内分布に関する統計的解析

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概要 九州大学粕屋演習林産の20年生および30年生若齢スギ(Cryptomeria japonica D.Don,品種:アヤスギ)の樹幹各部位から挽かれ,断面25×50,35×50と45mmx50mm,長さ3.2mの生状態ならびにそれらを気乾状態にした実大寸法の平割材について,その材長方向にわたる曲げ弾性係数(MOE) 分布を部分測定スパン20cm,測点間隔10cmの部分中間たわみ測定法によって求めた....ならびに,MOEに直接関与する力学的指標としての断面二次モーメントについて,各部分測定スパン内の全断面に対する節などの欠点部の比,すなわち欠点断面二次モーメント率(ROI)の材長方向分布を求めた.そして,それらのMOEとROIの材長方向分布を統計処理し,それぞれの標準偏差(SD_E,SD_I),および変動係数(CV_E ,CV_l)を求め,樹幹各部位から木取られた実大寸法の平割材の諸条件下における曲げ弾性係数の材長方向分布について検討した.研究結果を要約するとつぎの通りである.(1)樹幹半径方向中央部(髄側)からの材では,MOEは材長方向に低い値で分布し,ROIが材長方向に比較的均等に分布するためにSD_EおよびCV_E左は小さい.一方,樹幹半径方向外周部(樹皮側)からの材では,MOEは高い値で材長方向に分布し,ROIが材長方向に不連続的に分布してSD_EおよびCV_Eは大きい.(2)一番玉丸太の外周部からの材の根元寄りにおいてMOEがROIの大小にかかわらず必ず低い値をとる.それ以外では欠点断面二次モーメント率(ROI)の材長方向分布に対応して,MOEが変動する.(3)とくに,大きな節やあて材部での著大なROI値に対応して,材長方向の同一部位でMOEの異常に激しい低減が認められる.(4)実用場面でも起こりうる生状態から気乾状態(ここでは含水率14%)への移行によって,多くの場合にSD_E,CV_Eとも増大する.(5)構造設計上の現場施工における材の取付け型式として,断面に対する負荷方向がflatwise (長幅負荷:ここでは板目面負荷)とedgewise (短幅負荷:ここでは柾目面負荷)とでは,後者の方が一概にSD_E,CV_Eとも大きいことが認められる.
For each of 25 by 50, 30 by 50, and 45 mm by 50 mm green or air-dried lumbers 3.2 m long sawn from various positions of 20- and 30-year-old sugi (Cryptomeria japonica D. Don) logs which were grown in the Kasuya Forest of Kyushu University, the variation in localized modulus of elasticity in bending (MOE) along the length of the lumber was measured by a middle ordinate method using the gage length (the measuring span) of 20 cm at the intervals of 10 cm. In another measurement, the variation in localized ratioes of cross-sectional moment of inertia of defect, mainly, knot to that of the entire cross section within each measuring span (ROI) was determined throughout the length of the lumber, regarding its magnitude as an important indicator relevant to the variation in the MOE localized within the piece of lumber. Furthermore, the standard deviations, SD_E and SD_I, and the coefficients of variation, CV_E and CV_I, were calculated by the statistical analysis for both variations in MOE and ROI, respectively. The following results were obtained; (l) For the lumbers from the central part (pith side) of log in the radial direction, the MOE varied at a low level throughout their lengths and both the SD_E and CV_E were small because of the uniform distribution of ROI, irrespective of presence of many knots. For the lumbers from outer part (bark side) of log in the radial direction, the MOE varied at a high level throughout their lengths and both the SD_E and CV_E were large because of the discrete distribution of ROI and a marked descent of MOE around the bottom of stem in the longitudinal direction, irrespective of presence of only a few knots. (2) According to the variation in ROI within the piece of lumber, the MOE was distributed throughout the length, with the exception of the abrupt decrease in MOE within the piece of lumber from the bottom part of stem. (3) The infrequent, excessive enlargement of the localized ROI due to the presence of large knot and undue reaction wood reduced the MOE localized in the same zone to a very large extent. (4) By air-drying green lumber to approximately 14% moisture content, both the SD_E and CV_E became explicitly larger for the lumbers from the central part (pith side) than for those from the outer part (bark side). (5) In general, both the SD_E and CV_E were larger in the edgewise bending than in the flatwise one.
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登録日 2009.04.22
更新日 2021.03.03

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