- 期刊
柳杉疏伐木製作結構用製材品之目視與機械分等
Visual and Mechanical Grading of Structural Sawn Lumber from ＂Cryptomeria Japonica＂ Thinnings
摘要
本研究以羅東林區管理處94年度疏伐收穫之柳杉中小徑木所製成356支結構用製材品為試驗對象。每支製材品依CNS 14631標準進行目視分等，依14633標準及彎曲振動試驗得到之動彈性模數進行機械應力分等（MSR），並評估各等級製材品的收率和力學性質。目視分等結果中，結構級、標準級、普通級及級外材製材品的收率分別為25.3%、24.4%、37.9%及12.8%；以普通級的收率最高。不同目視等級製材品間之密度、彈性係數與靜曲強度經變異數統計分析後具有顯著差異性。由於靜曲彈性模數（MOE）與動彈性模數（DMOE）間具有良好之直線相關（決定係數R^2=0.96）；且靜曲強度與DMOE之直線相關決定係數R^2值為0.54，與相關研究相似，故以彎曲振動試驗法作為生產線上製材品機械應力分等，是可行的方法之一。根據試驗所設定之三種機械應力等級（2100Fb-1.8E、1650Fb-1.5E及1200Fb-1.2E）相關性質要求，共有178支（50%收率）的製材品符合MSR標準；其中2100Fb-1.8E、1650Fb-1.5E及1200Fb-1.2E等級之數量分別為25支、49支及104支。由於三種MSR製材品各等級內動彈性模數之變異係數皆在11%以下，明顯較各目視等級內變異係數（19%～26%）為低，故中小徑原木所生產MSR製材品較目視等級製材品可提供較高設計應力值。
並列摘要
356 samples, each with the size of 2×4, Japanese cedar structural sawn lumber manufactured from the thinned logs harvested by Luodong Forest District Office in 2005 were investigated in this study. Each piece was sorted into two types of grade categories: 1) visual grading; and 2) Machine-Stress-Rated (MSR) grading in accordance with CNS standard 14631, 14633, and dynamic modulus of elasticity (DMOE) obtained from flexural-vibration test. The grade yields and mechanical properties for different lumber grades were then evaluated. The yield of construction grade, standard grade, utility grade, and below grade lumber were 25.3%, 24.4%, 37.9%, and 12.8% respectively based on visual grading rules. The utility grade lumber made the highest yield in this study. There were significantly difference among various visually graded lumber in the values of density, modulus of elasticity, and bending strength according to ANOVA analysis. The relationship between MOE by static test and DMOE by flexural-vibration test was very good (R^2=0.96). The relationship between MOR and DMOE is typical of that found for relative studies (R^2=0.54). Therefore, flexural-vibration test could be a feasible approach adapted for mechanical grading system. MSR process was conducted on three selected MSR grades: 2100F_b-1.8E, 1650 F_b-1.5E, and 1200 F_b-1.2E. The results indicated that 178 pieces (50% of the sample) qualified as MSR lumber with respect to performance criteria. Of which, 25 pieces of lumber made 2100F_b-1.8E grade, 49 pieces of lumber qualified as 1650 F_b-1.5E grade, and 104 pieces of lumber met the 1200 F_b-1.2E grade requirements. Because according to MSR grading procedure, the lumber produced for three selected grades having a lower coefficient of variation (COV≦11%) in DMOE than those visual grading lumber (COV: 19%-26%) indicating the production of MSR lumber from small-diameter logs may offer a higher design value alternative to the production of visually graded lumber.