栽植距離對柳杉強度變異性影響之研究（I）－靜力機械性質

Effects of Planting Distance on the Strength Variation of Japanese Cedar (I) -Static Mechanical Properties

卓志隆(Chih-Lung Cho)

《林產工業》 17卷3期 (1998/09) Pp. 453-469

https://doi.org/10.6561/FPI.1998.17(3).1

摘要

本研究之柳杉試材取自本省溪頭實驗林區40年生之立木，採用‘中國國家標準之木材靜曲強度、壓縮強度、引張強度及剪斷強度試驗法測試五種不同栽植距離之無缺點小試材，在生材及氣乾狀態下（含水率約為15%）之各項強度性質，由強度之變異性分佈計算在95%信賴區間內5%之排外水準值作為基準應力，由此應力推估柳杉各品等之容許應力值。本研究得到如下結果：1.栽植距離1m × 1m之柳杉林木，其平均絕乾密度最大為426kg/m^3，栽植距離5m × 5m最低，密度與各項機械性質皆呈極顯著正相關關係。2.栽植距離1m × 1m之柳杉林木，其平均年輪寬最窄，為5.23mm。而平均年輪寬與絕乾密度間呈負相關。3.柳杉機械性質不論是氣乾或生材狀態以引張強度＞靜曲強度＞縱向壓縮強度＞剪斷強度。4.靜曲及縱向壓縮強度，不論是氣乾或生材狀態皆以1m × 1m栽植距離者最大，5m × 5m最小，而2m × 2m，3m × 3m，4m × 4m間，則不具有顯著差異。5.含水率對於柳杉壓縮強度的影響最大，對於引張強度的影響最小。6.溪頭地區各品等柳杉木材，依生材狀態之5%排外水準值所推估容許應力值如表14所列，以靜曲強度最大，剪斷強度最小。7.若以柳杉平均機械性質或密度考量材質，則柳杉林木採用1m × 1m栽植距離下生長至樹冠鬱閉後，再進行適當的疏伐作業，對於林木材質有正面效果。若以容許應力值考量，則各栽植距離間差異不大。

關鍵字

柳杉 ； 栽植距離 ； 機械性質 ； 密度 ； 5%排外水準值 ； 容許應力

並列摘要

The Japanese cedar (Cryptomeria japonica D.Don) specimens of this study were manufactured using the planted trees sampled from forty year old trees at Chi-Tou experimental forest in Taiwan. The mechanical properties of small, clear specimens from five plantation spacing samples were obtained by CNS static bending, compression parallel to grain, tension parallel to grain, and shear strength methods. The moisture content of tested specimens were green and air dry (l5%) respectively. From the variance of respective strength, the lower 5% exclusion limit (EL 5 %) of distributed population can be calculated with 95% confidence. We can estimate allowable properties of different grade lumber by EL 5% and adjustment factor. The following conclusions can be drawn from this study: 1.The oven dry density of the 1m x 1m plantataion spacing was the largest (426kg/m^3.and the 5m × 5m was lower. The two-type plantation spacings (1m × 1m , 5m × 5m) on oven dry density both show their significant difference, at 95% probability level,in comparison with the other three-type plantation spacings (2m × 2m, 3m × 3m,4m × 4m ).There were significant positive relationships between density and various mechanical strength of Japanese cedar. 2.The average annual ring width of 1m × 1m (5.23mm)was significantly lower than the other types. There was a negative relationship between oven dry density and average annual ring width. 3.The mechanical properties of Japanese cedar, regardless of green or air dry condition, were proved sequentially ordered as the followings: tensile strength＞ bending strength ＞ crushing strength parallel to grain ＞ shear strength. 4.Both at green or air dry condition, the crushing strength, bending strength and modulus of elasticity of the 1m × 1m was significantly higher than the other four plantation spacings. The mechanical strength of 5m × 5m was lower. There were no significant difference among 2m × 2m, 3m × 3m and 4m × 4m plantation spacings. 5.Among the various strength of Japanese cedar, the crushing strength depends greatly on moisture content, and the tensile strength was least affected by moisture content. 6.The allowable stress design values of different grade lumber of Chi-Tou area are given in Table 14. The bending strength is the highest, and shear strength is lower. 7.From the viewpoint of mechanical properties or density, it is recommended to use plantation spacing 1m×1m, and to thin properly after the crown is crowded. This can produce the better quality trees. But if we consider the lower 5% exclusion limit, it shows no significant difference between various plantation spacing.

並列關鍵字

Japanese cedar ； plantation spacing ； mechanical properties ； density ； lower 5% exclusion limit ； allowable stress