台灣杉等級內強度分佈變異數研究

Study on the In-grade Variance of Strength Distribution of Taiwania

王怡仁(Yi-Ren Wang) ； 陳柏璋(Bor-Jang Chen) ； 陳周宏(Jou-Horng Chern)

《林產工業》 11卷1期 (1992/03) Pp. 63-76

https://doi.org/10.6561/FPI.1992.11(1).5

摘要

本研究之目的在於驗證理論公式對於經非破壞性檢定分等後，等級內變異數之預測的準確性，同時也對現行之目測分等系統、台灣杉小徑木平割材之彎曲性質，及其與小試片之關係加以研究。研究方式首先以中國國家標準目測分等方式，將台灣杉之平割材分等，再以比重、靜曲彈性係數及動彈性係數為非破壞性檢定參數，將平割材分等，然後求其等級內之變異數，並與由公式所得之預測值相比較。本研究發現台灣杉平割材經目測分等後，各等級之靜曲強度並沒有顯著的偏差，顯示出目測分等方式的精度有待檢討。實大樑與小試片間之彎曲性質的相關性偏低，又因為小徑木平割材的缺點與強度之間關係尚未究明，對於實大材之性質宜以實大材直接試驗為佳。當以比重、靜曲彈性係數及動彈性係數為非破壞性檢定參數，發現此等參數與靜曲強度之相關性不高，最好的是動彈性係數，依次為比重及靜曲彈性係數，在利用非破壞性檢定參數所預測的強度值對平割材分等後，所求得等級內之變異數與公式預測的等級內變異數相比較，發現二者之相高關性極高，顯示出理論公式之準確性。

關鍵字

台灣杉 ； 靜曲強度 ； 靜曲彈性係數 ； 橫振動 ； 動彈性係數 ； 標準差 ； 等級內變異數

並列摘要

The proposed equation which can be used to predict the in-grade variance associated with nondestructive evaluation (NDE) grade is verified. The accuracy of the visual grading system currently employed in the Chinese National Standard (CNS), and the relationship of the bending properties of Taiwania between dimension lumber and the associated small-clear specimen are as well studied. Taiwania dimension lumbers are first visually graded by CNS grading rules. Then specific gravity, dynamic modulus of elasticity and modulus of elasticity are chosen as the nondestructive evaluation parameters. The dimension lumbers are graded by the individual NDE parameters. The in-grade variance is obtained and is compared with the one obtained from the proposed equation. It is found that the visual grading rule employed by CNS is not very sensitive in grading Taiwania dimension lumbers due to the insignificant difference of bending strengths among grades. Because of the relationship between defects such as knots and juvenile wood and strength is not thorough clear, and the low correlation of bending strength between dimension lumber and the relevant small-clear specimen, it is suggested to obtain the strength value of dimension lumber by full-size testing in stead of being predicted by small-clear specimen. The NDE parameters such as specific gravity, dynamic modulus of elasticity and modulus of elasticity do not have high correlation with the bending strength of Taiwania dimension lumber. The best predictor of the bending strength is the dynamic modulus of elasticity followed by the specific gravity and the modulus of elasticity. However, the predicted in-grade variance obtained by the proposed equation have good agreement with the actual in-grade variance. The equation may be used in predicting in-grade variance with acceptable bias.

並列關鍵字

In-grade variance ； Nondestructive evaluation grading ； Bending strength ； Taiwania ； Flexural vibration