成功大學校園中常見樹木傾倒行為研究

針對都市內許多樹木經常在風力不大時傾倒，造成公共安全威脅之議題，本研究針對成大校園中的120棵樹木進行拉伸試驗研究。首先參考國外學者Wessolly的廣義傾倒曲線，以電動絞盤進行拉伸試驗，繪出屬於臺灣樹種的傾倒曲線，發現黑板樹、阿勃勒及小葉欖仁的傾倒曲線比Wessolly的廣義傾倒曲線高，推測原因為Wessolly的廣義傾倒曲線多以針葉樹種於天然林中進行試驗，而本研究試驗對象為闊葉樹種。一般認知中，當樹木傾斜角小於0.25度時，拉力不會對根系造成損害，拉力與傾斜角會呈正相關。本研究透過手動絞盤施予樹木外力以模擬風荷載，並將傾斜角0.25度設定為測試值，分析其拉力與傾斜角大小之關係。本文並從結構學的角度，計算出該樹木的樹根盤剛度，與同樹種之間進行比較，判斷其大小是否有安全性不足的問題。本研究之試驗結果得出健康的樟樹、羊蹄甲、鳳凰木、臺灣欒樹與大葉桃花心木之平均樹根盤剛度與對應之枯立木樹根盤剛度大約相差1.5個標準差以上，而不健康樹木的樹根盤剛度大小分佈不似枯立木明顯的偏小，若測試樹根盤剛度低於平均值相差1.5個標準差以上，建議須採取適當措施降低傾倒的風險。

關鍵字

傾倒曲線；樹根盤剛度；樹木倒塌；拉伸試驗

並列摘要

Many trees fell over and resulted in casualty and property loss in the cities and in NCKU campus even when winds were not strong. This study tries to develop a mechanical testing method to evaluate the strength of a tree against tipping using the results of pulling 120 trees in the Tainan city area . This research also use an electric winch to conduct pulling tests to draw the tipping curve of the Taiwanese tree species, and compare to Wessolly's generalized tipping curve. It is found that Alstonia scholaris, Cassia fistula, and Terminalia mantaly had different generalized tipping curve patterns. The speculated reason may be that the tree species tested in this study were broad-leaved tree species, while the Wessolly's generalized tipping curve is mostly tested with coniferous tree species in natural forest. This study also performed non-destructive pulling tests using winch with the limit inclination set at 0.25 degrees. We analyzed pulling load and inclination for the root plate stiffness, and compared among trees of the same species. The results showed that the root plate stiffness of dying trees was distributed more than 1.5 of standard deviations (SD) lower than the average healthy root plate stiffness. We recommend the root plate of unhealthy trees with lower stiffness than 1.5 SD should be protected to reduce the risk of overturn.

並列關鍵字

pulling test ； root plate stiffness ； trees collapsing ； tipping curves

國際替代計量

成功大學校園中常見樹木傾倒行為研究

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