柳桉立木力学分析

Analyses of the Mechanics of Eucalyptus saligna Tree Stems

以柳桉立木为研究对象,重点分析不同状况下桉树应力和弯矩分布情况。结果表明:柳桉立木随着树高的增加,树干断面积呈指数迅速减少,而树干材积和质量均呈一元二次方程的增加。柳桉立木随着树高的增加,树干各截面的应力呈线性降低,而所受弯矩呈非线性减少。外力载荷下作用点与树干基部间各截面的应力会迅速增加,也使得其间的弯矩(绝对值)急剧增大。外力载荷随着树高上移,相对而言不会增加树高基部的应力,但会显著增加作用力位点截面的应力,也显著提高树干基部的弯矩。柳桉在树高3.9 m以上树干部位,由于惯性矩产生的抗弯矩应力能力趋于减少,而小于弯矩应力,易使树干发生变形导致树干折断。

The stress and bending moment distributions in the stems ofEucalyptus salignatrees were studied under different conditions. The results showed that with increasing tree height, stem basal area decreases at an exponential rate, while both stem volume and weight were increased in a quadratic relationship to height. But with increasing height the stress of in the stem cross-sections decreased linearly, and bending moments declined in a nonlinear manner. When an external force was applied to the standing stem, the stress between the point of applied forceand cross-section oftrunk’s base increased rapidly, bending moment （absolute value） between them also increased sharply. When the external force moved to the crown, the stress at the base of the trunk base was not increased, but the bending moment from the base of the trunk base up to the point of force application increased significantly increased, and so was the shear force. At points on the stem above heights of 3.9 m, moment of inertia tended to decrease with increasing height due to the ability to generate anti-moment stress, resulting in more common stem deformation and breakage.