海岸带防护林4种树木的风压应力分析

依据４种主要的海岸带防护林树种的调查数据，计算了各树种不同高度处和不同风压下的应力分布，分析了各树种遭受台风袭击时所受到的弯曲应力。结果发现树种的受害程度与其树冠形状密切相关。杨树和水杉的枝下高和树高之比（Ｌ／Ｈ）均小于０．２２，树冠宽度和树冠高度的比值（Ｗｃ／Ｈｃ）均小于０．３６；刺槐和泡桐枝下高和树高的比值（Ｌ／Ｈ）均大于０．４３，树冠宽度和树冠高度的比值（Ｗｃ／Ｈｃ）均大于０．５４，这是形成杨树和水杉有两个受力点，而刺槐和泡桐只有一个受力点的根本原因。在相同的风压下，无论在树干的任何部位，杨树所受应力超过水杉、刺槐和泡桐２．３、５．０和５．３倍以上，因而杨树的受损程度也最为严重。

The Bending Stress Analysis of 4 Species of Woods Caused by Wind Pressure in Coastal Shelter Forest

Based on the collected data of 4 kinds of tree damaged on August 19,1997, the bending stress and its distribution in various height of stem and under various wind pressure are calculated in this paper. The results indicate that there is a close relationship between the damage degrees of species and their crown shapes. It can be reflected by two ratios as follows: one is the ratio(L/H) of height at the bottom of crown(L) to their individual height(H), the other is the ratio(Wc/Hc) of crown width (Wc)to crown height(Hc). For Populus deltoides and Metasequoia glyptostroboides, both of the former index are less than 0.22 and both of the latter index are less than 0.36. To the contrary, for Robinia pseudoacacia and Paulownia fortunei, both of the former index are more than 0.43, and both of the latter index are more than 0.54. The differences of L/H and Wc/Hc among the 4 species bring about that there are two points of bending stress for Populus deltoides and Metasequoia glyptostroboides, and there is one point for Robinia pseudoacacia and Paulownia fortunei. Under certain wind pressure, the bending stress of poplar is the biggest one among the 4 kinds of tree in every position of its trunk, the stress at any height is more than 2.3 times of Metasequoia glyptostroboides, 5.0 times of Robinia pseudoacacia, and 5.3 times of Paulownia fortunei respectively. Therefore, poplar is damaged much more severely than other 3 species.