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结构用人造板(SWP)在冲击荷载下的承载性能是评价其能否应用于建筑结构的关键指标之一。以进口定向刨花板、国产定向刨花板、国产结构胶合板等SWP产品为对象,测试并对比了3种SWP的冲击荷载性能表现。研究结果表明,不同厚度的SWP适用的搁栅间距范围不同,产品厚度越大,搁栅结构体系适用间距亦越大;实际应用中可通过增加产品的抗弯弹性模量和降低搁栅间距来获得优异的冲击荷载性能。 相似文献
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采用迭代最佳阈值法将气干至全干、饱水状态过程中的开孔重组竹扫描图像处理为二值图,使用Image Pro Plus、Photoshop软件测量分析了开孔重组竹径向和弦向的干缩/湿胀率、孔洞面积干缩/湿胀率、孔洞干缩/湿胀垂直于顺纹方向的竖轴与平行于顺纹方向的横轴尺寸之比k,研究了开孔重组竹含水率与径向和弦向干缩/湿胀率、孔洞面积、k值的相关性,为开孔重组竹在建筑工程中的设计应用提供依据。研究结果表明:开孔重组竹径向和弦向的干缩率分别为1.14%和1.56%、湿胀率分别为1.49%和3.38%,弦面和径面孔洞面积干缩率分别为1.18%和1.24%、湿胀率分别为-1.14%和2.42%,弦面和径面孔洞干缩k值分别为97.09%和94.86%、湿胀k值分别为98.60%和97.89%;孔洞直径的变化对开孔重组竹的干缩湿胀性能影响不显著,对孔洞自身形状变化的影响显著;随着含水率的递增,开孔重组竹的干缩/湿胀率、孔洞面积呈线性增长趋势,孔洞k值呈指数增长趋势。基于尺寸稳定性角度,气干至全干、饱水状态过程中重组竹径向和弦向的干缩/湿胀差异显著,对重组竹开孔可改善其尺寸稳定性,孔洞自身因含水率变化而产... 相似文献
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钉连接是木结构中重要的连接节点,在轻型木结构建筑的剪力墙中起到重要的承载作用。不论国内还是国外,结构胶合板、定向刨花板、冷杉木材都是木结构建筑中主要的建筑材料。笔者研究了不同覆板类型与冷杉木材钉连接的动态荷载性能,对不同厚度胶合板、定向刨花板、钉直径与冷杉的连接性能进行了对比(静态荷载和动态荷载)研究。结果表明,钉直径、覆板种类和厚度对动态载荷性能、破坏位移影响显著,10D钉连接冷杉和不同覆板材料时,连接性能最佳;相同厚度的定向刨花板比结构胶合板与冷杉的连接性能好;厚度为16 mm的结构胶合板具有良好的连接性能。本研究为轻型木结构的建造提供理论和实际测试依据。 相似文献
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《林业工程学报》2016,(1)
分别对杨木单板进行高温加热和硅烷溶液喷淋处理,并与高密度聚乙烯(High Density Polyethylene,HDPE)薄膜胶合制备木塑复合胶合板,利用扫描电镜(SEM)和动态热机械仪(DMA)分析了两种改性方法对木塑复合胶合板抵抗水分子破坏能力的影响。结果表明:3次"湿-冷冻-热"循环对未处理和高温处理材的破坏程度较大,循环处理后胶接结构中存在明显的裂缝及脱落的HDPE碎片。硅烷处理可以显著提高木塑复合胶合板的耐湿循环能力,胶接结构中仅存在少量的裂纹。胶接结构的破坏引起了胶合强度不同程度的降低,未处理、高温处理和硅烷处理材的胶合强度保留率分别为57%,72%和84%。DMA结果表明:水分子的交替作用显著降低了未处理和高温处理材的热稳定性,而对硅烷处理材的影响较小。当环境温度达到200℃时,未处理和高温处理材的胶接界面结构完全破坏,木材单板与塑料薄膜两相完全分离。 相似文献
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在某些胶合板热压机机组中,如日本北川三十层胶合板热压机机组以及某些国产同类型机组,其必备辅机——卸运机均采用两长两短的托架形式,如图1a所示。在实际使用中,这种形式的托架非但无多大益处,反而削弱了卸机吊笼层架的刚度。致使吊笼层架在长期使用中极易产生变形,从而影响整个机组的使用寿命。另外,这种结构也给设备制造厂在设计和 相似文献
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《Scandinavian Journal of Forest Research》2012,27(5):427-435
In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(3):206-217
The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(1):53-61
This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(1):15-27
The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions. 相似文献
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Astra Zaluma Lauma Bruna Darta Klavina Natalija Burnevica Kristine Kenigsvalde Andis Lazdins Talis Gaitnieks 《Forest Pathology》2019,49(6)
Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered. 相似文献
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本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。 相似文献
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Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and
also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the
amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter
bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K
was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed
significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week−1 for leaves and from 0.0225 to 0.0633 week−1 for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed
during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly
between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species
provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient
enrichment capacity and slower decomposition rates which would minimize leaching losses.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(2):118-130
The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(2):139-149
Mean age, mean and top heights and yield were studied in 20 mixed stands of birch ( Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch < 17 m) was superior to that of pure spruce, while the difference was insignificant in older stands. The growth index correlated positively with the ratio between generatively and vegetatively regenerated birch trees, and negatively with the age of the oldest species in the mixture and with site quality. For the pine sites there was no significant difference in the growth index between mixed birch-pine and pure pine stands. A mixture effect of birch on the volume yield of spruce or pine could not be demonstrated. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(2):150-157
An outbreak of the needle-shortening pine gall midge, Thecodiplosis brachyntera , occurred on Scots pine, Pinus sylvestris (L.) and lodgepole pine, P. contorta (Dougl.) in central Sweden during 1995-1998. The larval feeding of T. brachyntera kills current-year needles and heavy infestation causes severe defoliation. A pattern of fluctuating defoliation among years and sites was found on both pine species. Defoliation was evenly distributed in the crown of P. sylvestris during years of high as well as low infestation; apical whorls had as much defoliation as basal whorls. In P. contorta , however, there was a tendency for defoliation to be concentrated on branches in the most apical whorls. Growth ring increments on P. sylvestris with high levels of defoliation (71%) did not differ from trees with moderate levels (26%) of defoliation. Shoot lengths were significantly shorter, however, on heavily infested trees the year after defoliation. 相似文献