兴安落叶松规格材握钉性能及钉连接承载性能研究与评价

钉连接是轻型木结构重要的连接方式之一,本文介绍了美国握钉性能和钉连接承栽性能评价方法,并以兴安落叶松为研究对象,对其握钉性能和钉连接承载性能进行了研究分析。     

冷杉木材与不同覆板材料钉连接节点的动态荷载性能研究

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。     

轻型木结构用秸秆定向板钉节点性能研究

以秸秆定向板(OSSB)代替常用的定向刨花板(OSB),研究其作为轻型木结构建筑覆面板的钉节点连接性能。结果表明:在覆面板与SPF(云杉-松-冷杉)的顺纹方向垂直,加载方向与覆面板长边平行的受力状态下,OSSB-SPF组合钉节点平均极限荷载比OSB-SPF组合提高了18%,所对应的平均位移下降了11%;当覆面板与SPF的顺纹方向平行,加载方向与覆面板长边平行的受力状态下,与OSB-SPF组合相比,OSSB-SPF组合的钉节点平均极限荷载提高了16%,所对应的平均位移下降了13.5%。在钉节点连接性能上OSSB可以代替OSB与SPF连接,能够成为轻型木结构墙体承重结构的一部分,是轻型木结构墙体外覆面板的良好选择。     

木结构节点的连接方式与性能

主要介绍榫卯、钉、螺栓、齿板几种主要木结构节点连接方式,从承载力分析、破坏形式及破坏机理入手,系统介绍其连接性能和国内外研究现状。针对目前研究存在的问题,提出几点建议,以期为木结构连接节点的合理选择和现代木结构在中国的发展提供借鉴。     

轻型木结构剪力墙木骨架的抗侧性能

轻型木结构是以规格材作为木骨架,通过木基结构板材或石膏板覆面而成的木结构建筑,规格材与规格材、骨架与面板之间通过钉子连接。轻型木结构墙体在试验研究和实际工程中的破坏往往是由钉节点失效导致的,面板钉节点破坏后水平侧向力仅由木骨架承担,因此,单独研究木骨架水平抗侧力很重要。为了解剪力墙中木骨架在单独作用时的最大承载能力与荷载-位移的关系,首先通过试验研究骨架钉和骨架钉节点力学性能以及空木骨架抗侧性能关系,推导出钉节点计算公式;再通过木骨架几何构造导出自身惯性矩,在水平力作用下,木骨架侧向变形主要由木骨架弯曲变形、骨柱轴向变形、骨架钉节点拔出、剪切和弯曲变形共同作用所至,通过木骨架力矩平衡和钉节点数据分析,导出木骨架抗侧性能计算公式。结果表明:理论推导骨架钉节点计算公式与试验结果相符合;木骨架侧向变形公式仅考虑荷载上升阶段,理论与试验结果相吻合,钉节点抗弯性能和边骨柱钉子拔出对木骨架抗侧承载能力影响最显著。减小木骨架高宽比和骨柱间距、增大其宽度有利于提高木骨架的抗侧承载能力。     

兴安落叶松钉连接施工技术研究

对我国东北地区落叶松在木结构中钉连接施工技术进行的试验研究表明，用兴安落叶松进行钉连接时，预钻孔直径应是钉直径的85％左右，预钻孔深度应该超过钉入深度；用于端部钉连接的钉不易太粗，可通过具体试验确定或采取相应技术措施，保证连接性能。     

花旗松与云杉木材钉连接节点侧向抗拉力学性能比较研究

钉连接是木结构中重要的连接节点,在剪力墙中起到重要的承载作用。笔者针对轻型木结构建筑剪力墙关键的连接节点,对花旗松、云杉与不同厚度结构胶合板、定向刨花板用不同结构单钉连接的30种连接节点的侧向抗拉力学性能和破坏位移进行了比较研究。研究结果表明,钉子的尺寸、覆板种类与花旗松和云杉木材形成的连接节点侧向抗拉力学性能和破坏位移影响显著。6D钉连接花旗松侧向抗拉力值大于云杉;8D钉连接云杉侧向抗拉力值大于花旗松;10D钉连接两种木材节点力值趋势一致;花旗松和云杉与不同钉尺度连接节点破坏位移趋势相似,随着钉尺度的增加,破坏位移差异显著;10D钉连接两种木材节点破坏位移趋势一致,云杉与22 mm厚定向刨花板用10D钉连接,节点破坏位移最大。     

旧面板对轻型木结构钉节点力学性能的影响

旨在通过新、旧定向刨花板(OSB)面板钉节点的对比研究,探究面板自然劣化对钉节点连接性能的影响,为今后的木结构设计和用材作参考。选取云杉-松木-冷杉规格材(SPF)、不同厚度的新旧OSB和国产麻花钉,将麻花钉垂直钉入OSB和SPF之间,依据荷载垂直于木材纹理和平行于木材纹理两种方向,共制作72个钉节点连接试件。试验参考ASTM D1761-12,对试件进行单调加载,研究不同厚度自然劣化后的旧OSB面板在横纹和顺纹连接情况下对轻型木结构钉节点力学性能的影响。结果表明:新旧OSB连接对比,除延性系数外,旧OSB面板与SPF连接的钉节点试件的荷载、刚度、耗能能力等都呈下降趋势;厚度不同的OSB连接对比,12. 0mm厚度的OSB面板连接的钉节点的荷载、刚度、延性系数、耗能能力都大于9.5 mm的OSB面板连接的试件,且12.0 mm旧板连接的力学性能下降幅度小于9.5 mm;在荷载、初始刚度、延性方面,旧板横纹连接小于顺纹连接的下降幅度;在耗能上,旧板横纹连接与顺纹连接区别不明显。试验中多发生钉子一铰弯曲和OSB、SPF破坏的试验现象,符合欧洲木结构设计规范中的破坏模式,因此可用欧洲规范计算本研究中钉连接节点最大荷载。     

落叶松规格材的钉连接性能

钉连接是木结构中常用的连接方式之一。依据美国钉连接的试验方法及设计值的确定方法,对我国东北地区落叶松的钉连接性能进行了检测。结果表明,随着圆钉直径的增大,落叶松的抗拔出力和抗剪切力基本呈上升趋势。并对东北地区落叶松钉连接的参考设计值进行了分析。     

轻型木结构用规格材握钉性能试验及钉连接承载性能评价方法

通过作者掌握的有关技术资料和标准,简述了轻型木结构用规格材的握钉性能及钉连接承载力评价方法,并对相关标准的试验评价方法进行比较。     

Analysis of load-slip characteristics of nailed wood joints: application of a two-dimensional geometric nonlinear analysis

We used a two-dimensional finite element method to analyze the load-slip characteristics of nailed wooden joints sheathed with a panel. We used tests of nail bending, nail shank embedment in a wood or a panel, nail-head embedment in a face of a panel, nail withdrawing from a wood, friction between a wood and a panel, and initial axial forces of the nails. The values of the material properties for the analytical models were determined with the above tests. With a conventional one-dimensional analysis it is impossible to evaluate the shearing performance accurately because the axial forces of the nail are not calculated. Therefore, we used two-dimensional geometric nonlinear analysis. The computed load-slip curves closely matched the original experimental results; and when the friction and initial axial forces were considered, the computed curves were more likely to match the original experimental results. Our results suggested that it is better to use geometric nonlinear analysis to analyze the shearing characteristics of nailed joints, and that friction and axial forces are important factors for accurate analysis.Parts of this report were presented at the 7th World Conference on Timber Engineering, Malaysia, August 2002     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

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.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

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.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

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.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

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.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

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.     

Growth of Phlebiopsis gigantea in wood of seven conifer species

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.     

CAD与建筑设计的关系

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。     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

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.     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.