On mechanical behavior of traditional timber shear wall in Taiwan I: background and theory derivation

The objectives of this study were to explore the mechanical behavior of traditional timber shear walls in Taiwan and to propose a theoretical model to predict their lateral force resistance. An extensive field investigation was conducted, and the dimensions, tectonic detail, and materials used were recorded. The data collected were used as the reference for theoretical derivation and experimental design. In the theoretical model, the moment resistance of entire shear walls was derived from the contributions of the moment-resisting capacity supplied not only by embedment and friction action between board units and beams but also the dowel action of bamboo nails. Timber shear walls with various geometric conditions and material properties are considered. The theoretical model demonstrated in this study can be used to predict the mechanical behavior of timber shear walls and will be verified by experiments in our next article.     

A simulation model for economic analysis of timber/forage production alternatives in rocky mountain aspen stands

A simulation model was developed to analyze possibilities for timber and forage joint production in Rocky Mountain aspen stands. Given harvest possibilities from timber yield tables and information concerning site characteristics, the model calculates the physical production levels for timber and forage, and then uses these figures to make an economic analysis based on present net worth and financial maturity criteria. The model was applied to different sets of sites, harvest possibilities, and costs and revenues. The results indicated that the optimal joint production strategy varies with the economic criterion, the discount rate and harvest strategy.     

基于表面主要缺陷的锯材外观质量量化评价方法

【目的】提出一种锯材外观质量量化评价方法,探索锯材外观质量数字化检测与评价分级的可行性,为实现锯材外观质量的实时在线检测提供基础理论和技术支撑。【方法】建立由密闭暗室、光源、工业相机等组成的锯材表面缺陷在线检测系统,在稳定光环境下采集样本锯材彩色图像。基于图像处理技术开发软件试验系统,实现对锯材缺陷的检测和识别。分别建立节疤、孔洞和裂缝缺陷外观质量评价模型,并据此提出外观质量综合量化评价方法;通过与国家标准对照,验证本研究提出方法的科学性和可行性。【结果】量化评价方法与锯材材质指标等级进行对照,二者线性相关系数为0.85;锯材材质指标等级除了2级和3级对应的综合量化评价值分布比较分散、等级之间数据有部分交叉外,其他等级之间对应的综合量化评价值分布几乎没有交叉。量化评价方法与集成材层板外观质量要求进行对照,二者线性相关系数为0.88;锯材材质指标等级4级对应的综合量化评价值分布比较集中,与其他等级之间没有数据交叉;锯材材质指标等级1级、2级和3级相邻等级对应的综合量化评价值分布比较分散,等级之间数据有部分交叉,不相邻等级间数据分布没有交叉。【结论】综合量化评价值与依据有关国家标准确定的锯材材质指标等级、集成材层板外观质量要求的线性相关性相对较好,可为实现锯材外观质量数字化检测与评价奠定基础;通过调整模型有关影响系数,可满足不同树种和不同应用需求,以达到较好评价效果。     

轻型木结构建筑台风荷载响应研究进展

主要介绍了国内外轻型木结构建筑台风荷载响应的相关研究。简述了台风对木结构建筑作用的分析与计算方法;详细介绍了佛罗里达国际大学风墙实验;概述了用于预测风致荷载响应的有限元数值模型建模技术的发展与模型的加载和验证方法;分析了建模方法对结构行为的影响。该文可为轻型木结构建筑的风工程学理论、材性研究及防台风的设计提供借鉴。     

On mechanical behavior of traditional timber shear wall in Taiwan II: simplified calculation and experimental verification

In the previous report of this ongoing study, results of an extensive field survey were collated and a theoretical model was proposed to predict the mechanical behavior of timber shear walls of traditional design in Taiwan. The initial objective of the present report was to propose a simplified calculation method for estimating the initial stiffness and yield strength of traditional timber shear walls. Based on the results of the field survey, a total of 15 full-scale specimens were tested to verify the theoretical model and simplified calculation proposed previously. Good agreement was found from comparison of analytical and experimental results. The results of this study show that the friction behavior between board units and beams plays the major role in resisting the lateral force applied on the timber shear wall, followed by the resistance supplied by embedment. The resistance provided by bamboo nails is minor due to the small section. Another trend found was that for set dimensions of a timber shear wall, the board width can be increased to obtain higher stiffness and strength of the shear wall.     

计算机在木材细胞数字化理论中的应用

根据木材细胞微观构造差异，建立木材细胞生长的数学模型，利用计算机仿真技术模拟细胞生长过程。并预测木材材性的变化，达到评价树种优劣的目的，为国家选用具有优良材性的树种植树造林提供科学依据。     

Capacity prediction of welded timber joints

Linear vibration welding of timber structural elements provides new opportunities to potentially achieve structural joints. This paper investigates to which extent welded joints can be considered for load-bearing structural joints. On the basis of a series of experimental and numerical investigations on a series of welded single-lap joints, failure modes were identified, and the associated failure criterion was quantified. A probabilistic method subsequently allowed accurately predicting the capacity of the tested wood welded joints exclusively based on objective input data, including an estimate of the scattering due to the material’s inherent variability.     

Finite element study of growth stress formation in wood and related distortion of sawn timber

Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-related stresses (distortions appearing when logs are split up to timber boards by sawing). To get more knowledge on how these distortions can be reduced in wooden products, there is a need for improved understanding of this material behaviour through good numerical tools developed from empirical data. A three-dimensional finite element board distortion model developed by Ormarsson (Doctoral thesis, Publ. 99:7, 1999) has been extended to include the influence of growth stresses by incorporating a one-dimensional finite element growth stress model developed here. The growth stress model is formulated as an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The simulation results presented include how stresses are progressively generated during the tree growth, distortions related to the redistribution of growth stresses during log sawing, and distortions and stresses in drying reflecting the effects of growth stresses. The results show that growth stresses clearly vary during tree growth and also form a large stress gradient from pith to bark. This in itself can result in significant bow and crook deformations when logs are sawn into timber boards. The distortion results from the simulations match well with the results observed in reality. The parametric study also showed that the radial growth stress distribution is highly influenced by parameters such as modulus of elasticity, micro fibril angle and maturation strain.     

Development of constitutive model for laminated veneer lumber using digital image correlation technique

This paper describes the development of a three-dimensional constitutive model for laminated veneer lumber (LVL) needed for new developments using this material. The LVL was manufactured in New Zealand from Radiata Pine. Experimental testing has been performed according to European timber testing standards. Block compression testing has resulted in modulus of elasticity values in the three material directions. Digital image correlation (DIC) technique has been used to determine the six Poisson’s ratios. Shear testing, whereby timber specimens were glued between two steel plates, has given stiffness values using DIC measurements. Experimental testing results have been compared with values found in literature. Results from this experimental testing programme have made it possible to create a three-dimensional elastic material model of LVL for the use in finite element analysis programmes. Although the material properties do not result in a symmetrical constitutive matrix, only minor adjustments are needed to gain the benefits of a symmetrical matrix.     

浅谈利用小径木制作木结构房屋

通过小径木的力学性能分析，确定小径木可以作为新式木结构房屋的主要建筑用材，从而拓展了小径材在建筑行业的应用领域，使低价值的小径木原材料变成高附加值的建筑产品。     

A three-dimensional paradigm of fiber orientation in timber

Knowledge of the three-dimensional orthogonal directions of wood material at any position within a tree is necessary for the understanding of strength reducing effects of knots and essential for the continuation of research in areas which relate small clear wood specimen behavior to the behavior of full size structural timber. A complete three-dimensional paradigm describing the geometry of knots and related fiber distortion, initially derived to predict the strength-reducing behavior of knots in structural timber of Norway Spruce with the finite element method, is presented in this article. Besides strength prediction analyses, it is believed that the paradigm may be useful in other areas of research on structural timber that are effected by fiber orientation, such as drying and form change of structural timber. The paradigm generates fiber orientation in any position within a log or lumber from assumed fiber patterns in planes parallel to the longitudinal direction of the original tree. Fiber patterns in the radial and tangential directions are derived from physical restraints related to fiber production within the annual increase surfaces of the tree and from theories of knot formation. The adaptability of the paradigm allows practically any softwood knot to be modeled with an accuracy that is limited only by input-data. The knot-axis may be non-linear, and the knot cross-section oval with its vertical and horizontal axis increasing from the pith of the stem at chosen rates. Spiral grain may also be included in the paradigm and vary with the annual growth layers. Investigations presented in this article showed that generated fiber orientations for Picea abies complied well with measured fiber distortions, and that the general trends of fiber orientation, explained by the applied knot formation theory, is reflected in the measured specimens. Received 12 May 1999     

A three-dimensional wood material model to simulate the behavior of wood with any type of knot at the macro-scale

This article presents a three-dimensional wood material model implemented in finite element (FE) software which is capable of predicting the behavior of timber at the macro-scale taking into account the effect of any type of knot. The model was built in Ansys using the ansys parametric design language, such that the whole simulation process, including the creation of geometries, grain deviation, meshing and failure prediction, is automatically calculated by only introducing conventional measuring parameters of knots and locations of the pith. Knots are generated as elliptical, rotated and oblique cones. The local and global grain deviation is estimated by solving a multiphysics problem and equating the fibers of wood to the trajectory of laminar streamlines in 3-D. Wood is considered a transversely isotropic material with anisotropic plasticity in which the failure prediction is given by means of several phenomenological failure criteria. The model was validated with 4-point bending tests of Scots pine specimens showing errors in failure prediction of 5 %, errors in initial fracture location of less than 20 mm and errors of 9 % in photogrammetrically measured displacements of an average of 65 FE nodes, in which the heterogeneity of wood caused variations of up to 6 %.     

木兰林管局华北落叶松大径级材培育基地建设初探

建设大径级用材林基地是解决中国目前木材供需矛盾问题的出路之一,对中国、我省以及木兰林管局大径材基地培育的现状进行了系统的总结,并对木兰林管局发展大径级材培育提出了相关对策。     

Private forest investment and long-run sustainable harvest volumes

Private timberlands in the United States have the biological potential to provide larger quantities of timber on a sustainable basis than they do today. Most opportunities for increasing growth and harvest lie on nonindustrial private lands in the South. Past studies, based on fixed scenarios of future prices, also suggest that many of these opportunities for intensified management can be undertaken with positive economic returns. Translation of these physical and apparent economic potentials into projections of future management and harvest requires a model of private timber management investment behavior. This study examines the dynamics of investment in private forest management according to a model of timber markets and timber supply in which intertemporal levels of private investment, harvest, and timber prices are all endogenous. The results of this model are used to examine the extent and types of possible future private management investments and how these will affect timber supply. In addition, the sensitivity of these projections to variations in key market and behavioral determinants is examined through simulation of alternative scenarios involving reduced public timber harvest and constraints on planting investment of nonindustrial private owners.The base case illustrates the substantial potential of timberlands for increased growth and harvest. This requires, however, investments in planting well beyond those observed in recent years. Given this, the area in planted forests would almost triple within the next 30 years. Expanded investment would allow immediate increases in timber harvest and sustained increases in timber inventory, with virtually no trend in softwood log prices. Projected increases in plantation area would concentrate timber production on fewer hectares, with more hectares managed passively. Naturally regenerated forests in the future would cover at least three-quarters of the private timberland area, with hardwoods continuing to dominate. Restricting nonindustrial private plantation investment to levels observed in the recent past markedly alters projections for softwoods, thus raising prices and reducing timber harvest relative to the base case across the full projection period. In contrast, reductions in public timber harvest alone result in increased prices and reduced total cut in the near term, but have limited impact on the outlook three-five decades hence, because private investment effectively compensates for public timber harvest reductions.     

展平竹与木材正交胶合材性能研究进展

因我国天然林禁伐,人工速生林木材和竹材成为当前木材加工利用的主要原材料,但人工速生林材质不及天然林材质,且竹材也存在截面尺寸小、用胶量大、原料利用率低等缺点.展平竹与木材正交胶合材(CLBT)由展平竹材和人工林锯材层板正交层叠制成,充分发挥了竹材优异力学性能与木材易加工等优势,既保留竹子和木材的天然纹理与结构特性,又克...     

浅析我国造纸工业木材原料市场及发展趋势

随着纸及纸板生产与消费数量的不断提高,我国造纸工业结构调整的发展对木材原料的需求将持续增加。我国木材市场数据显示,以原木、锯材等为代表的木材原料,以木浆、木片为代表的造纸原料进口均呈平稳增长趋势,木材市场供需矛盾突出。造纸工业竞争的核心是木材原料的争夺,而我国木材市场自有木材供给的严重不足性和进口总量的绝对依赖性特征决定了造纸工业木材原料未来仍将依靠进口。     

Investigation of elastic constants and ultimate strengths of Korean pine from compression and tension tests

Korean pine (Pinus koraiensis) is a wood species recently adopted in China for the rehabilitation of traditional timber buildings. This paper investigates its mechanical properties with laboratory tests on typical specimens to obtain the moduli of elasticity, Poisson’s ratios, shear moduli, coefficients of mutual influence, crushing strengths and tension strengths in various directions. Highly different failure patterns of specimens in compression test were observed when loaded in different directions relative to the grain while only brittle failure mode was observed for tension specimens. The measured parameters of Korean pine were compared with those obtained from theory of orthotropic elasticity, the empirical formula and the Norris failure criterion, good agreements were reached for all examinations in general which indicate it is admissible to treat Korean pine as ideal orthotropic material.     

关于木材需求曲线修正法的讨论

木材需求曲线与森林环境需求曲线的价格需求弹性是不同的,后者远比前者大。在这种的情况下,用木材需求曲线近似代替计算森林环境价值,会严重低估森林环境价值,理论上有严重的缺陷。加上以木材价值替代全部森林非木材产品的价值,也会导致对森林环境价值的低估。这2个相同方向的差异累积后,导致木材需求曲线修正法严重低估森林环境价值。另外,木材需求曲线修正法也不能评价具体的涉及森林环境价值的项目,因此,没有实际的应用价值。     

人工林香叶树木材物理性质的研究

研究了福建省三明莘口教学林场香叶树人工林的木材物理性质。结果表明：香叶树人工林木材生材密度0.826 g/cm3,基本密度为0.529 g/cm3;木材径向、弦向和体积干缩系数分别为0.235%,0.337%,0.603%,收缩大,木材不易开裂和变形,是良好的家具及室内装饰用材。     

森林资源连续清查进界木与漏测木确定标准的研究

对森林资源连续清查中进界木和漏测木传统确定方法进行分析，指出其存在的随意性和缺乏科学性、明确性；提出应用数理统计方法，通过对已往取得数据的分析，制定出科学、合理、明确的标准。并以云南省2002年森林资源连续清查中楚雄州云南松检尺数据对这一方法进行了具体分析。