北美规格材目测分等概述

目测分等方法是北美一种很重要的锯材分等体系, 即依据目测分等规则通过肉眼观测方式测定木材的缺陷状况进而确定规格材的材质等级。因此, 对木材缺陷与材质等级之间关系的正确把握以及对分等规则的正确应用, 是对规格材进行科学、正确分等的基本要求。合理地依据目测分等规则划分规格材等级, 不仅可以使规格材生产厂家的经济效益最大化, 而且有利于规格材产品使用性能的充分、合理发挥。经过目测分等的规格材具有客观的力学性质以及外观质量等级, 可以为其作为结构用材使用时提供科学的依据。直到今天, 目测分等方法依然是北美进行规格材分等的主要分等方法和基础。文中介绍了北美目测分等方法的发展、原理、意义以及世界上其他一些国家和地区的目测分等标准, 并对中国目测分等标准与北美目测分等规则进行了比较, 希望对完善我国的目测分等规则有所启示。     

中国与加拿大规格材目测分等规则的比较

分析我国GB 50005-2003<木结构设计规范>与加拿大规格材目测分等规则NLGA 2002的异同,并根据NLGA对中国杉木人工林规格材进行了目测分级试验.在此基础上,为我国规格材目测分等规则的修订与完善提出建议.     

落叶松规格材目测分等的研究

依照GB 50005-2003《木结构设计规范》规格材目测分等规则,对3种尺寸的兴安落叶松规格材进行目测分等,并分析降等缺陷。结果表明:不同尺寸规格材的等级比例不同;节子、轮裂/干裂和漏刨是规格材主要的降等缺陷。建议优化落叶松规格材加工方法,进一步完善干燥工艺,减少裂纹等缺陷,提高规格材加工质量和使用价值。     

基于不同目测分等规则落叶松锯材的试验研究

采用GB 50005—2003（木结构设计规范》、日本JAS 1152（集成材日本农林标准》和美国ASTMD 245-2006《确立目测分等木材的结构等级及有关允许性能的标准规程》三个目测分等规则,对黑龙江产536根规格为4000mm&#215;110mm&#215;30mm的人工林落叶松锯材进行目测分等。结果表明,中国标准的目测分等结果与美国标准近似,而日本标准对木材材质要求最为严格。     

落叶松规格材机械应力分等方法的研究

对东北人工林落叶松规格材机械分等方法及其特征值进行了研究.结果表明,抗弯弹性模量与抗弯强度相关性较好,纵向振动法可作为落叶松规格材机械分等的有效方法.按照我国GB 50005-2003<木结构设计规范>的规定,落叶松规格材可归类为M14～M35之间的等级;通过机械分等,大大提高了落叶松规格材的强度设计值.     

我国规格材机械应力分等检测技术现状与发展

随着规格材在国内木材领域中的应用范围越来越广泛,对规格材进行机械应力分等检测则显得越来越重要。笔者针对我国规格材机械应力分等检测技术的研究现状,归纳分析了现阶段主要的规格材机械应力分等检测方法的工作原理;介绍了国外比较常见、典型的规格材机械应力分等检测设备及国内开展该领域的研究状况,阐述了我国规格材机械应力分等检测方法的未来发展趋向。     

落叶松锯材外观分等与机械应力分等的试验研究

根据中国、日本、美国三国的外观分等标准,对落叶松试材进行了以强度为基础的外观分等;采用机械应力分等机对落叶松试材进行了应力分等试验,并分析比较了三国不同的外观分等结果与机械应力分等检测的相关关系。     

木材规格材研究现状与展望

从轻型木结构房屋的角度阐述了规格材的用途, 包括规格材基本概念、规格材分等研究现状、规格材测试研究现状及与规格材有关的标准的研究现状等; 通过对规格材研究的展望, 提出了今后进行规格材研究的主要方向。     

基于虚拟仪器技术的规格材应力分等系统设计

介绍了一种基于虚拟仪器技术的规格材应力分等测试系统.该系统在LabVIEW编程环境下完成对信号的采集、显示及数据分析,实现对试件力学性能的检测,并成功应用于木结构规格材的应力分等试验中,取得较满意效果.     

落叶松锯材外观分等与振动检测试验的研究

根据中国、日本和美国的外观分等标准对落叶松试材进行了以强度为基础的外观分等,并对试材进行了振动检测,分析比较了三国不同外观分等结果与振动检测的相关关系。     

落叶松锯材目测分级与力学性能相关性的研究

以落叶松锯材为试验对象,依据GBS0005—2003《木结构设计规范》中外观分等的相关规则。对人工林落叶松锯材进行了以节子为检量对象的外观分等试验,并对分等后的锯材进行了弯曲破坏试验,分析比较了外观分等结果与其弯曲破坏检测结果的相关关系。     

Differences of tensile strength distributions between mechanically high-grade and low-grade Japanese larch lumber III: effect of knot restriction on the strength of lumber

It is well known that the presence of knots in structural lumber is one of the most important strengthreducing factors. For practical purposes, visual grading including knot restriction is an effective method for nondestructive evaluation of strength. Edge knot restriction for not only visually graded lumbers but also mechanically graded lumbers is specified in the Japanese agricultural standards for glued laminated lumber. We conducted experimental studies on differences of tensile strength distributions between mechanically high-grade and low-grade Japanese larch (Larix kaempferi, carriere) lumbers daily used for manufacturing glued laminated timbers in Nagano, Japan. We then examined the additional visual grading of mechanically graded lumbers for nondestructive evaluation. We visually graded the prepared mechanically graded lumber by focusing on the knots' area ratio of grouped knots. We confirmed that the higher visual grade related to the stronger tensile strength, similar to our present knowledge; but the effects of knot restriction were reduced when the length of the lumber increased in view of nonparametric 5th percentiles of tensile strength. The differences in the strength/elasticity ratio between mechanically high-grade and low-grade lumber were negligible. It was clear that the length effect on the ratio in visually graded high-grade lumber was smaller than that of visually graded low-grade lumber. It was thus concluded that knot restriction should have little effect on the tensile strength of mechanically graded lumber.     

Applicability of Visual Grading to Chinese Fir Structural Lumber

As one of the most important plantations, Chinese fir has drawn more and more attention from domestic wood researchers. And as the development and increasing of plantation resource of Chinese fir, research and development of the product will become a hot point. In this paper, we chose 1 571 pieces of structural lumbers from 4 areas to research grading. After sawing, drying and dressing, the lumbers were separated into 3 main grades by GB50005-2003 Code for Design of Timber Structures, namely SS, No. 1 and No.2. The conclusions are that knot as the maximum strength reduced defect （MSRD） is a main character in the lumber, the visual quality of Fujian structural lumbers is polarized, and the applicability of visual grading to the lumber is poor, so we hold the point that we should adjust the grading rules to gain a better grading result.     

规格材强度性能测试方法的研究进展

规格材是现代轻型木结构建筑的主要用材.本文简要阐述了规格材的相关概念、北美分级测试系统的研究进展,分析了不同测试条件对强度测试值的影响,结合我国现状,预测今后规格材强度测试的发展趋势并提出建议.     

Stress wave sorting of red maple logs for structural quality

Existing log grading procedures in the United States make only visual assessments of log quality. These procedures do not incorporate estimates of the modulus of elasticity (MOE) of logs. It is questionable whether the visual grading procedures currently used for logs adequately assess the potential quality of structural products manufactured from them, especially those for which MOE is of primary concern. The purpose of this study was to investigate the use of stress wave nondestructive evaluation techniques to sort red maple logs for the potential quality of lumber obtained from them. Ninety-five red maple logs were nondestructively evaluated using longitudinal stress wave techniques and sorted into four stress wave grades. The logs were then sawn into cants and lumber. The same procedure was used to obtain stress wave times in the cants and lumber. The lumber specimens were then dried and graded using a transverse vibration technique. The results of this study showed that good relationships existed between stress wave times measured in logs, cants, and the lumber produced from the logs. It was found that log stress wave grades have positive relationships with the lumber grades. Logs with high stress wave grades produced high-grade lumber. These findings indicate that the longitudinal stress wave technique has potential in sorting logs and cants for the production of high MOE products.The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin. This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright.     

Prediction of bending stiffness and moment carrying capacity of sugi cross-laminated timber

Cross-laminated timber (CLT) panels consist of several layers of lumber stacked crosswise and glued together on their faces. Prototype sugi CLT floor panels were manufactured and bending tests were carried out under the different parameters of lumber modulus of elasticity (MOE), number of layers, thickness of lumber and thickness of CLT panels. On the basis of above tests, bending stiffness and moment carrying capacity were predicted by Monte Carlo method. MOE of lumber was measured by using grading machine and tensile strength of lumber was assumed to be 60 % of bending strength based on the obtained bending test. Bending stiffness EI of CLT panels could be estimated by adopting composite theory and equivalent section area. Experimental moment carrying capacity showed 12 % higher value than the calculated moment carrying capacity by average lumber failure method, and also showed 45 % higher value than the calculated moment carrying capacity by minimum lumber failure method due to the reinforcement of the outer layer by the neighboring cross layer.     

Stiffness gradients in radiata pine trees

A mill study of 62 trees, in which boards were reassembled into their original logs, permitted the construction of wood quality maps. In this instance stiffness profiles were obtained from butt to upper-top logs, based on machine stress grading of all boards and then averaging values from the 62 trees. Traditionally the butt log has been perceived to be the most valuable log in a tree, because it is bigger and gives a higher recovery of lumber. However, it is shown to contain a wide cone of very low stiffness wood that is confined to the first 2.4–2.7 m above ground level. Above this point stiffness gradients become cylindrical with no noticeable decrease in stiffness up the tree stem. Stiffness in all logs increased radially from pith to cambium with the greatest change being associated with the wood nearest the pith. The low stiffness at the base of the tree suggests that an alternative log bucking strategy should be considered, namely cutting a short 2.4–2.7 m butt log for plywood/LVL or for bolter sawing and only cutting standard length logs above this point.The least stiff logs (lowest 20%) yielded lumber that had an average stiffness that was over 1 GPa less than the average for the population. A case can be made for separating these logs and processing them differently.