共查询到19条相似文献，搜索用时 157 毫秒
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北美规格材目测分等概述 总被引：1，自引：1，他引：0
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。 相似文献
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为使规格材力学性能满足制造足尺正交胶合木(CLT)楼板和墙板的需要,笔者采用横向振动法,对加拿大铁杉规格材的顺纹弹性模量进行动态测试及其应力分等研究,并从被测试件中随机抽取50根通过应力波法进行对比测试,以验证测试及分等结果的可靠度。研究表明,所用铁杉规格材顺纹弹性模量平均值均达到制造CLT性能要求;顺纹弹性模量测试结果基本符合威布尔分布规律;依据其顺纹弹性模量性能进行应力分等后,达到1.5E应力等级的铁杉锯材占总数的35.0%,达到2.0E应力等级的铁杉锯材占总数的34.8%;横向振动法测试结果与应力波法测试结果相关系数达到0.815,具有较高的吻合度。上述有利于确保后续CLT的结构设计、性能预测、加工制造和性能评估等工作,并对促进国内CLT木建筑的良性发展具有工程应用价值。 相似文献
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根据中国、日本、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,然后对试材进行应力波检测,分析比较不同外观分等结果与应力波检测的相关关系。 相似文献
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The main objective of this study was to determine which property, of the six strength and stiffness properties used in structural timber design, was the most influential in the design of nail-plated roof trusses. Thirty recently completed nail-plated roof truss designs were randomly selected from three roof truss manufacturing plants and a total of 8 758 individual truss members were analysed for bending stress, shear stress parallel to grain, tensile stress parallel to grain, compression stress parallel to grain and deflection. The mean strength and stiffness capacity utilised of all the different design properties was well below 50% for all of the different dimension classes. Of all the individual strength properties, the mean bending strength capacity utilised per member was found to be the highest. The results of this study can be used for decision support related to wood property evaluation through? out the structural lumber value chain where roof truss members are the end products. 相似文献
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Philip L Crafford 《Southern Forests》2016,78(1):61-71
South Africa is a timber-scarce country that will most probably experience a shortage of structural softwood lumber in the near future. In this study the concept of using young, green finger-jointed Eucalyptus grandis lumber was evaluated for possible application in roof truss structures while the timber is still in the green, unseasoned state. Drying will occur naturally while the lumber is fixed within the roof truss structure. The objectives of this study were (1) to investigate the strength and stiffness variation of the finger-jointed E. grandis product in both the green and dry state for different age and dimension lumber, (2) to investigate the variation in density, warp and checking in the lumber when dried in a simulated roof-space environment and (3) to evaluate the potential of this finger-jointed product as a component in roof truss structures. Green finger-jointed E. grandis lumber of ages 5, 11 and 18 years and dimensions 48×73?mm and 36×111?mm from Limpopo province were evaluated. The study showed that the young finger-jointed E. grandis timber had very good flexural, tensile parallel to grain, and shear properties in both the green and dry state. The mean and characteristic modulus of elasticity and modulus of rupture values of the finger-jointed E. grandis product were higher and the variation lower in comparison to currently used South African pine sources. The tensile perpendicular to grain and compression perpendicular to grain strength did not conform to SANS requirements for the lowest structural grade (S5). Both tree age and product dimension were sources for variation in the physical and strength properties. Based on the results from this study the concept of producing roof trusses from green, finger-jointed young E. grandis timber has potential. 相似文献
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原木等级及径级对规格材质量及出材率的影响 总被引：1，自引：1，他引：0
选用不同径级和质量等级的兴安落叶松原木,采用毛板下锯法和四面下锯法加工规格材,并检测分析了不同等级规格材的出材率。结果表明,原木径级在26～28cm时,规格材出材率较高;原木的等级与径级,及下锯法与原木径级交互因素,对规格材的出材率有显著的影响。要提高规格材出材率,应根据规格材尺寸优化匹配各因素。 相似文献
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In this report, the 575 specimens were divided into ten groups based on range of growth ring width. The modulus of elasticity
(MOE) and modulus of rupture (MOR) of 45 × 90 mm specimens of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantation dimension lumber were analyzed by average growth ring width and average density of each group.
The results showed that the average growth ring width was in inverse proportion to density, MOE, and MOR of the dimension
lumber. Furthermore, average density was in direct proportion to MOE and MOR of the dimension lumber. The coefficient of determination
(R
2) for all the regression equations ranged from 0.7340 to 0.9207 at a significance level of 0.001. However, without such group
classification, there was poor relationship between growth ring width, density, MOE, and MOR with a determination coefficient
of 0.0901–0.1855. This finding suggested that it was feasible to predict the flexural properties of Chinese fir plantation
dimension lumber by average growth ring width after specimen group classification. 相似文献
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采用高温热处理工艺固定杨木板材的压缩变形,比较分析了处理前后杨木板材的物理力学性能.结果表明:杨木板材的压缩变形得到很好的固定;杨木板材经过热压及高温热处理后,密度和尺寸稳定性得到提高,吸湿性降低,弯曲性能变化不大. 相似文献
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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. 相似文献
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Summary The within member variation of tensile strength parallel to grain in nominal 38×89 mm No. 2 Spruce-Pine-Fir lumber has been experimentally evaluated. Window analyses yielded the within member tensile strength cumulative probability distributions of lumber segments with various lengths. Semivariogram and regression analyses have been performed to characterize the spatial correlation of the tensile strength of lumber. The results indicate that the tensile strength values within a piece of lumber separated by a distance greater than 1.83 m can be considered statistically independent.The Authors gratefully acknowledge the support of the Forestry Canada and the technical assistance of Mr. H. Sue, Mr. B. Deacon and Dr. J. Cook for this study. The research was performed while the principal author was working at Forintek Canada Corp. 相似文献