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首页> 外文学位 >Mechanical and physical properties of three timber species of potential structural use in Rwanda.
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Mechanical and physical properties of three timber species of potential structural use in Rwanda.

机译：卢旺达可能用于结构用途的三种木材的机械和物理特性。

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摘要

This study was undertaken in an effort to derive allowable stresses for three wood species grown in Rwanda. Wood properties will vary between species, between locations within a species and even within a single tree. This variability must be well understood in order to establish design values for wood and wood composites. Estimates of the mean and the near-minimum values of small, clear samples of wood were obtained using the international testing standards (ISO).; An indepth review of current sampling techniques used in wood engineering strongly suggests that the random technique of sampling and its variations remains a reliable technique which, when designed properly, will yield accurate estimates. Several samples of the three timber species chosen by using the random technique of sampling were tested for both the physical (density, specific gravity, swelling and shrinkage characteristics) and the mechanical properties (bending strength and stiffness, compressive strength parallel to grain, tensile strength parallel to grain and shear strength parallel to grain) using universal testing machines available both at the National University of Rwanda (UNR) and at Marquette University. Unadjusted for end use data were obtained in the unseasoned and at 12 percent moisture content.; A randomized two factor factorial analysis was performed in an effort to quantify the effects of a particular species and the forest location from where it was sampled on the value of the property mean. The conclusion reached was that not enough evidence existed to support or reject the hypothesis that forest location and species have any effect on the strength values of the wood sampled. The effects of each factor individually and the interaction effect were not significant at the 5% point level.; Using the Australian and the Andean Pact Structural Grading Rules and data obtained in this study, a grading rule is proposed for structural lumber in Rwanda. This Grading Rule describes three structural grades based upon the tolerance limits established on the strength-reducing factors. Allowable design values are derived for the three timber species for bending, compression, shear, tension and modulus of elasticity using small, clear data and a number of adjustment factors. Furthermore, a species independent stress system is proposed with the primary objective of reducing the volume of information that in the past faced the engineer and other wood end-users.; Regression and correlation analysis performed to obtain the relationships between the primary property (MOR) and the secondary properties suggests that strength grouping is desirable not only for its marketing and technological flexibilities, but also for the optimization gained in the structural use of the timber resource.; Based upon the findings of this study, a number of recommendations are made for future research in wood engineering in Rwanda.
机译：进行这项研究是为了得出卢旺达生长的三种木材的容许应力。木材的特性在物种之间，物种内甚至单个树上的位置之间都会变化。为了确定木材和木材复合材料的设计值，必须很好地理解这种可变性。使用国际测试标准（ISO）获得小的透明木材样品的平均值和接近最小值的估计值。对木材工程中使用的当前采样技术的深入研究强烈表明，随机采样技术及其变化仍然是一种可靠的技术，如果设计合理，它将产生准确的估计值。使用随机抽样技术从三种木材中选择了几种样品进行了物理（密度，比重，膨胀和收缩特性）和机械性能（弯曲强度和刚度，平行于纹理的抗压强度，抗张强度）的测试使用卢旺达国立大学（UNR）和马奎特大学提供的通用测试机来测量与颗粒平行的剪切强度和与颗粒平行的剪切强度）。未经调整的最终用途数据是在未经调味的且水分含量为12％的情况下获得的。进行了随机的两因素因子分析，以量化特定物种和从中取样的森林位置对属性均值的影响。得出的结论是，没有足够的证据支持或拒绝有关森林位置和物种对所采样木材的强度值有任何影响的假设。在5％的水平上，各个因素的影响和相互作用的影响均不显着。利用澳大利亚和安第斯协定结构等级规则和本研究获得的数据，提出了卢旺达结构木材的等级规则。该等级规则基于基于强度降低因素建立的公差极限来描述三个结构等级。使用小的，清晰的数据和许多调整因子，可以得出三种木材的弯曲，压缩，剪切，拉伸和弹性模量的允许设计值。此外，提出了一种与物种无关的压力系统，其主要目的是减少过去面对工程师和其他木材最终用户的信息量。进行回归和相关分析以获得主要特性（MOR）和次要特性之间的关系，表明强度分组不仅对于其营销和技术灵活性，而且对于木材资源的结构使用中获得的优化都是理想的。 ;根据这项研究的结果，为卢旺达的木材工程未来研究提出了许多建议。

著录项

  • 作者

    Nyandwi, Ignace.;

  • 作者单位

    Marquette University.;

  • 授予单位 Marquette University.;
  • 学科 Engineering Civil.; Agriculture Wood Technology.; Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 1990
  • 页码 305 p.
  • 总页数 305
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 建筑科学;森林采运与利用;工程材料学;
  • 关键词

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