Veneer strand flanged I-beam with MDF or particleboard as web material IV: Effect of web material types and flange density on the basic properties

The balance of strength between the flange and web parts of veneer strand flanged I-beam was investigated by the following methods: (1) use of different web material types, such as plywood, oriented strand board (OSB), particleboard (PB), and medium density fiberboard (MDF), that have different strength properties; and (2) fabrication of I-beams with low-density flanges using low-density strands with PB web material. Replacing PB or MDF with plywood showed slight significant improvement in the modulus of rupture but not in the modulus of elasticity of the entire I-beam. However, PB and MDF showed competent performance in comparison with OSB, thus strengthening the promising future of the use of PB or MDF as web material to fabricate I-beams. Hot-pressing conditions used for I-beam production exerted slightly adverse effects on the bending properties of PB, but not on MDF, OSB, and plywood web materials. The flange density of 0.60 g/cm³ was considered to be the lower limit that provides I-beams with balanced mechanical properties and dimensional stability.     

Veneer strand flanged I-beam with medium density fiberboard or particleboard as web material I: the forming method and fundamental properties

I-beams flanged with veneer strands with medium density fiberboard (MDF) or particleboard as web material were produced by hot pressing. The forming and pressing method used a special metallic mould that allowed flanges to be formed and bonded to the web at the same time. Many I-beams were able to be produced in a single hot pressing cycle and this method allows the utilization of residues and wastes from wood and wood-composite industries. The forming and pressing method was found to be technically suitable for the production of such I-beams. The fundamental properties of the specimens produced were assessed and the results indicated that the I-beams had promising mechanical properties; for example, the modulus of rupture ranged from 40 to 56MPa depending on the flange density. The bond quality between the web and flange was found to have a critical effect on the strength of the entire I-beam. The I-beams were found to have relatively high bond strengths between the web and flange, ranging from 3.3 to 5.0MPa in the parallel direction. The dimensional stability of the I-beams was found to be excellent in the thickness direction of the beam, but not in the compression (width) direction.Part of this paper was presented at the 53rd Annual Meeting of the Japan Wood Research Society in Fukuoka, March 2003     

Simulation method to generate the strength of glulam using correlated random variables

Many reports have been published about designing the strength of glulam using simulation methods. In simulation methods, one of the most important problems is how to deal with correlations among strength factors, i.e., modulus of elasticity (MOE), modulus of rupture (MOR), tensile strength (σ_T), and compression strength (σ_C). For example, in the case that the MOR criteria of glulam is σ _ni /f _ni + σ _bi /f _bi ≥ 1 (where σ _ni and σ _bi are the axial stress and the bending stress of the i-th lamina respectively, and f _ni and f _bi are the axial strength and the bending strength of the i-th lamina respectively), a correlation between f _ni and f _bi exists. How can we account for this correlation when calculating the strength of glulam, bearing in mind that it is very difficult to measure the correlation coefficients among MOR, σ_T, and σ_C? We developed a method by which these problems could be solved, and, using random variables generated by this method, the strengths of glulam were simulated. The simulated values were almost the same as the experimental values. The results indicated the usefulness of the method.     

The evaluation of long-term mechanical properties of wood-based panels by indoor exposure tests

Wood-based panels such as plywood, oriented strand board, particleboard, and medium-density fiberboard are used for roof, wall and floor sheathing materials in residential construction. However, the service life of these panels is still unknown due to the lack of long-term durability data. In this paper, test results from six different indoor exposure experiments were integrated to investigate the long-term durability of wood-based panels. The indoor exposure tests lasted for a maximum of 10 years, providing the panels with the changes in moisture content that ranged between 5 and 18%. The reduction in mechanical properties was determined to be in the range of 0–16% for the bending strength, 3–22% for the modulus of elasticity, 11–31% for the internal bond strength and 0–8% for the nail-head pull-through strength. No reduction was recognized for the lateral nail resistance. Furthermore, the concept of deterioration intensity (DI) based on the moisture content history was introduced to predict the long-term durability of the panels, and various calculation methods for DI were discussed so as to increase the correlativity of this property with the reduction in a mechanical property.     

基于视觉识别的小麦收获作业线快速获取方法

针对小麦生长分布不均等情况下激光作业线检测系统精度偏低的问题,提出了基于视觉的小麦收获作业线快速获取的方法。通过对成熟期麦田的彩色图像进行对比度增强和降低亮度的处理,将其转换为灰度图像,利用阈值分割方法分离已收获与待收获区域,对二值图像采用互相关函数法检测已收获与待收获区域的分界点,利用Hough变换法拟合目标直线。所提方法在激光作业线识别系统的基础上扩大了视野范围,并限制了图像处理的范围,试验结果表明该方法对小麦收获作业线的检测结果平均偏差为2.35 cm,标准差为3.26,能够满足小麦收获导航线识别的要求,是一种有效的检测算法。