预组型木质工字梁静态力学性能设计思路的探讨

以钢质工字梁的设计理论和木质材料学与工艺为依据,对预组型木质工字梁(IJ)的部件——翼缘、腹板,以及两者之间的连接木质工字梁整体进行受力分析,并结合材料的蠕变等影响木质IJ静态力学性能的因素以及木结构建筑对木质IJ的要求,提出了IJ的基本设计思路。     

预制木质工字梁翼缘/腹板接口力学性能的研究

木质工字梁是一种资源高效利用型现代木质建筑材料，梯形槽胶连接是预制木质工字梁翼缘/腹板最常用的接口方式。对其力学性能的研究表明：接口角角度β和接口槽深i是影响接口力学性能和工字梁整体承载能力最为关键的技术参数。     

木结构工字梁的优化设计研究

对木结构工字梁结构进行优化设计,并对木结构工字梁的规格尺寸及主要技术指标进行测试。研究结果表明:经优化设计后,木结构工字梁具有卓越的物理力学性能,能够满足使用相关性能的要求;木结构工字梁作为替代实木梁的木建筑构件,具有其突出的自身优势,木结构工字梁比实木梁具有更高的强度、刚度、尺寸稳定性,具有更大的跨度能力以及更小发生几率的翘曲、扭曲和劈裂,有更低的伸缩率。     

工字搁栅用落叶松单板类足尺翼缘和腹板基材生产工艺及性能评价

阐述了木质工字搁栅的特点,介绍了利用胶合板生产设备加工制造工字搁栅用落叶松单板类足尺翼缘和腹板基材的工艺技术.对腹板和翼缘物理力学性能的研究结果表明:落叶松单板类足尺翼缘和腹板的主要性能可以达到美国APA相关标准的要求.     

基于静态弯曲性能的木质工字梁设计计算方法探讨

参照钢质工字梁静态弯曲理论,对木质工字梁（IJ）的“荷载一位移”曲线、IJ正应力理论计算值与实测值、IJ整梁挠度理论计算值与实测值的对比分析,结果认定：1）钢质工字粱的静态弯曲理论计算公式,可用于IJ弹性段应力和挠度的分析计算;2）IJ整梁静态弯曲性能的分析计算时,应注意IJ上翼缘压缩特性和下翼缘拉伸特性的差异。     

预组型木结构工字梁承压能力研究

本文对预组型木质工字梁的结构性能进行分析研究。通过对梁接口承压能力的测试结果表明:IB翼缘/腹板接口的端头承压破坏可分为先期破坏(对应的是无效胶合或胶合不良)和终极破坏(对应的是有效胶合)二种主要形式,先期破坏主要是翼缘/腹板胶合层的剪切破坏或工字梁槽底木材的横纹拉伸破坏,终极破坏的形式是工字梁胶合层剪切、翼缘槽底木材横纹拉伸和压缩的综合性全面破坏。由于终极破坏荷载是工字梁接口的最大垂向抗压破坏荷载,因此要求木结构工字梁接口几何尺寸的设计应努力避免垂向受压时不发生先期破坏。     

水分对木质工字梁翼缘/腹板接口性能的影响研究

为研究水分对木质工字梁(IB)翼缘/腹板接口力学性能及尺寸稳定性的影响,通过单因素试验,检测不同含水率下IB翼缘/腹板接口的垂向承载能力、胶合性能、以及抗劈裂性能。结果表明,IB的综合性纤维饱和点只有25%左右;含水率从8.9%提高到25%的接口的承压能力下降了47.2%,含水率从25%提高到53%的接口的承压能力仅下降了0.6%;水分对IB翼缘和腹板尺寸变化的影响是水分影响接口承载能力的间接因素;吸湿后接口的承载能力并不能恢复到吸湿前的初始水平;解吸至8.9%含水率的IB接口的承载能力比吸湿前同等含水率的IB接口低了17.8%。     

佐治亚—太平洋木材公司推出新一代木材工字梁产品

美国:佐治亚-太平洋木材公司(Georgia-Pacific)推出了XJ-85型工字梁新产品。这是该类产品中唯一的一种预制工字梁。采用这种产品,建筑者可以很容易地安装管道、HVAC和电路系统。由于很少需要返修,XJ-85型工字梁可以降低建筑者和承包商的安装成本,预留的孔道便于快速安装,减少在现场的工时。除了安装更容易以外,XJ-85型工字梁     

木质工字梁翼缘用杨木-酚醛树脂LVL密度的控制意义

对不同密度木质工字梁(IJ)翼缘用杨木酚醛树脂LVL(P-PF-LVL)垂直胶层静曲弹性模量(MOEB)、纵向抗拉强度(MORT)、静曲强度(MORB)和水平剪切强度(MORS)的检测,分析结果表明:1)可以利用MOEB、MORT、MORB和MORS与密度的正相关关系来设计包括IJ翼缘用LVL在内LVL的适当密度,以控制结构用LVL的目标力学性能;2)梁问距为490mm、梁跨为4 500mm、设计荷载为2.5kN/m2的241mm高的IJ翼缘用P-PF-LVL的最小安全密度应略大于0.553g/cm3同时建议提高国标GB/T20241-2006对结构用LVL的MORB的要求,增设结构用LVL的MORT.     

重组竹工字梁抗弯特性研究及模拟分析

开展了6根腹板与翼缘板之间采用异氰酸酯胶黏剂胶接和螺栓连接的重组竹工字梁抗弯试验研究,考察重组竹工字梁抗弯承载力特性和破坏模式。试验表明:重组竹工字梁的破坏模式为腹板受拉区撕裂破坏;随着荷载的增加,截面各部位应变发展迅速,尤其是腹板边缘处应变发展最快,首先进入塑性变形并发生撕裂破坏;继续加载,该裂纹发生纵向延伸,逐渐形成通缝,并且螺栓连接处出现撕裂。此时,试件两端上、下翼缘变形明显小于腹板边缘处,翼缘和腹板之间变形极其不协调,上翼板下端与腹板上边缘发生脱胶现象,说明腹板和翼缘连接处的剪应力传递效果不佳,影响了构件的刚度和承载力。重组竹工字梁破坏时挠度较大,工字梁的受力变形明显,6根试验工字梁的延性系数为6.0~9.0,说明重组竹工字梁的延性较好,并且工字梁的设计控制因素是变形而不是承载力。进行重组竹工字梁抗弯特性的非线性有限元模拟,分析得到的工字梁荷载-位移曲线与试验结果吻合较好,工字梁的变形及应力分布特征均与试验相一致。     

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.     

Hygromechanical behaviour of wooden composites

Summary The objective of this research is to study the moisture deformation of densified in technological pressing wooden composite materials. By generalizing Cosserat's couple-stress theory a structural model for determination of mid-surface strains and curvatures of composite board taking into account asymmetric structure and nonuniform distribution of moisture as well as nonlinear swelling functions of the wooden stuff and dependence of strain characteristics on moisture content is developed. On the basis of a laminate analogy the optimum flake or veneer alignment in board has been estimated for the real composite production process. According to analysis performed, the optimum alignment for hygromechanical properties may not coincide with that for mechanical properties, and for every type of loading, material with a definite structure should be used.     

木质材料缺陷无损检测主要研究进展

从基于成像技术、信号传播速度变化、人工模拟缺陷和信号处理的木质材料缺陷无损检测以及木质材料缺陷对其力学性能的影响5个方面论述了木质材料缺陷无损检测的研究进展, 简要分析了目前研究中存在的主要问题及其发展趋势。     

Design of humidity sensitive wooden materials for multi-objective application

This study is devoted to the estimation of hygromechanical and mechanical behaviour of different systems of continuous layers (veneers) or layers consisting of wooden flakes. The hygroexpansion and warping of wooden composite depends on the moisture content and material configuration. Hygrodeformation in the board plane is a dimensional problem and can cause buckling due to restrained linear expansion, whereas thickness swelling has a deteriorating effect. Methods of predicting how humidity, material structure and various loading parameters affect the behaviour of layered wooden materials are displayed. The optimum orientation of layers for hygromechanical properties may not coincide with that for mechanical properties, thus for every type of loading—humid environment, biaxial compression or flexure—boards with a definite structure should be designed.     

Veneer strand flanged I-beam with MDF or particleboard as web material II: effect of resin type,application rate,strand dimension,and pressing time on the basic properties

Optimization of the manufacturing conditions of the veneer strand flanged I-beam invented in the previous study was investigated using different combinations of strand dimensions, resin types between web and flange, different pressing times, and different wood–resin moisture contents under conventional hot pressing conditions. The main results revealed that the strand dimensions have no effect on the bending properties of the flange part and the dimensional stability of the I-beam. Increasing the resin application rate between strands was found to improve the dimensional stability of the I-beams. The use of isocyanate (MDI) resin between web and flange significantly improved the bond strength between web and flange, the modulus of rupture of the I-beam, and the modulus of rupture of the flange part. Dimensional stability was also improved. Shortening the pressing time from 20 to 12min was found to be feasible. Using low wood-resin moisture content was found to interfere with the curing of the phenol–formaldehyde (PF) resin at the flange part resulting in poor quality beams. Of the three moisture content levels tested, 12% was found to be the optimal level for producing I-beams with balanced mechanical properties and dimensional stability.Part of this work was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003     

我国木质家具出口市场结构的实证分析

出口市场结构不合理是制约我国木质家具对外贸易可持续发展的重要影响因素。利用出口市场集中度指数、出口市场多样性指数、出口市场均匀度指数,文中对我国木质家具出口市场结构进行实证分析。研究结果表明,我国木质家具出口市场集中度不断降低,出口市场多元化正在形成,出口市场均匀度不断提高。研究结论可以为我国木质家具出口市场政策的调整提供科学依据。     

Anatomical characteristics, properties and use of traditionally used and lesser-known wood species from Mozambique: a literature review

Mozambique is a country with vast forestry resources that include native wood species with high commercial value. Thus, the trade of timber as raw material, as well as wooden finished products are commercial options of considerable valuable for the country. This work presents information about anatomical characteristics, physical and mechanical properties and use of some native wood species from Mozambique, namely, Afzelia quanzensis, Androstachys johnsonii, Erytrophleoum suaveolens, Khaya nyasica, Pterocarpus angolensis, Milletia stuhlmannii and the emerging lesser-known species Pericopsis angolensis, Sterculia appendiculata and Sterculia quinqueloba. The study concludes that these Mozambican wood species are similar in several aspects. They are generally described as very hard, dense, having high mechanical strength and durable. The study also concludes that although the lesser-known wood species, S. quinqueloba, has similar properties to the traditionally used one, A. quanzensis, it is less used because of its poorly known properties and potential uses. Thus, further research to determine the properties and suitable end uses of other lesser know species is likely to be beneficial to the country.     

ANSYS在木结构构件中的应用

介绍了大型通用有限元软件ANSYS的特点和进行有限元分析的一般步骤。通过在木桁架、木结构剪力墙和木结构楼板3种结构中应用得知,ANSYS可以用于对木结构构件的建模和应力分析以及进行相应的力学性能预测,且研究精度高、速度快,可节约大量的产品试制和试验经费,同时还可以实现对结构的优化。     

微米木纤维模压制品握钉结合部载荷分布系数的确定方法

微米木纤维模压制品是通过细胞纵向劈裂而成的微米木纤维模压成型的新型高强度人造木基材料制品.以人造木基材料为主要材料的各种握钉力的计算均以栽荷沿轴向分布的积分方程为基础,而有关其栽荷分布系数的精确计算尤为重要.为此本文首先建立了握钉结合部裁荷分布的力学模型,然后给出了螺纹牙受力变形协调条件,推导出了轴向载荷分布强度与螺纹牙侧面上比压的关系式,分析了微米木纤维铺装纹理方向对其模压制品弹性模量的影响,从而详细地推导出了微米木纤维模压制品握钉结合部载荷分布系数的计算公式.