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。     

胶合成材

胶合成材北京天昌木工有限公司１胶合成材所谓胶合成材，是指通过胶合拼接等方法，将小规格木材沿纤维方向相互平行接长、加宽、增厚，加工成在性质和外观上都保留了实木固有特性的一类大规格材。目前国内已有指接材，地板块和胶合梁等产品，但都以特定产品的名称命名，尚...     

建筑构件

北美和欧洲建筑业工程木材市场稳步发展 木材工业专家对定向刨花板、胶合板、单板层积材、胶合层积材、工字梁、刨花板、中密度纤维板和硬质纤维板等产品的市场进行了研究后,对北美和欧洲建筑业中工程木材的利用前景做出了预测。     

柚木苯醇抽提物对西南桦木材MUF胶合效果的影响

经柚木苯醇抽提物液作木材表面处理的西南桦木材试件的MUF胶合效果的试验结果表明:积聚在其木材表面的柚木木材苯醇抽提物(LEBAT)妨碍了MUF对被胶合材表面的润湿性和物理渗透性,从而影响了被胶合材与MUF胶合层胶钉的机械结合效应的形成,降低了被胶合材的胶合效果;但LEBAT并不影响被胶合材与MUF化学结合中的胶合效应。故为获得柚木木材满意的胶合效果,应采取避免柚木木材苯醇抽提物在其木材表面积聚的措施。     

杉木胶合木湿应力研究

为揭示环境湿度变化引起的木材含水率非均匀性分布对胶合木构件内部湿应力的影响规律,从材料层面测试了变湿度条件下290个国产杉木木材的平衡含水率,以及横纹径向和横纹弦向干缩性、湿胀性、水分扩散系数、抗拉强度和弹性模量等物理力学性能参数,并从理论层面利用有限元模拟分析周期性变湿度条件下层板厚度对杉木胶合木湿应力的影响。研究结果表明:利用Nelson方程能够较好地拟合变湿度中杉木的平衡含水率;杉木横纹径向干缩和湿胀性均小于横纹弦向,横纹径向水分扩散系数、抗拉强度和弹性模量均高于横纹弦向,这决定于横纹径向排列的木射线以及管胞径面壁上大量纹孔导致的实质物质减少的微观构造;减小层板厚度有助于降低胶合木湿应力,当层板厚度由40 mm降至20 mm时,构件内部最大湿应力降低19.32%,但其最大值仍高于木材横纹抗拉强度,湿应力的降低程度不足以避免构件的横纹开裂;木结构工程设计和应用中必须考虑其他有效的方法减小湿应力以避免木材横纹开裂。     

人工林难胶合木材的研究现状

从木材密度、抽提物、加工性能等方面讨论人工林难胶合木材胶合困难的主要原因,阐述改善胶合性能的主要措施.胶合面加工质量的改善、抽提物处理和润湿性改进等,是目前改善人工林难胶合木材胶合性能的主要方法,但是效果不显著,还有待进一步研究.     

林产工业专业文摘

<正>节子对木材胶合性能的影响文章研究樟子松的节子类型、尺寸和组坯方式对其胶合性能的影响。结果表明:胶合面上节子的存在会降低木材的胶合性能,以节子尺寸的影响较显著,而节子类型的影响不显著;随着两胶合面节子相对面积的增加,木材的胶合性能降低。在集成材的生产过程中,建议去除直径25mm以上的节子,或避免两胶合面上直径25mm节子的对接,可避免节子对木材胶合性能     

高温热处理木材胶合性能的研究

笔者研究了桦木、落叶松和樟子松高温热处理材的胶合性能,并与常规干燥材进行了对比。测试结果表明木材的胶合剪切强度与所用的胶黏剂有关,聚氨酯胶合的三个树种木材的剪切强度普遍大于白乳胶胶合的木材。无论是室内用的白乳胶或室外木结构用的聚氨酯胶都能与三个树种的高温热处理材很好地胶合,胶合试件的浸渍剥离率或煮沸剥离率皆为零。木材经高温热处理后,其剪切强度均有不同程度的降低,阔叶材桦木下降幅度最大,针叶材落叶松下降幅度最小。     

高温预处理对足尺胶合木梁力学性能的影响

【目的】研究高温预处理对足尺胶合木梁力学性能的影响,明确高温热改性和环境湿度对木材平衡含水率、木材顺纹抗剪强度和顺纹抗拉强度的影响规律,揭示高温预处理对胶合木梁抗弯性能影响的作用机制,为高温热改性技术在木结构领域中的应用提供参考。【方法】以高应力等级的兴安落叶松为研究对象,采用工业化热处理技术对落叶松木材进行高温热改性,以高温热改性后的落叶松木材为层板,制备12个足尺胶合木梁。基于EN 408标准四点弯曲方法,分析高温热改性和环境湿度对胶合木梁抗弯弹性模量、抗弯强度、破坏模式、跨中截面荷载-应变曲线和跨中截面应变分布规律等抗弯性能的影响。【结果】高温热改性会在一定程度上降低胶合木梁的抗弯强度,但可明显提高高湿度条件下胶合木梁的抗弯弹性模量,与90%环境湿度下未处理胶合木梁相比,高温热改性后,同湿度下胶合木梁的抗弯强度降低29. 79%,抗弯弹性模量提高23. 71%;高温热改性可降低胶合木梁抗弯弹性模量对环境湿度的敏感性,环境湿度从60%提高到90%,未处理胶合木梁的抗弯弹性模量降低23. 27%,经高温热改性预处理的胶合木梁抗弯弹性模量降低7. 55%; 60%和90%环境湿度下的荷载-位移曲线和跨中截面应变分布曲线表明,胶合木梁在高湿环境中具有更明显的非线性特性,高温预处理后的胶合木梁表现为线弹性。环境湿度对胶合木梁的抗弯性能具有较为明显的劣化作用,90%湿度下胶合木梁抗弯强度和抗弯弹性模量分别为43. 98 MPa和12. 191 GPa,比60%湿度下未处理胶合木梁低17. 07%和23. 27%;环境湿度对木材平衡含水率影响明显,高温热改性是降低木材平衡含水率的有效措施,环境湿度从60%提高到90%,高温热改性处理后落叶松木材平衡含水率分别从10. 74%和20. 62%降至4. 76%和11. 18%。【结论】60%和90%环境湿度条件下,未处理胶合木梁为拉伸破坏,高温热改性构件为拉剪联合破坏,高温热改性后材料的顺纹抗剪强度和顺纹抗拉强度降低是材料破坏模式改变的根本原因。高温热改性后胶合木梁在高湿环境条件下抗弯弹性模量明显改善。     

竹材的键槽胶合效应

根据机械结合理论,通过对竹材弦向胶合面上导管数量和直径以及胶合效果的检测分析和与木材的对比分析,本文认为竹材可以获得"键槽连接"的机械胶合效应,但要得到与木材相近的胶合效果,竹材胶合需要消耗更多的胶粘剂或填料。     

Acoustoelastic birefringence effect in wood II: influence of texture anisotropy on the polarization direction of shear wave in wood

Ultrasonic shear waves were propagated through the breadth direction of a wood beam which was subjected to a bending load such that it was in a plane-stress state. The oscillation direction of the shear waves with respect to the wood beam axis was varied by rotating an ultrasonic sensor, and the relationship between the shear wave velocity and the oscillation direction was examined. The results indicate that when the oscillation direction of the shear wave corresponds to the tangential direction of the wood beam, the shear wave velocity decreases sharply and the relationship between shear wave velocity and rotation angle tends to become discontinuous. When the oscillation of the shear waves occurs in the anisotropic direction of the wood beam instead of in the direction of principal stress, the shear wave velocity exhibits a peak value. In addition, the polarization direction was found to correspond to the direction of anisotropy of the wood beam according to the theory of acoustoelastic birefringence with respect to plane stress. This indicates that when the acoustoelastic birefringence method is applied to stress measurement of wood, it is appropriate to align the oscillation direction of the shear wave with the principal axial direction of anisotropy in order to carry out ultrasonic measurement.     

Acoustoelastic birefringence effect in wood III: ultrasonic stress determination of wood by acoustoelastic birefringence method

Stress conditions produced in wood were analyzed by means of the acoustoelastic birefringence method. Bending load was applied against a wood beam specimen. Under loading, ultrasonic shear waves were propagated through the breadth direction of the wood beam specimen. The velocities of shear waves polarized in the longitudinal or tangential direction of the wood beam specimen were measured with the sing-around method. Bending stresses were determined by dividing the difference between the acoustic anisotropy and the texture anisotropy by the acoustoelastic birefringence coefficient. Shear stresses were also determined. These stress distributions of the beam specimen were in good agreement with those obtained by the strain gauge method and mechanical calculation.     

Derivation and application of an equation for calculating shear modulus of three-ply laminated material beam from shear moduli of individual laminae

In a detailed study of the relation between the deflection caused by shear force and the constitution of a laminated material beam, we derived an equation for calculating the shear modulus of a laminated material beam from the shear moduli of individual laminae. The validity of the derived equation was investigated using crosslaminated wood beams made with five species. The calculated shear moduli parallel to the grain of face laminae ranged from 48.3 MPa to 351 MPa, while those perpendicular to the grain of face laminae ranged from 58.0 MPa to 350 MPa. The calculated shear moduli increased markedly with increasing shear modulus in a cross section of perpendicular-direction lamina of a cross-laminated wood beam. The calculated apparent modulus of elasticity (MOE) of cross-laminated wood beams agreed fairly well with the measured apparent MOE values. This fact indicated that the apparent MOE of cross-laminated wood beam was able to be calculated from the true MOE values and shear moduli of individual laminae. The percentage of deflection caused by shear force obtained from the calculated apparent MOE (Y _sc) was close to that obtained from the measured apparent MOE (Y _s) and there was a high correlation between both values. From the above results, it was concluded that the derived equation had high validity in calculation of shear modulus of a cross-laminated wood beam.     

城市废弃木材的回收利用及其处理工艺

针对我国城市大量废弃木材不能有效利用、而人造板企业又原料紧缺的实际状况,提出了废弃木材回收利用的重要性,分析了废弃木材回收利用现状和存在的问题,并根据废弃木材特性提出了废弃木材制作木片的处理工艺。     

利用西北六省区农业剩余物发展人造板产业

我国西北地区森林资源贫乏，其木材供应问题是实施西部大开发进程中的一个重要问题。本文论述了西部地区发展农业剩余物人造板的必要性和重要意义，提出农业剩余物是替代木材的潜在资源。     

Use of Leicester's “rheological model for mechano-sorptive deflections of beams”

Summary The model for mechano-sorptive deformation proposed by Leicester is used to predict stress relaxation of wood drying under constraint from apparent creep of drying wood under constant load. The predictions are compared with measurements on four pairs of beams, one beam in each pair being tested under constant load, the other at constant deflection. Agreement was sufficiently close to demonstrate the value of the model.     

Quasi-non-linear fracture mechanics analysis of the double cantilever beam specimen

A quasi-non-linear fracture mechanics model based on beam on elastic foundation theory is applied for analysis of the double cantilever beam (DCB) specimen for determination of fracture energy of wood. The properties of the elastic foundation are chosen so that the perpendicular-to-grain tensile strength and fracture energy properties of the wood are correctly represented. It is shown that this particular choice of foundation stiffness makes a conventional maximum stress failure criterion lead to the same solution as the fracture mechanics compliance method. Results of linear elastic fracture mechanics are obtained as a special case by assuming an infinitely large value of the perpendicular-to-grain tensile strength. The quasi-non-linear fracture mechanics model is compared with other models and with results of tests conducted to reveal the influence of the geometrical properties of the DCB specimen. In addition, the appropriateness of choice of the foundation stiffness is investigated.     

Shear strengths of wood measured by various short beam shear test methods

We conducted three types of short beam shear tests of western hemlock (Tsuga heterophylla Sarg.) under various span/depth ratios, and examined whether the maximum shear stress was used as the shear strength. The following results were obtained. (1) In the short beam shear tests under the three-point loading method, it was difficult to have the specimen failing by horizontal shear. We thought that this method should not be recommended for determining the shear strength of wood. (2) In the short beam shear tests under the asymmetric four-point loading of the specimen with a rectangular cross-section, the failure caused by horizontal shear occurred under some span/depth ratio range. Nevertheless, this range was dependent on the specimen geometry and was quite restricted. We therefore think that this method should not be recommended for determining the shear strength of wood. (3) In the short beam shear tests under the asymmetric four-point loading of the I-shaped specimen, failure caused by horizontal shear occurred under the span/depth ratio range wider than that applicable for the asymmetric four-point loading of the specimen with a rectangular cross-section. The maximum shear stress was stable in a certain span/depth ratio range and the value of the maximum shear stress is effective as a parameter for comparing the shearing strength of materials with each other.     

高性能重组竹制造技术研究

基于丛生中小径级竹材资源丰富,工业化利用水平低的现状,开发了以竹代木的高性能重组竹新材料。高性能重组竹可代替木材、节约木材资源,形成新型资源产业链;同时,解决三农问题,推进社会、生态、经济的平衡发展。     

Effect of combinations of wood and counterface materials on three-body abrasive wear

The abrasion characteristics of various combinations of wood and counterface materials in three-body abrasive wear were investigated. Various wood samples were examined in combination with wood, plastic, and metal counterface materials. The wear coefficient in the wood samples was calculated as the wear volume of the friction surface divided by the sliding distance and the applied load. The results showed that the wear coefficient was smaller in cases where the wood samples had greater yield stress. The wear coefficient increased as the yield stress of the various counterface materials increased, reaching a maximum value and then decreased as the yield stress increased. This result indicated that a peak value existed for the wear coefficient in combination with the counterface material.Part of this report was presented at the 51st Annual Meeting of the Japan Wood Research Society, Tokyo, April 2001