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1.
A finite element nonlinear analysis was conducted on bolted timber joints under lateral loads parallel and perpendicular to the grain. The results obtained from this analysis were compared with the experimental results and calculated values based on the yield theory. The analysis and experiment were performed on double shear bolted joints parallel and perpendicular to the grain with steel side plates and a slotted-in steel plate. It was found from the analysis that the yielding of wood and bolt occurred before the overall yielding of the bolted joint. Shear strength of bolted joints calculated from the yield theory using the embedding yield strength of wood and the yield moment of the bolt showed comparatively good agreement with the shear strength evaluated by 5% offset of the load–slip curve in the experiment and analysis. The shear strength of the bolted joint calculated from the yield theory using the embedding ultimate strength of wood and the ultimate moment of the bolt agreed quite well with the shear strength evaluated by the maximum load up to 15mm slip in the analysis. The former, parallel and perpendicular to the grain, were 11% and 34%, on average smaller than the latter in the experiment.Part of this paper was presented at the 52nd Annual Meeting of the Japan Wood Research Society, Gifu, April 2002; the Annual Meeting of Architectural Institute of Japan 2002, Ishikawa, August 2002; and the World Conference on Timber Engineering 2002, Shah Alam, Malaysia, August 2002 相似文献
2.
Philipp Schlotzhauer Alexander Ehrmann Susanne Bollmus Holger Militz 《Wood material science & engineering》2020,15(5):278-288
ABSTRACT Knowledge about perpendicular to grain tension behavior of wood is essential, since in construction tension stresses perpendicular to grain cannot be avoided completely. Especially for hardwoods, the data basis is scarce. EN 338 design values are with 0.6 N/mm² characteristic strength set very low. The US-American National Design Specifications even set this value to zero and make local reinforcements mandatory. This paper compares strength and stiffness values attained with newly-designed, little, prismatic specimens and EN 408 structural timber specimens to evaluate the current European design values. Little specimen’s characteristic strength values range from 7.2 to 10.6?N/mm² and are assumed to be real material properties. EN 408 specimen values are with approximately 4.0?N/mm² lower. These lower values are mainly due to stress peaks introduced by the force introduction. Strength values attained for the medium-dense European hardwoods beech, ash and maple exceed EN 338 design values by a factor of six to seven. Adaptation of the EN 338 design value is not recommended, though. The abundance of influencing factors makes clear that the design value and the ensuing design code have to be synchronized carefully by tedious testing in order to make use of the perpendicular to grain tension strength potential of the selected hardwoods. 相似文献
3.
The crack initiation and propagation of multiplybolted joints subjected to lateral forces perpendicular to the grain were analyzed. Two types of bolted joint were subjected to lateral loads perpendicular to the grain. One had joints of two bolts aligned with the wood grain (type H), and the other had joints of two or three bolts aligned perpendicular to the grain (type V). The crack initiation and propagation were analyzed by means of the average stress method (ASM) and linear elastic fracture mechanics (LEFM), respectively. The maximum loads calculated by LEFM agreed comparatively well with the experimental results, and it was proved that the LEFM was an appropriate tool to analyze the fracture of multiply-bolted joints subjected to a force perpendicular to the grain. It was also found that the multiply-bolted joints failed with the fracture of the wood before the joints yielded, and that it caused a considerable decrease of the maximum loads. The reduction of strength should be considered in the design of multiply-bolted joints subjected to lateral forces perpendicular to the grain.Part of this work was presented at the annual meeting of the Architectural Institute of Japan, Hikone, September 1996 相似文献
4.
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
5.
J. C. M. Schoenmakers A. J. M. Jorissen A. J. M. Leijten 《Wood Science and Technology》2010,44(4):579-595
Different test setups for determining perpendicular to grain embedment strength of timber have been reported in literature.
In addition, different definitions of strength have been used associated with the deformation level underneath the fastener.
It is shown that all reported experimental results can be related, which enables comparison on a common basis. Furthermore,
several models for embedment strength perpendicular to the grain which primarily depend on timber density (specific gravity)
and fastener diameter are evaluated. It is shown that the model currently prescribed by the European structural timber design
code [Comité Européen de Normalisation (CEN) EN 1995-1-1: 2004: Eurocode 5—design of timber structures. Part 1.1: general
rules and rules for buildings. CEN, Brussels, 2004] is unable to accurately predict the strength and an alternative is proposed. This may result in more reliable timber connections
in applying the European Yield Model to determine the connection strength. 相似文献
6.
The gloss of wood is a unique texture compared to that of other materials. To express it quantitatively, two digital-image analyses were performed. One method was multiresolutional contrast analysis, which was the new method developed in this study. The other method was fractal image analysis. Twenty-four specimens, including solid woods, wood-plastic composites (WPCs), printed grains, and granites, were prepared. Digital images of specimens were obtained in five sizes and in two illuminant directions (perpendicular and parallel to the grain). The multiresolutional contrast values of perpendicular illuminated images were calculated and compared among specimens. The result of this quantitative analysis was that the gloss of wood was characterized by bright spots in a relatively small area. Using fractal analysis, the fractal dimension of a digital image was used as an index of brightness changes, not for expressing the self-similarity. These indices showed results similar to those of the multiresolutional contrast analysis.Part of this paper was presented at the 47th annual meeting of the Japan Wood Research Society in Kochi, April 1997 相似文献
7.
Andriy Kovryga Peter Stapel Jan Willem G van de Kuilen 《Wood material science & engineering》2020,15(5):289-302
ABSTRACT The usage of hardwoods for engineered wood products, such as glulam, requires defined mechanical properties reflecting the actual tensile strength of the material. Currently, the European strength class system EN 338 only covers profiles for hardwoods tested in bending. In this study, the material properties of medium-density hardwoods are analysed with the focus on a total of 3663 European ash (Fraxinus excelsior) and European beech (Fagus sylvatica) specimens tested in different loading modes (tension, compression, bending, and shear). The relationships between the material properties—tensile strength, stiffness, and density—are analysed on grouped data of both graded and ungraded specimens. As a result, a tailored ratio of tensile strength to tensile MOE and density is given, which allows to utilize a higher tensile strength of hardwoods (ft,0,k over 30?N/mm²) compared to softwoods. Furthermore, the relationship of the test values and the derived values is checked. The equations for deriving the compression and bending strength from tensile strength are verified based on available data. For tensile and compression strength perpendicular to the grain and for shear strength of both beech and ash, higher strength values than the ones listed in EN 338 are possible. The relationship between the mechanical properties are combined to tensile strength profiles for hardwoods. 相似文献
8.
木材顺纹抗压强度是评价木材力学性能的重要指标,而传统测量方法操作复杂、精确度低。以桦木为例,提出基于近红外光谱技术(NIR)的SEPA-VISSA-RVM木材顺纹抗压强度模型,实现对其更加精确的预测。试验选取100个木材试件,在900~1700 nm近红外光谱波段上采集数据并测量抗压强度真值;然后采用卷积平滑(SG)方法进行光谱预处理;使用采样误差分布分析(SEPA)作为变量空间迭代收缩算法(VISSA)的改进策略进行特征波长优选;最后通过粒子群优化算法(PSO)优化核函数参数并建立相关向量机(RVM)的预测模型。试验表明:在特征波长优选方面,以偏最小二乘法(PLS)建模为基础的SEPA-VISSA方法,其预测决定系数为0.9593,预测均方根误差为2.8995,相对分析误差为3.0256,光谱变量数由512减小到111个,占总波长的22%,均优于VCPA、CARS和VISSA算法;在建模预测方面,以SEPA-VISSA所选波长为基础的RVM模型,PSO优化的拉普拉斯(Laplacian)核函数的核宽度为10.4043,决定系数为0.9449,预测均方根误差为2.0432,相对分析误差为4.2936,预测效果优于PLS和SVR。因此,基于近红外光谱的SEPA-VISSA-RVM建模能够实现对桦木顺纹抗压强度更准确和稳定的无损检测。 相似文献
9.
Thirty types of three-ply parallel- and cross-laminated woods were prepared from five species, and their static bending strength performance were investigated. The modulus of elasticity (MOE), proportional limit stress, and modulus of rupture (MOR) perpendicular to the grain were increased by cross-laminating, and the extent of the increase increased with decreasing density of the species. The measured values of MOE parallel and perpendi-cular to the grain of parallel-laminated woods and perpendicular to the grain of face laminae of cross-laminated woods were approximately equal to those calculated from true MOEs of individual laminae. However, the MOE parallel to the grain of face laminae of cross-laminated woods was much lower than the calculated MOE owing to the effect of the deflection caused by shear force on the MOE. The percentage of deflection caused by shear force versus total deflection (Y
s) showed high values, from 16.1% (buna) to 40.5% (sugi), and it decreased linearly with increasing shear modulus in the cross section of the core. In addition, there was an extremely high positive correlation between the MOR and the measured MOE parallel to the grain of face laminae of cross-laminated woods. The MOR was also highly dependent on the shear modulus in cross section of the core.Part of this paper was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000 相似文献
10.
单板的厚度和配置方式对复合定向刨花板性能的影响 总被引：1，自引：0，他引：1
研究了单板厚度和配置方式对复合定向刨花板性能的影响。试验发现：１．复反的强度与刚度随着单板配置方向的改变而明显改变。当单板纹理方向与ＯＳＢ定向方向平行时，复合板在平行于ＯＳＢ定向强度与刚度明显增加，而且在纵横两个方向上的差异也增大；而当单板纹理方向与ＯＳＢ定向方向垂直时，复合板在纵横两个方面的强度与刚度趋于均匀。２．本试验中如果单板以纹理方向的与ＯＳＢ定向方向垂直配置，则在单板厚度为０．８５ｍｍ时 相似文献
11.
Ali Awaludin Watanachai Smittakorn Takuro Hirai Toshiro Hayashikawa 《Journal of Wood Science》2007,53(3):204-210
Empirical equations to determine the bearing strength have been proposed by many researchers and design standards. Because
these equations have been developed mainly based on test results of softwood species, it is a matter of great importance (to
ASEAN structural engineers) to verify the applicability of these equations for tropical hardwood species, which are commonly
used in many ASEAN countries. In this study, wood specimens of Shorea obtusa (a tropical hardwood species) were used and the bearing test under full-hole confi guration was carried out for fi ve different
loading angles to the grain. The bearing stress-embedment curve obtained from the test was approximated by a linear elastic-plastic
diagram indicating the initial and fi nal stiffness of the curve. Testing showed that the average bearing strength parallel
to the grain was 7.25% lower than the prediction given in Eurocode 5. The bearing strength perpendicular to the grain evaluated
based on bearing load at initial cracking was substantially different from any predictions given by previous studies or design
standards. It was also found that the bearing strength and initial stiffness from the bearing stress-embedment curve for loading
at intermediate angles to the grain could be satisfactorily predicted with Hankinson’s formula. 相似文献
12.
13.
Variations in compression strength and surface roughness of heat-treated Turkish river red gum (Eucalyptus camaldulensis) wood 总被引：1，自引：0，他引：1
This article reports the effects of heat treatment on compression strength parallel to the grain, the surface roughness [average roughness (Ra)], and the air-dry den-sity of wood from the river red gum tree (Eucalyptus camaldulensis Dehn.) planted in Turkey. Eucalyptus wood was heat-treated at temperatures varying from 120° to 180°C for durations of 2–10 h. Samples cut from the heat-treated wood were tested for air-dry density, compression strength parallel to grain, and surface roughness properties. Roughness measurements by the stylus method were made in the direction perpendicular to the fiber. Based on the findings in this study, the results showed that density, compression strength, and surface roughness values decreased with increasing treatment temperature and treatment times. Eucalyptus wood could be utilized by using proper heat treatment techniques without any losses in strength values in areas where working, stability, and surface smoothness, such as in window frames, are important factors. 相似文献
14.
Static bending tests and compressive test parallel to the grain of sugi (Japanese cedar, Cryptomeria japonica) green round timber were conducted to confirm whether its strength would satisfy the referenced strength determined by the Construction Ministry. The strength of green round timber and air-dried round timber were compared for bending and compression parallel to the grain. The strength change ratio in response to a 1 % change in the moisture content of round timber was compared with that of small clear specimens and timber. The results revealed that a 5 % parametric tolerance limit of bending and compressive strength parallel to the grain satisfied the referenced strength, even when using green round timber. The average strength of air-dried round timber was higher than that of green round timber, in both bending and compression parallel to the grain, with significant differences indicated at a 5 % significance level. The relation between the cross-section area that includes round timber, timber and the small clear specimens, and the strength change ratio in response to a 1 % change in moisture content change was fitted to a logarithm curve. Thus, the size of the specimen was considered to affect the strength change ratio. 相似文献
15.
The main objective of this study was to evaluate embedding strength on Uruguayan wood to apply the European yield theory (EYT) for double shear bolted joints’ on Eucalyptus grandis H.(EGH). To introduce the dowel-type connection performance, double shear tests were conducted. The embedding tests were conducted to calculate the yield strength of bolted joint by EYT and the compression test, to estimate the embedding strength. The yield strength obtained from the experiments showed a good agreement with the yield strength calculated by EYT method. The yield strength of double shear bolted joint evaluated from compressive strengths is a very close to the yield strength calculated by EYT. The average value and variability of the yield strength of double shear bolted joint calculated by EYT applying the embedding strengths of experimental results were very close to the yield strength or 5 % offset method of experimental results. The results from this study showed a good behavior to structural design with EGH in accordance to the Japanese standard code. 相似文献
16.
采用杉木和泡桐为试材,对经过KY-FW阻燃剂处理的木材与未经处理的木材进行对比研究,分析KY-FW阻燃剂对木材力学性能的影响.结果表明,木材经KY-FW阻燃剂处理后,除冲击韧性降低外,其它主要力学性能指标(如抗弯强度、顺纹抗压强度及硬度)都有所提高.KY-FW阻燃木材的力学性能达到了一级水基型阻燃剂标准规定的相应指标. 相似文献
17.
18.
钩梢对5年生毛竹竹材物理力学性质的影响 总被引：2，自引：0，他引：2
毛竹(Phyllostachys edulis)秆形通直、材性优良,是利用范围最广、经济价值最大的竹种(刘亚迪等,2008);但同时因毛竹秆高大、枝叶繁茂,是受风雪灾害影响较大的林种之一(肖本权,2003)。2008年初,我国南方遭受了严重的雨雪冰冻灾害,涉及湖南、安徽、浙江、江西等19个省(区、市),受灾森林面积1860万hm2(祝列克,2008),受灾中心区域为毛竹的主分布区,占我国毛竹林面积的70%以上。据统计,全国竹林受灾面积约400万hm2,其中80%为毛竹林(李潇晓,2008)。在竹林培育中,为应对雨雪冰冻灾 相似文献
19.
The strength and fracture behavior of dowel-type connections with stiff dowels loaded perpendicular to grain was studied by nonlinear 3D finite element (FE)-analysis. A cohesive zone model was used to model the perpendicular to grain fracture of the wood, i.e., failure by wood splitting along the grain. The influence of load eccentricity and dowel-to-loaded-edge distance was studied for a plate type of geometry loaded in tension and for a simply supported beam loaded in bending. The strength found from the FE-analysis is compared to strength from experimental tests with centric loading, showing overall good agreement. Numerical results for centric loading are further compared to strength predictions according to the linear elastic fracture mechanics (LEFM)-based design criterion present in Eurocode 5 (EN 1995-1-1:2004). The comparison showed good agreement regarding the relative influence of connection geometry, but the design criterion appears, however, to yield unconservative strength predictions. The results of the FE-analyses regarding dowel load eccentricity showed that such loading conditions may yield significantly lower strengths compared to centric loading. An approximate engineering method to account for the strength reduction due to load eccentricity is, furthermore, presented. 相似文献
20.
通过单因变量两因素重复试验,以毛竹竹篾和桦木单板为原料,使用酚醛树脂胶黏剂压制竹木复合层积材,分析热压温度及板材密度对竹木复合层积材顺纹抗压强度的影响。结果表明,在试验选定因素水平范围内,热压温度和板材密度对竹木复合层积材顺纹抗压强度影响显著,板材顺纹抗压强度随热压温度的升高而增强,但145℃与160℃两水平之间差异并不显著;不同密度对板材顺纹抗压强度的影响差异显著,板材的顺纹抗压强度随板材密度的增大而增大;在其他工艺参数相对不变的情况下,热压温度与板材密度的交互作用对板材顺纹抗压强度的影响并无显著的影响。 相似文献