Cost optimization of cross-laminated timber panels in one-way bending

European Journal of Wood and Wood Products - For the purposes of structural design, cross-laminated timber (CLT) panels are typically chosen from tables detailing standardized layups. While this is...     

Modeling the bending vibration of cross-laminated timber beams

Cross-laminated timber (CLT) is an economical construction material combining good structural properties and environmental advantages. Due to the layered geometry and the associated internal stress boundary conditions, modelling its dynamic behavior is complex. However, accurate vibration level estimations are necessary to estimate the sound insulation performance of CLT constructions. This paper outlines a method to determine the relevant elastic constants and the appropriate equations of motion to predict the vibration of beams cut from a three-ply CLT plate. Modal analysis performed on strips cut along the two principal directions provides insight in the material’s dynamics. The bending mode frequencies are determined experimentally by analyzing the sweep response spectrum using the linear prediction method. In a second step, analytical beam vibration models of increasing complexity are fitted to the measurements using a genetic optimization algorithm. Thin beam theory—the simplest model—does not predict the bending modes with sufficient accuracy. Depending on the strip direction, the bending vibrations can be modeled using Timoshenko’s theory for thick beams, or by a model for three layer sandwich beams respectively. The results show that taking the beam geometry into account is as important as estimating the orthotropic material constants to model the bending modes properly.     

Load-carrying capacity prediction of single rods glued into cross-laminated timber

European Journal of Wood and Wood Products - Timber engineering is currently crossing new frontiers in terms of performance, as illustrated by the increasing number of high-rise buildings. This has...     

The evaluation of panel bond quality and durability of hem-fir cross-laminated timber (CLT)

To better use the second-growth wood resources in value-added applications, this work addressed the manufacturing aspects of cross-laminated timber (CLT) products from western hemlock (Tsuga heterophylla (Raf.) Sarg) and amabilis fir (Abies amabilis (Dougl.) Forbes) (or hem-fir) harvested from coastal British Columbia, Canada. Small CLT billets (nominal 610 mm?×?610 mm) were made to examine CLT bond quality and durability through block shear and delamination tests. Two types of adhesives, single-component polyurethane (PUR) and emulsion polymer isocyanate (EPI) and two critical applied pressure parameters (0.28 and 0.83 MPa) were adopted to manufacture hem-fir CLT. It was found that the adhesive type and applied pressure significantly affected wood failure percentage (WFP) and delamination of hem-fir CLT. When PUR adhesive was used, CLT made at 0.83 MPa pressure yielded significantly higher WFP and lower delamination than that made at 0.28 MPa pressure. The results demonstrated that despite the fact that hem-fir lumber is not particularly specified in the current North American CLT standard, it could be used for manufacturing CLT with the required panel bond quality.     

Prediction of strength and stiffness of concentrated compressive load applied to the narrow face of cross-laminated timber

European Journal of Wood and Wood Products - The behavior of the concentrated compressive load applied to the narrow face of cross-laminated timber (CLT) panels is an essential parameter in the...     

Experimental study on glued laminated timber beams with well-known knot morphology

Nowadays, the impact of knots on the failure behaviour of glued laminated timber (GLT) beams is considered by subjecting the single lamellas to a strength grading process, where, i.a., tracheid effect-based laser scanning is used to obtain information about knot properties. This approach single-handedly defines the beam’s final strength properties according to current standards. At the same time, advanced production processes of such beams would allow an easy tracking of a scanned board’s location, but, at this point, previously obtained detailed information is already disregarded. Therefore, the scanning data is used to virtually reconstruct knot geometries and group them into sections within GLT beams. For this study, a sample of 50 GLT beams of five different configuration types was produced and tested under static four-point-bending until failure. As for each assembled lamella the orientation and position within the corresponding GLT beam is known, several parameters derived from the reconstructed knots can be correlated to effective GLT properties. Furthermore, the crack patterns of the tested beams are manually recorded and used to obtain measures of cracks. A detailed analysis of the generated data and their statistical evaluation show that, in the future, dedicated mechanical models for such timber elements must be developed to realistically predict their strength properties. A potential approach, using fluctuating section-wise effective material properties, is proposed.     

Influence of wood moisture content on bending and shear stiffness of cross laminated timber panels

The bending and shear stiffness of cross-laminated timber (CLT) made from softwood depend on the moisture content of the panel. In principle, the stiffness properties drop with increasing moisture content within the hygroscopic range. However, swelling provokes closing of open gaps of the middle layers and leads to an apparent increase of stiffness due to internal friction. This increase in stiffness is only relevant for low deflections and can provoke misinterpretation of measuring results when deriving stiffness properties of CLT by means of dynamic methods such as modal analysis. Drying, on the other hand causes cracking within CLT, which manifests itself in a distinct reduction of the bending stiffness perpendicular to the grain direction of the face layers. Calculating bending stiffness of CLT perpendicular to the grain direction of the face layers by means of the compound theory not taking into account the face layers therefore is a common and correct procedure.     

木结构建筑墙体吸声性能研究发展

吸声性能是建筑重要的物理特性之一,墙体有良好的吸声性能是表征建筑室内舒适度的重要指标。本文通过对国内外木结构建筑墙体吸声性能的研究现状及其成果进行了归纳总结,并加以分析,指出目前墙体吸声性能研究方面存在的问题并提出建议,以期对木结构的墙体吸声性能评价提供参考,为木结构的基础应用研究工作提供借鉴。     

木结构建筑墙体隔声性能研究发展

中国传统木结构建筑历史悠久,文明世界。近年来随着国外轻型等现代木结构建筑进入我国市场,因其施工周期短,耐久性高等特点而受到国内的广泛关注。轻型木结构墙体隔声性能是该建筑的一项重要物理特性,为了制造出隔声性能好的墙体,本文通过对国内外轻型木结构建筑隔声性能的研究成果进行概述与分析,以期为促进我国木结构基础应用研究工作,提高我国木结构建筑行业的综合水平提供借鉴。     

由三维经编纺织品制成的三维纺织墙板

德国下莱茵应用技术大学的一篇学士论文提出了利用纺织品吸音材料改善房间传声效果的方案。该纺织品材料因兼具美观和吸音功效而引人注目。众所周知,来自言语、键盘、电话铃声等的噪声,不仅会降低室内人员的行为能力和注意力,而且可能对健康产生不良影响。其中,回声是一个特别需要解决的问题,尤其在多用途房间,如开放式办公室、会议室和餐厅。     

Shear strength of glued laminated timber made from European beech timber

This paper describes an investigation into the shear strength of glued laminated timber (GLT) made from European beech. Special consideration was paid to the possible strength influence of a frequently occurring discolouration of the timber, termed red heartwood, which is inherent to the species. The beech lamellae were visually graded according to German hardwood grading standard DIN?4074-5. Grade LS13, conforming to European hardwood strength class D40, was split into two sub-grades LS13? and LS13+. Additionally, modulus of elasticity (MOE) was determined by ultrasound pulse, longitudinal vibration and static tension tests. Sub-grade LS13+ showed a mean density and MOE of 690 kg/m³ and 14,800 N/mm², respectively. The GLT shear strength was evaluated by means of four-point bending tests on structural sized I-shaped beams with a depth of 0.6?m and a span to depth ratio of 5:1. The slightly inhomogeneous build-up of the cross-section conformed to glulam strength class GL42c. Two beam samples were investigated, each with seven specimens, where one grouping had no red heartwood and the other with a high red heartwood in the web laminations. Additionally block shear tests on bond line strength were performed with standardized small specimens according to EN?392. Neither the beam shear capacity tests nor the bond line block shear tests revealed an influence of the red heartwood discolouration on strength. The fifth-percentile value of shear strength of all beams was 3.5?N/mm². The results of the block shear tests indicate that the present requirements on minimum block shear strength are set too low in the European standard EN 386 with regard to beech GLT.     

An experimental and numerical study of shape stability in laminated timber columns

The study concerns the question of how the shape stability features of laminated columns of Norway spruce can be improved in terms of twist through optimal orientation of the individual laminates. Both experimental testing and numerical simulations were employed for evaluating twist stability. In all the columns studied, deformations were measured experimentally at different moisture content levels. A number of columns were also selected for numerical analysis in order to obtain a more thorough understanding of the twist behavior involved, their geometries and material properties of interest being determined. The experimental results showed the twist stability of the columns to be highly dependant upon the internal orientation of the individual laminates. It was also found that high quality columns in terms of shape stability could be manufactured, even when the center-core material has a strong twist tendency. The numerical simulations performed were in close agreement with the experimental results.     

木材复式弯曲成形方法分析

在分析以前木材复式弯曲成形方法的基础上,提出了木材数控复式弯曲方法,解决了小曲率和无固定旋转中心弯曲构件的弯曲成形问题,并分析了复式弯曲方式对木材密度等方面的影响,在利用钢带弯曲的基础上完善了木材弯曲工艺,为家具和门窗上应用的复杂曲线形状弯曲构件提供新的加工方法,对于木材加工企业新的木质弯曲件产品开发利用提供了新的思路和解决方案。     

Air emission from timber drying: high temperature drying and re-drying of CCA treated timber

The nature and mass flows of atmospheric emissions from an industrial kiln, drying radiata pine (Pinus radiata D.Don) timber at 140°C dry bulb and 90°C wet bulb, which was subsequently copper-chrome-arsenic (CCA) treated and redried at 90°C dry bulb and 60°C wet bulb, were assessed by measuring the concentration of chemical components in the kiln atmosphere at regular time intervals and determining air-flows and temperature differentials across the stack. The volatile organic compounds (VOCs) emitted were trapped and analyzed by GC-MS. The two major VOCs found during high temperature pre-drying and CCA re-drying were α-pinene and β-pinene, which made up 87% and 60% of the total discharge (2433 and 145 g/m³ wood), respectively. Most of the VOC fraction was released during the early stages of drying. The polar compounds were trapped in water. Total combined amount of methanol, ethanol, acetic acid and formic acid released over the two runs were 283, 281, 117, and 260 g/m³ wood, respectively. The aldehydes were trapped in 2,4-dinitrophenyl-hydrazine solution and the aldehyde derivatives analysed by HPLC. The total release of formaldehyde and acetaldehyde during the high temperature pre-drying run were 13 and 15 g/m³ wood and the CCA re-drying run were 14 and 4 g/m³ wood, respectively.     

Bending creep performance of modified timber

The present study is a supplement to Epmeier and Kliger (2005), which investigated the effect of three different modification methods (acetylation, modification with methylated melamine resin and heat treatment in vegetable oil) on four material properties (density, modulus of elasticity (MOE), creep deflection and relative creep) and their inter-relations. In this study, another modification method (furfurylation) and four additional material parameters (“relative stiffness”, i.e. MOE/density, moisture content, change in moisture content and anti-creep efficiency) and their correlations are included. In addition, the creep curves were analysed to assess the development of bending creep performance. The properties were assessed by experimental work on 132 specimens of Scots pine sapwood with dimensions of 45×70×1100 mm³. It was found that modification leads to significant changes in material properties. Furfurylation increases density and reduces creep deflection, relative creep and moisture content. Modified timber tends to deflect and creep significantly less than untreated timber. However, the extent of reduction in relative creep appears not to be related to the extent of reduction in creep deflection. Initial deflection and/or modulus of elasticity are suitable for predicting the creep deflection of untreated and modified timber.