Engineered Wood/Bamboo Laminated Composites for Outdoor Hydrophilic Platforms:Structural Design and Performance

Landscape designers increasingly prefer to use wood/bamboo-based composites for outdoor hydrophilic platforms owing to their natural surface texture,high performance,and sustainability to facilitate extensive interaction between people and water and enable the full range of ecological functions of water resources.In this study,four laminated composite(LC)structures were designed and manufactured using fluffed bamboo and wood veneers.Their surface textures,profile densities,water resistances,and mechanical properties were then evaluated.The type of fluffed veneer of the surface layer determined the texture of the LC surface.The specific structures of fluffed bamboo and wood veneer laminations were found to affect the LC profile density variability,water resistance,and mechanical properties owing to the differences in the strength and interfacial properties of bamboo and wood fibers.Finally,the water resistance and mechanical properties of all four LCs were found to be much higher than the highest level specified in GB/T 20241-2006 for“laminated veneer lumber”and GB/T 30364-2013 for“bamboo scrimber flooring”,indicating that they are promising materials for structures and flooring,particularly for outdoor hydrophilic platforms.

Effect of Extractive-Dissolving Treatment on the Characteristics of Laminated Wood Assembled from Oily Keruing Wood

Utilization of oily keruing wood for laminated wood product has not been optimal yet because of the appearance of extractive substance as oil on wood surface and hence disturbing the bonding process. A study has been conducted by manufacturing laminated wood from oily keruing wood （Dipterocarpus hasseltii） after extracting its oil by boiling the wood in the mixture of water and ethanol solution in several proportions. The assessment on the treated wood and the resulting laminated wood covered some characteristics i.e., wettability, static bending, bonding strength, ethanol-water solution can improve wetting properties significantly and delamination. The results show that boiling treatment in The extractive does not affect mechanical characteristics of the laminated wood. Increasing of water proportion in ethanol-water solution causes the decreasing of the bonding strength and increasing delamination value of the laminated wood. The result also shows that oily keruing wood after the treatment can be used as material for laminated wood.

The effect of number of joints on bending properties of laminated lumber made from poplar (Populus nigra)

Connection plays an important role in structural components and end jointing is one of the most common connections in structural applications. This study was designed to investigate some mechanical properties （MOE and MOR） of solid wood samples manufactured from poplar （Populus nigra）, joined together through end jointing. As well, we studied combinations of lumber manufactured from 10-mm veneer, using a polyvinyl acetate adhesive. The results show that non-jointed lumber （control samples） have better bending properties （MOE and MOR） than jointed specimens and lumber made from laminated layers. On the whole, side-by- side joints have a negative effect on the MOR and MOE of laminated products, which is more pronounced in the MOR. By increasing the number of joints, the properties of combination of three-ply, i.e., bending strength and modulus of elasticity, decreased.

Performance of Densified Wood Glulam as Building Bio-Material

In this research,some practical aspects of densified wood glulam were investigated.For this aim,poplar wood specimens were densified by hygro-thermo-mechanical technique.Glulam specimens were produced by finger joint technique and polyurethane glue was used as resin.Physical and mechanical properties of glulams were investigated according to ASTM D 143-09,ASTM D 905-03 and ISO 8375 standards.Based on obtained results,using this process(steam and pressurize compaction)resulted in improvement of physical and mechanical prop-erties of glulam specimens.Optical microscopic and scanning electron microscopic(SEM)pictures were proved structural changes on wood material during of applied technique.Generally,the increase of wood density and hygrothermal treatment has a positive role on the glulam properties especially its dimensional stability.This tech-nique showed a significant effect on water absorption;the steaming temperature and holding time significantly decreased water absorption but densification process increased this parameter.Also,delamination of specimens was decreased by hygrothermal treatment while densification showed negative effect on delamination.Moreover,modulus of rupture,modulus of elasticity,shear strength and compression strength parallel to grain were decreased by this technique but it is depend to treatment temperature and holding time.Higher temperature and holding time cause to higher decrease in the glulam mechanical strength.

Effects of Freeze-Thaw Cycles on Physical and Mechanical Properties of Glulam Exposed to Outdoor Environment

This paper presents an experimental investigation to identify suitable indices to assess durability of glulam when subjected to freeze-thaw cycles in an exposed enviroenment.In this study,two types of glulam specimens were tested for their performance when subjected to different levels of aging due to freezing and thawing.Effect of aging treatment on various parameters including thickness swelling rate,static bending strength,elastic modulus,shear strength,and peeling rate of adhesive layer were studied.Obtained results showed that freeze-thaw aging treatment did not affect the water-resistance of the specimens as measured by thickness swelling rate and had little effect on the dimensional stability of the material.However,the applied aging treatment weakened the bending resistance of the glulam specimens with more pronounced effects on on low-density wood.On the other hand,bond strength of high-density wood was relatively more affected due to the appliedfreeze-thaw cycles.For highdensity wood,it is suggested that the shear strength of the adhesive layer be taken as an important index to determine the durability of freeze-thaw cycles aging.For low-density wood,on the other hand,the static bending strength can be used as an index to determine the durability of glulam under freeze-thaw cycles aging.

Mechanical Analysis of Sisal Fibers to Use as a Reinforced Material in Wood Beams

Natural fibers have recently raised attention for presenting adequate mechanical characteristics for reinforcement of structural elements. The use of both natural fibers, in especial Sisal fibers, in wood laminated beams and also wood from reforestation, is in accordance with the current economic interest and ecological appeal. Specifically, the strengthening of wood laminated beams with Sisal fibers is more effective for structures that require an increase in their structural capacity without a significant increase in height of the cross section. Furthermore, it is recommended that this type of reinforcement is used in wood structural elements where the elastic modulus is at least equal to the Sisal fibers. The composition of Sisal fibers is basically of cellulose, lignin and hemicelluloses. In particular, the amount of cellulose and the angle that the micro-fibers with the axis of the fiber characterize the failure strength and the modulus of elasticity. The average mechanical characteristics of the Sisal fiber are： tensile strength 347 to 378 （MPa） and elastic modulus 15.2 （GPa） whereas these properties are lower for strips of Sisal fibers. In this context, this paper deals with the analysis and the viability of the use of Sisal fibers in wood structures as a reinforced material.

高温预处理对杨木正交胶合木剪力墙抗侧力性能的影响

[目的]研究往复荷载作用时国产速生杨木正交胶合木(CLT)剪力墙的抗侧力性能,阐明木材高温预处理和加速老化对剪力墙抗侧力性能的影响,为高温改性技术和国产速生木材在建筑结构中的高效利用提供参考。[方法]以木结构建筑常用的进口欧洲云杉规格材为对照,以相同强度等级的国产速生杨木为研究对象,选用180℃为预处理温度对杨木进行高温改性,制备5面全尺寸正交胶合木剪力墙,开展往复荷载作用时加速老化前后正交胶合木剪力墙的抗侧力性能试验。[结果]与相同层板强度等级的欧洲云杉正交胶合木剪力墙相比,往复荷载作用时未处理杨木正交胶合木剪力墙的极限承载力、弹性抗侧刚度、耗能能力分别降低5.8%、12.9%、8.0%;木材经高温预处理、墙体经加速老化或二者联合处理后,杨木正交胶合木剪力墙的抗侧力性能指标不同程度降低;与未处理杨木正交胶合木墙体相比,加速老化处理后,墙体的极限承载力、弹性抗侧刚度、耗能能力分别降低9.4%、9.7%、11.2%;木材经高温预处理后,经加速老化,墙体的极限承载力、弹性抗侧刚度、耗能能力变化较小,分别降低2.9%、2.4%、5.0%。[结论]往复荷载作用时,国产速生杨木正交胶合木剪力墙的抗侧力性能略低于相同层板强度等级的欧洲云杉正交胶合木剪力墙,水平力作用时二者具有相似破坏模式,均为抗拔连接件节点处钉子被剪断;木材经高温预处理、墙体经加速老化或二者联合处理后,杨木正交胶合木剪力墙的破坏模式均为底部墙角抗拔连接件处木材被拉断或劈裂破坏;木材高温预处理能够有效降低加速老化对剪力墙抗侧力性能的影响,具有相对较好的抗老化能力;建立正交胶合木剪力墙极限承载力计算模型,理论值与试验值误差小于10%。

竹集成材-SPF复合正交胶合木的研发及性能评估

运用相同工艺分别制备足尺垂直型竹集成材-SPF复合CLT(简称V-BWCLT)与足尺水平型竹集成材-SPF复合CLT(简称H-BWCLT)。依据国内外相关标准对两种BWCLT的胶层剪切强度、胶合耐久性、抗弯弹性模量(MOE)、抗弯强度(MOR)和层间剪切强度进行了测试,并用三维非接触式应变测量系统(DIC)对抗弯和层间抗剪试验过程中的受力变形情况进行记录。结果表明:在相同制备工艺条件下,两种BWCLT平均胶层剪切强度接近,浸渍剥离率均可达到相关标准要求。V-BWCLT的平均MOE与MOR分别为7941 MPa和56.7 MPa,而H-BWCLT的平均MOE与MOR分别为10144 MPa和54.0 MPa,H-BWCLT比V-BWCLT具有更高的弯曲刚度,但两者MOR较为接近。对比SPF-CLT,两种BWCLT的抗弯强重比均有显著提高,上述研究和分析为新型竹木复合CLT的实际工程应用提供了设计参考与理论依据。

LVL结构调控及应用研究进展

在我国木材资源紧缺、人工林材质较差、而竹材资源较为丰富的背景下,单板层积材(Laminated Veneer Lumber,LVL)作为一种生物质工程材料,具备高效利用现有资源的优势,并且以其出色的力学性能可实现标准化、系列化生产,展现出广阔的应用前景。本文结合我国人造板产业的发展现况,概述了LVL的起源和发展,着重从复合材料力学性能的角度分析了LVL的结构特点,对单板分等和LVL组坯特点进行了介绍。同时,综述了酚醛树脂浸渍和纤维材料复合两种LVL增强方式。最后,对比讨论了国内外LVL的评价标准,并针对我国木结构建筑产业的发展现状和LVL应用过程中存在的问题,提出了若干建议。

定向重组展平竹集成材生产工艺

以竹展平板为基本单元制造定向重组竹集成材的工艺方法。将竹展平板涂布间苯二酚树脂胶黏剂,涂胶量为200-300 g/m 2,按照竹青面对竹青面、竹黄面对竹黄面的方式进行组坯,热压加工制成展平竹层积材,再采用指接的方式进行接长,获得性能优异的定向重组展平竹集成材,产品的尺寸规格一般为长1000-3500 mm,宽50-300 mm,厚60-150 mm。指接时相邻层板的指接接口需错开组坯,在常温下冷压4-5 h,冷压压力为1.0-1.5 MPa,后固化养生。

浸渍纸层压实木复合地板耐水工艺研究

采用单因子试验方法,分步探讨了薄型高密度纤维板(HDF)的吸水厚度膨胀率、面板覆贴工艺、胶合板基材结构、面板与基材热压工艺及封边工艺对浸渍纸层压实木复合地板耐水性能的影响。研究结果表明,通过优化薄型HDF的吸水厚度膨胀率、面板覆贴工艺、改进胶合板基材表层结构和面板与基材热压参数、筛选合适的封边涂饰工艺,可以显著提升浸渍纸层压实木复合地板的耐水性能,使地板的吸水厚度膨胀率降低至6%以下,有效减少地板在潮湿环境下出现鼓包的问题。

现代木结构在高层观景塔中的设计研究——以第七届全国高等学校木结构设计竞赛获奖作品为例

高层建筑与构筑物是现代木结构自21世纪以来新的应用领域,在科技、生态与人文精神并重的时代背景下,对此进行研究具有十分重要的现实意义。因此,文章从第七届全国高等学校木结构设计邀请赛获奖作品——“鱼·跃”着手,通过研究现代木结构在高层观景塔的应用,对正交胶合木(CLT)筒中筒结构体系在其中的设计全过程进行解析,初步探索了现代木结构在高层构筑物建筑设计中带来的空间和造型的新变化。

CLT发展现状与展望

在“双碳”和生态文明背景下,木质建筑材料作为一类环保型建材,具有绿色可再生、低碳、可持续发展的优势,是实现我国“双碳”目标的重要助力。本文介绍了一种典型的木结构建筑材料——正交胶合木的特点和发展现状,讨论了目前存在的问题,并对正交胶合木的未来发展进行了展望。

一起换流变压器试验故障诊断和分析

针对一起换流变压器试验故障,结合多种试验排查进行变压器故障分析与定位,通过内部检查确定了内部放电故障的位置为阀3.2引线出线层压木螺杆。根据试验现象、排查情况以及对螺杆的材质分析,确认螺杆内部异物是导致故障的根本原因。

胶合木结构的发展、应用及展望

回顾了木结构发展的历史,阐述了当今社会所面临的巨大环保压力及对绿色建筑、绿色施工技术的迫切需求。木材是一种可再生资源,而胶合木结构由于具有绿色高性能特点而得到广泛应用。胶合木结构的应用领域涵盖大型公共建筑及桥梁领域,其不仅在发达国家是一种常见的结构形式,近年来在中国也相继出现了一些大型工程实例;同时,国内的设计和加工水平也在快速提高。最后,指出了胶合木结构在中国广阔的应用前景。

胶合木设计制作与质量控制

胶合木是一种强质比高、美观、可降解的工程复合材,且被广泛应用于桥梁、建筑等工程领域。而落叶松在我国分布面广,蓄产量丰富且强度高,适合于木材的工业化加工利用。针对国内落叶松结构用胶合木制造及利用现状,结合工厂的制造试验情况,本研究从层板的选择、指接工艺、胶合工艺、组坯工艺、质量检验等方面介绍了胶合木生产工艺及其质量控制,简述了整个制造流程中的工艺参数和要求,为胶合木的工业化生产提供了依据。最后提出了胶合木制造在我国推广存在的问题及建议。

结构用胶合木性能若干影响因素

以落叶松、杉木为研究对象,研究了影响胶合木强度性能的齿顶宽、指接方向、指接单元等级、指接头、层积施胶量和压力等若干重要因素.试验选取744块落叶松锯材、2 516块杉木锯材,采用2种结构用胶、5种齿长、2种指接单元等级、6种层积涂胶量、5种层积压力等作为指标变量,测试了指接材抗弯、抗拉强度和层积材的胶合性能.结果表明:指接材的强度不总是随齿长的增大而提高,其胶合后的强度主要受同截面内齿顶宽累积量所决定;垂直指接材的平向抗弯、顺纹抗拉强度不低于水平指接材,指接方向应由产品的承载方向确定;指接工艺不会降低大尺寸指接材的强度设计指标;层积施胶量和压力应与使用设备的实际产出相协调.

木结构建筑构件耐火性能试验研究

对木结构建筑构件进行一系列标准耐火试验,研究木结构建筑构件的耐火性能、破坏模式以及验证构件的耐火极限值。所测试的构件包括木构架墙体、木构架楼板与天花板吊顶,以及胶合木梁和木柱。研究结果表明,木结构建筑构件具有较好的耐火性能,能达到所要求的耐火极限。木构架墙体和楼板的耐火性能与石膏板的厚度和层数有关。截面尺寸较大的胶合木梁和木柱,因木材炭化速度慢,能保持1.0h以上的承载功能。试验结果为合理确定木结构的耐火性能提供了相关知识和数据。

结构用集成材落叶松层板指接工艺

【目的】研究指榫对接所需端向压力（指接压力）与榫型参数和嵌合度的关系,探讨榫型、嵌合度、指接压力对指榫胶接力学性能的影响规律,以获得较佳的指榫胶接工艺。【方法】采用5种不同型号的指榫铣刀,分别将兴安落叶松层板的一端加工成具有不同嵌合度的垂直型指榫,将两指榫对接并在力学试验机上加压至齿顶和槽底紧密接触,读取其压力值（各种榫型和嵌合度的试件各10对）,研究指榫对接所需端向压力（指接压力）与榫型参数和嵌合度的关系;对指榫进行手工涂胶（双面施胶,施胶量为180 g·m-2）,根据测试得到的指接压力对各种榫型和嵌合度的开榫木板进行对接加压胶合,试件放置24 h后按照GB/T 26899—2011《结构用集成材》中5.3.3抗弯试验方法 C和5.4抗拉强度试验测试指接部位的弹性模量、静曲强度和抗拉强度（各种榫型和嵌合度的试件各10个,一半用于测试静曲强度和弹性模量,另一半用于测试抗拉强度）,探讨榫型、嵌合度、指接压力对指榫胶接力学性能的影响规律,获得较佳的指榫胶接工艺。【结果】指接压力受嵌合度的影响十分显著,随嵌合度的增大而显著增大,但各榫型下嵌合度与指接压力的关系不尽相同,同时受榫齿长、榫齿角、齿距和槽底宽等影响;各种榫型下嵌合度对指接力学性能（抗拉强度、静曲强度和弹性模量）的影响有很大差别,但仔细比较各榫型嵌合度下的指接压力与抗拉强度、静曲强度和弹性模量的关系可以发现,当指接压力在8-15 MPa时各榫型都有较大的力学强度,且该值随榫齿长度的增加而基本上呈比例地增大。【结论】1）指榫胶接所需指接压力随嵌合度的增大而显著增大,且榫齿角和槽底宽度较小时更加显著;指接压力随榫齿长度的增加而增大;指接压力与嵌合率基本上呈正比,其斜率随榫齿角的增大而减小。2）各榫型的指接强度随榫齿长度的增加而增大;指接压力过小或过大其指接强度均下降,指接压力在8-15 MPa时各榫型都呈现较大的力学强度。3）短齿榫型产生最大指接强度的嵌合度比长齿榫型的大,榫长9和27 mm的榫型产生最大指接强度的嵌合度分别约为0.2和0.1 mm。4）从安全和经济2方面综合考虑,兴安落叶松层板的较佳指接工艺为：榫齿角9.8°、榫齿长15-20 mm、齿槽底宽0.8-1.2 mm、指接压力10-15 MPa、嵌合度0.12-0.20 mm（榫齿较长时嵌合度取较小值）。

节子对木材胶合性能的影响

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的影响。