Experimental Investigation on the Strength and Ductility Performance of Steel-Timber-Steel Joints with Screw and Steel-Tube Fasteners

This article presents experimental results of steel-timber-steel(STS)joints loaded parallel to grain.Eight groups of specimens were designed,and tensile tests were performed.The fastener types and fastener numbers were considered to evaluate the tensile strengths and ductility performances of the STS joints.The screws with 6 mm diameter and the innovative steel-tubes with 18 mm diameter were adopted as connecting fasteners.The experimental results were discussed in terms of yielding and ultimate strengths,slip stiffness,and ductility factors.The ductility classification and failure mechanisms of each group of specimens were analyzed.It was demonstrated that the STS joint with large diameter steel-tubes showed acceptable ductility,which was close to the ductility of the STS joint with small diameter screws,thanks to the hollow structure of the steel-tube.The theoretical strengths of various failure modes for the joints with small diameter screws or large diameter steel-tubes were calculated and compared with the experimental results.The ductile performance of the STS joint was discussed by comparing the theoretical strengths of various failure modes.The effective number of the STS joint with multifasteners was also analyzed by considering the failure mechanisms in aspects of tensile strength and slip stiffness.

An Experimental Study of Composite Columns Filled with Eucalyptus nitens Timber under Axial Compression

Eucalyptus nitens(E.nitens)has been much used for producing paper but also shows promise for structural applications.In this study,static compressive tests were undertaken to examine its suitability to be used in an innovative composite column.The composite column was comprised of a rectangular steel tube with E.nitens timber infill.The nonlinear compressive behaviour of the composite column filled with E.nitens wood for both dry and wet conditions was examined.The same tests on rectangular steel tubes and bare dry and wet E.nitens samples were also undertaken as a comparison.For samples with different conditions,the ultimate capacity was evaluated and the effect of each condition on the compressive behaviour of the composite column was clarified.The steel tubes showed greater ductile behaviour,and more ductility was found in the wet samples.The steel tubes with E.nitens timber infill samples exhibited a greater linear elastic range connected with higher maximum loads,while the bare timber samples could support only lower maximum loads.The results from this research were promising for the use of rectangular steel tubes with E.nitens timber infill in structural applications.

Three-dimensional inversion of knot defects recognition in timber cutting

The comprehensive utilization of wood is the main goal of log cutting,but knot defects increase the diffi-culty of rationally optimizing cutting.Due to the lack of real shape data of knot defects in logs,it is diffi cult for detection methods to establish a correlation between signal and defect morphology.An image-processing method is proposed for knot inversion based on distance regularized level set segmentation(DRLSE)and spatial vertex clustering,and with the inversion of the defects existing relative board position in the log,an inversion model of the knot defect is established.First,the defect edges of the top and bottom images of the boards are extracted by DRLSE and ellipse fi tting,and the major axes of the ellipses made coplanar by angle correction;second,the coordinate points of the top and bottom ellipse edges are extracted to form a spatial straight line;third,to solve the intersection dispersion of spatial straight lines and the major axis plane,K-medoids clustering is used to locate the vertex.Finally,with the vertex and the large ellipse,a 3D cone model is constructed which can be used to invert the shape of knots in the board.The experiment was conducted on ten defective larch boards,and the experimental results showed that this method can accurately invert the shapes of defects in solid wood boards with the advantages of low cost and easy operation.

In Situ Generation of Copper Nanoparticles in Heat-Treated Copper-Containing Masson’s Pine as a Preservative Process for Sawn Timber

Heat-treated wood has good dimensional stability,durability,and color,but its susceptibility to fungal growth affects its commercial value.In this study,lumber harvested from mature Masson’s pine(Pinus massoniana Lamb.)was vacuum impregnated with a basic copper salt solution(copper hydroxide,diethanolamine,and polyethylene glycol 200)prior to heat-treatment at 220℃ for 3 h.Antifungal properties,surface chemistry,crystal structure and sugar contents were tested,compared with heat treatment alone.The results showed that the samples treated by heating without copper salt treatment showed poor suppression of fungal growth,the copperimpregnated heat-treated wood suppressed(100%)the growth of Botryodiplodia theobromae Pat.,Aspergillus niger V.Tiegh.,Penicillium citrinum Thom,and Trichoderma viride Pers.The combined results of X-ray photoelectron spectroscopy,X-ray diffraction and sugars analysis suggested that fungal inhibition by the heat-treated copper-bearing Masson’s pine was mainly due to the reduction of the metal salt by PEG200 at high temperature to generate copper nanoparticles.In addition,the reduced sugar content of the treated timber,and hence the nutrient substrate for spoilage microbes,reduced in the presence of the metal salts at high-temperature.This study has demonstrated an effective method of increasing low-grade wood’s utility and commercial value.

Verification of Depth Adjustment Factor in Eurocode 5 for Tropical Hardwood Timbers

The depth adjustment factor for bending strength stated in Eurocode 5(EC5)is only applicable to timbers having a characteristic density below 700 kg/m^(3).However,most Malaysian timbers are hardwood,some with a characteristic density reaching above 700 kg/m^(3).Therefore,the objective of this study was to examine whether the depth adjustment factor stipulated in EC5 is valid for Malaysian hardwood timbers.Six timber species were selected for this study,namely Kapur(Dryobalanops C.F.Gaertn.),Kempas(Koompassia Maingay ex Benth.),Keruing(Dipterocarpus C.F.Gaertn.),Light red meranti(Shorea Roxb.ex C.F.Gaertn.),Geronggang(Cratoxylum Blume)and Balau(Shorea Roxb.ex C.F.Gaertn.).The determination of bending strength and characteristic density was conducted according to BS EN 408:2010 and BS EN 384:2016,respectively.A graph for mean bending strength vs.(150/h)was plotted for each timber species.The power function was selected to analyze the relationship between the two variables.The power of the regression equations varied depending on the characteristic density of the timber species.For species with a characteristic density below 700 kg/m^(3),such as Kapur,Keruing,and Light red meranti,the power was between 0.16 to 0.17.In contrast,for species having a characteristic density above 700 kg/m^(3),namely Kempas and Balau,the power was higher at 0.23 and 0.24,respectively.Geronggang was an exception to this pattern.These values are close to the depth adjustment factor given in EC5,which is 0.2.Based on the results,it can be suggested that the adjustment factor of 0.2 is also applicable to Malaysian hardwood timbers with a characteristic density above 700 kg/m^(3).

Determination of the Properties of Some Selected Timber Species for Structural Application

One of the alternative sustainable and green construction materials to concrete is timber. Timber is of numerous varieties, and this acts as a barrier to the extent of its usage, especially in structural application. Despite many researches on wood’s mechanical and physical properties, only a few are geared toward the structural application of wood. The present work investigated the mechanical properties of five timber species;Gmelina arborea, Tectona grandis (Teak), Terminalia superba (Afara), Ayin (Anogeissus leiocarpus), and Acacia (Robinia pseudoacacia), to determine their suitability for constructing long-span roof trusses. These are available in the South Western part of Nigeria. Their mechanical properties;bending strength, compressive strength, shear strength, tensile strength, Modulus of Elasticity (MOE), Modulus of Rupture (MOR), and density, were determined in the laboratory. The results obtained showed that all the timber types, except Terminalia superba (Afara), have higher values of mechanical properties than the values that are obtainable for classes of strength D30 to class D70 in the British Code of Practice. It means these species are of higher quality than the stipulated strength classes in the British code. The results also show that the order of relevance of the species for structural design (or work) is Acacia (Robinia pseudoacacia), Ayin (Anogeissus leiocarpus), Gmelina Arborea, and Tectona grandis (Teak). Terminalia superba (Afara) is not recommended for structural works.

古建筑木构件开裂机制、评估与加固研究进展

开裂作为古建筑木构件最常见的残损类型之一,影响木构件的长期服役性能,是古建筑稳定性与安全性评估的重要考查内容。本文从古建筑木构件开裂情况、原因、影响,评估方法及修复加固等方面,系统梳理古建筑木构件开裂残损相关研究成果。分析发现我国古建筑木构件开裂的主要原因为木材干缩与受力破坏,主要类型为纵向开裂,开裂可降低木构件力学性能,也可为其他不利因素作用于木构件提供条件。目前主要通过实际试验与数值模拟评估开裂对木构件性能的影响,利用金属材料、纤维增强复合材料(fiber reinforced polymer,FRP)与高分子树脂材料对开裂木构件进行修复加固。然而,由于古建筑的特殊性与木材变异性,仍需进一步探索木构件的不同尺度开裂机制,开发适用于古建筑开裂木构件的检测、评估与加固方法,建立科学系统性的古建筑保护体系。

Novel Proposal of Bio-based Sewing Timber Joint:Learning from Diatoms

The twenty-first century is one of the most complex in the history of humanity,mainly due to the ecological crisis it is going through.The construction sector generates about 40%of CO2 emissions into the environment;the foregoing should motivate this sector to seek new alternatives to develop new building practices.Taking these current needs into account,this document classifies and presents a multidisciplinary solution that integrates biology,engineering and architecture to develop a new and innovative lightweight timber structure;it divides with a main structure made of timber and an innovative joint system made of bio-polymers connecting all the panels.Through the study of diatoms,it was able to analyze the bio-morphology of the structure,joints and in particular the geometry since they were the inspiration for the design of this structure that presents an innovative and novel design of structural optimization.Through parametric design and digital fabrication,it was able to create a complex geometry that obtains excellent structural behavior.This research discusses and explores how materials,geometry led to the optimization of a structure and how new structures can arise,thanks to biology new solutions can be obtained that are completely sustainable,being a clear example of how to combat the effects of the climate change and in a precise way it highlights the advantages of the bio-design in the architectural design.

出踩与面宽方向柱头科斗栱抗震性能对比试验及数值分析

为研究加载方向对斗栱抗震性能的影响,文章基于地震作用的随机性和斗栱出踩与面宽方向的构造差异,对2个足尺柱头科斗栱分别沿出踩和面宽方向进行拟静力试验,得到斗栱的破坏模式、承载力、刚度与强度退化、耗能和变形能力。结果表明:斗栱在出踩和面宽方向分别加载时,大斗均相对平板枋滑移,馒头榫挤压剪断。出踩方向受力时单昂与桃尖梁相对滑移,面宽方向受力时整体明显转动。相比面宽方向受力的斗栱,出踩方向受力的斗栱具有更高的承载力、初始刚度和耗能能力,而变形能力较差。文章开展柱头科斗栱的数值分析,模拟结果与试验结果吻合较好,研究出踩和面宽不同加载方向、轴压荷载、木构件之间摩擦系数和木材弹性模量对其抗震性能的影响。结果表明:面宽方向是柱头科斗栱的最不利受力方向,其正负向承载力比出踩方向分别低19.21%和17.03%;轴压荷载和木构件之间摩擦系数越大,斗栱承载力越大,而木材顺纹弹性模量和横纹径向弹性模量对斗栱的初始刚度和承载力影响较小。

高立地指数下杉木生长量及材种结构的立地及密度效应

[目的]探讨立地质量和林分密度对杉木人工林生长量及材种结构的影响,为杉木大径材培育提供理论依据。[方法]以林龄28~36年生的杉木人工林为研究对象,按上、中、下不同坡位以及不同坡向设置63块标准样地,调查林分生长量及林分基本情况,通过相关性分析和回归拟合分析进行数据处理和分析。[结果]当林分密度相近时,立地指数越高,培育相同年限所获得的单株材积、蓄积量和大径材出材率越高;同一立地条件下,在一定的密度范围内林分树高、胸径、单株材积和大径材出材率随密度增加而减小,蓄积量随密度增加而增大;立地指数相同时,密度对胸径生长分化的影响大于树高,立地指数不同时林分密度对树高和胸径生长分化的影响程度也不同。[结论]在立地指数达22及以上的立地条件下培育杉木大径材,可通过3次间伐进行密度控制,林分最终保留密度宜为650~1000株·hm^(−2)。

增设角部阻尼器箍头榫木节点的抗震性能

为了给广府木结构的修复提供理论依据,采用菠萝格木材设计制作了5个箍头榫节点试件。考虑到榫卯构造尺寸的影响,首先进行了未加固无损节点的拟静力试验。然后,采用对原有外观影响较小的雀替型阻尼器对上述节点损坏试件进行加固,以尽可能保留建筑的原始风貌。最后,对加固节点进行拟静力试验,以研究节点的抗震性能变化以及阻尼器的加固效果。结果表明:采用阻尼器加固后的节点试件在加载至破坏时,榫卯处压痕明显,梁外榫外侧劈裂、脱榫现象明显,阻尼器脚部的橡胶与钢板有一定的脱离现象;对节点增设阻尼器能够弥补节点初期损伤导致的受力性能下降,为残损榫卯节点提供较好的后期刚度,提高节点的承载能力和耗能能力;与未加固试件相比,增设阻尼器后,试件的后期刚度、极限承载力、总滞回耗能均有所增加,分别提高18%、19%、20%以上。文中还在已有简化力学模型的基础上,结合OpenSees,提出了一种应用于箍头榫木结构的宏观模型建模方法。采用该方法得到的节点滞回曲线与试验结果吻合良好,可以有效模拟阻尼器加固的箍头榫木节点的滞回耗能特性。

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%。

某高层木混合结构抗震分析与性能测试

木混凝土混合结构在多高层木结构建筑中应用广泛,但此类结构的整体抗震性能以及楼盖动力特性有待研究。本文以江苏省康复医院医技楼为例,应用反应谱法与弹性时程分析法分别开展木混合结构的抗震性能分析,并对局部正交胶合木(CLT)楼盖通过原位测试,开展力学性能、动力特性以及人致振动研究。结果表明:结构抗震指标符合规范要求;CLT楼盖荷载位移关系呈双折线,挠度、应力理论计算时,建议板两端按简支考虑;CLT楼盖竖向自振频率均值约15.49 Hz,满足建筑楼盖限值要求,但在单人快走、单人小跑以及多人随机人致振动工况下,楼盖的峰值加速度偏大,应考虑增加现浇建筑面层,改善纯CLT楼盖舒适度不足的问题。可见,木混合结构通过设计可满足抗震要求,但轻质楼盖应注意舒适度构造措施。

苹果等6种经济林不同时期果实BVOCs成分分析

为探究常见经济林树种不同时期果实在自然状态下释放植物源挥发性有机物(BVOCs)组成成分差异,并分析其香气类型,选取苹果、桃、李、梨、山楂和枣6种经济林树种为研究对象,采用动态顶空采集法收集释放的BVOCs,结合自动热脱附-气相色谱/质谱联用技术进行BVOCs分析。结果表明,6种果实膨大期和成熟期均检测出12类BVOCs,组分总数量前者(305)大于后者(275),2个时期果实释放烷烃类、烯烃类、芳香烃类、酯类和醛类BVOCs占比最大;不同时期6种果实有10种共有BVOCs为2,2,4,6,6-五甲基庚烷、正十九烷、a-柏木烯、正戊醛、庚醛、辛醛、天然壬醛、癸醛、苯乙酮和庚胺醇;苹果、桃、李和梨随着果实生长发育BVOCs成分数量减少;不同时期6种果实香韵涵盖香型有差异,并随果实生长发育,青草香、果香、檀木香、醛香和柑橘香占比明显增加。表明不同时期6种经济林植物果实释放BVOCs组成成分和相对含量差异明显,在果实成熟期,主要香气BVOCs成分相对含量较高,是果实香精开发的最佳时期。

木材老化对古建筑木梁抗弯性能的影响分析

为研究木材老化对古建筑木梁抗弯性能的影响,分析了木材的老化机理,采用等效截面法并结合国内木梁老化深度经验公式,提出了老化木梁抗弯承载力退化模型,并对某古建筑的木梁进行了承载力退化评估。对未老化与老化木梁进行了单调加载数值模拟,并通过试验验证了模型的合理性;在此基础上,进一步分析了老化均匀度与老化深度对木梁抗弯性能的影响。结合《木结构设计标准》(GB 50005—2017)中受弯构件的承载力计算公式,提出了考虑老化影响的木梁抗弯承载力折减系数计算公式。结果表明:老化对木梁抗弯承载力的影响与老化均匀度呈线性相关,与老化深度呈一元二次多项式关系。老化深度越深且老化均匀度越大,木梁承载力越低。

密度控制和追肥对杉木近熟林改培大径材林的效应分析

为构建南岭山区杉木大径材高效培育技术体系,提高大径材产量与质量,将现有林分改培为大径材林是切实可行的途径。本研究以杉木近熟林为对象,采用正交设计进行疏伐与配方施肥改培试验研究。结果表明:在杉木树高-胸径生长模型研究中,幂函数模型有较好的拟合效果,是最理想的树高-胸径生长模型选择;杉木近熟林改培后第3年,处理前、后各材种变化总体呈现出小、中径材逐步减少,大径材逐步增加的趋势,大径材增量最大的是处理2。影响处理前后树高、胸径和单株材积增量的因子效应大小依次为追施尿素、追施过磷酸钙、保留密度,影响大径材出材量及出材率增量的试验因子有差异,增加大径材出材量和提高大径材出材率的最优组合一致。试验结果表明,当密度处于中等或中等偏高水平、尿素和过磷酸钙均处于中等水平时,最利于提高大径材出材量和出材率。

歪闪古建木构架整体纠偏方法与数值模拟

由于环境与人为等因素的长期影响,木结构古建筑普遍存在倾斜歪闪等损伤问题,严重影响了古木建筑的安全,亟需纠偏修复。研究尝试提出一种整体纠偏方法,构建木构架结构纠偏理论计算模型,通过数值模拟方法分析了纠偏过程的可行性,并以某多层木结构建筑的纠偏复位过程为例加以验证。结果表明:纠偏后结构楼层偏移明显减小,纠偏过程中主要结构构件仍然处于弹性范围内,纠偏效果良好,可为同类古建木构架纠偏理论研究提供借鉴。

明清木结构古建筑底层数据标准化研究

现有IFC标准体系中,存在无法表达中国古建筑中特有的形制、结构、属性、艺术等特性的问题.基于UML,构建了斗栱、榫卯等古建筑结构的语义关系图,根据IFC四层架构体系,采用实体扩展和属性集扩展的方式,分层扩展了相应的构件实体、关系实体和属性集等,并以EXPRESS语言对扩展内容进行描述.通过使用IfcOpenShell工具包解析、VScode编辑的模型文件;并以Solibri和Blender为验证平台,检验IFC文件的可视化、可读性和实体与属性集信息的内容.根据验证结果,文中提出的古建筑领域的扩展符合IFC的扩展体系方法,对实现古建筑的结构和艺术等特性在信息模型中的交互和共享具有重要意义,可为古建筑工程勘察、修缮和运维的信息化保护提供强有力的支撑.

层板销合木的界面滑移与木梁受弯性能

层板销合木(简称销合木)是一种由规格材通过销组合而成的新型结构用木材,与胶合木相比具有加工快捷、成本低且更加绿色环保等优点。为研究销合木梁的弯曲性能,设计了8组木梁的四点弯试验,试验参数包括销的种类(木销和竹销)、销间距(70、100和140 mm)和层板的数量(3、4和6层)。此外,为揭示层积材界面销连接抗剪性能对销合木梁受弯性能的贡献,开展了木销和竹销连接销合木推出试验研究。研究结果表明:与木销连接相比,竹销连接的抗滑移刚度更高且延性更好;销合木梁的受弯性能介于无销接叠合木梁和胶合木梁之间,其组合效率为0.11~0.15;随层板数量的增加,梁截面的增高使销合木梁的抗弯性能显著上升;减小销间距对销合木梁的抗弯承载力与刚度均有一定的提升作用。采用欧洲规范5中的γ法预测销合木梁的抗弯刚度时结果偏大,因此认为对销合木梁的抗弯刚度进行计算时须对销连接的滑移刚度进行折减。

正交胶合木新型抗剪及抗拉连接耗能特性试验

连接节点是保证木结构抗震性能的重要因素,节点的耗能能力是衡量其是否适用于抗震区的重要指标。提出了适用于正交胶合木(cross laminated timber,CLT)结构的新型耗能抗剪连接节点和新型耗能抗拉连接节点,为研究该类连接节点的破坏模式及力学性能,开展了15组低周往复加载试验。试验结果表明,新型耗能连接节点试件延性系数(D)均大于9.0,满足欧洲规范Eurocode 8中对高延性节点D>6的要求,属于高延性范围;新型耗能连接节点工作阶段强度退化系数均低于20%,具备工程适用性;新型耗能连接节点工作阶段等效黏滞阻尼系数为12%~22%,普通商用连接节点等效黏滞阻尼系数为2.5%~15.8%,两类新型耗能连接节点具有较好的耗能能力。