Evaluation of Mechanical Properties of Cross-Laminated Timber with Different Lay-ups Using Japanese Larch

Japanese larch is one of the main plantation tree species in China.A lack of engineered wood products made by Japanese larch,however,limits its application in wood stnuctures.In this study,based on optimum process parameters,such as pressure(12 MPa),adhesive spread rate(200 g/m^(2))and adhesive(one-component polyurethane),the mechanical properties of Japanese larch-made cross-laminated timber(CLT)with different lay-ups were evaluated by means of the static method.Results of this study showed that variations in lay-ups significantly affected the mechanical properties of CLT.The strength and modulus of bending and parallel compression for CLT increased with the thickness of lumber,while that of bending,parallel compression and rolling shear all decreased with the number of layers.Thickness,layup orientation and the number of layers all had an impact on the strength of CLT.Failure modes obtained from numerical simulation were basically the same as those of experimental tests.There was also strong alignment between theoretical value and test value for effective bending stifness and shear stifness.Thus,the shear analogy method can be used to predict the mechanical properties of CLT effectively.This study proved great potential in using Japanese larch wood for manufacturing CLT due to its good mechanical properties.

Comparative Study on Various Strength Parameters of Structural Elements Made from Cross-Laminated Timber

Cross laminated timber(CLT)is an innovative and environment friendly engineered timber product with superior structural performance.CLT offers strong resistance against both in-plane and out-of-plane loading.Hence,it is widely used as floors,roofs or wall elements.Considerable experimental research on CLT under various loading conditions has been done in the recent past.This article presents a comprehensive review of various design methods to determine basic mechanical properties such as tension,compression and rolling shear strength of CLT with primary focus on Norway spruce.All relevant experimental data available from existing literature were collated and consequently been used to evaluate the performance of various methods to design CLT structures.The comparison revealed that different methods show considerable variance in predicting the capacity of CLT panels due to the variation in timber species,which affects the corresponding mechanical properties of the lamella.In addition to species,rolling shear properties can also vary considerably depending on the type of experimental technique used for testing.A predictive model has also been proposed to correlate rolling shear strength obtained from shear analogy method to that obtained using planar shear.

Analysis of Crack Expansion and Morphology of Cross-Laminated Timber Planar Shear Test

To describe the dynamic cracking process of the CLT vertical layer,the correlation between a load-displacement curve,specimen cracking,and planar shear failure mechanism of the CLT were explored.A three-point bending test and an improved planar shear test are used to evaluate the shear performance of the CLT.In this study,the load-displacement curve is recorded,the experimental part is synchronized with the video,the dynamic process of cracking of the vertical layer is observed and analyzed throughout the test.From the load-displacement curve,the image characteristics of the initial cracking and the sudden increase of the cracking of the specimen are summar-ized.The description results of the whole dynamic process of the CLT vertical layer cracking are analyzed by pla-nar shear strength value,cracking phenomenon,and azimuth angle of cracking surface.The main conclusions show that the three-point bending test and the improved plain shear test can be used to test the plain shear strength of the CLT,with a difference of only 5.7%.The original crack and the new crack expansion account for 18.9%and 81.1%of the main cracking surface,respectively.And the vertical layer of the CLT specimen under three-point bending has three cracking morphologies,such as radial shake,ring shake,neither along with the radial shake nor along with the ring shake.The azimuth angle of the cracking surface of the CLT vertical layer under planar shear is quite consistent with the first main plane azimuth of the vertical layer of the CLT specimens under the three-point bending test and the shearing test.The shape in the cracking direction of the left half-span or the right half-span of the vertical layer of the specimen is similar to the Chinese character eight.

Understanding the Impacts of Plant Capacities and Uncertainties on the Techno- Economic Analysis of Cross-Laminated Timber Production in the Southern U.S.

Understanding the economic feasibility of cross-laminated timber(CLT),an emerging and sustainable alternative to concrete and steel,is critical for the rapid expansion of the mass timber industry.However,previous studies on economic performance of CLT have not fully considered the variations in the feedstock,plant capacities,manu-facturing parameters,and capital and operating costs.This study fills this gap by developing a techno-economic analysis of producing CLT panels in the Southern United States.The effects of those variations on minimum sell-ing price(MSP)of CLT panels are explored by Monte Carlo simulation.The results show that,across all the plant capacities from 30,000 to 150,000 m^(3)/year,the MSP ranges from$345 to$609/m^(3) with a±6%–9%range caused by the variations in feedstocks,key manufacturing parameters,capital and operating cost.The MSP decreases sig-nificantly along the increasing capacities.A sensitivity analysis exhibits that the lumber price,lumber preparing loss,plant capacity,and the installed costs of layering and gluing,finishing,and miscellaneous,are the top driving factors to CLT MSP.Supported by Geographic Information System,this study also studies the transportation cost of delivering CLT to customers under three CLT demanding levels(1%,5%,15%).The results show that the trans-portation cost is 1%–8%of the MSP.Lower demanding level or higher plant capacity can increase the transporta-tion cost due to average longer delivering distance.When considering the delivered cost that sums MSP and transportation cost,larger plant capacity does not necessarily generate lower delivered cost.

Bending,Compression and Bonding Performance of Cross-Laminated Timber(CLT)Made from Malaysian Fast-Growing Timbers

This study investigated the bending,compression as well as the bonding performance of CLT panels made from fast-growing timber species,i.e.,Laran(Neolamarckia cadamba)and Batai(Paraserianthes falcataria).The variables studied were timber species(Laran and Batai),layers of lamination(3-layer and 5-layer),loading direction in bending(in-plane and out-of-plane),loading direction in compression(x-,y-,and z-axis)and different treatment conditions for bonding performance test.The desired outputs of this study were bending and compression properties(strength and stiffness)as well as bonding performance(block shear strength,wood failure percentage and delamination value).The bending and compression test were conducted according to EN16351:2015 and EN408:2012,respectively.On the other hand,the bonding performance test was determined by block shear and delamination test based on EN16351:2015 and EN14374:2004,respectively.Prior to block shear test,the samples were subjected to three different treatment conditions.The results showed that CLT made from 3-layer Laran timber,loaded at out-of-plane direction exhibited the highest bending properties.Contrarily,CLT made from 5-layered Batai timber,loaded at in-plane direction showed the lowest bending properties.Laran samples for compression loaded at x-axis exhibited the best compressive properties.Generally,Laran CLT showed greater bonding performance determined by shear test compared to Batai CLT for both 3-and 5-layer panels.On the contrary,delamination results showed that Batai CLT demonstrated better bonding performance compared to Laran CLT.In terms of bonding performance measured by wood failure percentage(WFP),most samples under various treatment conditions showed WFP≥80%except for samples under wet condition with WFP≤60%.

Evaluation of the Out-of-Plane Shear Properties of Cross-Laminated Timber

The out-of-plane shear properties of cross-laminated timber(CLT)substantially influence the overall mechanical properties of CLT.Various testing methods and theories related to these properties have recently been developed.The effects of the number of layers(three and five layers)and testing method(short-span three-and four-point bending tests)on the out-of-plane shear properties of CLT were evaluated.The out-of-plane shear strength values were calculated based on different theories for comparison.The failure mode in the short-span four-point bending(FPB)method was mainly the rolling shear(RS)failure in the cross layers,indicating that the FPB method was appropriate to evaluate the RS strength of CLT.The out-of-plane shear capacity obtained using the three-point bending(TPB)method was higher than that tested by the FPB method.The testing methods significantly influenced the out-of-plane shear capacity of the three-layer specimens but not that of the five-layer specimens.With an increase in the number of layers,the out-of-plane shear strength of the specimens decreased by 24%.A linear correlation was found among the shear strength values obtained from different theories.

Mechanical Experimental Study on Tensile Bolted Connections of Cross-laminated Timber

In order to explore a kind of high-strength,earthquake-resistant,eco-nomical and suitable connection,4 groups of cross-laminated timber wall-to-floor and wall-to-wall bolted connections were tested under monotonic and cyclic load-ing.The defommation characteristics and failure modes of the cross-laminated tim-ber wall-to-floor and wall-to-wall bolted connections were exploited.Load-slip curves,bearing capacity,yielding point,stiffness and ductility of each group of specimens were analyzed.The test results indicate that the loading process of cross-laminated timber bolted connections under tension can be categorized as five stages,namely the elastic stage,the slip stage,the embedding stage,the yield-ing stage and the ultimate stage.The ultimate tensile capacity of cross-laminated timber bolted wall-to-floor connections is 2.67 times that of the wall-to-wall bolted connections.Compared with cross-laminated timber self-tapping screwed connections,the ultimate tensile capacity of the cross-laminated timber wall-to-floor bolted connections is 2.70 times that of the self-tapping screwed connec-tions,and the ultimate tensile capacity of the cross-laminated timber wall-to-wall bolted connections is 3.83 times that of the self-tapping screwed connections.The crosslaminated timber bolted connections have larger yielding displacement and wider plastic range,and they are more energy dissipative and more ductile.Furthermore,the cost of the cross-laminated timber wall-to-floor bolted connec-tions is 46%that of the self-tapping screwed connections,while the cost of cross-laminated wall-to-wall bolted connections is 53%that of the self-screwed connections.

Cross-laminated Timber(CLT)in China:A State-of-the-Art

As a new type of green low-carbon engineered wood product,cross-laminated timber(CLT)is widely used in various types of wooden buildings in Europe and North America,and the number of high-rise wood construction is also increasing.Based on the introduction of the structural characteristics of the CLT and the development status of the CLT in developed countries,this paper focused on the review of the status of research and development of the CLT in China,with an emphasis on the breakthrough technologies of new bamboo-wood composite CLT developed.Finally,the prospects of the CLT in China were discussed.

An Experimental and Analytical Study on Cross-Laminated Bamboo Rocking Walls with Friction Dampers

Cross-laminated bamboo(CLB)have a high strength to weight ratio and stable bidirectional mechanical properties.Inspired by the investigation on cross-laminated timber(CLT)rocking walls,CLB rocking walls with conventional friction dampers(CFDs)are studied in this paper.To investigate the mechanical properties of the CLB rocking wall,seven tests are conducted under a cyclic loading scheme,and different test parameters,including the existence of the CFDs,the moment ratio,and the loading times,are discussed.The test results show a bilinear behavior of the CLB rocking wall.The small residual displacements of the CLB rocking wall demonstrate an idealized self-centering capacity.The cumulative energy dissipation curves indicate that the energy dissipation capacity of the CLB rocking wall can be greatly improved with CFDs.The limit states of the CLB rocking wall under a lateral force are proposed based on the strains,stress,and damage level of the CLB material and posttensioned rebar.In addition,an analytical model of the CLB rocking wall is developed based on the proposed limit states of the CLB rocking wall to evaluate the hysteretic response of the CLB rocking wall,and the model is validated by the experimental data.The comparison results show the potential value of the analytical model for engineering design.

Study on Thermal Insulation Performance of Cross-Laminated Bamboo Wall

In recent years,bamboo,as a green building material,has attracted more and more attention worldwide.Inspired by the investigation of cross-laminated timber in structural systems,a new engineered cross-laminated bamboo(CLB)consisting of the cross lamination of bamboo scrimber plates is proposed in this paper.To evaluate its potential in structural applications,the thermal insulation performances of the CLB walls and CLB walls with the EPS foam plate were studied and evaluated by the temperature-controlled box-heat flow meter method.Test results indicated that the thermal insulation performance improved with the increase of thickness,but different wall configurations had little effect on the thermal insulation performance under the same thickness of the CLB wall.The thermal insulation performance of EPS-CLB composite wall was much better than that of CLB wall.In addition,a relatively acceptable accuracy of the theoretical calculations was proved.Finally,the influence of different locations of the EPS foam plate on heat transfer coefficient can be neglected as it was studied based on the validated numerical models.

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.

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.

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.

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).

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.

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.

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.

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。

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。

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。