Properties Of Timber Research Articles

Long-term bending properties of cross-laminated timber made from Japanese larch under constant environment

Cross-laminated timber (CLT) has been used extensively in timber construction. CLT panels are typically used in roofs and floors that carry a continuous load, and it is important to examine the long-term loading capacity of CLT. However, studies that focus on the long-term loading capacity of CLT are limited. To this end, we conducted long-term out-of-plane bending tests on seven-layer CLT made from Japanese larch (Larix kaempferi) under constant environmental conditions, investigated creep performance and duration of load, and experimentally analyzed creep rupture behavior. The mean estimated relative creep after 50 years was 1.49. The sample showed a satisfactory resistance to creep as a building material. The duration of load of most of the specimens in this study was shorter than the conventional value of small clear wood specimens. Specimens had a lower duration of load capacity than solid lumber. According to the results of survival analysis, a loading level of 70% or more caused the initial failure of specimens. Creep rupture of most of the specimens occurred at less deflection than displacement at failure in the short-term loading test. Additional studies focusing on the effects of finger joints, transverse layers, and width of a specimen on creep rupture behavior are suggested.

Timber Properties and Cellulose Crystallites Size in Pine Wood Cut in Different Sawing Patterns after Pretreatment with CH3COOH and H2O2 and Densification

One process to improve wood quality is densification or wood surface compression. Our study analyzed the changes in some basic properties of pine wood, including its anatomical structure, density, modulus of elasticity (MOE), and dimensions of cellulose crystallites, after densification following soaking pretreatment in CH3COOH and H2O2 at a concentration of 20%. Samples were sawn in radial and tangential directions for analysis of the wood. The results showed a change in the shape of tracheid cells from hexagonal to oval, as well as damage to the ray cell constituents on the tangential surface. The thickness decrease of the samples was in accordance with the target, which meant that spring-back was short. In general, the tangential boards had a higher density than the radial boards, with a lower MOE and crystallite dimensions. Our findings showed that the densified tangential board was stronger than the radial board.

Qualitative timber structure assessment with passive IR thermography. Case study of sources of common errors

The use of infrared thermography, a non-destructive technique for detecting structural failures or hidden defects, has become ever more common in the last 10 years. The combination of its growing popularity, the relatively small price tag on low-resolution devices and the lack of operator experience has fostered significant errors in the interpretation of the resulting images. This paper describes the use of infrared thermography and imaging to assess the condition of a historic timber-roofed building in Madrid, Spain. It aimed primarily to determine the utility of thermographic techniques in the detection of flaws such as cracks, moisture content and detachment. On the other hand, the limitations of IR techniques and the errors most commonly committed in interpreting the results must be identified to determine how to avoid misleading interpretations. The survey methodology deployed here followed a procedure established for earlier studies of historic buildings in which preliminary fact sheets were drawn up to determine the areas of the building’s structural members most in need of assessment. Changes in timber properties and weather-mediated moisture content were identified on the grounds of material emissivity using passive thermography. Active thermography is recommended to detect internal flaws.

Embedment properties of thermally modified spruce timber with dowel-type fasteners

This study investigates the effect of thermal modification, ThermoWood Thermo-D treatment versus no treatment, on the embedment properties of Norway spruce timber (Picea abies [L.] Karst.) with dowel-type fasteners. The test specimens were reinforced to prevent splitting of the wood. The influence of density, load direction, test specimen configuration (full hole versus half hole), moisture content, gauge points and calculation method were also evaluated. Thermal modification primarily affected the embedment strength parallel to the grain, which was ∼ 25% higher after thermal modification, mainly due to the change in physical properties because of the treatment, i.e. the lower equilibrium moisture content. The influence of the investigated parameters on embedment properties of thermally modified spruce followed similar trends as for unmodified spruce. It was for example seen that the density–embedment strength relationships still hold after the treatment despite the decrease in density and the increase in embedment strength parallel to the grain. However, after thermal modification, the influence of load direction on embedment strength was ∼30% larger and the influence of calculation method (yield versus ultimate strength) on embedment strength perpendicular to the grain was ∼10% smaller.

Comprehensive Evaluation Method of Historical Timber Structural Building Taking Fujiu Zhou House as an Example

Physical and mechanical properties of timber components are the basis of developing the technical measures for the conservation and restoration of historical timber structural buildings. By means of integrating on-site investigation (such as a visual survey, moisture content test, micro-drilling resistance test, and material samples collection of historical timber components) and laboratory tests, this study proposed a series of methodologies for comprehensively evaluating the physical and mechanical properties of timber. This method can be quickly mastered by various non-professionals and can help the cross-learning of various disciplines engaged in the research of architectural heritage protection. As a trial, the methodologies were applied to survey and assess a typical historical Chinese timber structural building named the Fujiu Zhou house (the house is located in No. 19, Qinglian lane, Yangzhou city, Jiangsu province, China). The paper studies the 224 components of the main structure of the building, including 128 columns and 96 beams. With the help of the components’ defects and damage status, GB/T13942.2-1992 and the National Lumber Grades Authority (NLGA), the grade of timber components was distinguished. The modulus of elasticity (MOE), modulus of rupture (MOR), and other related material properties parameters of timber components were also obtained. The trial results verify that the proposed methodologies are reasonable, and they can be helpful for the conservation of a historical timber structural building.

Geometric representation of the irregular cross-section of old timber elements: Comparison of different approaches for mechanical characterisation

The assessment and the mechanical evaluation of the wooden elements in historical buildings are prerequisites to guarantee their conservation and safety at the same time. The availability of reliable reference values for the mechanical properties of old timber is crucial and they must refer to a well-defined cross-section. This could be a huge problem when the structural elements are irregular, as frequently happens with historical timber.A sample of 24 wooden elements dismantled from the roof of two buildings located in central Italy dated to the late nineteenth century and with very irregular cross-sections was used to investigate the geometry that best represents the actual cross-section for the mechanical characterization. Rectangular, elliptical and octagonal geometry patterns were defined and compared.Bending strength and stiffness were underestimated of 23% on average when calculated on rectangular cross-section and overestimated of 30% on average when the ellipse was used as a reference. The representation by an irregular octagon proved to be an excellent schematization of the actual cross-section, with an average overestimation of just 1%.For the tested elements, the value of 0.66 (2/3 of the side) of mean wane was identified as the threshold above which the elliptical representation should be preferred to the octagonal one. The data also suggested a sufficient representativeness of the rectangle for an average wane of less than 0.2 (1/5 of the side). The last conclusions, however, need further confirmation on a wider sample.

Experimental investigation on the rheological behavior of timber in longitudinal and transverse compression

Understanding the rheological behavior of timber is vital for evaluating the long-term performance of timber structures. In this study, short-term experiments were first conducted to obtain the short-term mechanical properties of timber including yield strength and elastic modulus in both longitudinal and transverse compression. Subsequently, creep tests were carried out to capture the rheological behavior of timber over 360 days. Different loading types of compression and stress levels were chosen in the creep tests. Environmental temperature and relative humidity, moisture content, environmental strain and creep strain were monitored. The coefficients of environmental deformation and irrecoverable mechano-sorptive creep were obtained in longitudinal and transverse directions. Various creep models of timber were calibrated against the experimental data. Weighted nonlinear regression was adopted to better simulate the secondary creep behavior. The creep coefficients over 50 years were estimated using the calibrated models, which were compared with values from existing national standards and research. The experimental results demonstrate that the limit of linear creep in longitudinal compression was bigger than that in transverse compression. Also, the transverse timber creep was much bigger than the longitudinal creep.

Assessing the density and mechanical properties of ancient timber members based on the active infrared thermography

The objective of this study was to assess the density and mechanical properties of ancient timber members based on the active infrared thermography (IRT). Based on the unsteady heat transfer theory, the cooling constant (Ve) was proposed and the relationship between Ve and density as well as the mechanical properties of timber was analyzed. The cooling tests were conducted on 50 small clear specimens of ancient timber members to obtain the Ve and the cooling law of specimens. In addition, the effect of heating on the dynamic modulus of elasticity (Eus) and color of ancient timber members was investigated. At the same time, static mechanical tests and density measurement test were carried out to analyze the relationship between Ve and density as well as mechanical properties. The results indicated that there was unobservable influence on Eus and color parameters (L*, a* and b*) of specimens with its heating process in evaluation of the density and mechanical properties based on active IRT. Meanwhile, the initial excess temperature θ0 and initial temperature T0 had no influence on the cooling constant Ve as well as the relationship between τ and θ in the cooling process of specimens. Moreover, Ve had a strong negative correlation with density, modulus of elasticity (MOE), modulus of rigidity (MOR) and compressive strength parallel to grain (CSPG) of specimens (R2 = 0.9768, 0.8493, 0.8714 and 0.8865). In addition, the validation test result show that there is satisfactory predictive ability for density, MOE, MOR and CSPG of ancient timber members based on the prediction models established.

Assessing the Utilization of Young Falcata [Falcataria moluccana (Miq.) Barneby & J.W. Grimes] for Veneer Production

This paper presents the mechanical properties, veneer recovery including the cost benefits, of 3-, 5-, and 7-yr-old falcata [Falcataria moluccana (Miq.) Barneby & J. W. Grimes] for veneer production. Mechanical properties covered modulus of rupture (MOR), stress at the proportional limit, and modulus of elasticity (MOE) in static bending; compression paralleland perpendicular-to-grain; shear; and hardness and toughness. The study was conducted to evaluate the effects of age on these properties and the cost-benefits of converting the species at different ages, and to recommend the optimum age and price for the utilization of the species for veneer production. The experimental materials consisted of six plus-size trees each per age from superior seeds of known origin in Caraga, Philippines. Standard procedures for testing the strength properties of timber (ASTM D143-14) were followed. Veneering was conducted using a spindleless lathe with a fixed setting for each designated veneer thickness output. Gross veneer recovery was 52% for both 3- and 5-yr-olds and 55% for the 7-yr-old. Net recovery, on the other hand, was 46% for the 3- and 5-yr-olds while 49% for the 7-yr-old. Utilizing falcata trees as young as 3-yr-old can generate positive cash flows for veneering plants, making it a worthwhile investment. However, from the perspective of falcata farmers and plantation owners, selling at 3-yr-old would be unfavorable considering the low selling price.

Mechanical properties of Glued-laminated timber made up of mixed tropical wood species

ABSTRACT This paper deals with an innovative experimental study performed on glued-laminated timber (GLT) beams, machined and made with three tropical hardwood species. Defect-free beams were obtained by combining alternatively the lamellas taken from the densest to the least dense species, to have TRIO and DUO specimens. Then, static 3-point bending tests were performed on these beams, to assess their mechanical properties and their reliability. Finally, the shear strength tests of the various glue joints are done to understand the failure mode of the beams observed during the bending tests and their impact on the mechanical behaviour of the GLT beams tested. The results show for the two types of GLT (DUO and TRIO’s beams) studied here that: (i) comparatively to the combinations of two lamellas (DUO’s beams), by taking into account the solid woods and homogeneous beams as references, beams with three lamella combinations (TRIO’s beams) present the best mechanical characteristics; (ii) There is a significant influence of the individual lamella’s position or the type of lamella on the global behaviour of the GLT’s beams. Moreover, the advantages of this type of timber beam material are investigated and shown herein.

A review of thermal properties of timber and char at elevated temperatures

Timber is one of the most frequently adopted combustible materials in the built environment. The thermal properties are the determining factors for assessing the fire risk in a building. The main thermal properties of timber and their char are reviewed, especially those temperature-dependent and moisture-dependent properties, including kinetic properties, ignition properties, thermal conductivity, specific heat capacity, effective heat of combustion and thermal diffusivity. The study has collected and summarized various thermal properties data and empirical models of hardwood and softwood with different mass percentages in cellulose, hemicellulose and lignin, as temperature increases. The average ignition temperature and effective heat of combustion of softwood are about 12.9% and 9.5% higher than those of hardwood, respectively. From most of the previous models, the thermal conductivity of timber char increases as temperature rises. Cellulose with a high density shows a higher thermal conductivity, but its impacts on the specific heat capacity are limited. Models to predict the main thermal properties of the hardwood, softwood and char are recommended. The collected data, together with those empirical models, can provide useful data resources and tools for the related fire risk assessments.

A review of kowhai (Sophora spp.) and its potential for commercial forestry

Background: Demand for imported sawn timbers in New Zealand has increased over the last decade, reflecting the lack of New Zealand-grown, naturally durable timber in the domestic market. Therefore, a market opportunity exists for sustainably grown, naturally durable timbers in New Zealand for specialty applications. Kowhai (Sophora spp.) are New Zealand native tree species, known for their bright, yellow flowers and reported to produce coloured, naturally durable heartwood.Methods: Information on kowhai was collated from literature, focusing on their potential for commercial forestry. The taxonomic relationships, species descriptions, establishment, and growth rates of kowhai were examined, along with timber properties and historical uses, as well as medicinal applications. The review identified potential market opportunities for kowhai and key areas for further research.Results: Kowhai refers to eight different Sophora species that are endemic to New Zealand. Kowhai is easily established and the different species hybridise readily. While growth and form of kowhai varies with species, site, and management, examples of straight single-stemmed trees and annual diameter increments exceeding 20 mm have been found. Kowhai timber properties might be comparable to those of teak (Tectona grandis L.f.). Kowhai contains alkaloids, a class of compounds used in pharmaceutical applications. The species have been used for timber and traditional medicine by Maori in the past, while European settlers used kowhai for their durable and flexible timber.Conclusions: Kowhai could be established as a sustainable, domestic source of high-quality timber and substitute imported specialty timbers in New Zealand on account of their natural durability, strength, stiffness, colour, and density properties. The residues could support a secondary industry, as a source of alkaloids for pharmaceutical applications or natural dyes. Key areas that require further study include growth rates and silviculture, mechanical timber properties, machining/processing characteristics, natural durability and cytisine levels in kowhai, as well as the cultural, economic, and ecological framework required for a commercial kowhai forestry industry. Lack of literature on, and expertise in the use of native timbers in general are barriers to promoting native species for commercial forestry in New Zealand.

Numerical flexural strengthening investigation of timber-CFRP composite beams

Timber is among the most important construction materials with unique characteristics in comparison with other materials for instance steel and concrete. It is one of the first sustainable materials and continues to be a favoured selection in the current infrastructure. In the last decade, to refine the mechanical properties of timber, structural elements reinforcing fiber polymers have developed. In this study, to improve the flexural properties of timber beams, carbon fiber-reinforced polymer (CFRP) laminates are attached externally and internally between timber layers. For numerical simulations, first finite element model was validated according to the data obtained from experimental tests, then a series of simulations with different parameters were executed to investigate the flexural behaviour. The considered parameters include CFRP laminates’ existence and position. The linear elastic orthotropic material model was used to represent linear behaviour while the 3D anisotropic Hill material model was assumed to define the nonlinear behaviour of the material. Finite element simulations are executed by commercial software ABAQUS.

Rolling shear performance of cross-laminated bamboo-balsa timber panels

This research aimed to develop a set of practical and straightforward test methods to evaluate the rolling shear properties of cross-laminated bamboo and timber (CLBT) panels. Meanwhile, firsthand experimental data on the shear performance of panels laminated with unidirectional engineered bamboo panels and balsa wood lumbers were reported. The mechanical test results for balsa wood used in the hybrid CLBT panels were given. The bonding line's shear test between the out-layer bamboo panels and core wood was performed through the oblique compression shear test. The rolling shear tests of CLBT panels were performed with the two-plate planer shear test method and short-span bending shear test method. The full strain fields of specimens near ultimate loading conditions were given based on the two-dimensional Digital Image Correlation (DIC) method. This study showed that the rolling shear performance of core wood is determined by the annual ring geometrical parameters of wood products in the RT plane. The mean rolling shear moduli were 43 MPa and 48 MPa for two-plate specimens measured with dial gauges and strains, which is estimated through the Digital Image Correlation (DIC) method. The mean shear strength was 0.96 MPa obtained through two-plate shear tests and 2.50 MPa through the short-span bending shear test. The force corresponding to first-crack development instead of the maximum load is suggested to be adopted to calculate the shear strength of CLBT and other hybrid cross-laminated panels. Relatively small modulus and strength values were noticed for the hybrid panels due to the limited contribution of bamboo layers; thus, reinforcement at the stress-concentration regions was suggested for further researches on such lightweight hybrid cross-laminated panels.

A regulatory network driving shoot lignification in rapidly growing bamboo.

Woody bamboo is environmentally friendly, abundant, and an alternative to conventional timber. Degree of lignification and lignin content and deposition affect timber properties. However, the lignification regulatory network in monocots is poorly understood. To elucidate the regulatory mechanism of lignification in moso bamboo (Phyllostachys edulis), we conducted integrated analyses using transcriptome, small RNA, and degradome sequencing followed by experimental verification. The lignification degree and lignin content increased with increased bamboo shoot height, whereas phenylalanine ammonia-lyase and Laccase activities first increased and then decreased with shoot growth. Moreover, we identified 11,504 differentially expressed genes (DEGs) in different portions of the 13th internodes of different height shoots; most DEGs associated with cell wall and lignin biosynthesis were upregulated, whereas some DEGs related to cell growth were downregulated. We identified a total of 1,502 miRNAs, of which 687 were differentially expressed. Additionally, in silico and degradome analyses indicated that 5,756 genes were targeted by 691 miRNAs. We constructed a regulatory network of lignification, including 11 miRNAs, 22 transcription factors, and 36 enzyme genes, in moso bamboo. Furthermore, PeLAC20 overexpression increased lignin content in transgenic Arabidopsis (Arabidopsis thaliana) plants. Finally, we proposed a reliable miRNA-mediated “MYB-PeLAC20” module for lignin monomer polymerization. Our findings provide definite insights into the genetic regulation of bamboo lignification. In addition to providing a platform for understanding related mechanisms in other monocots, these insights could be used to develop strategies to improve bamboo timber properties.

Rolling shear properties of cross-laminated timber made of fibre-managed plantation eucalyptus under short-span bending

ABSTRACT Eucalyptus globulus and Eucalyptus nitens are the most dominant hardwood plantation species in Australia. Although containing a considerable amount of growth irregularities, there is an increasing interest by the industry in developing structural products, especially cross-laminated timber (CLT), from these plantation resources. In this study, for the first time, the rolling shear (RS) properties of CLT made of these two species were evaluated. Two groups of higher-grade and lower-grade CLT panels were fabricated from each species using polyurethane adhesive. The effects of the sawn-timber’ density in the cross-layer and the MOE of sawn timber in the top and bottom layers on the RS properties and failure modes of the CLT were then evaluated under three-point bending test. The results showed a positive correlation between the average MOE of the sawn timber in top and bottom layers and both GAeff (LB) and τ value of the specimens from both species. The high-grade specimens from both species showed the highest shear stiffness and shear strength values compared to lower-grade ones. Furthermore, the RS values obtained were higher than those recommended in European standards for softwood CLT. These results provide useful information towards successful development of high-value CLT from the low-grade plantation eucalypts timber.

An insight into mechanical properties of heartwood and sapwood of large French Douglas-fir LVL

The French resource of large diameter Douglas-fir is currently still growing, while these large diameter trees are complicated to process efficiently by the sawmilling industry. The rotary peeling process appeared to be particularly adapted as an alternative to the usual sawing. This primary processing method produces veneers used to make a wood engineered product material called Laminated Veneer Lumber (LVL). The manufacturing process of LVL enables the distribution of the resource defects, allowing for increased mechanical behaviour compared to the solid wood from which it comes from. The main objective of this study is to provide an insight into the principal Douglas-fir heartwood LVL mechanical properties such as longitudinal and shear moduli of elasticity, bending, shear and compressive strengths. Up to now, there was no study on LVL derived from this resource. This study focuses on heartwood because of its very interesting natural durability properties for constructive outdoor applications. Moreover, a comparison with structural timber properties and a comparable industrial engineering product, made of Norway spruce and called Kerto® S was also achieved to place the material in terms of mechanical performance among the market. Globally, this Douglas-fir heartwood LVL showed high compressive and shear properties. Even though the bending properties were significantly lower than data from Douglas-fir LVL of the literature, they seemed appropriate for structural applications. A larger experimental campaign fully representative of the industrial process and dealing with larger samples will be needed to finally conclude on the characteristic values to be used in structural design.

A Sawn Timber Tree Species Recognition Method Based on AM-SPPResNet.

Sawn timber is an important component material in furniture manufacturing, decoration, construction and other industries. The mechanical properties, surface colors, textures, use and other properties of sawn timber possesed by different tree species are different. In order to meet the needs of reasonable timber use and product quality of sawn timber products, sawn timber must be identified according to tree species to ensure the best use of materials. In this study, an optimized convolution neural network was proposed to process sawn timber image data to identify the tree species of the sawn timber. The spatial pyramid pooling and attention mechanism were used to improve the convolution layer of ResNet101 to extract the feature vector of sawn timber images. The optimized ResNet (simply called “AM-SPPResNet”) was used to identify the sawn timber image, and the basic recognition model was obtained. Then, the weight parameters of the feature extraction layer of the basic model were frozen, the full connection layer was removed, and using support vector machine (SVM) and XGBoost classifier which were commonly used in machine learning to train and learn the 21 × 1024 dimension feature vectors extracted by feature extraction layer. Through a number of comparative experiments, it is found that the prediction model using linear function as the kernel function of support vector machine learning the feature vectors extracted from the improved convolution layer performed best, and the F1 score and overall accuracy of all kinds of samples were above 99%. Compared with the traditional methods, the accuracy was improved by up to 12%.

Near-Surface Mounted Reinforcement of Sawn Timber Beams-FEM Approach.

The demand for timber has increased significantly in recent years. Therefore, reliable tools are needed to predict the mechanical properties of sawn timber, especially for structural applications. Very complex models require a lot of input data for analysis, which cannot always be guaranteed, especially in industrial practice. Thus, a simplified model for material description was developed and assessed with experiments (static bending tests carried out in accordance with the guidelines suggested in the European standard EN 408) and an analytical approach (gamma method according to the guidelines given in the European standard EN 1995). The effective stiffness was calculated as a major parameter, which has an influence on the elements’ behavior. The model included a near-surface mounted (NSM) local reinforcement technique, with CFRP strips of Scots pine timber beams being subjected to bending stresses. It is anticipated that the developed model can be a starting point for the repair engineering field, contributing to decision-making regarding conservation technique selection and range. Next, improvements of the model will provide more and more realistic results for numerical analysis in terms of the obtained failure mechanisms for sawn timber elements.

Flammability properties of fire-retardant timber

Introduction. At present, the house-building industry, that produces timber structures, is in the process of sufficiently intensive development; however, high flammability of wood is the factor that restrains widespread use of timber in construction. The purpose of this work is to optimize the conditions of application of fire-retardant timber in the construction industry. The co-authors believe that the following problems are to be solved to attain this objective:● a comparative analysis of the fireproofing efficiency of several fire-proofing agents applied to different species of wood;● determination of the character of influence produced by fire proofing agents on fire retardant properties of wood.Methods of research. The fire proofing efficiency of sample compositions designated for wood was measured in compliance with the benchmark testing method specified in GOST R 53292 (p. 6.2). Experiments were launched pursuant to the methodology and with the help of measurement instruments specified in GOST 30244–94 (Method 2) to study the extent of the pine-tree timber flammability suppression. Critical values of thermal loads that may trigger inflammation and flame propagation in timber structures, that can be described using values of the critical surface density of the heat flow, were determined pursuant to GOST 30402–96 and GOST R 51032–97. The toxicity of combustion products and the smoke generation ability of fire-retardant pine-tree samples was assessed using standard methods and measurement instruments pursuant to GOST 12.1.044–89 (paragraphs 4.18 and 4.20).Research results and discussion. Biological flame retardants, integrated biological flame retardants that also ensure moisture protection, intumescent coatings, lacquers and varnishes that are ready for use and labelled as having group I and II fire-retardant efficiency pursuant to GOST R 53292, were studied in the course of this research project. The co-authors have identified that the mass loss by all fire-retardant compositions is below 9 %, if applied to samples of larch and oak-tree timber, same as if it were applied to standard samples of pine-tree timber.The findings of the experiment conducted to assess the flammability, ignitibility, flame propagation, smoke generation ability and toxicity of combustion products have proven the maximal efficiency of the composition designated for full-cell pressure impregnation of timber that ensures the properties of the material labelled as G1, V1, RP1, T2, D2.Conclusions. Hence, the research results have enabled the co-authors to assess the discrepancy between average mass loss values demonstrated by the samples of different species of timber (alder, linden, pine-tree, larch, and oak-tree).The comprehensive study of flammability properties of timber, treated by compositions that vary in their chemical composition and mode of action of the fire proofing agent, enabled the co-authors to identify the impact produced by versatile fire-proofing agents on different flammability properties of pine-tree timber with regard taken of the fire-safe use of construction materials and constructions of buildings and structures.