European Softwood Research Articles

Diffusion properties of Gabonese tropical hardwoods and European softwoods measured with low-tech equipment and by an inverse method

This paper presents an experimental approach to studies of the sorption and diffusion properties of wood. Five timber species - three African tropical hardwoods, Padauk, Okoume and Iroko, and two temperate softwoods, Silver fir and Douglas fir - were studied in adsorption mode. Specimens with 10- and 20-mm longitudinal (L) and transverse (RT) thickness were waterproofed on their sides to force diffusion in those directions. After kiln drying the specimens were hung with nylon wires under cover in a home-made box in which salt solutions provided constant relative humidity (RH), and conditioned at 43, 55, 75, 84 and 97% RH in successive steps. Temperature was maintained between 20 and 24°C. During the equilibration steps the samples were periodically weighed without altering the environmental conditions imposed, by hanging the nylon wire to a spring gauge through a small hole in the box cover. The sorption isotherm properties and diffusion parameters were obtained using an inverse method based on optimization of a 1D finite difference model. The parameters obtained show a decreasing correlation between diffusion coefficient and density, as observed by several authors in the literature. They also illustrate the impact of extractives on the sorption isotherm parameters. These results show that tropical species with high density or many extractives behave very differently to European softwoods, which impedes the application of Eurocode 5 equilibrium standards for these species.

Influence of test methodology on the characterization of the parallel-to-grain timber embedment strength and foundation modulus of dowels

ABSTRACT A reliable determination of the embedment strength and foundation modulus of timber elements is critical for the design and safety assessment of joints in timber structures. However, the existence of various test configurations for characterising the embedding properties of large diameter steel fasteners in timber elements poses challenges in directly comparing and utilising available test data. This paper aims to provide an insight into the influence of embedment property test methods, comparing experimental results from different test setups within the guidelines of the EN 383 and ASTM D 5764-97a standards for European softwood species, Scots pine wood (Pinus sylvestris) and Norway spruce (Picea abies). In addition to the test guidelines, the thickness of the specimen and the application of the load was evaluated within the protocols. A comprehensive statistical analysis was performed to identify statistically significant differences between the groups evaluated. The results of the analysis revealed disagreement between the standards in the evaluation of the strength of the embedding, highlighting the potential bias inserted by the experimental setup and protocol. Furthermore, it was proven that the thickness of the specimens influences both the embedding strength and the foundation modulus of the wood species tested. Finally, no distinctions were observed between tensile and compressive loading within the guidelines of the EN 383 standard.

Use of Pyrolysis-Gas Chromatography/Mass Spectrometry as a Tool to Study the Natural Variation in Biopolymers in Different Tissues of Economically Important European Softwood Species.

Intraspecific macromolecule variation in stemwood, knotwood, and branchwood was studied using analytical pyrolysis with the intention of introducing a rapid working method to assess the variance in lignin content using analytical pyrolysis and highlight variability markers. The study was performed on Picea abies, Abies alba, and Pseudotsuga menziesii. Lignin determined via analytical pyrolysis-GC/MS (Py-lignin) can be used to identify variations in lignin content, compared to using classical Klason lignin values as a reference method for lignin determination, which requires a correction factor. Principal component analysis (PCA) was performed to identify biopolymer pyrolysis product markers for different species, tissues, or heights that could help highlight structural differences. Douglas fir was differentiated from spruce and silver fir in the levoglucosan amount. Guaiacol was more present in spruce wood, and creosol was more present in Douglas fir. Knotwood was structurally close to stemwood in spruce and silver fir, but there was a clear transition between stemwood and branchwood tissue in Douglas fir. Knotwood was differentiated by higher furan compounds. Branchwood was clearly separate from stemwood and knotwood and presented the same markers as compression wood in the form of phenylpropanoid lignins (H-lignin) as well as isoeugenol and vinyl guaiacol, the two most produced lignin pyrolysis products.

Douglas-fir outperforms most commercial European softwoods

One of the main ideas of non-native tree species introduction into forest stands is to replace declining native species. The same is also valid for industry; the wood of native species should be replaced by a wood of the same or even better quality. Douglas-fir is often compared to other coniferous tree species based on its production. This study compared Douglas-fir wood properties with European commercial species, namely Norway spruce, Scots pine, and European larch. Trees representing different sites and ages were tested for wood density, shrinkage, and compression strength. In all cases, Douglas-fir outclassed spruce and pine in density and strength. The difference was striking, especially for spruce, where the density was surpassed by Douglas-fir by more than 100 kg.m−3 (above 25%). In the case of compression, the strength of Douglas-fir was up to 12.3 MPa higher (above 33%) compared to spruce. The only species that obtained higher figures was larch. Wood shrinkage was comparable to European softwoods. Therefore, Douglas-fir wood can be regarded as an excellent and promising substitute for the European processing industry.

Improving the accuracy of wood moisture content estimation in four European softwoods from Spain

Aim of study: To obtain improved models to predict, with an error of less than ± 2.0%, the gravimetric moisture content in four different softwoods commonly present in the Spanish and European markets, based on electrical resistance measurements. This improved moisture content estimation is useful not only for assessing the quality of wood products, especially in the case of laminated products, during the transformation and delivery process, but also for accurately monitoring the evolution of moisture in wood present in bridges and buildings, which is of great importance for its maintenance and service life improvement.Area of study: The study was carried out on samples of Scots, laricio, radiata and maritime pines of Spanish provenances.Material and methods: On 50x50x20 mm3 solid wood samples (36 per species, 9 per condition), conditioned at 20ºC (±05ºC) and 40±5%, 65±5%, 80±5% or 90±5% Relative Humidity (RH), electrical resistance and oven-dry moisture content was measured. The Samuelsson's model was fitted to data to explain the relationship between the two variables. The accuracy of the model was evaluated by the use of an external sample.Main results: With the proposed mathematical functions the wood moisture content can be estimated with an error of ±0.9% in the four species, confirming the effectiveness of this nondestructive methodology for accurate estimation and monitoring of moisture content.Research highlights: our results allow the improvement of the moisture content estimation technique by resistance-type methodologies.Keywords: Resistance-type moisture meter; species correction.Abbreviations used: MC: Moisture content; RH: relative Humidity; R: electrical resistance; RP: wood electrical resistance measured parallel to the grain; RT: electrical resistance measured perpendicular (transversally) to the grain; GM-MC: gravimetrically measured moisture content.

Mechanical properties of Gmelina arborea for engineering design

Gmelina arborea is a fast-growing hardwood species whose material properties according to available data have never been properly studied. This work presents an extensive study on the process of acquiring, preparing, testing and all analyses involved in determining the mechanical properties of Gmelina arborea for the design of load bearing structures. Samples obtained from 25-year-old Gmelina trees harvested from a plantation in South Western Nigeria, were transported to the laboratory of the Department of Timber Structures and Building Rehabilitation, University of Kassel where they were seasoned, prepared, and tested in accordance with European and German standards, afterwards, detailed statistical analyses were carried out on the experimental data. While the distribution functions in the Joint Committee for Structural Safety model code were validated for some material properties, they could not be validated for others. The material properties of the hardwood species were found to compare well with those of European softwood species and shows good potentials for use as a construction material.

Improving the accuracy of wood moisture content estimation in four European softwoods from Spain

Aim of study: To obtain improved models to predict, with an error of less than ± 2.0%, the gravimetric moisture content in four different softwoods commonly present in the Spanish and European markets, based on electrical resistance measurements. This improved moisture content estimation is useful not only for assessing the quality of wood products, especially in the case of laminated products, during the transformation and delivery process, but also for accurately monitoring the evolution of moisture in wood present in bridges and buildings, which is of great importance for its maintenance and service life improvement.Area of study: The study was carried out on samples of Scots, laricio, radiata and maritime pines of Spanish provenances.Material and methods: On 50x50x20 mm3 solid wood samples (36 per species, 9 per condition), conditioned at 20ºC (±05ºC) and 40±5%, 65±5%, 80±5% or 90±5% Relative Humidity (RH), electrical resistance and oven-dry moisture content was measured. The Samuelsson's model was fitted to data to explain the relationship between the two variables. The accuracy of the model was evaluated by the use of an external sample.Main results: With the proposed mathematical functions the wood moisture content can be estimated with an error of ±0.9% in the four species, confirming the effectiveness of this nondestructive methodology for accurate estimation and monitoring of moisture content.Research highlights: our results allow the improvement of the moisture content estimation technique by resistance-type methodologies.Keywords: Resistance-type moisture meter; species correction.Abbreviations used: MC: Moisture content; RH: relative Humidity; R: electrical resistance; RP: wood electrical resistance measured parallel to the grain; RT: electrical resistance measured perpendicular (transversally) to the grain; GM-MC: gravimetrically measured moisture content.

European beech log and lumber grading in wet and dry conditions using longitudinal vibration

Abstract In Central Europe, European beech (Fagus sylvatica L.) is the most frequently occurring hardwood species. An efficient grading method has the potential to promote its utilisation as construction material. Wood density, eigenfrequency and length were measured in 99 European beech logs for calculating the dynamic modulus of elasticity (MOEdyn ) obtained by longitudinal vibration (resonance). In addition, the log taper was measured. Of those logs, 867 boards were cut using a bandsaw. The MOEdyn in green condition was determined on 505 of the boards and the MOEdyn in dry conditions was determined on all of them. The r2 value between the MOEdyn of a log and the mean of MOEdyn of its boards was 0.72 in the wet condition. The MOEdyn,12% of boards significantly increased by 88 N mm−2 for each centimetre away from the pith. The negative effect of log taper on MOEdyn of boards was barely significant (P-value = 0.050). The MOEdyn,12% was highly dependent on the MOEdyn,wet (r2 = 0.83) and was 17% higher than the MOEdyn,wet . The mechanical properties of European beech timber exceed those of European softwood species. However, the relationships regarding MOEdyn between different grading levels in the processing chain appear to be similar to those of softwoods.

Rolling shear: Test configurations and properties of some European soft- and hardwood species

Shear stresses in planes perpendicular to the grain, so-called rolling shear stresses, need to be considered in the ultimate and serviceability limit state design of many timber structural elements. Knowledge about the rolling shear modulus and strength has further gained in importance since the invention and increased use of cross laminated timber (CLT). As a result of the orthogonal orientation of adjacent layers within CLT, rolling shear stresses develop when CLT is subjected to out-of-plane bending. Previous numerical and experimental studies on rolling shear are largely restricted to Norway spruce (Picea abies (L.) Karst.). In the present study, experimental investigations on the rolling shear properties were carried out on six timber species. The two investigated coniferous species were Norway spruce (Picea abies (L.) Karst.) and pine (Pinus sylvestris L.). Four deciduous species, namely European beech (Fagus sylvatica L.), European ash (Fraxinus excelsior L.), poplar (Populus tremula L.), and European birch (Betula pendula R.) were investigated. Furthermore, different board geometries and sawing patterns were investigated. In comparison to Norway spruce, all other investigated species featured higher rolling shear properties. In particular, these of European beech and European ash were roughly three-times higher. In agreement with previous findings, the aspect ratio (board width vs. board thickness) as well as sawing pattern were identified as main influencing parameters on the rolling shear properties. In addition to single board segments, multi-segment systems were experimentally tested and numerically investigated. Parallel systems consisting of either two or four board segments were tested to obtain information on potential system effects of laminations within single CLT cross layers regarding rolling shear strength and rolling shear modulus, i.e. stresses may be distributed depending on the local stiffness. This system effect may influence the shear strength, the shear modulus, and the failure behaviour compared to the results of single segment testing. Often, CLT elements consist of more than one cross layer. Layups can also feature parallel layers, however, usually with grain in direction of the main span direction. Some of these layups have a remarkable potential for two-dimensional load transfer. Thus, these commonly double or triple layers are exposed to rolling shear by stresses in the weak load transfer direction. As rolling shear failure of one of the cross layers in layups featuring alternating orthogonal layers as well as layups featuring some parallel layers leads to the ultimate failure of the entire element, such elements can be considered as serial systems with regard to the rolling shear strength and rolling shear modulus. In order to investigate the serial-parallel system behaviour, multi-segment systems consisting of 4 × 3 board segments were tested. The investigated systems should allow linking the results obtained from single element testing to the actual behaviour of CLT laminations and, subsequently, to give recommendations for rolling shear test configurations as well as related rolling shear properties. The outcomes show a good comparability between the results from out-of-plane bending tests on CLT elements featuring rolling shear failures and EN 408-alike shear tests conducted on board segments. The analysis of the within- and between-boards variation of rolling shear properties and density is also a part of this paper. The results of this study provide an overview of the rolling shear properties of tested European softwood and hardwood species. The investigated species are already in use, or have a significant potential to be used for construction purposes in the near future. The findings regarding the influential material- and product-related parameters contribute to a better understanding of the mechanical behaviour of timber subjected to rolling shear.

Survey of selected adhesive bonding properties of nine European softwood and hardwood species

Due to the increasing interest in applying a wider range of wood species for structural purposes, nine European softwood and hardwood species (ash, beech, birch, hornbeam, larch, oak, poplar, black locust and spruce) were assessed for their ability to be bonded with three different commercial adhesive systems (melamine–urea–formaldehyde, one-component polyurethane and phenol–resorcinol–formaldehyde). Tensile shear strength and delamination tests were conducted according to European standards, for all tests including the corresponding wood species as adhesive joints and as a solid wood reference. When tested in dry condition, the threshold of solid wood tensile shear strength was reached by all species–adhesive combinations. By contrast, testing in wet condition revealed distinct performance reductions for certain combinations. This trend was confirmed by delamination testing. Overall, the results indicate that extrapolation of test results achieved with a specific wood species (as recommended in the current standard for lap-joint tests) towards other species is highly problematic and has to be done with caution.

Characterization of condensed tannins and carbohydrates in hot water bark extracts of European softwood species

Condensed tannins extracted from European softwood bark are recognized as alternatives to synthetic phenolics. The extraction is generally performed in hot water, leading to simultaneous extraction of other bark constituents such as carbohydrates, phenolic monomers and salts. Characterization of the extract’s composition and identification of the extracted tannins’ molecular structure are needed to better identify potential applications.Bark from Silver fir (Abies alba [Mill.]), European larch (Larix decidua [Mill.]), Norway spruce (Picea abies [Karst.]), Douglas fir (Pseudotsuga menziesii [Mirb.]) and Scots pine (Pinus sylvestris [L.]) were extracted in water at 60°C. The amounts of phenolic monomers, condensed tannins, carbohydrates, and inorganic compounds in the extract were determined. The molecular structures of condensed tannins and carbohydrates were also investigated (HPLC-UV combined with thiolysis, MALDI-TOF mass spectrometry, anion exchange chromatography).Distinct extract compositions and tannin structures were found in each of the analysed species. Procyanidins were the most ubiquitous tannins. The presence of phenolic glucosides in the tannin oligomers was suggested. Polysaccharides such as arabinans, arabinogalactans and glucans represented an important fraction of all extracts. Compared to traditionally used species (Mimosa and Quebracho) higher viscosities as well as faster chemical reactivities are expected in the analysed species. The most promising species for a bark tannin extraction was found to be larch, while the least encouraging results were detected in pine. A better knowledge of the interaction between the various extracted compounds is deemed an important matter for investigation in the context of industrial applications of such extracts.

Quantification and characterization of knotwood extractives of 12 European softwood and hardwood species

Key message Extractives are present in much larger amounts in knotwood than in heartwood in the 12 tested hardwood and softwood species. The chemical identity of the extractives varies largely among species, lignans being only present in softwood species. Context Extractives from knotwood may constitute an important source of new chemicals and remain still poorly known. Aims The content of extractives (and particularly lignans) in knots was compared to that of heartwood in a number of different European softwood and hardwood species. Methods Twelve species characteristic of European forests were sampled. Extractions were carried out with four solvents of increasing polarity (dichloromethane, acetone, toluene/ethanol and water). Gas chromatography-mass spectrometry (GC-MS) was used for the identification of the compounds present in acetone extracts which are expected to contain lignans. Results In all tested species, knotwood presented larger contents of extractives than heartwood. The main compounds were lignans, stilbenes and flavonoids, lignans being present only in softwood species. With the exception of oak, knotwood in softwood species contain larger amounts of extractives than that in hardwood species. Conclusion The chemical nature of extractives present in knotwood varies with species. Their amount is generally much higher in softwood than heartwood species.

Effect of heat treatment intensity on some conferred properties of different European softwood and hardwood species

Effect of heat treatment intensity on some conferred properties like elemental composition, durability, anti-swelling efficiency (ASE) and equilibrium moisture content (EMC) of different European softwood and hardwood species subjected to mild pyrolysis at 230 °C under nitrogen for different durations has been investigated. Independently of the wood species studied, elemental composition is strongly correlated with the mass losses due to thermal degradations which are directly connected to treatment intensity (duration). In all cases, an important increase in the carbon content associated with a decrease in the oxygen content was observed. Heat-treated specimens were exposed to several brown rot fungi, and the weight losses due to fungal degradation were determined after 16 weeks, while effect of wood extractives before and after thermal treatment was investigated on mycelium growth. ASE and EMC were also evaluated. Results indicated important correlations between treatment intensity and all of the wood conferred properties like its elemental composition, durability, ASE or EMC. These results clearly indicated that chemical modifications of wood cell wall polymers are directly responsible for wood decay durability improvement, but also for its improved dimensional stability as well as its reduced capability for water adsorption. All these modifications of wood properties appeared simultaneously and progressively with the increase in treatment intensity depending on treatment duration. At the same time, effect of extractives generated during thermal treatment on Poria placenta growth indicated that these latter ones have no beneficial effect on wood durability.

Thermo-vacuum Modification of some European Softwood and Hardwood Species Treated at Different Conditions

Three softwood species, spruce (Picea abies Karst.), fir (Abies alba Mill.), and larch (Larix decidua Mill.), and five hardwood species, oak (Quercus petraea Liebl.), ash (Fraxinus excelsior L.), beech (Fagus sylvatica L.), cherry (Prunus avium L.), and black locust (Robinia pseudoacacia L.) were treated at high temperatures under vacuum conditions with Termovuoto® technology. All of the wood species were treated at different temperatures (from 160 to 220°C), different times (from 45 minutes to 5 hours), and under different pressure conditions (160, 210, and 330 mbar). The treated material was characterized in terms of mass loss, color changes, and equilibrium moisture content. Results showed dissimilar behavior of various wood species and their different sensitivities to treatment schedules. Consequently, the series of tests performed allowed a detailed characterization of the Termovuoto® process and its effect on product quality.

Stiffness moduli of various softwood and hardwood species determined with ultrasound

Comprehensive data sets of the elastic constants are available for only a few European wood species. The goal of this study was to provide stiffnesses for the principal directions and planes for further selected European softwoods and hardwoods, to extend the currently existing data sets. For this purpose, a dynamic technique was chosen: the moduli were estimated on the basis of sound velocity and density measurements. The collected data may be helpful for specialists in the relevant research and practical fields, particularly when stresses and strains of structural elements have to be calculated using modelling approaches.

The sustainability of bamboo products for local and Western European applications. LCAs and land-use

Bamboo has some positive aspects compared to wood: - it can grow on slopes and other areas where foresting of wood is not possible, and it grows fast. - it can replace tropical hardwood, so it can mitigate the decrease of tropical forest area. - it can support the local economies in the third world. This article is based on a bamboo species from China ( Phyllostachys Pubescens, also called Moso), and its industrially processed products: Plybamboo and Strand Woven Bamboo. Life Cycle Assessment (LCA) is used in this paper to compare the environmental impact of bamboo materials, shipped to Western Europe, with commonly used materials such as timber. The calculations are based on the LCI databases of Ecoinvent v2 (2008) and Idemat 2008, applied to the eco-costs 2007 method for LCIA. The annual yield of harvesting is calculated as well, and compared with other wood products. General conclusions are: - bamboo products have less eco-costs than tropical hardwood (FSC certified) - bamboo products imported in Europe have more eco-costs than local European softwood. - the yield of bamboo is high compared to most other wood species: the yield of bamboo for production of biofuel is extremely high.

Invention from War: a circumstantial modernism for Australian architecture

Between 1942 and 1945, Australian architects and engineers within the Allied Works Council and the US Army Corps of Engineers undertook a vast programme of building works to assist the campaign to drive Japanese forces northward through the Southwest Pacific and avoid invasion.1 Huge distances, lack of time and the need to wage a campaign from the air lay behind US General Douglas Macarthur’s phrase that it would be an ‘engineer’s war’. By necessity, buildings such as airfields, hospitals, camps, warehouses, and other structures had to be light weight, constructed quickly, and inevitably dropped in by air as easily handled pre-cut packages. With the lack of American and European softwoods in the Australasian region, an unlikely local material was pressed into war service – unseasoned or ‘green’ Australian hardwood. It was a material choice that would have profound implications for two reasons. First, in the years of conflict, circumstances dictated the unprecedented innovation and experiment in light-weight timber structures. Second, in an echo of Lewis Mumford’s poignant maxim that ‘war is the health of the machine’2, the systematisation and ruthless economy inherent in wartime timber buildings would influence the development and practice of a particular form of modern architecture in Australia in the late 1940s and the 1950s.

Water protection of wooden window joinery painted with low organic solvent content paints with known composition. Part 1. Results of inter-laboratory tests

An investigation of the water protection capacity of modern paints with low organic solvent content was carried out as part of an European research project. The wider scope of the project was to establish the performance and durability of these new coatings applied to window joinery made from European softwood species. The aim of the moisture studies was to employ well-proven methods to determine the liquid water absorption of the coatings. A range of standard moisture permeability tests, carried out on coating systems applied to pine and spruce substrates, indicated a high correlation between similar data obtained using different techniques at different laboratories. The results showed that permeability of the coatings tested did not depend on the timber substrate, as long as the permeability was expressed in absolute terms and not relative to the absorption of uncoated wood. The results from this study will be used to determine whether laboratory measurements of the moisture transmission properties of a coating can be used to predict outdoor weathering performance.

THE QUALITY OF MATUREPINUS PATULAANDP. INSIGNISTIMBER GROWN IN SOUTH AFRICA

SUMMARY This paper was presented to the Fifth British Empire Forestry Conference in London, 1947, and is reprinted here with the kind permission of the Director of Forestry In this paper data are presented which enable an accurate comparison to be made of the quality of the timber from locally-grown, mature trees of Pinus patula Schl. and Cham. and P. insignis Doug. (Syn. P. radiata D. Don) with that of imported European softwoods. This subject is fully discussed. Complete details are given of the site factors and treatments in respect of each stand sampled and of the growth pattern and form of all the trees analysed. It is shown that properly-handled mature timber of these species grown in South Africa is of a grade quite equal to the general run of imported softwood timber as represented by Scots pine (Pinus sylvestris, commonly known in South Africa as “deal”). Current pruning prescriptions should effect a marked improvement in the quality of timber herein disclosed.

The Swedish State College of Forestry Centenary Celebrations, 1928

ON Oct. 14–16 the State College of Forestry, situated in the vicinity of Stockholm, celebrated its centenary. This College, formerly known as the Forestry Institute, was founded on Oct. 15, 1828, by that far-seeing man, Israel Adolf av Strom, who even at that distant date endeavoured to arouse his countrymen to a realisation of the economic importance of the forests of the country. The change in materials used for construction, especially in ships and buildings, witnessed the rise in demand for coniferous timbers, and during the second half of last century Sweden was mainly occupied in capturing and maintaining her hold on the European softwood timber markets. The advice of the few, who understood the danger which the more or less unrestricted lumbering in the forests which had been acquired by the great timber companies and in those numerous areas of varying size (designated farm-forests), owned by tenant farmers, went unheeded. The power of the lumbering interests predominated and the country undoubtedly prospered thereby. Before the end of the century, however, the Government became alarmed at the position and appointed a committee to consider what legal restrictions could be placed on the unchecked exploitation combined with a want of effective management in the greater bulk of the privately owned forests of the country. As a result of the committee's report a General Forest Law was enacted in 1903 and brought into force in 1905, which made it imperative that all areas of forest felled should be replaced by a new young tree crop within a reasonable period. At the same period a revival in the scientific aspects of forestry took place, and in order to endeavour to associate the scientific and commercial aspects of this question the Swedish Forestry Association was founded in 1903.