Characteristics Of Timber Research Articles

Quasi-brittle fracture and size effect of glued laminated timber beams

The load bearing capacity of glued laminated timber beams is size dependent. A material based size effect occurs due to the natural variability of the timber properties and can be explained with the Weibull weakest link theory. The Weibull type size effect has received much attention in the timber research community in the past as it is the dominating size effect regarding the load bearing capacity of timber beams. In this paper, it is shown that a further deterministic size effect, which originates from the timber fracture behavior, influences the load bearing capacity of glued laminated timber beams. It is the size effect associated with quasi-brittle behavior. The paper covers a short theoretical review on fracture related size effects and a study comparing experimentally tested beams of several sizes with detailed numerical simulations considering the natural growth characteristics of timber. Further, an analytical model illustrating the features of the fracture related size effect on the load bearing capacity of glued laminated timber beams is presented. It is demonstrated that the simulated load bearing capacity of the tested glued laminated timber beams distinctively improves if the quasi-brittleness is taken into account by using a softening constitutive law.

Developmental Changes in Scots Pine Transcriptome during Heartwood Formation.

Scots pine (Pinus sylvestris L.) wood is desired in woodworking industries due to its favorable timber characteristics and natural durability that is contributed by heartwood extractives. It has been discussed whether the Scots pine heartwood extractives (mainly stilbenes and resin acids) are synthesized in the cells of the transition zone between sapwood and heartwood, or if they are transported from the sapwood. Timing of heartwood formation during the yearly cycle has also not been unambiguously defined. We measured steady-state mRNA levels in Scots pine transition zone and sapwood using RNA sequencing. Year-round expression profiles of selected transcripts were further investigated by quantitative RT-PCR. Differentially accumulating transcripts suggest that, of the Scots pine heartwood extractives, stilbenes are synthesized in situ in the transition zone and gain their carbon-skeletons from Suc and triglycerides. Resin acids, on the other hand, are synthesized early in the spring mainly in the sapwood, meaning that they must be transported to the heartwood transition zone. Heartwood formation is marked by programmed cell death that occurs during the summer months in the transition zone.

Dendrochronological analyses of wood samples from a Late Bronze to early Iron Age site at Lake Luokesa, Lithuania

Tree rings of 184 archaeological wood samples from two Late Bronze to early Iron Age lake sites at Lake Luokesa (Luokesai ežeras), Lithuania, Moletai district, were analyzed. Despite severe difficulties with synchronization, Pinus (pine), Quercus (oak) and Alnus (alder) yielded some cross-datable series. The general picture is that the settlers chose small trees as timber, which they used in their natural round shape. The trees did not grow in homogeneous even-aged stands, but show very different ages and growth levels. Despite the generally low numbers of tree rings in the individual samples, the strong archaeological framework allowed cross-dating of some series and the building of chronologies for single structures. Based on these attempts, a 90 year long first floating chronology of the settlement structures is presented. Luokesa Site 2 (L2) was mainly built within the relative year 53. Luokesa Site 1 (L1) was certainly in use from the relative year 74 onwards. All fences at L1 show their main building activity in the relative year 81, four years after the main building activities in the village itself. It can be concluded that the settlement L1 was in use for at least 16 years. Because of the lack of a standard dendrochronological curve for the Baltic region, wiggle-matching was applied to obtain an absolute date for both settlements. The data clearly show that all samples relate to the Late Bronze–early Iron Age. The period where all wiggle matching results overlap is the period between 625 and 535 bc (the 2σ ranges are given). Based on the dating, duration and timber characteristics of the occupation, comparisons with Polish early Iron Age sites are made, which indicate a close resemblance in terms of wood use and settlement concept.

Monitoring in-service performance of fibre-reinforced foamed urethane sleepers/bearers in railway urban turnout systems

Special track systems used to divert a train to other directions or other tracks are generally called 'railway turnout'. A traditional turnout system consists of steel rails, switches, crossings, steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or ground-borne noise) to railway neighbors. In a brown-field railway track where an existing aged infrastructure requires renewal or maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to seek for high-quality timbers with dimensional stability, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt an alternative material that could mimic responses and characteristics of timber in both static and dynamic loading conditions. A critical review has suggested an application of an alternative material called fibre-reinforced foamed urethane (FFU). The full-scale capacity design makes use of its comparable engineering characteristics to timber, high-impact attenuation, high damping property, and a longer service life. A field trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, 'fibre-reinforced foamed urethane (FFU)' bearers, has been carried out at a complex turnout junction under heavy mixed traffics at Hornsby, New South Wales, Australia. The turnout junction was renewed using the FFU bearers altogether with new special track components. Influences of the FFU bearers on track geometry (recorded by track inspection vehicle 'AK Car'), track settlement (based on survey data), track dynamics, and acoustic characteristics have been measured. Operational train pass-by measurements have been analysed to evaluate the effectiveness of the replacement methodology. Comparative studies show that the use of FFU bearers generates higher rail and sleeper accelerations but the damping capacity of the FFU help suppress vibration transferring onto other track components. The survey data analysis suggests a small vertical settlement and negligible lateral movement of the turnout system. The static and dynamic behaviours of FFU bearers appear to equate that of natural timber but its service life is superior.

Withdrawal strength of threaded steel rods glued with epoxy in wood

In this study, the axial strength of joints made with threaded steel rods glued in timber with epoxy is investigated. Although numerous experimental studies have investigated these joints made in glued laminated timber (glulam) from softwood, experimental data concerning tests on a whole range of hardwood species are still lacking. Thus, to evaluate the influence of timber characteristics on the behaviour of the joint, test results from different species are presented and discussed in this paper. The experimental results from samples using softwood as well as high-density hardwood glued laminated timber are compared. Diverse geometries of the joint are studied in both cases. From this experimental analysis, a formula to predict the strength of the glued-in bars is proposed. The prediction of the strength is made from two parameters that are easily quantifiable the density of the timber and the slenderness of the glued joint. This model shows a good accuracy with the test results of joints made on different species both from softwood and hardwood.

A Finite Element Analysis of Bearing Resistance of Timber Loaded through a Steel Plate

Decrease projected length of bolts due to bending deformation in timber joints compresses the steel washers onto timber member and increases lateral resistance of the joints. As this lateral strength increase primarily depend on bearing characteristics of timber beneath the steel washers, a finite element analysis was performed to predict their bearing-embedment behavior. A 3-D finite element model consisting of 8-node solid and contact pair elements was developed using ANSYS assuming an anisotropic plasticity model for timber and an elastic-perfectly plastic model for the washers. Material constants for both steel washer and timber member were obtained from previous test data. The results of the analysis were in good agreement with the experimental load-embedment curves as well as the analytical curves obtained in a previous study based on a rigid-body-spring-model. The same approach was also used to evaluate the effective bearing length (under uniform compression) of a 50 mm depth timber block partially compressed.

Construction of Genetic Linkage Maps of Larch (Larix Kaempferi × Larix Gmelini) by Rapd Markers and Mapping of QTLS for Larch

ABSTRACTGenetic linkage mapping was performed with an interspecific mapping pedigree of 145 full-sib hybrids individuals of Japanese larch x Chinese larch (Larix kaempferi x Larix gmelini). A total of 210 random amplification of polymorphic DNA (RAPD) primers were used for mapping, and 581 segregating loci were identified. According to pseudo-testcross mapping strategy, we used mapping software to construct parent-specific linkage maps. The constructed linkage maps consisted of 48 sites in 5 linkage groups (four or more sites per group), 4 triplets, 6 linkage pairs for the maternal parent, and covered the map distance of about 546.5 cM, with the average map distance of 11.9 cM between adjacent markers. In addition, 91 sites in 9 linkage groups (four or more sites per group), 2 triplets, and 5 linkage pairs for the male parent covered the map distance of about 262.0 cM; the average map distance between adjacent markers was 6.1 cM. We detected the quantitative traits of the group by composite interval mapping, and analyzed the quantitative trait loci (QTL) with LOD ≥1.5. During analysis of the relationship between marker loci and traits, we obtained 4 and 20 QTLs, which were related to growth and timber characteristics. We found one QTL each for tracheid length and tracheid Length to Width ratio in Larix Kaempferi and nine, four, and five QTLs for specific gravity of wood, tracheid Length tracheid Width, respectively, in Larix gmelini. The LOD of every QTL was 1.5∼11.9, and the contribution rate was 0.0105∼45.9986%.

An effective thermal property framework for softwood in parametric design fires: Comparison of the Eurocode 5 parametric charring approach and advanced calculation models

Timber, like other structural materials such as concrete and steel, has its own Eurocode (Eurocode 5 part 1.2) for the structural fire design of buildings. However unlike other fire parts of the Eurocodes it is not widely adopted due to its inherent limitations. With the exception of a single Annex, the timber Eurocode (EN 1995-1-2) is only applicable to standard fire exposure. Annex A gives guidance on the charring rates of initially un-protected timber members in parametric fires, however in the UK the use of the Annex is prohibited by the national Annex to the code. The concrete and steel industries have undoubtedly benefited from performance based design whereby the structural fire design strategy is centred on a design fire (typically a parametric fire), which is more credible than the standard fire curve. Such an approach has resulted in more flexible, innovative buildings which have been designed based upon fundamental structural mechanics at elevated temperature, using advanced numerical models. At present however the same principals cannot be applied to the advanced fire design of timber buildings due to current limitations in the timber Eurocode. Where advanced calculation procedures are considered by the code (Annex B), much like many of the methods contained therein, the procedures are only applicable to standard fire exposure. The scope of applicability of the code stems from a fundamental problem regarding a lack of understanding of the heat transfer characteristics of timber in natural fires. The thermo-physical properties contained in the code are ‘effective’ properties. This essentially means that they are calibrated against test results to account for a lack of understanding regarding mass transfer, cracking and ablation both within the timber and char layer. Such calibrations have only been performed on timber members exposed to standard furnace conditions. To attempt to overcome this barrier and extend the scope of thermo-physical properties in the code a study has been undertaken to establish how the conductivity properties of the char layer influence the depth of char in parametric fires. Through calibration of an effective conductivity of the char layer against the parametric charring method contained in Annex A of EN 1995-1-2, it has been possible to establish a relationship between ‘heating rate’ and the effective conductivity of the char layer, in the heating phase of parametric fires. The modified conductivity model is shown to be applicable to a range of densities and moisture contents of timber and also variations in heating rate and fire load density. The latter is a direct result of the method used in the adaptation of the properties. The modified model is objectively critiqued and proposed further work is discussed in detail. The applicability of the modified model in the cooling phase of fires is also discussed.

The prehistoric pile-dwelling settlement of Stagno (Leghorn, Italy): wood and food resource exploitation

A pile-dwelling settlement, dated to the final Bronze–early Iron Age (XII–XI century BC), was excavated at Stagno, near Leghorn (Tuscany, Italy). The site presented a well-preserved portion of the wooden foundation structure buried by sediments rich in plant remains: both wood and plant remains were subjected to archaeobotanical investigation. The ultimate goal was to improve our knowledge on agricultural economy and wood usage in Tuscany during the prehistoric ages. The results pointed to a farming system based on Triticum spp. (wheat), Hordeum spp. (barley) and Leguminosae cultivation in addition to the gathering of wild fruits, such as Corylus avellana, Cornus mas, Prunus spp., Vitis spp. Many of these plant remains are associated to a wetland context. Mesohygrophilous trees, such as deciduous Quercus, Ulmus minor, Fraxinus cf. excelsior, and Sorbus were used for the construction of the pile-dwelling structures; the choice of these plants indicates a good knowledge of the technological characteristics of timber.

Buckling Strength of Timber Structures

The design procedures for the buckling strength of structures involves a complex interaction of strength and deformation equations. For timber structures, this complexity is amplified by the non-homogeneous, anisotropic and creep characteristics of timber. This paper describes some of the concepts used in the development of equations given in the Australian Standard AS1720.1 (Standards Australia, 1997), the Australian engineering code for the design of timber structures. The structural elements discussed include beams, columns, beam-columns, buckling restraints and plywood membranes.

Determination of Drying Characteristics of Timber by Using Artificial Neural Networks and Mathematical Models

In this research, poplar and pine timbers have been dried in heat pump dryer functioning on the basis of 24-h operation. The change in weight in all of the timbers was followed in the drying chamber and drying stopped when the desired weight was achieved. Initial moisture content of the poplar timbers was 1.28 kg water/kg dry matter, and the moisture content was reduced to 0.15 kg water/kg dry matter moisture content in 70 h; the moisture content of the pine timbers, which was 0.60 kg water/kg dry matter, was reduced to the same amount in 50 h. Drying air temperature, relative humidity, and stack weight were measured and collected during drying and saved on a computer and analyzed afterwards. The moisture ratios were analyzed with Statgraphic computer program by using semitheoretical models and empirical values. Correlation and standard error of estimation (SEE) and R 2 values were achieved.

Retention of wind-felled trees and the risk of consequential tree mortality by the European spruce bark beetle Ips typographus in Finland

Autumn storms felled about 7 million m3 of forest in southern Finland in 2001. Windthrow area and timber characteristics, as well as numbers of standing spruce trees attacked and killed by Ips typographus, were recorded in 61 Norway spruce [Picea abies (L.) Karst.]-dominated windthrow areas. Generalized linear models were used to identify significant variables predicting the risk for consequential tree mortality by I. typographus. None of the windthrow areas with fewer than 20 wind-felled spruce trees (WFS) (n=28) and only half of the areas with 20 or more WFS (n=33) harboured trees killed by I. typographus during the years 2003–2005. The quantity and diameter of WFS and the basal area of recently dead standing spruce trees correlated positively with the risk of tree deaths. This study indicates that in Finland, at endemic I. typographus population levels, it is safe to leave fewer than 20 WFS in managed forests. Retention of even larger quantities of trees does not seem to evoke significant numbers of consequential tree deaths by I. typographus in managed forests. However, in stands where the natural mortality of spruce trees is high, the risks of consequential tree deaths after wind disturbance will also be higher.

Technological advances in temperate hardwood tree improvement including breeding and molecular marker applications

Hardwood forests and plantations are an impor- tant economic resource for the forest products industry worldwide and to the international trade of lumber and logs. Hardwood trees are also planted for ecological reasons, for example, wildlife habitat, native woodland restoration, and riparian buffers. The demand for quality hardwood from tree plantations will continue to rise as the worldwide consumption of forest products increases. Tree improve- ment of temperate hardwoods has lagged behind that of coniferous species and hardwoods of the genera Populus and Eucalyptus. The development of marker systems has become an almost necessary complement to the classical breeding and improvement of hardwood tree populations for superior growth, form, and timber characteristics. Molecular markers are especially valuable for determining the reproductive biology and population structure of natural forests and plantations, and the identity of genes affecting quantitative traits. Clonal reproduction of commercially important hardwood tree species provides improved plant- ing stock for use in progeny testing and production forestry. Development of in vitro and conventional vegetative propagation methods allows mass production of clones of mature, elite genotypes or genetically improved genotypes. Genetic modification of hardwood tree species could potentially produce trees with herbicide tolerance, disease and pest resistance, improved wood quality, and reproduc- tive manipulations for commercial plantations. This review concentrates on recent advances in conventional breeding and selection, molecular marker application, in vitro culture, and genetic transformation, and discusses the future challenges and opportunities for valuable temperate (or "fine") hardwood tree improvement.

加力方法の違いが木造軸組工法耐力壁の復元力特性に及ぼす影響とそのモデル化手法 : 木造軸組工法耐力壁の耐風性能評価用復元力特性に関する研究 その1

In this paper, two kinds of statically cyclic loading experiments are carried out in order to obtain the restoring force characteristics of timber framed shear walls for evaluation of wind resistance performance. The cyclic loading programs are made in consideration of features of wind forces. One of loading programs is carried out under displace control state and the other is carried out under load control state. The restoring force characteristics obtained from those experiments are modeled for response analyses. Although the basic idea of modeling is based on the combination of a normal bilinear model and a slip model, the reduction of stiffness and energy absorption ability, or shift of displacement are also taken into consideration.

Molecular phylogenetic study of Hopea and Shorea (Dipterocarpaceae): Evidence from the trnL–trnF and internal transcribed spacer regions

Abstract Hopea and Shorea are economically important timber tree genera distributed throughout South‐East Asia. The taxonomic limits of these genera are problematic. Molecular phylogenies of Hopea and Shorea were inferred using two non‐coding regions of chloroplast (trnL–trnF) and nuclear ribosomal (internal transcribed spacer) DNA. The inferred phylogenetic relationships between Hopea and Shorea indicate that Shorea is paraphyletic and that Hopea is potentially monophyletic (particularly section Dryobalanoides). The inferred groupings within Shorea are very similar to a previous classification based on timber characteristics. The present study also identified four anomalous taxa, whose phylogenetic positions and taxonomic status require further investigation.

The influence of windthrow area and timber characteristics on colonization of wind-felled spruces by Ips typographus (L.)

Leaving wind-felled Norway spruces in forests is one way to increase the amount of dead wood. Many forest species would benefit because of these actions but unfortunately also forest pests such as the spruce bark beetle ( Ips typographus) reproduce in newly wind-felled trees. To minimize the risk of subsequent attacks on living trees, the decisions of removing trees out of the forest in high risk areas should be done as early as possible. If fallen trees are not colonized or if there are only a few colonized trees the risk of subsequent attacks on living trees are also minor. For this reason, it is essential to estimate the windthrow area and timber characteristics influencing the colonization of wind-felled trees. We studied the colonization of Norway spruce dominated windthrow areas by I. typographus (L.) in 65 stands in southern Finland on two consecutive summers after the storms in November 2001. The studied areas ranged from single tree gaps to large gaps with over 3000 wind-felled spruces. Using generalized linear modelling, we evaluated the significance of windthrow area and timber characteristics for the probability of the windthrow area to be colonized by I. typographus, the percentage of colonized wind-felled spruces, the number of egg galleries, and the colonization density. In the first summer (2002) after the wind-felling 71% of studied windthrow areas were colonized by I. typographus. Only 1 of the 19 areas not colonized in 2002 was colonized in 2003. The number and mean diameter of wind-felled spruces and the basal area of recently dead standing spruces were the most important windthrow characteristics influencing colonization. The models showed that an increase in these characteristics also increased the values of the response variables. This study shows that local population levels of I. typographus varied greatly within the study area (appox. 200 km × 200 km) and that this variation should be included in models predicting the colonization risks of windthrown areas.

Moisture detection in wood and plaster by IR thermography

In the last decade, many research have been carried on the application of IRT to detect moisture in the materials of historic buildings, but only few studies are comprehensive of IRT application on wood. The thermal characteristics of timber are highly different from the porous materials ones; particularly, the thermal capacity of wood is lower than bricks, stone and mortar. Laboratory researches and scientific literature determined that the water content detection in porous materials is more related the evaporation rate of the surfaces and the presence of soluble salts than to the absorption capability of the materials. Moreover a correlation between moisture content, evaporation and boundary conditions was studied by analyzing evaporation fluxes at different environmental conditions and water content. Because of the lower heat capacity of the timber, the thermographic shot after the heating can be affected by the influence of water presence. Lab tests and study cases show the advantages and the limit of the IRT techniques, and the results obtained permit the comparison between the different heating systems applied.

Mechanical characterization of timber from Spanish provenances of laricio pine according to European standards

The Spanish grown laricio pine (pinus nigra subsp. saltzmannii) covers an area of 353,000 hectares and produces an annual figure of 310,000 m3 of roundwood. It ranks as the fourth most important Spanish conifer and its timber is frequently used in construction. The results of the mechanical characterization of laricio pine timber coming from three different Spanish regions of provenance (R. 6 “Alto Maestrazgo”, R. 7 “Sistema Iberico Meridional” y, R.8 “Cordilleras Beticas”), carried out in accordance with the methodologies and requirements of EN 408, EN 384 and EN 338, are considered in the present study. 3612 boards, from 15 different samples ranging in size from 100×40×2500 mm to 200×70×4500 mm have been tested in accordance with EN 408. The samples represent the variety of cutting patterns, log sources, sizes and quality of the material present in the market.

Resistographic inspection of ancient timber structures for the evaluation of mechanical characteristics

Among non-destructive testing methods for the analysis of ancient timber structures, the Resistographic method is gaining great diffusion. This method is based on the registration of density variations through timber sections by means of an electronic drill and nowadays it is generally employed only to detect the presence of defects and damage. The present study is about the use of Resistographic method to evaluate mechanical characteristics of timber and, with this aim, an experimental program on wood-worm damaged timber has been carried on. Results show the usefulness of this non-destructive testing method as it allows the investigation through the interior part of timber and thus can give a quite reliable idea of local strength of wood in the examined section. That gives an useful parameter for the detection of recoverable elements in standing timber structures to be restored. In the present research, beech compressive strength has been evaluated from small clear wood specimens, while the evaluation of strength of dimensional lumber is outside the scope of the work.

Relationships between surface growth strain and some tree, wood and sawn timber characteristics ofEucalyptus cloeziana

SYMMARY To assess the utility of the CIRAD-Fort% growth strain gauge for estimating stein growth stress, the relationship of longitudinal growth strain (LGS) with log-end splitting, sawn timber distortion and other tree and wood properties was studied in 23 ten-year-old Eucalyptus cloeziana trees. The CIRAD-Foret growth strain gauge appears to be useful as a means of predicting sawn timber distortion in young E. cloeziana trees. LGS correlated well with bow and spring and accounted for 50 and 30% of the respective total variation. The relationships of LGS with log end splitting, wood density, tree diameter and height were weak. However, distinct differences in wood density and sawtimber distortion were observed between trees with low and high strain. Trees with high growth strain were generally smaller with wood of significantly higher basic density and bow. Sampling position around the stem was not important and LGS increased with tree height.