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Perpendicular to grain and shear mechanical properties of veneer-based elements glued from single veneer sheets recovered from three species of juvenile subtropical hardwood plantation logs

Authors:
Benoit P Gilbert at Griffith University
Benoit P Gilbert
Julien M. Husson
Julien M. Husson
Julien M. Husson
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Henri Baillères at Queensland University of Technology
Henri Baillères
Robert L McGavin at Qld Department of Agriculture and Fisheries
Robert L McGavin
  • Qld Department of Agriculture and Fisheries
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Abstract and Figures

This paper quantifies the mechanical properties perpendicular to the grain and in shear of glued rotary peeled veneers, as would be encountered in veneer-based structural products (i.e. by including both the effects of hot pressing the veneers and the glue used during the manufacturing process), of three species recovered from juvenile (early to mid-rotation) subtropical hardwood plantation logs. This underutilised resource has currently little to no commercial value in Australia but proven potential to produce attractive veneer-based structural products. Determining these unknown properties is important as they constitute essential input data to ultimately predict the behaviour and design properties of veneer-based structural products in cost-effective numerical simulations. Two species planted for solid timber end-products (Gympie messmate—Eucalyptus cloeziana and spotted gum—Corymbia citriodora) and one species traditionally grown for pulpwood (southern blue gum—Eucalyptus globulus) are considered in the paper. The dynamic modulus of elasticity, compressive and tensile strengths perpendicular to the grain of veneer-based elements, each manufactured from single veneer sheets, were experimentally measured and are analysed herein. These properties are found to have no to weak correlation to the parent veneer sheet dynamic modulus of elasticity parallel to the grain, a value which is commonly measured in line to grade veneers. The shear modulus (in the longitudinal-tangential plane), also referred to as “modulus of rigidity”, through-the-thickness and rolling shear strengths were also experimentally measured, and the results are discussed in the paper. Little to no correlation to the veneer sheet dynamic modulus of elasticity parallel to the grain was found for these properties. Weibull distributions are fitted to all test results and presented to probabilistically consider the investigated properties in numerical simulations of veneer-based structural products.
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Vol.:(0123456789)
1 3
European Journal of Wood and Wood Products (2018) 76:1637–1652
https://doi.org/10.1007/s00107-018-1350-8
ORIGINAL
Perpendicular tograin andshear mechanical properties ofveneer-
based elements glued fromsingle veneer sheets recovered fromthree
species ofjuvenile subtropical hardwood plantation logs
BenoitP.Gilbert1 · JulienM.Husson1· HenriBailleres2· RobertL.McGavin2· MaximeF.Fischer1
Received: 8 May 2018 / Published online: 20 September 2018
© Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
This paper quantifies the mechanical properties perpendicular to the grain and in shear of glued rotary peeled veneers, as
would be encountered in veneer-based structural products (i.e. by including both the effects of hot pressing the veneers
and the glue used during the manufacturing process), of three species recovered from juvenile (early to mid-rotation) sub-
tropical hardwood plantation logs. This underutilised resource has currently little to no commercial value in Australia but
proven potential to produce attractive veneer-based structural products. Determining these unknown properties is important
as they constitute essential input data to ultimately predict the behaviour and design properties of veneer-based structural
products in cost-effective numerical simulations. Two species planted for solid timber end-products (Gympie messmate—
Eucalyptus cloeziana and spotted gum—Corymbia citriodora) and one species traditionally grown for pulpwood (southern
blue gum—Eucalyptus globulus) are considered in the paper. The dynamic modulus of elasticity, compressive and tensile
strengths perpendicular to the grain of veneer-based elements, each manufactured from single veneer sheets, were experi-
mentally measured and are analysed herein. These properties are found to have no to weak correlation to the parent veneer
sheet dynamic modulus of elasticity parallel to the grain, a value which is commonly measured in line to grade veneers. The
shear modulus (in the longitudinal-tangential plane), also referred to as “modulus of rigidity”, through-the-thickness and
rolling shear strengths were also experimentally measured, and the results are discussed in the paper. Little to no correlation
to the veneer sheet dynamic modulus of elasticity parallel to the grain was found for these properties. Weibull distributions
are fitted to all test results and presented to probabilistically consider the investigated properties in numerical simulations
of veneer-based structural products.
1 Introduction
When a manufacturer of engineered wood products wishes
to introduce new veneer-based structural products on the
market, such as those manufactured from new timber species
(Boughton and Crews 2013) or from an optimisation strategy
of the existing veneered stock, an experimental campaign
must be undertaken. The campaign aims at determining the
strength and stiffness distributions of the new products and
ultimately derive the design properties. A minimum of 30
and 32 tests per design property is required in the Australian/
New-Zealand (AS/NZS 2269.1 2012; AS/NZS 4357.2 2006)
and European (EN 1058 2009) standards, respectively. A
costly trial-and-error procedure may therefore be needed to
achieve targeted design properties.
Nevertheless, to efficiently determine and optimise
the mechanical properties of new veneer-based structural
products, numerical models which aim at determining the
Electronic supplementary material The online version of this
article (https ://doi.org/10.1007/s0010 7-018-1350-8) contains
supplementary material, which is available to authorized users.
* Benoit P. Gilbert
b.gilbert@griffith.edu.au
Henri Bailleres
henri.bailleres@daf.qld.gov.au
Robert L. McGavin
robbie.mcgavin@daf.qld.gov.au
1 School ofEngineering andBuilt Environment, Griffith
University, GoldCoast, QLD4222, Australia
2 Salisbury Research Facility, Queensland Government,
Salisbury, QLD4107, Australia
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Other properties were taken from the literature, either for Gympie messmate (when available) or for hardwood species of similar density. Specifically, the MOE in the radial ER and tangential ET directions, and the shear modulus in the longitudinal-radial GLR and longitudinal-tangential GLT planes were taken as the typical values encountered for juvenile Gympie messmate [28]. Note that these values were shown to be uncorrelated to EL [28] and were herein assumed as constants. ...
... Specifically, the MOE in the radial ER and tangential ET directions, and the shear modulus in the longitudinal-radial GLR and longitudinal-tangential GLT planes were taken as the typical values encountered for juvenile Gympie messmate [28]. Note that these values were shown to be uncorrelated to EL [28] and were herein assumed as constants. The shear modulus in the radial-tangential GRT plane and the Poisson ratios γLR, γLT, γRT were taken for species of similar density in [29]. ...
... The shear strengths in the longitudinal-radial fs,LR and longitudinal-tangential fs,LT planes were taken as the median value measured for the 145 mm diameter CHS in [2] (rounded to the closest integer). The rolling shear strength fs,RT was taken as the 50 th percentile value measured in [28] on the same resources used in manufacturing the CHS. Table 4 summarises all tensile and shear strength values used. ...
Veneer-based timber circular hollow section beams: Behaviour, modelling and design
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Various forms of timber hollow structural profiles have either been proposed in the literature or are already commercially available. Tests performed on Circular Hollow Section (CHS) beams showed failure modes not usually encountered in timber structures. For relatively thin-walled profiles, a sudden failure in the compression zone, with the opening of the cross-section, was observed. To confidently use and market CHS timber products, design rules considering all possible failure modes must be developed. This paper presents a Finite Element (FE) model of CHS timber beams which captures all experimentally observed failure modes. Cohesive zone elements were used to model the quasi-brittle failure modes of the timber material. The model was validated against ten experimental tests performed on CHS of three different cross-sectional slenderness and manufactured from juvenile hardwood Gympie messmate (Eucalyptus cloeziana) rotary peeled veneers. The model was found to accurately capture the measured structural behaviour and resulted in an average experimental-to-predicted bending capacity ratio of 1.02. The model was also used to explain the mechanisms leading to the sudden compressive failure mode. A parametric study was finally performed on 72 CHS beams of different cross-sectional slenderness. Results showed a strong correlation between the cross-sectional slenderness ratio and section capacity. Design rules are proposed and discussed.
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... Unlike plywood products, which have alternate cross-laminated veneers (Walker 2006), LVL-C that is usually manufactured with one-fifth of veneers glued crosswise was proposed to overcome the low mechanical properties perpendicular to the grain typically encountered in LVL, resulting in the possibility of premature splitting failure in structural connections (Kobel et al. 2014). Especially, relevant to this study, low tension perpendicular to the grain capacity (about 1.0 to1.5 MPa) were reported for VBP manufactured from small-diameter plantation-grown SPG logs (Gilbert et al. 2018a). ...
... Tensile strength perpendicular to the grain The tensile strength perpendicular to the grain was determined following the configuration in the ASTM D143-14 (2014) that was developed for solid timber specimens. The procedure was successfully adopted in the literature to LVL samples (Ardalany et al. 2011;Gilbert et al. 2018a). Three samples were cut per panel to the dimensions given in Fig. 3a. ...
Key Mechanical Properties of Cross-banded Laminated Veneer Lumbers Manufactured from Blending Spotted Gum and Hoop Pine Veneers
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The main objective of this study was to investigate the key mechanical properties of cross-banded laminated veneer lumbers (LVL-C) manufactured from blending veneers recovered from sub-optimal native forest spotted gum and plantation hoop pine logs. The recovered veneers were separated into three grades based on their dynamic modulus of elasticity (MOE). Additionally, the spotted gum veneers were visually graded to evaluate whether a relationship exists between the MOE-based and visual grades. In total, six 12-ply reference LVL and six mixed-species 12-ply LVL-C panels were manufactured and analyzed for (i) flatwise and edgewise bending performance; (ii) bearing and tension strength perpendicular to the grain; and (iii) longitudinal-tangential shear strength. Little correlation was found between MOE-based and visual grades for the spotted gum veneers. The LVL- C showed flatwise and edgewise MOE up to 24% and 13% lower, respectively, than the reference mixed-species LVL. The flatwise and edgewise modulus of rupture were up to 39% and 19% lower, respectively. On average, the tensile and bearing strengths of the LVL-C were considerably higher than the hoop pine LVL and mixed-species LVL, with the former being approximately three times higher. The manufactured LVL-C showed markedly higher bending properties and tensile strengths than commercial LVL-C products.
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... Guo and Altaner [4] combined rotary peeled veneer of eucalyptus (hardwood) and radiata pine (softwood) to examine the effect of growth-strain on the mechanical behaviour of hybrid LVLs. Gilbert et al. [5] explored the suitability of using juvenile wood from three different hardwood species. Other studies on mechanical properties of LVL examine the influence of veneer thickness [6][7][8], the proportion of juvenile wood [7], orientation of loose (the side with lathe checks) and tight side of the veneers [7,9], the effect of loading directions [10], the bonding quality at the veneer interface [6] and knot proportions within the veneers [8]. ...
Damage resistance and open-hole strength of thin veneer laminates: Adopting design and testing principles from fibre-reinforced polymers
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Bulky, thick solid wooden parts are typically used despite the fact that such cross-sections do not yield the optimal load transfer. This study investigates thin quasi-isotropic [90∕45∕0∕ − 45] Beech veneer laminates subjected to a range of mechanical tests derived from fibre-reinforced counterparts. The results of standard tension, open-hole tension and compact tension tests in combination with digital image correlation and cross-sectional microscopy reveal that Beech veneer laminates can be tested and analysed in the same manner as fibre-reinforced laminates, leading to consistent values of strength and damage resistance as a result of reliable and repeatable damage patterns. It is found that modulus (5.5 GPa), tensile strength (70 MPa) and open-hole strength as well as translaminar fracture energy (5-14 kJ/m 2) are one order of magnitude lower compared to fibre-reinforced polymer composites.
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... In this regard, Eucalyptus globulus Labill (also known as southern blue gum) stands out as a highperformance hardwood of significant interest, due to its fast growth, high mechanical properties, and good natural durability. Recently, there has been increasing industrial and institutional interest driving scientific research on E. globulus in different fields, such as silviculture [5][6][7][8], mechanical characterisation of the material with small clear specimens [9,10] and structural size [11,12], performance of bonded joints for laminated products [13,14], as well as research related to the development of higher added value building and engineering wood products using this species, such as finger-jointed solid timber [11], glued laminated timber [15], cross-laminated timber (CLT) [16,17], laminated veneer lumber (LVL) and plywood [18][19][20] or nail-laminated timber (NLT) and NLTconcrete composite floor panels [21]. ...
Splitting capacity of Eucalyptus globulus beams loaded perpendicular to the grain by connections
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In timber structures, knowledge of the splitting capacity of beams loaded perpendicular to the grain by dowel-type connections is of primordial importance since brittle failure can occur. In the present work, single-and double-dowel-type connections following different loaded edged distance arrangements are experimentally investigated to derive the splitting behaviour of Eucalyptus globulus L., which is a hardwood species of increasing interest for structural use due to its high mechanical performance , fast growth, and good natural durability. The correlation of experimental failure loads with those theoretically predicted by the expression included in Eurocode 5 and by eight analytical models based on an energetic approach is discussed. Most of the analytical models studied overpredict the splitting capacity. However, the code splitting expression, derived from softwoods, proves to be very conservative in predicting the eucalyptus splitting failure load.
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... Specifically, (1) the tension strength perpendicular to the grain was estimated by testing five samples, cut from five different LVL products, following the methodology and sample size recommended in the ASTM D143-14 [69]. While provided for small clear timber specimens, this methodology has been applied to LVL samples in [70][71][72]. The samples were tested in a 30 kN Instron universal testing machine at a stroke rate of 0.3 mm/min. ...
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In this study, an experimental program was carried out to investigate the dynamic behaviour of post-and-beam mass timber frames, manufactured from LVL structural products, under a sudden column removal scenario. Twenty-five free-fall and two additional static tests were performed on scaled-down frames assembled with three beam-to-column connection types, referred to as “Double-beam”, “Megant type” and “T-section”, currently used in mass timber buildings. The structural responses, failure modes and dynamic increase factors (DIF) are presented and discussed. For frames assembled with connections exhibiting a brittle failure in the timber, the cracks were found to develop earlier in dynamic tests than in static tests, resulting in large experimental DIF values over 2.0. However, for connections displaying ductile failure modes, the design DIF value of 1.5 proposed in the literature was found to be reasonable. Pseudo-static responses were calculated and found to be inconsistent in predicting the dynamic responses. This paper presents an essential understanding of the dynamic behaviour of post-and-beam mass timber frames and lay the foundation for future further studies aiming at investigating the dynamic responses of the entire post-and-beam mass timber buildings with, e.g. cross laminated timber (CLT) floors.
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... (iii) The tensile strength perpendicular to the grain was measured following the configuration in ASTM D143-14 (2014), which was devised for solid timber specimens. The procedure has been previously applied to LVL samples and proven successful (Ardalany et al. 2011;Gilbert et al. 2018). The sample dimensions are shown in Fig. a. ...
A Comparative Study on the Mechanical Properties of Laminated Veneer Lumber (LVL) Produced from Blending Various Wood Veneers
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Rotary veneers from spotted gum (Corymbia citriodora) and white cypress pine logs (Callitris glaucophylla) recovered from the native forest in Queensland, as well as Queensland plantation hoop pine (Araucaria cunninghamii) logs were used to manufacture LVL products following six different lay-up strategies including blended species LVL. The different lay-up strategies were to determine the opportunities for improving the mechanical performance of plantation softwood LVL by including native forest veneers. The manufactured products were evaluated for their bending performance, tension, bearing strength perpendicular to the grain, and longitudinal-tangential shear strength. The all-spotted gum LVL showed superior performance in all testing compared to other construction strategies. Blending even a small amount of spotted gum veneer with plantation hoop pine veneer resulted in improved mechanical performance, especially in flatwise bending. Opportunities exist to develop more optimised construction strategies that target specific product performances while optimising the use of the variable veneer qualities generated from log processing.
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TECHNOLOGICAL PROCESS OF OBTAINING PEELED VENEER: THE INFLUENCE OF EXTERNAL TEMPERATURE CONDITIONS ON THE DEFROSTING AND WARMING UP OF WOOD
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To obtain high-quality peeled veneer, heating of wood is a mandatory technological operation. In winter, it is necessary to first thaw, and then warm up the wood to a certain temperature on the surface of the pencil. The operation of thawing and warming up is performed in open or closed water pools. One of the main factors of this technological operation is their duration. The available calculation formulas for employees of plywood enterprises are quite complex, since a number of values are selected from a large number of literary sources, and in the future, a number of parameters are calculated that determine the duration of thawing and heating of wood. In recent years, enterprises, in order to intensify the process of heating wood, are switching from open to closed pools. The results of the continuation of the TRP of wood in a closed water basin presented in the work will allow specialists to determine the desired time parameters without additional calculations. The results obtained showed that the determining factors for the duration of the TRP of wood in the production of plywood are not only the temperature of the air and the temperature of the water in the pool, but also the density of wood. Thus, for denser types of wood (birch, larch) used in the production of plywood, more time is required for thawing and heating. Moreover, the main heating of wood occurs at a pool water temperature of 60 °C, when thawing of wood occurs. After that, the duration of heating the wood to a temperature of 20 °C on the surface of the pencil is significantly reduced, especially at a pool water temperature of 80 °C.
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Mechanical Properties of Rotary Veneers Recovered from Early to Midrotation Subtropical-Hardwood Plantation Logs for Veneer-Based Composite Applications
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This paper experimentally investigates the mechanical properties of rotary veneers peeled from small-diameter hardwood plantation logs, recovered from early to midrotation subtropical hardwood plantations. The study aims at providing essential probabilistic data needed to ultimately predict the capacity and reliability of veneer-based composites structural products [such as laminated veneer lumber (LVL) and plywood] from characteristics that can be measured in line during manufacturing. Two species planted for solid timber endproducts (Gympie messmate, Eucalyptus cloeziana, and spotted gum, Corymbia citriodora) and one species traditionally grown for pulpwood (southern blue gum, Eucalyptus globulus) were studied. The compressive and tensile modulus of rupture (MOR) of the veneers, parallel to the grain and for veneer-based composite applications, were experimentally investigated. Results show that the compressive MOR for all species typically ranges from 30 to 50 MPa [for modulus of elasticity (MOE) < 12,000 MPa] to 60 to 90 MPa (for MOE > 22,000 MPa). The tensile MOR is typically lower than or in the range of the compressive MOR for MOE less than 12,000 MPa, while for larger MOE (MOE > 22,000 MPa) tensile MOR greater than 140 MPa were observed. The total knot area ratio (tKAR) of the veneers is also analyzed and Weibull distributions were found to provide a good characterization of the statistical repartition of the tKAR value along the length of a veneer sheet. For each species, equations to best predict a veneer MOR from its measured MOE and tKAR value are derived and fit the experimental results with a coefficient of determination between 0.63 and 0.74. The variability of the MOR of each species was accurately modeled by Weibull distributions, with the distribution parameters determined based on the experimental data. Results shown that southern blue gum and Gympie messmate are the most and least sensitive species to size effects, respectively.
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Tension perpendicular to grain strength of wood, Laminated Veneer Lumber (LVL) and Cross-Banded LVL (LVL-C)
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Recent experimental tests carried out on structural timber members have highlighted the importance of tension perpendicular to grain strength, particularly in beams with holes and notches, in connection regions, in curved beams, and in post-tensioned timber frames, Innovative engineered wood products such as Cross Banded Laminated Veneer Lumber (LVL-C) have been introduced into the market specifically to improve the perpendicular to grain properties of normal Laminated Veneer Lumber (LVL), This paper reports on tests that were performed at the University of Canterbury using specimens of sawn timber Radiata Pine, LVL and LVL-C. The perpendicular to grain tension strengths of LVL was generally lower than those for sawn timber, but the LVL-C showed a significantly improved strength. The paper also compares the experimental results with strengths predicted using both coupled elastic Finite Element Method (FEM) and Linear Elastic Fracture Mechanics (LEFM) models. These models were found to predict the average strength with reasonable accuracy.
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Commercial interest in Australian hardwood plantations is increasing. The timber industry is investigating alternative supplies of forest resources, and the plantation growing industry is eager to explore alternative markets to maximize financial returns. Identifying suitable processing strategies and high-value products that suit young, plantation-grown hardwoods have proven challenging; however, recent veneer processing trials using simple veneer technology have demonstrated more acceptable recoveries of marketable products. The recovered veneers have visual qualities that are suitable for structurally-based products; however, the mechanical properties of the veneer are largely unknown. Veneers resulting from processing trials of six commercially important Australian hardwood species were used to determine key wood properties (i.e., density, dynamic modulus of elasticity (MoE), and specific MoE). The study revealed that a wide variation of properties existed between species and also within species. Simple mathematical modeling, using sigmoidal curves, was demonstrated to be an effective method to model the evolution of key wood properties across the billet radius and along the resulting veneer ribbon with benefits for tree breeders and processors.
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Variation in Rotary Veneer Recovery from Australian Plantation Eucalyptus globulus and Eucalyptus nitens
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The processing of Australian plantation-grown Eucalyptus globulus and E. nitens into rotary veneer was shown to produce acceptable recoveries. Three plantation sites for each species were sampled. Silvicultural treatments (thinning and pruning) and growing environments varied between sites. Graded veneer recoveries were dominated by D-grade veneer across all six sites. Variation between the E. nitens sites was evident, with recoveries differing between sites reflecting silvicultural treatments. However, only minimal variation in recovery was shown between the E. globulus sites. The presence of similar levels of defects across all E. globulus sites indicates that the intensive silvicultural management at one site studied was not effective in the production of clear wood, and may possibly have adversely affected grade recovery. Veneer value analysis demonstrated only minimal differences between E. globulus sites. More variation was observed in the E. nitens value analysis; however, intensive silvicultural management implemented did not necessarily result in higher veneer value.
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Compressive Strength Prediction of Veneer-Based Structural Products
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Veneer-based structural products, such as laminated veneer lumber (LVL) or plywood, are commonly used in timber construction. When a manufacturer wishes to use new timber species or optimize the use of its veneered stock, the nominal design values of the new products need to be determined from comprehensive and expensive experimental investigations. In an effort to cost-effectively determine these characteristics, this paper introduces a methodology to numerically predict the compressive strength of veneer-based structural products. The method combines a classical elastoplastic approach with a probabilistic strength-prediction model of the wood veneers. The veneer strength is determined from its size and characteristics which can be measured in line during manufacturing. The accuracy of the approach is verified against experimental tests performed on 24 LVL samples manufactured from two different timber species and of various sizes. Results show that the approach accurately predicts the strength of the LVL samples with an overall predicted:experimental ratio of 1.05 and low coefficient of variation of 0.08. The methodology is applied to determine the compressive strength distributions of LVL columns and plywood boards manufactured from a new resource, namely early to midrotation (juvenile) hardwood plantation logs. The approach considers three different species, Gympie messmate (Eucalyptus cloeziana), spotted gum (Corymbia citriodora), and southern blue gum (Eucalyptus globulus). The modeled compressive design strength of the new products is found to be of the same order of magnitude of and up to 1.6 times greater than the strength of commercialized LVL columns and plywood boards.
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Eucalyptus nitens laminated veneer lumber structural properties
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Veneer peeled from Eucalyptus nitens (Deane et Maiden) Maiden unpruned second logs was segregated into three stiffness classes using an acoustic test. Laminated veneer lumber (LVL) was manufactured using sheets from each stiffness class tested. Strength tests showed that the sheets were successfully segregated by the acoustic stiffness test. The E. nitens LVL had strength and stiffness properties which were higher than those of LVL made from New Zealand-grown Pinus radiata D.Don veneer.
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