ArticlePublisher preview available

Embedment strength of mixed-species laminated veneer lumbers and cross-banded laminated veneer lumbers

DOI:10.1007/s00107-020-01504-1
Authors:
Hoan Nguyen at Griffith University
Hoan Nguyen
Benoit P Gilbert at Griffith University
Benoit P Gilbert
Robert L McGavin at Qld Department of Agriculture and Fisheries
Robert L McGavin
  • Qld Department of Agriculture and Fisheries
Henri Baillères at Queensland University of Technology
Henri Baillères
Show all 5 authorsHide
Read publisher preview
Download citation
To read the full-text of this research, you can request a copy directly from the authors.

Abstract and Figures

This paper experimentally evaluates the embedment strength of laminated veneer lumbers (LVL) and cross-banded laminated veneer lumbers (LVL-C) manufactured from blending spotted gum (Corymbia citriodora) or white cypress pine (Callitris glaucophylla) veneers with hoop pine (Araucaria cunninghamii) veneers. Nominal 3.0 mm thick veneers were rotary peeled from small diameter (less than 30 cm) native forest sourced spotted gum and white cypress pine logs, and plantation grown hoop pine logs. 12-ply × 1.2 m (long) × 0.9 m (wide) LVL and LVL-C panels were manufactured using ten different construction strategies by mixing (i) the number of veneers from each species, (ii) the modulus of elasticity of the veneers and (iii) the veneer orientations (cross-banding). A total of 672 embedment tests, using three different dowel diameters and four different load-to-grain orientation angles, were performed using the half-hole test method described in the ASTM D5764-97a. This paper (i) compares the proportional limit strength, 5%-offset embedment strength and maximum embedment strength across the different construction strategies adopted in the study, and (ii) discusses the results in terms of load-to-grain angle and dowel diameter. More importantly, the test results are also compared to the embedment strength prediction equations detailed in the Eurocode 5 to determine their suitability for mixed-species LVL and LVL-C products. Overall, the mixed-species LVL and LVL-C showed significantly higher 5%-offset embedment strengths than single-species commercial softwood LVL products. The effect of the cross-banded veneers on the embedment strength was not found to be significant. However, the LVL-C samples exhibited a highly ductile behaviour for all load-to-grain angles and dowel diameters when compared to the LVL samples. The experimentally determined 5%-offset and maximum embedment strengths for the mixed-species LVL were on average equal to and 7% higher than the predicted values given in Eurocode 5.
Figures - available from: European Journal of Wood and Wood Products
This content is subject to copyright. Terms and conditions apply.
  • A preview of this full-text is provided by Springer Nature.
  • Learn more
Preview content only
Content available from European Journal of Wood and Wood Products
This content is subject to copyright. Terms and conditions apply.
Vol.:(0123456789)
1 3
European Journal of Wood and Wood Products (2020) 78:365–386
https://doi.org/10.1007/s00107-020-01504-1
ORIGINAL
Embedment strength ofmixed‑species laminated veneer lumbers
andcross‑banded laminated veneer lumbers
HoanH.Nguyen1 · BenoitP.Gilbert1· RobertL.McGavin2· HenriBailleres2· HassanKarampour1
Received: 4 June 2019 / Published online: 6 February 2020
© Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
This paper experimentally evaluates the embedment strength of laminated veneer lumbers (LVL) and cross-banded laminated
veneer lumbers (LVL-C) manufactured from blending spotted gum (Corymbia citriodora) or white cypress pine (Callitris
glaucophylla) veneers with hoop pine (Araucaria cunninghamii) veneers. Nominal 3.0mm thick veneers were rotary peeled
from small diameter (less than 30cm) native forest sourced spotted gum and white cypress pine logs, and plantation grown
hoop pine logs. 12-ply × 1.2m (long) × 0.9m (wide) LVL and LVL-C panels were manufactured using ten different construc-
tion strategies by mixing (i) the number of veneers from each species, (ii) the modulus of elasticity of the veneers and (iii) the
veneer orientations (cross-banding). A total of 672 embedment tests, using three different dowel diameters and four different
load-to-grain orientation angles, were performed using the half-hole test method described in the ASTM D5764-97a. This
paper (i) compares the proportional limit strength, 5%-offset embedment strength and maximum embedment strength across
the different construction strategies adopted in the study, and (ii) discusses the results in terms of load-to-grain angle and
dowel diameter. More importantly, the test results are also compared to the embedment strength prediction equations detailed
in the Eurocode 5 to determine their suitability for mixed-species LVL and LVL-C products. Overall, the mixed-species
LVL and LVL-C showed significantly higher 5%-offset embedment strengths than single-species commercial softwood LVL
products. The effect of the cross-banded veneers on the embedment strength was not found to be significant. However, the
LVL-C samples exhibited a highly ductile behaviour for all load-to-grain angles and dowel diameters when compared to the
LVL samples. The experimentally determined 5%-offset and maximum embedment strengths for the mixed-species LVL
were on average equal to and 7% higher than the predicted values given in Eurocode 5.
1 Introduction
Connections with dowel-type fasteners are very common
in timber structures and are generally deemed to be the
weakest structural link (Leijten 1993). This type of connec-
tion can be either ductile, brittle or a combination of both
(Habkirk 2006; Quenneville and Mohammad 2000; Quen-
neville 2008). To estimate their ductile failure capacity, the
European Yield Model (EYM) (Johnsen 1949) forms the
basis of the prediction equations in standards such as the
Eurocode 5 (EN1995-1-1 2004), and is considered to be
accurate (Franke and Quenneville 2011). In this model, the
embedment strength of the timber is one of the key input
parameters to determine the overall connection capacity and
is related to the capacity of wood or wood-based products to
resist the force induced by a rigid fastener.
The estimation of the embedment strength of various
timber species and fastener types has been extensively stud-
ied, see Ehlbeck and Werner (1992), Hirai (1989), Hübner
(2008), Larsen (1973), Whale etal. (1986, 1989), Wilkinson
(1991) for instance. This led to the development of vari-
ous forms of empirical equations. Wilkinson (1991) derived
Eqs.(1) and (2) (in psi and inches) below for the 5%-offset
embedment strength (ASTM D5764-97a 2018) from tests
performed on several softwood and hardwood species with
load-to-grain angles of 0° (parallel to grain) fh,0 and 90°
(perpendicular to grain) fh,90. These equations were con-
structed based on the timber specific gravity (G) (i.e. the
ratio between the weight densities of timber and water) and
* Hoan H. Nguyen
hoan.nguyenhai@griffithuni.edu.au;
nguyenhaihoanvfu@gmail.com
1 School ofEngineering andBuilt Environment, Griffith
University, Brisbane, QLD, Australia
2 Queensland Department ofAgriculture andFisheries,
Horticulture andForestry Science, Salisbury Research
Facility, Brisbane, QLD, Australia
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Confirming the study´s results, hybrid products using low-quality hardwood such as mixed hardwood LVL Nguyen et al. 2020, innovative mixed-hardwood pulp (Olsson et al. 2019), and mixed soft-and hardwood pulp (Fišerová et al. 2019) are actually under investigation. ...
Developing and evaluating strategies to increase the material utilisation rate of hardwoods: a hybrid policy Delphi-SWOT analysis
Article
Full-text available
The indigenous hardwoods in German forests have a substantial ability to store carbon, and forestry reconstruction measures are anticipated to result in an increase in availability of hardwood on the wood market. Despite this, its material usage is declining with over two thirds of the harvested quantity being used for energy production. This study aims to identify policy measures and promising strategies for increasing hardwood utilisation using a combined policy Delphi-SWOT approach with literature review undertaken to identify the barriers and driving factors for an increase in its material use. The results were then ranked by a panel of experts and used as basis for the SWOT analysis, which was then applied to an extended SWOT approach. The resulting strategies were then discussed by the panel and ranked further in the 2nd and 3rd Delphi round. After three Delphi rounds, three strategies and associated policy recommendations were ranked as most effective by the experts: innovative hardwood products including manufacturing processes, research transfer and lobbying. This study provides both strategic analyses and effective strategies to stimulate the production of hardwood-based products and ends with a concise description of these strategies and policy recommendations, which are benchmarked against current literature and best practise examples.
Experimental Study of Aluminium-Timber Composite Bolted Connections Strengthened with Toothed Plates
Article
Full-text available
  • Jul 2022
This paper presents the first experimental study of the load-slip behaviour of aluminium-timber composite bolted connections reinforced with toothed plates. The effectiveness of the strengthening was evaluated in laboratory push-out tests. The push-out test samples consisted of laminated veneer lumber panels, aluminium alloy I-beams, and bolts (grade 8.8 10 mm × 125 mm and 12 mm × 135 mm bolts, grade 5.8 10 mm × 125 mm and 12 mm × 135 mm bolts). A group of 16 specimens had toothed plates as additional reinforcement, while 16 specimens had no reinforcement. The impact of the bolt diameter (10 and 12 mm) and bolt grade (5.8 and 8.8) on the behaviour of the connections was also analysed. The values of the ultimate load and the slip modulus for the bolted connections with grade 8.8 10 mm and 12 mm bolts and with grade 5.8 12 mm bolts reinforced by toothed-plate connectors were comparable to the values for the non-reinforced connections. This was because, in the case of grade 8.8 10 mm × 125 mm and 12 mm × 135 mm bolts and grade 5.8 12 mm × 135 mm bolts, the laminated veneer lumber (LVL) slabs split both in the reinforced and non-reinforced connections. The toothed-plate connectors reduced timber destruction in the bearing zones in the LVL slabs. However, they did not protect the LVL slabs against splitting. Therefore, the impact of the toothed plate connectors on the stiffness and strength of the bolted connections with grade 8.8 10 mm and 12 mm bolts and with grade 5.8 12 mm bolts analysed in this paper was found to be negligible. In the case of grade 5.8 10 mm bolts, the LVL slabs did not split. The mean slip modulus k0.6 of the connections with grade 5.8 10 mm bolts reinforced with toothed plate connectors was 2.9 times higher than that of the non-reinforced connections. However, the strength of the connections with grade 5.8 10 mm bolts was 1.2 times lower after reinforcing. This was because the shanks of the bolts were sheared faster in the reinforced connections than in the non-reinforced connections as a result of the bolt shanks being under the bearing pressure of the aluminium flange, the LVL slab, and the toothed-plate flange. This situation did not occur for the remaining connections because they had a higher strength (grade 8.8 bolts) or a larger diameter (12 mm), and their bolts were less prone to cutting off. The investigated load–slip curves of the reinforced bolted connections can be used for designing and numerical modelling of aluminium-timber composite beams with this type of connection.
Discussion of testing and evaluation methods for the embedment behaviour of connections
Conference Paper
Full-text available
  • Aug 2014
Timber, embedment, standards, testing methods, full-hole test, half-hole test, evaluation methods, discussion
Experimental Analysis on the Structural Behaviour of Connections with LVL Made of Beech Wood
Conference Paper
Full-text available
  • Oct 2013
Despite its higher strength and stiffness properties as compared to most softwood species, beech wood is today almost entirely used for energetic purposes or non-structural applications. Benefitting from elevated mechanical properties and a reliable high degree of homogeneity, Laminated Veneer Lumber (LVL) made of beech has a great potential for applications in high performance structural elements, for instance in large span truss structures. As the performance of timber truss structures predominantly depends on the efficiency of the connections, an experimental analysis of dowel-type connections in beech LVL was performed. A series of embedment tests was carried out according to EN 383:2007, the parameters being the dowel diameter and the end distance of the connectors. The tests showed a very ductile behaviour of the material, high values of embedment strength and a low scatter in the results (CoV < 5%). These findings were confirmed in subsequent tensile tests on full dowel connections. The tested connections consisted of four dowels and two slotted-in steel plates, the examined parameters were the dowel diameter and the spacing. Provided that an adequate spacing is guaranteed, the full connections also showed a very ductile behaviour. The common problem of premature splitting failure did not occur due to the favourable effect of the cross-layers in the LVL. It was further found, that the adequate spacing has to be determined with regard to shear plug failure. The experimental analysis has confirmed the potential for efficient dowel-type connections with LVL made of beech.
Comparison of Processing Methods for Small-diameter Logs: Sawing versus Rotary Peeling
Article
Currently there are limited markets in Australia for small-diameter native forest logs. This has resulted in much of this resource being underutilized and regarded as sub-optimal in quality and of low value. This is despite the fact that the wood properties are favorable for a wide range of high-value products. Traditional processing approaches either have not been able to accommodate small-diameter logs or the resulting product recovery is too low for profitable production. Alternative processing approaches are necessary to enable the efficient recovery of wood from this resource in a form that is usable for high-value product manufacturing. Processing small-diameter spotted gum (Corymbia citriodora) and white cypress pine (Callitris glaucophylla) logs into rotary veneer using new spindleless veneering technology has been demonstrated to yield more acceptable recoveries compared with more traditional sawing approaches. The veneer processing approach was also found to be less impacted by the diameter than sawing, with more consistent recovery rates across the three small-diameter log groups included in this study. The resulting veneer, especially the spotted gum veneer, had visual qualities and mechanical properties well suited to the manufacturing of veneer-based engineered wood products.
Load-to-grain angle dependence of the embedment behavior of dowel-type fasteners in laminated veneer lumber
Article
Load-to-grain angle dependence of the embedment behavior of steel dowels in laminated veneer lumber, as a consequence of the anisotropic material behavior of wood, is experimentally investigated in this study. As a novel issue, in addition to the stress dependence, the displacement path of the dowel depending on the load-to-grain angle, is discussed. Full-hole embedment tests of screw-reinforced LVL specimens up to dowel displacements of two times the dowel diameter and thus, representative for highly ductile dowel connections were conducted. Tests were performed with unconstrained lateral displacement boundary conditions of steel dowels with a diameter of 12 mm and 16 mm. Surface deformations were monitored with a full-field deformation measurement system. Increasing the load-to-grain angle caused reduced quasi-elastic limits and loading stiffness. However, for load-to-grain angles of 60° and higher, a pronounced displacement-hardening effect, leading to high embedment stresses at large dowel displacements, was observed. For the investigated dowel diameters, surface strains and plastic deformations around the dowel indicate an almost dowel diameter independent load bearing area, which might explain higher nominal embedment stresses and consequently a more pronounced hardening effect of the smaller dowel diameter. Dowel displacements perpendicular to the initial loading direction, i.e., nonlinear displacement paths of the dowel, were related to the anisotropic stiffness of wood and densification effects close to the dowel. The established experimental dataset was compared to current European timber engineering design equations and could serve as input to analytical and numerical models of dowel connections.
Bolted and dowelled connections in radiate pine and laminated veneer lumber using the European yield model
Article
  • Jan 2011
Connections with mechanical fasteners are important for all cases of timber structures. The failure of these connections may occur in either ductile or brittle manner. For the calculation of the ductile failure strength or the load carrying capacity, the European yield model (EYM) is used in many standards and accepted as a very accurate model. In the current New Zealand timber standard NZS 3603:1993 (Standards New Zealand, 1993) and the Australian one AS1720.1-1997 (Standards Australia, 1997), the design concept for bolted or dowelled connections is not based on the EYM, and depends only on the diameter, the timber thickness and the species group. The most important parameters for the EYM are the fastener yield moment and the timber embedment strength, but embedment strength values are not available for New Zealand Radiata pine or laminated veneer lumber (LVL). To obtain the missing information and to implement the EYM into the New Zealand and Australian standards, embedment tests parallel, perpendicular and under various load-to-grain angles with different dowel diameters in Radiata pine lumber and LVL were conducted and compiled to build a database of embedment strength values. This paper includes the latest results of the investigations with dowel diameters extended up to 30 mm. Furthermore, different international testing standards are compared and their evaluation methods are used. The test results are also compared with the corresponding results using the Eurocode 5 formulas, and show that adjusted formulas of the Eurocode 5 can be used to predict the load carrying capacity of bolted and dowelled connections in Radiata pine lumber and LVL. Design examples comparing the current methods from the New Zealand/Australian design standards and the proposed method adopted from the EYM of the European design standard are given as well.
Integrative experimental characterization and engineering modeling of single-dowel connections in LVL
Article
In order to be able to realistically and consistently elucidate and subsequently simulate the load–displacement behavior of single-dowel connections, the material behavior of the individual components, namely steel dowels and wood, needs to be investigated. The behavior of slotted-in, single-dowel steel-to-laminated veneer lumber (LVL) connections with dowel diameters of 12 and 20 mm is thoroughly discussed here in relation to steel dowel and LVL properties. In addition to connection tests at different load-to-grain directions of 0°, 45° and 90°, the corresponding embedment behavior of LVL was tested up to dowel displacements of three times the dowel diameter. The material behavior of steel dowels was studied by means of tensile and 3-point bending tests and accompanying finite element simulations. A pronounced nonlinear behavior of the single-dowel connections was observed for all load-to-grain directions. In case of loading perpendicular to the grain, a significant hardening behavior was obvious. Due to the anisotropic material properties of wood, enforcing a loading direction of 45° to the grain resulted in an additional force perpendicular to the load direction which was quantified in a novel biaxial test setup. Thus, a comprehensive and consistent database over different scales of observations of dowel connections could be established, which subsequently was exploited by means of engineering modeling. The comparison of experimental and numerical data illustrates the potential of the engineering modeling approach to overcome drawbacks of current design regulations, which are unable to appropriately predict stiffness properties of dowel connections. Moreover, the quasi-elastic limit of dowel connections was calculated and discussed by means of the model.
Dowel-Bearing Strength Properties of Two Tropical Hardwoods
Conference Paper
  • Sep 2013
Bearing strength of wood is one of the properties that are use to estimate the lateral connection of wood design strength based on the European Yield Model (EYM), National Design Specification [NDS 2005 in National design specification for wood construction american forest and paper association (AFPA), Washington D.C, 2005] theory. This study investigated the characterisation of load to grain directions and two dowel sizes in two high-density Malaysian hardwood species; Kempas (koompassia Malaccensis) and Kapur (Dryobalanop spp.). Experimental work as stipulated in ASTM 5764-9a [American Standard Testing Method (ASTM) D 5764-95a in ), Standard test method for evaluating dowel-bearing strength of wood and wood-based products, 2007] was adopted. Result shows that according to the species, the lower strength group of species attributes to higher bearing strength of wood. It was also found that the bearing strength of parallel to the grain is higher than the perpendicular to the grain. In terms of dowel diameter, the bearing strength perpendicular and parallel to the grain decreased slightly as the dowel diameter increased regardless of the timber species. The EYM equations were found viable and sufficient in predicting the dowel-bearing strength of bigger dowel diameter for Kempas but not for the smaller dowel diameter. Contradict to Kempas species; the EYM equations were viable for the smaller dowel diameter and not for the bigger dowel diameter for Kapur. Thus, in the case of the insufficient predictions, three modified equations based on EYM, were proposed according to the specific gravity, density, species, dowel diameter and loading directions respectively.