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  • 1.
    Akter, Shaheda T.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Bader, Thomas K.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Experimental assessment of failure criteria for the interaction of normal stress perpendicular to the grain with rolling shear stress in Norway spruce clear wood2020Ingår i: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 78, s. 1105-1123Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The anisotropic material behavior of wood, considered as a cylindrically orthotropic material with annual rings, leads to several different failure mechanisms already under uniaxial stresses. Stress interaction becomes important in the engineering design of structural elements and is often predicted by failure criteria based on uniaxial properties. The prediction quality of failure criteria has been assessed with longitudinal shear stress interaction, though less is known on rolling shear stress in interaction with stress perpendicular to the grain. The study aims at investigating the corresponding mechanical behavior of Norway spruce (Picea abies) clear wood by validating failure envelopes for stress combinations in the cross-sectional plane, based on experimental investigations. For this purpose, a test setup that controls the stress interaction and loading of clear wood along pre-defined displacement paths needed to be developed. Experimentally defined failure states could then be compared to failure surfaces predicted by the phenomenological failure criteria. Material behavior was quantified in terms of stiffness, strength, and elastic and post-elastic responses on dog-bone shaped specimens loaded along 12 different displacement paths. A comparison with failure criteria for two nominal compressive strain levels showed that a combination of failure criteria would be required to represent the material behavior and consider the positive effect of compressive stresses on the rolling shear strength. The findings of this work will contribute to studying local stress distribution of structural elements and construction details, where stress interactions with rolling shear develop.

  • 2.
    Akter, Shaheda T.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Bader, Thomas K.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Enquist, Bertil
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Failure envelope for interaction of stresses perpendicular to the grain with rolling shear stress in wood2018Ingår i: 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK, 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    The orthotropic material property in combination with ductility in compression, brittleness in shear and tension, very low shear modulus in radial-tangential (RT) plane etc. requires anisotropic stress failure criteria, as well as their evolution with increasing strains. Three- dimensional failure criteria have been proposed for this purpose, but their validation in the RT plane with interaction of rolling shear stresses has attracted less attention. Corresponding stress interactions are however important for modelling of engineered wood-based products under compression perpendicular to the grain when taking into account influence of the annual ring structure.

    The work aims at defining failure envelopes for stresses perpendicular to the grain with rolling shear stress interaction based on experimental investigations performed on Norway spruce. The experimental set-up was realized in a biaxial testing frame and consisted of stiff steel plates to transfer load from the testing machine to wood specimen. Mechanical grips prevented rotation and uplifting of the specimen in case of pure shear and tensile loading, respectively. In addition to conventional linear variable differential transformers, a digital image correlation system was used to measure strain fields on the surface of wood specimens and steel plates. Measurements of dog-bone shaped specimens were carried out along different stress interaction paths by displacement controlled loading.

    The experimental dataset was then compared with commonly used phenomenological failure criteria, namely Tsai-Hill, Tsai-Wu [1], Norris [2] and Hoffman, as well as with regression equations from previous works [3].Experiments revealed that the stress-strain relationship under compression, shear, and biaxial loading differs in radial and tangential directions. None of the three-dimensional stress failure criteria provided good prediction of experiments under compression and rolling shear, but experimental data was closer to the regression equation proposed in [3].

  • 3.
    Akter, Shaheda T.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Bader, Thomas K.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Serrano, Erik
    Lund University, Sweden.
    Modeling of wood under combination of normal stresses with rolling shear stress2019Ingår i: Presented at CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from material properties to Timber Structures, Växjö, Sweden, June 17-19, 2019, Växjö, Sweden, 2019Konferensbidrag (Refereegranskat)
    Ladda ner fulltext (pdf)
    Abstract
  • 4.
    Akter, Shaheda T.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Bader, Thomas K.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Serrano, Erik
    Lund University, Sweden.
    Modelling of wood under compression perpendicular to the grain with rolling shear in cross-laminated timber2019Ingår i: Presented at COMPLAS 2019 - XV International Conference on Computational Plasticity: Fundamentals and Applications, Barcelona, Spain, September 3-5, 2019, Barcelona, Spain: European Community on Computional Methods in Applied Sciences (ECCOMAS), 2019Konferensbidrag (Refereegranskat)
    Ladda ner fulltext (pdf)
    Abstract
  • 5.
    Akter, Shaheda T.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Bader, Thomas K.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Serrano, Erik
    Lund University, Sweden.
    Stiffness of cross-laminated timber (CLT) wall-to-floor-to-wall connections in platform-type structures2021Ingår i: World Conference on Timber Engineering 2021, WCTE 2021, Santiago, Chile: World Conference on Timber Engineering, WCTE , 2021, artikel-id WPC0232Konferensbidrag (Refereegranskat)
    Abstract [en]

    Wall-to-floor-to-wall connections are important for the performance of multi-storey, platform-type cross-laminated timber (CLT) structures. Their stiffness properties are studied by means of a numerical model, which was previously validated with experimental data from material testing and CLT connections loaded perpendicular to the grain. In this work, the stiffness of CLT wall-to-floor-to-wall connections is derived and its dependence on the compressive loading in the CLT walls and on wall and floor thicknesses were investigated. The compatibility of the local model with the connection size in structural design models, was investigated by studying the effect of the floor length and the wall height in the numerical model. The results showed that both rotational elastic stiffness and moment capacity of the floor connection increase with increasing compressive force on the CLT wall. However, a moderate decrease in stiffness, but a stronger rotation hardening was found for higher wall pressures, while lower wall pressures yielded an ideal plastic behaviour. The wall thickness showed a higher influence on the connection stiffness and moment capacity than the floor thickness. The influence of the support condition on the deflection of a CLT floor was exemplified. This study includes novel stiffness data for the design of CLT floors in platform type constructions.

    Ladda ner fulltext (pdf)
    fulltext
  • 6.
    Akter, Shaheda T.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Binder, Eva
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Bader, Thomas K.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Moisture and short-term time-dependent behavior of Norway spruce clear wood under compression perpendicular to the grain and rolling shear2023Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 18, nr 2, s. 580-593Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Material properties of wood under compression perpendicular to the grain and rolling shear are important for the engineering design of timber structures. This regards the short-term stiffness and strength, their dependence on the moisture content of wood, as well as the time-dependent behavior. Norway spruce clear wood properties in the transverse plane of wood were studied inan experimental campaign exploiting an earlier developed biaxial test setup. The moisture dependence of the stiffness and strength and the short-term time-dependent creep deformations under compression in the radial direction and under rolling shear were characterized. Loading and unloading stiffness, as well as the strength, were determined in quasi-static tests at five different moisture contents from 4% to 29%. The elastic and viscous stiffnesses were identified in creep tests at three compressive stress levels of 0.50, 0.75, and 1.00 N/mm2, and at two rolling shear stress levels of 0.33 and 0.50 N/mm2. The test data complements the existing experimental database, especially with novel data regarding the moisture dependence of the rolling shear strength, which showed less moisture dependence than the compressive strength perpendicular to the grain. The results of the creep tests revealed different material properties for the different loading and material directions of wood.

  • 7.
    Akter, Shaheda T.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Schweigler, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Serrano, Erik
    Lund University, Sweden.
    Bader, Thomas K.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    A Numerical Study of the Stiffness and Strength of Cross-Laminated Timber Wall-to-Floor Connections under Compression Perpendicular to the Grain2021Ingår i: Buildings, E-ISSN 2075-5309, Vol. 11, nr 10, artikel-id 442Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The use of cross-laminated timber (CLT) in multi-story buildings is increasing due to the potential of wood to reduce green house gas emissions and the high load-bearing capacity of CLT. Compression perpendicular to the grain (CPG) in CLT is an important design aspect, especially in multi-storied platform-type CLT buildings, where CPG stress develops in CLT floors due to loads from the roof or from upper floors. Here, CPG of CLT wall-to-floor connections are studied by means of finite element modeling with elasto-plastic material behavior based on a previously validated Quadratic multi-surface (QMS) failure criterion. Model predictions were first compared with experiments on CLT connections, before the model was used in a parameter study, to investigate the influence of wall and floor thicknesses, the annual ring pattern of the boards and the number of layers in the CLT elements. The finite element model agreed well with experimental findings. Connection stiffness was over estimated, while the strength was only slightly under estimated. The parameter study revealed that the wall thickness effect on the stiffness and strength of the connection was strongest for the practically most relevant wall thicknesses between 80 and about 160 mm. It also showed that an increasing floor thickness leads to higher stiffness and strength, due to the load dispersion effect. The increase was found to be stronger for smaller wall thicknesses. The influence of the annual ring orientation, or the pith location, was assessed as well and showed that boards cut closer to the pith yielded lower stiffness and strength. The findings of the parameter study were fitted with regression equations. Finally, a dimensionless ratio of the wall-to-floor thickness was used for deriving regression equations for stiffness and strength, as well as for load and stiffness increase factors, which could be used for the engineering design of CLT connections.

  • 8.
    Akter, Shaheda T.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Serrano, Erik
    Lund University, Sweden.
    Bader, Thomas K.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Numerical modelling of wood under combined loading of compressionperpendicular to the grain and rolling shear2021Ingår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 244, artikel-id 112800Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Numerical modeling is an efficient tool for experimental validation and for gaining a deeper understanding of complex material phenomena, especially when causal relationships are overlaid by material variability. Wood is such a highly orthotropic and complex material, which in engineering problems however is considered as macro- homogeneous. The aim of this study is to numerically investigate stress and strain states of wood in the radial- tangential plane and the influence of the orthotropic material behavior on the structural response. Model vali-dation is based on experiments performed on clear wood of Norway spruce (Picea abies) by using a biaxial test setup. Three material models were used, namely Hill’s plasticity model, the Hoffman criterion and a novel quadratic multi-surface (QMS) criterion. After validation on the local material scale, the models were applied to the engineering problem of compression perpendicular to the grain for studying the effect of the unloaded length. As a novel part, the influence of the annual ring structure on the local material behavior and the global elasto- plastic force–displacement behavior of wood under compression perpendicular to the grain were numerically investigated. Hill’s failure criterion was found to be the least suitable at both length scales, local material behavior and global structural response. The Hoffman and the QMS criteria showed quite good agreement with the biaxial experiments in terms of force–displacement relations and strain distributions for different loading situations, especially for combinations with radial compression, while there was less agreement with experiments for  the  behavior of  combinations with tangential compression. Application of  these material models to compression perpendicular to the grain for studying the unloaded length effect yielded similar trends as observed in structural tests. A reasonable and similar force–displacement response by Hoffman and QMS criteria was observed, while Hill’s model yielded significantly overestimated force carrying capacity. Differences in force-–displacement response for different loading situations were well in line with literature findings and the infl-ence of the annual ring curvature on the overall force–displacement behavior could be quantified.

    Ladda ner fulltext (pdf)
    fulltext
  • 9.
    Alfredsen, Gry
    et al.
    Norwegian Forest and Landscape Institute, Norway.
    Bader, Thomas K.
    Vienna University of Technology, Austria.
    Dibdiakova, Janka
    Norwegian Forest and Landscape Institute, Norway.
    Filbakk, Tore
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Thermogravimetric analysis for wood decay characterisation2012Ingår i: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 70, nr 4, s. 527-530Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper focuses on the use of thermogravimetric analysis (TGA) as a fast method for estimating the change of lignocellulosic materials during fungal degradation in laboratory trials. Traditionally, evaluations of durability tests are based on mass loss. However, to gain more knowledge of the reasons for differences in durability and strength between wooden materials, information on the chemical changes is needed. Pinus sylvestris sapwood was incubated with the brown rot fungusGloeophyllum trabeum and the white rot fungus Trametes versicolor. The TGA approach used was found to be reproducible between laboratories. The TGA method did not prove useful for wood deteriorated by white rot, but the TGA showed to be a convenient tool for fast estimation of lignocellulosic components both in sound wood and wood decayed by brown rot.

  • 10.
    Alfredsen, Gry
    et al.
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Bader, Thomas K.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Basidiomycete colonization of Scots pine sapwood quantified by qPCR and TGA2011Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Scots pine (Pinus sylvestris L.) is an important softwood species in Northern Europe and is frequently used as material for various wood protection systems. In Europe, EN 113 is the standard basidiomycete laboratory durability test method, using mass loss as evaluation criteria. In this paper quantitative real-time PCR (qPCR) and thermogravimetric analysis (TGA) was used to characterize colonization by basidiomycetes in Scots pine sapwood, but also to learn more about the EN 113 test. Two different wood sample sizes were tested. For Gloeophyllum trabeum the largest sample size gave the highest mass loss, while for the smallest samples Trametes versicolor gave the highest mass loss. As expected, fungal DNA content and mass loss in Scots pine sapwood samples decayed by G. trabeum became higher with increasing incubation time of 16 weeks. More unexpectedly, the T. versicolor DNA content in Scots pine sapwood samples was highest at the start of the incubation period and declined during the incubation period, while mass loss increased during the 28 week incubation period. The fungal colonization in the side and middle of EN 113 samples was tested. Highest DNA contents of G. trabeum were measured in the sides during 16 weeks of incubation. The T. versicolor DNA content was higher or similar in the side compared to the middle of the samples until week 20. For weeks 20 and 22 the DNA content was higher in the middle than in the sides, while for the remaining incubation period (weeks 24, 26 and 28) it was quite similar. TGA was shown to be a useful and fast method for chemical characterization of brown rot decayed wood, but cannot be used for white rot decayed wood. For T. versicolor moisture and fungal DNA explained most of the variation in mass loss, while for G. trabeum moisture explained most of the variation in mass loss. 

  • 11. Bader, Thomas K.
    Adaptability and Structural Design of Stadia2008Bok (Övrigt vetenskapligt)
    Abstract [en]

    The aim of this master's thesis is to analyse recent developments in the design of stadia. In particular, the aim to make stadia adaptable in terms of use led to new challenges for the structural design. On one side, in order to increase event days per year, there are multi-purpose stadia for various sports, as well as for non-sporting events. Movable structures for seating tiers, pitches, and roofs developed for stadia that are suitable for various events. The design of these structures is discussed in this thesis. On the other side, major events require stadia with pre-determined capacities, which may be unsuitable for a long-term use. For this purpose, demountable structures for spectator accommodation are used to increase the capacity just temporary for the duration of a major event. Furthermore, general concepts for the structural design of stands and roofs are discussed. In addition, case studies of recent developments for major events, multi-purpose stadia, and stadia in the UK are analysed. Due to a study in the UK, there are British guidelines discussed in this thesis.

  • 12.
    Bader, Thomas K.
    Vienna University of Technology, Austria.
    Mechanical properties of sound and of deteriorated softwood at different length scales: Poromicromechanical modeling and experimental investigations2011Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Due to its natural origin and its inherent heterogeneities, mechanical properties of wood are highly anisotropic and show a broad variability, not only between different wood species, but also within a tree. Similar to other biological materials, the wood mi- crostructure is well organized and hierarchically structured from the annual rings visible to the naked eye down to the wood polymers cellulose, hemicellulose, and lignin at the nanometer-scale. This thesis aims at a deeper understanding of the role of different hi- erarchical levels and their corresponding physical and chemical characteristics in relation to mechanical properties of sound wood and of deteriorated wood. This is achieved by means of micromechanical modeling and experimental analyses.

    This thesis starts with the re-formulation of an existing micromechanical model for the elastic behavior and elastic limit states of wood in the framework of poromechanics. The mechanical role of cell wall water at different hierarchical levels is investigated by means of this model. In a broader sense, the developed model allows to investigate the transition of eigenstresses from the cell wall to the softwood level. Moreover, this poromicromechanical model forms the basis for subsequent consideration of a microscopic failure criterion for lignin for the derivation of softwood failure stresses. The suitability of the modeling approach is underlined by a satisfactory agreement of the model-predicted failure stresses with experimental results of biaxial strength tests on Norway spruce.

    As a result of partly considerably different microstructural characteristics, Common yew exhibits exceptional mechanical properties compared to other softwood species. The re- lationship between microstructure and stiffness properties of Common yew and Norway spruce is investigated by means of the poromicromechanical model and mechanical tests across various length scales. Moreover, this offers the opportunity of a broader model validation. The influence of differences in microfibril angle of the S2 cell wall layer and in mass density between yew and spruce is found to be more dominant than the influence of differences in the annual ring characteristics.

    The suitability of the poromicromechanical model to predict changes in mechanical prop- erties upon fungal decay is demonstrated. For this purpose, relationships between mi- crostructure and mechanical properties of deteriorated wood are experimentally explored. Changes in mechanical properties and in the microstructure, measured at pine wood samples after standard wood durability tests using one brown rot fungus (Gloeophyl- lum trabeum) and one white rot fungus (Trametes versicolor), are presented. Transverse stiffnesses are revealed to be more sensitive to degradation than longitudinal stiffness, particularly as a result of pronounced degradation of hemicelluloses. Moreover, ultrason- ically derived anisotropy ratios of elastic stiffnesses allow to identify certain degradation mechanisms of the two considered fungi. The experimental campaign is complemented by micromechanical modeling. For this purpose, the micromechanical model is extended to take into account degradation-specific microstructural characteristics. 

  • 13.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Bocquet, Jean-Francois
    University of Lorraine, France.
    Schweigler, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Lemaitre, Romain
    University of Lorraine, France.
    Numerical modeling of the load distribution in multiple fastener connections2018Ingår i: Design of Connections in Timber Structures: A state-of-the-art report by COST Action FP1402/WG3 / [ed] Carmen Sandhaas, Jorgen Munch-Andersen, Philipp Dietsch, Aachen: Shaker Verlag, 2018, s. 221-239Kapitel i bok, del av antologi (Refereegranskat)
  • 14.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Bocquet, Jean-Francois
    University of Lorraine, France.
    Schweigler, Michael
    Vienna University of Technology, Austria.
    Lemaitre, Romain
    University of Lorraine, France.
    Numerical modeling of the load distribution in multiple fastener joints2017Ingår i: International Conference on Connections in Timber Engineering – From Research to Standards: Proceedings of the Conference of COST Action FP1402 at Graz University of Technology / [ed] Reinhard Brandner, Andreas Ringhofer & Philipp Dietsch, Graz: Verlag der Technischen Universität Graz , 2017, s. 136-152Konferensbidrag (Refereegranskat)
    Abstract [en]

    Numerical modeling approaches, for the determination of load distribution in laterally loaded joints, as well as for the assignment of stiffness properties of joints for the structural analysis, are summarized in this contribution. The effect of the nonlinearity and the load-to-grain orientation dependence of connection slip, of elastic deformation in the surrounding wood matrix, and of the deviation between load and displacement direction are discussed. Comparison of various models demonstrates the pronounced effect of the load-to-grain orientation dependence and the nonlinearity in connection slip on the load distribution, particularly in case of moment loading. The effect of elastic deformation in the wood matrix on the load distribution increases with increased size of joints, even more pronounced when joints are loaded by a shear force perpendicular to the grain. In case of normal force loading, the non-uniform load distribution due to elastic deformation in the wood matrix reduces rapidly with increased relative joint displacement. Pros and cons of the modeling approaches as well as necessary input data are discussed in relation to the design process and European standardization.

  • 15. Bader, Thomas K.
    et al.
    Braovac, Susan
    Fackler, Karin
    Hofstetter, Karin
    Stiffness Properties of the Archaeological Oak Wood from the Oseberg Ship2011Ingår i: Cultural Heritage Preservation.EWCHP - 2011: Proceedings of the European Workshop on Cultural Heritage Preservation. Berlin, Germany, September 26 to 28, 2011, Fraunhofer IRB Verlag, 2011, s. 164-170Konferensbidrag (Refereegranskat)
  • 16.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Braovac, Susan
    University of Oslo, Norway.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Microstructure-Stiffness Relations of the Ancient Oak Wood from the Oseberg Ship2010Ingår i: International Workshop on "Modeling Mechanical Behavior of Wooden Cultural Objects", Krakow, 2010, s. 22-23Konferensbidrag (Övrigt vetenskapligt)
  • 17.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Dastoorian, Foroogh
    Vienna University of Technology, Austria ; University of Tehran, Iran.
    Ebrahimi, Ghanbar
    University of Tehran, Iran.
    Unger, Gerhard
    Vienna University of Technology, Austria.
    Lahayne, Olaf
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Pichler, Bernhard
    Vienna University of Technology, Austria.
    Combined ultrasonic-mechanical characterization of orthotropic elastic properties of an unrefined bagasse fiber-polypropylene composite2016Ingår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 95, s. 96-104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Use of wood-fiber plastics for construction purposes calls for comprehensive understanding of their anisotropic mechanical properties. As a respective contribution, we here report the first-ever complete elasticity characterization of an orthotropic bagasse fiber polypropylene composite, requiring identification of nine independent constants. For this purpose, we carry out characterization in principal material directions. Six diagonal stiffness tensor components are quantified based on ultrasonic longitudinal and shear wave velocity measurements; and three diagonal compliance tensor components are identified as the inverses of three Young’s moduli derived from unloading regimes of quasi-static uniaxial compression tests. Combination of all measurement data in the framework of orthotropic linear elasticity provides access to all off-diagonal stiffness and compliance tensor components, opening the door to quantifying six Poisson’s ratios. 

  • 18.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    de Borst, Karin
    University of Glasgow, UK.
    Poroelastic properties of hardwood at different length scales2013Ingår i: Poromechanics V: proceedings of the fifth Biot Conference on Poromechanics, July 10-12, 2013, Vienna, Austria / [ed] Christian Hellmich, Bernhard Pichler, Dietmar Adam, Reston: American Society of Civil Engineers (ASCE), 2013, s. 1830-1836Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Hardwoods show a very complex, hierarchically organized microstructure. Slight structural differences at various length scales bring about a huge variety of hardwood species. This motivates the development of a micromechanical model for hardwood. Since differences in the microstructure of the material can be considered in the model, it offers the opportunity to explain the variability of mechanical properties of the whole class of hardwood. The micromechanical model is formulated in the framework of poroelasticity. In this contribution, poroelastic properties at different length scales of the material are discussed. Validation of the micromechanical model is based on an extensive experimental database covering elastic properties and microstructural characteristics of different temperate and tropical hardwood species. Exemplary parameter studies demonstrate the ability of the model to study the contribution of specific microstructural characteristics to the load transfer and the deformation characteristics of wood. 

  • 19.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    de Borst, Karin
    University of Glasgow, UK.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Micromechanical modeling of Common yew and Norway spruce2013Ingår i: Proceedings in Applied Mathematics and Mechanics: PAMM, E-ISSN 1617-7061, Vol. 13, nr 1, s. 185-186Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this contribution, a micromechanical modeling approach in the framework of poromechanics is adopted to study structure-stiffness relations of two quite different species, namely spruce and yew, in detail. In particular, microstructural specialties of yew and spruce are assessed. A dominant influence of the cellulose content and its orientation on the stiffness of the cell wall is revealed, while on the macroscopic scale, density is found to be the governing microstructural characteristic for elastic properties.

  • 20.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    de Borst, Karin
    University of Glasgow, UK.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Micromechanical Modeling of Wood: Multiscale Modeling and Model Validation2013Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Due to its natural origin and its inherent heterogeneities, mechanical properties of wood are highlyanisotropic and show a broad variability, not only between different wood species, but also within a tree [1].Similar to other biological materials, the wood microstructure is well organized and hierarchically structuredfrom the annual rings visible to the naked eye down to the wood polymers cellulose, hemicellulose, andlignin at the nanometer-scale. The aim of the research conducted at the Institute for Mechanics of Materialsand Structures is a deeper understanding of the role of different hierarchical levels and their correspondingphysical and chemical characteristics in relation to mechanical properties of softwood and hardwood. This isachieved by means of micromechanical modeling and experimental analyses at various length scales.

    A micromechanical model provides the opportunity to predict poroelastic properties of softwood andhardwood tissues at different hierarchical levels from microstructural and compositional data [1,2]. Thehierarchical organization of wood is mathematically represented in a multiscale model. Effective poroelasticproperties are predicted by means of continuum micromechanical approaches (self-consistent method andMori-Tanaka method), the unit cell method, and laminate theory. These approaches are extended to accountfor water-induced eigenstresses within representative volume elements and repetitive unit cells, which aresubsequently upscaled to the macroscopic wood level.

    Verification of the micromechanical model for softwood and hardwood with a comprehensive experimentaldataset, shows that it suitably predicts elastic properties at different length scales under the assumption ofundrained conditions [3,4]. Moreover, Biot tensors, expressing how much of the cell wall water-induced porepressure is transferred to the boundary of an overall deformation-free representative volume element (RVE),and Biot moduli, expressing the porosity changes invoked by a pore pressure within such an RVE can bestudied at different length scales. Consequently, the relevance and the contribution of specificmicrostructural characteristics to the load transfer and the deformation characteristics in case of moisturechanges in wood can be studied. Besides the scientific interest in structure-function-relationships, theseinvestigations are motivated by the growing importance of wood as building material.

  • 21.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    de Borst, Karin
    University of Glasgow, UK.
    Fackler, Karin
    Vienna University of Technology, Austria.
    Ters, Thomas
    Vienna University of Technology, Austria.
    Braovac, Susan
    University of Oslo, Norway.
    A nano to macroscale study on structure-mechanics relationships of archaeological oak2013Ingår i: Journal of Cultural Heritage, ISSN 1296-2074, E-ISSN 1778-3674, Vol. 14, nr 5, s. 377-388Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mechanical properties of wood at different length scales of its hierarchical structure are governed by structural and compositional properties on smaller length scales. This opens up the possibility to use microstructural data for estimating mechanical properties, which are difficult to assess by conventional, destructive testing but are nevertheless of high relevance for conservation practice. Herein, we investigate such microstructure-mechanics relationships for a particular example, namely the load bearing archaeological oak of the Oseberg Viking ship, displayed at the Viking Ship Museum in Oslo, Norway. In order to identify the effects of degradation on the mechanical behavior and their relations to the microstructure, recent oak specimens of different geographical origin (Norway and Austria) are investigated as well. Wood exhibits a cellular structure. Its cell walls are composed of an amorphous polymer matrix consisting of lignin and hemicelluloses and embedded, stiff cellulose fibers. At the cell level, experimental studies comprised microscopic investigations of the cellular structure, chemical analyses of the composition of the cell walls, as well as nanoindentation tests on single cell walls. The same samples were also analyzed on the macroscopic level, where additionally mass density and annual ring data were measured together with ultrasonic stiffnesses. The chemical data clearly indicate deterioration in the archaeological oak, affecting mainly hemicelluloses and amorphous cellulose. At the cell wall scale, however, this does not necessarily lead to a weaker material behavior. The nanoindentation modulus, as a measure of the cell wall stiffness, was found to even increase. This is counterintuitive to our understanding of the effects of chemical degradation. It might be due to possible modification of lignin in the Oseberg oak, and thus have a stronger effect on the indentation modulus than the concurrent weakening of the interfaces between the load-carrying cellulose fibers and the connecting cell wall matrix when analyzing wood at the microscopic level. A similar effect is also observed for the transversal stiffness of macroscopic samples, which increases. In tension-dominated loading modes, however, the degradation of the interfaces is the dominant effect, resulting for example in a considerable reduction of the macroscopic stiffness in longitudinal direction. This underlines the utmost relevance of the loading condition on the remaining load-carrying capacity of degraded wood. On the macroscale, effects of the geographical origin (i.e. growth conditions) on ring characteristics of the oak tissues override the effects of degradation on the mechanical behavior. They have to be carefully extracted in order to come up with conclusions on the effect of degradation from macroscopic test results. The identified microstructure-mechanics relationships provide the basis for–in further research steps–building mathematical models describing the relations between microstructural characteristics and macroscopic mechanical properties and, thereon, for structural analyses of historical wooden objects.

  • 22.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Dorn, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Esser, Gerold
    Vienna University of Technology, Austria.
    Hochreiner, Georg
    Vienna University of Technology, Austria.
    The Historical Roof Structure of the Leopold Wing of the Vienna Hofburg Palace: Structural Assessment2015Ingår i: Proceedings of the International Conference on Structural Health Assessment of Timber Structures (SHATIS'15), 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this case study, the structural behaviour of the historic roof structure of the “Leopold Wing”, part of the Hofburg, the Vienna Imperial Palace, is assessed. The current appearance of the roof is a consequence of several adaptions and extensions of the original structure that dates back to the 17th century. The main part of the roof was reconstructed in the early 1670s following a disastrous fire in February 1668. The structure had the shape of an M-roof consisting of two adjacent gable roofs. Probably in the 19th century, the centre part was closed, creating a mansard roof over the entire width of the building. Basically, the geometry of the structure is symmetric with respect to the middle wall. However, since the position of the middle wall is partly asymmetric, also the roof structure becomes asymmetric. Herein, the influence of the building history on the load-deformation behaviour of the roof structure is investigated. Therefore, structural analyses of the original M-roof and of the mansard roof are performed. The modelling of the historic roof structure is based on a deformation-accurate survey. In addition, the influence of the nonlinear, compliant behaviour of connections on the load-deformation behaviour of the timber structure is taken into account. A considerable influence of the connection slip on the deformation of the structure becomes obvious from the analysis. Consequently, consideration of the nonlinear behaviour of the joints reveals a realistic load transfer within the structure. The addition of structural elements caused additional dead loads, which increase long-term deformations.

  • 23.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    de Borst, Karin
    University of Glasgow, UK.
    Shear stiffness and its relation to the microstructure of 10 European and tropical hardwood species2017Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 12, nr 2, s. 82-91Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, shear stiffness properties of 10 different hardwood species and their relation to the corresponding species-specific microstructure are investigated. For this purpose, shear stiffness of 10 different hardwood species is experimentally measured by means of ultrasonic testing. In addition, a micromechanical model for hardwood is applied in order to illustrate the influence of certain microstructural characteristics such as mass density and volume fractions of vessels and ray cells on the shear stiffness. Comprehensive microstructural and mechanical data from previous investigations of the same hardwood material support the interpretation of the microstructure–shear stiffness relationships. Mass density was confirmed to be the dominant microstructural characteristic for shear stiffness. Also, ultrasound shear wave propagation velocity increases with density, particularly in the radial-tangential (RT) plane. In addition to density, comparably higher shear stiffness GLR can be explained by comparably higher ray content and lower vessel content. As for GLT, a ring porous structure seems to lead to higher shear stiffness as compared to a diffuse porous structure. For this shear stiffness, vessel and ray content were found to have a less impact. Also, the rolling shear stiffness GRT was found to be higher for a diffuse porous structure than for a ring porous one. Moreover, the data supports that ray cells act as reinforcements in the RT plane and lead to higher GRT

  • 24.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Füssl, JosefTechnische Universität Wien, Austria.Olsson, AndersLinnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    CompWood 2019 - Computational Methods in Wood Mechanics -: From Material Properties to Timber Structures: Book of Abstracts.2019Proceedings (redaktörskap) (Refereegranskat)
  • 25. Bader, Thomas K.
    et al.
    Hofstetter, Karin
    Technische Universität, Austria.
    Pilzabbau von Holz: Quantifizierung des Steifigkeitsverlusts auf Basis von mikromechanischen Überlegungen2010Ingår i: Wiener Holzschutztage 2010: 25. - 26. November 2010, Wien, Wien: Wiener Holzschutztage , 2010, Vol. 28, s. 50-55Konferensbidrag (Övrigt vetenskapligt)
    Abstract [de]

    Pilzbefall bewirkt eine Zersetzung des Materials durch Mikroorganismen und damit unweigerlich auch eine Veränderung des mechanischen Verhaltens von Holz. Die Auswirkung der mikrostrukturellen Änderungen auf makroskopisch beobachtbare mechanische Materialkennwerte wie Steifigkeit und Festigkeit lassen sich mittels Mehrskalenmodellierung abschätzen und quantifizieren. Die Eignung solcher Mehrskalenmodelle als Prognosewerkzeuge für Dauerhaftigkeitsbetrachtungen wurde im WoodWisdom-Netzwerk „WoodExter“ im Rahmen eines umfangreichen Testprogramms untersucht. Es wurde dabei sowohl ein Braunfäule verursachender Pilz (Gloephyllum trabeum) als auch ein Weißfäule verursachender Pilz (Trametes versicolor) verwendet. Die Vorgehensweise sowie die gewonnenen Einblicke und Erkenntnisse sind in diesem Beitrag zusammengefasst. Nach einer Kurzbeschreibung der hierarchischen Struktur von Holz und deren Modifikation durch Pilze folgt ein Abriss über die verwendeten Verfahren der Mehrskalenmodellierung. Der Schwerpunkt liegt in der Präsentation der Ergebnisse sowie der experimentellen Validierung des Modells durch Vergleich von Messwerten mit zugehörigen Modellvorhersagen. Schließlich werden im Ausblick mögliche Anwendungen der Modellierung skizziert. 

  • 26.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Alfredsen, Gry
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Changes in microstructure and stiffness of Scots pine (Pinus sylvestris L) sapwood degraded by Gloeophyllum trabeum and Trametes versicolor Part II: Anisotropic stiffness properties2012Ingår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, nr 2, s. 199-206Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fungal decay considerably affects the macroscopic mechanical properties of wood as a result of modifications and degradations in its microscopic structure. While effects on mechanical properties related to the stem direction are fairly well understood, effects on radial and tangential directions (transverse properties) are less well investigated. In the present study, changes of longitudinal elastic moduli and stiffness data in all anatomical directions of Scots pine (Pinus sylvestris) sapwood which was degraded by Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot) for up to 28 weeks have been investigated. Transverse properties were found to be much more deteriorated than the longitudinal ones. This is because of the degradation of the polymer matrix between the cellulose microfibrils, which has a strong effect on transverse stiffness. Longitudinal stiffness, on the other hand, is mainly governed by cellulose microfibrils, which are more stable agains fungal decay. G. trabeum (more active in earlywood) strongly weakens radial stiffness, whereas T. versicolor (more active in latewood) strongly reduces tangential stiffness. The data in terms of radial and tangential stiffnesses, as well as the corresponding anisotropy ratios, seem to be suitable as durability indicators of wood and even allow conclusions to be made on the degradation mechanisms of fungi.

  • 27.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Alfredsen, Gry
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Decrease of stiffness properties of degraded wood predicted by means of micromechanical modeling2011Ingår i: Proceedings of the International Research Group on Wood Protection IRG/WP 11-40570, International Research Group on Wood Protection , 2011, s. 2-15Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Wood exhibits a highly anisotropic mechanical behavior due to its heterogeneous microscopic structure and composition. Its microstructure is organized in a strictly hierarchical manner from a length scale of some nanometers, where the elementary constituents cellulose, hemicelluloses, lignin, and extractives are found, up to a length scale of some millimeters, where growth rings composed of earlywood and latewood are observed. To resolve the microscale origin of the mechanical response of the macro-homogeneous but micro-heterogeneous material wood, micromechanical modeling techniques were applied. They allow for prediction of clear wood stiffness from microstructural characteristics. Fungal decay causes changes in the wood microstructure, expressed by modification or degradation of its components. Consequently, macroscopic mechanical properties are decreasing. Thus, in the same manner as for clear wood, consideration of alterations of wood in a micromechanical model allows predicting changes in the macroscopic mechanical properties. This contribution covers results from an extensive experimental program, where changes in chemophysical properties and corresponding changes in the mechanical behavior were investigated. For this purpose, Scots pine (Pinus sylvestris L.) sapwood samples were measured in the reference condition, as well as degraded by brown rot (Gloeophyllum trabeum) or white rot (Trametes versicolor). Stiffness properties of the unaffected and the degraded material were not only measured in uniaxial tension tests in the longitudinal direction, but also in the three principal material directions by means of ultrasonic testing. The experiments revealed transversal stiffness properties to be much more sensitive to degradation than longitudinal stiffness properties. This is due to the degradation of the polymer matrix between the cellulose fibers, which has a strong effect on the transversal stiffness. On the contrary, longitudinal stiffness is mainly governed by cellulose, which is more stable with respect to degradation by fungi. Consequently, transversal stiffness properties or ratios of normal stiffness tensor components may constitute suitable durability indicators. Subsequently, simple micromechanical models, as well as a multiscale micromechanical model for wood stiffness, were applied for verification of hypotheses on degradation mechanisms and model validation.

  • 28.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Alfredsen, Gry
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Microstructure and stiffness of Scots pine (Pinus sylvestris L) sapwood degraded by Gloeophyllum trabeum and Trametes versicolor Part I: Changes in chemical composition, density and equilibrium moisture content2012Ingår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, nr 2, s. 191-198Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fungal degradation alters the microstructure of wood and its physical and chemical properties are also changed. While these changes are well investigated as a function of mass loss, mass density loss and changes in equilibrium moisture content are not well elucidated. The physical and chemical alterations are crucial when linking microstructural characteristics with macroscopic mechanical properties. In the present article, a consistent set of physical, chemical and mechanical characteristics is presented, which were measured on the same sample before and after fungal degradation. In the first part of this two-part contribution, elucidating microstructure/stiffness-relationships of degraded wood, changes in physical and chemical data are presented, which were collected from specimens of Scots pine (Pinus sylvestris) sapwood degraded by Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot) for up to 28 weeks degradation time. A comparison of mass loss with corresponding mass density loss demonstrated that mass loss entails two effects: firstly, a decrease in sample size (more pronounced for G. trabeum), and secondly, a decrease of mass density within the sample (more pronounced for T. versicolor). These two concurrent effects are interrelated with sample size and shape. Hemicelluloses and cellulose are degraded by G. trabeum, while T. versicolor was additionally able to degrade lignin. In particular because of the breakdown of hemicelluloses and paracrystalline parts of cellulose, the equilibrium moisture content of degraded samples is lower than that in the initial state.

  • 29.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Keunecke, Daniel
    ETH Zürich, Switzerland.
    Microstructure–Stiffness Relationships of Common Yew and Norway Spruce2012Ingår i: Strain, ISSN 0039-2103, E-ISSN 1475-1305, Vol. 48, nr 4, s. 306-316Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Yew (Taxus baccata L.) exhibits among conifers a unique macroscopic elastic behaviour. For example, it shows a comparatively low longitudinal elastic modulus related to its comparatively high density. We herein explore the microstructural origin of these peculiarities, aiming at the derivation of microstructure–stiffness relationships. We measure stiffness properties of yew at different hierarchical levels and compare them to corresponding stiffnesses of Norway spruce (Picea abies [L.] Karsten). Cell wall stiffness is investigated experimentally by means of nanoindentation in combination with microscopy and thermogravimetric analysis. On the macroscopic level, we perform uniaxial tension and ultrasonic tests. Having at hand, together with previously reported stiffnesses, a consistent data set of mechanical, chemical and physical properties across hierarchical levels of wood, we discuss influences of microstructural characteristics at different scales of observation. Moreover, a micromechanical model is applied to predict trends of effects of the microstructure on the investigated stiffness properties. On the cell wall level, particularly, the amount of cellulose and its orientation – which was earlier reported to be distinctly different for yew and spruce – result in differences between the two considered species. On the macroscopic scale, model predicted effects of the annual ring structure on transverse stiffness and shear stiffness are found to be smaller than effects of the microfibril angle and mass density.

  • 30.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    From lignin to spruce: Poromechanical upscaling of wood strength2011Ingår i: 2010 MRS Fall Meeting: Symposium V/NN/OO/PP – Soft Matter, Biological Materials and Biomedical Materials—Synthesis, Characterization and Applications / [ed] A.J. Nolte, K. Shiba, R. Narayan, D. Nolte, Warrendale, Pennsylvania, USA: Materials Research Society, 2011, Vol. 1301, s. 75-80Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Wood strength is highly anisotropic, due to the inherent structural hierarchy of the material. In the framework of a combined random-periodic multiscale poro-micromechanics model, we here translate compositional information throughout this hierarchy into the resulting anisotropic strength at the softwood level, based on “universal” elastic properties of cellulose, hemicelluloses, and lignin, and on the shear strength of the latter elementary constituent. Therefore, derivation of the elastic energy in a piece (representative volume element – RVE) of softwood, stemming from homogeneous macroscopic strains prescribed in terms of displacements at the boundary of the RVE and from pressure exerted by water filling the nanoporous space between the hemicelluloses-lignin network within the cell walls, with respect to the shear stiffness of lignin, yields higher order strains in the lignin phase, approximating micro-stress peaks leading to local lignin failure. Relating this (quasi-brittle) failure to overall softwood failure (or strictly speaking, elastic limit of softwood) results in a macroscopic microstructure-dependent failure criterion for softwood. The latter satisfactorily predicts the biaxial strength of spruce at various loading angles with respect to the grain direction. The model also predicts the experimentally well-established fact that uniaxial tensile and compressive strengths, as well as the shear strength of wood, depend quasi-linearly on the cell water content, but highly nonlinearly on the lumen porosity. 

  • 31.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Homogenization and Localization in a Multiscale Microporomechanical Model for Wood Strength2009Konferensbidrag (Övrigt vetenskapligt)
  • 32.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Multiscale Microporomechanics Model for Estimation of Elastic Limit States of Softwood Materials2009Konferensbidrag (Övrigt vetenskapligt)
  • 33.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Multiscale Microporomechanics of Softwood: Applications and Experimental Model Validation2010Ingår i: IV European Conference on Computational Mechanics (ECCM 2010), Paris, France: European Community on Computional Methods in Applied Sciences (ECCOMAS), 2010Konferensbidrag (Övrigt vetenskapligt)
  • 34.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    On the Relevance of Lignin Failure for Softwood Strength: a Poromicromechanical Approach2011Ingår i: XI International Conference on Computational Plasticity - Fundamentals and Applications, Barcelona: International Center for Numerical Methods in Engineering (CIMNE), 2011Konferensbidrag (Övrigt vetenskapligt)
  • 35.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Poromechanical scale transitions of failure stresses in wood: from the lignin to the spruce level2010Ingår i: Zeitschrift für angewandte Mathematik und Mechanik, ISSN 0044-2267, E-ISSN 1521-4001, Vol. 90, nr 10-11, s. 750-767Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wood strength is highly anisotropic, due to the inherent structural hierarchy of the material. In the framework of a combined random-periodic multiscale poro-micromechanics model, we here translate compositional information throughout this hierarchy into the resulting anisotropic strength at the softwood level, based on “universal” elastic properties of cellulose, hemicellulose, and lignin, and on the shear strength of the latter elementary constituent. Relating, through elastic energy-derived higher-order strains in a poromechanical representative volume element, the (quasi-)brittle failure of lignin to overall softwood failure, results in a macroscopic microstructure-dependent failure criterion for softwood. The latter satisfactorily predicts the biaxial strength of spruce at various loading angles with respect to the grain direction. The model also predicts the experimentally well-established fact that uniaxial tensile and compressive strengths, as well as the shear strength of softwood, depend quasi-linearly on the cell water content, but highly nonlinearly on the lumen porosity.

  • 36.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Hellmich, Christian
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    The poroelastic role of water in cell walls of the hierarchical composite “softwood”2010Ingår i: Acta Mechanica, ISSN 0001-5970, E-ISSN 1619-6937, Vol. 217, nr 1, s. 75-100Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wood is an anisotropic, hierarchically organized material, and the question how the hierarchical organization governs the anisotropy of its mechanical properties (such as stiffness and strength) has kept researchers busy for decades. While the honeycomb structure of softwood or the chemical composition of the cell wall has been fairly well established, the mechanical role of the cell wall water is less understood. The question arises how its capability to carry compressive loads (but not tensile loads) and its pressurization state affect mechanical deformations of the hierarchical composite “wood”. By extending the framework of poro-micromechanics to more than two material phases, we here provide corresponding answers from a novel hierarchical set of matrix-inclusion problems with eigenstresses: (i) Biot tensors, expressing how much of the cell wall water-induced pore pressure is transferred to the boundary of an overall deformation-free representative volume element (RVE), and (ii) Biot moduli, expressing the porosity changes invoked by a pore pressure within such an RVE, are reported as functions of the material’s composition, in particular of its water content and its lumen space. At the level of softwood, where we transform a periodic homogenization scheme into an equivalent matrix-inclusion problem, all Biot tensor components are found to increase with decreasing lumen volume fraction. A further research finding concerns the strong anisotropy of the Biot tensor with respect to the water content: Transverse components increase with increasing water content, while the relationship “longitudinal Biot tensor component versus volume fraction of water within the wood cell wall” exhibits a maximum, representing a trade-off between pore pressure increase (increasing the longitudinal Biot tensor component, dominantly at low water content) and softening of the cell wall (reducing this component, dominantly at high water contents). Soft cell wall matrices reinforced with very stiff cellulose fibers may even result in negative longitudinal Biot tensor components. The aforementioned maximum effect is also noted for the Biot modulus.

  • 37.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Muszynski, Lech
    Oregon State University, USA.
    Integrative Method for Micromechanical Characterization of Wood in Steel-Dowel Connections2012Ingår i: COST Action FP 0802: Experimental and Computational Micro-Characterization Techniques in Wood Mechanics, Edinburgh, UK, 2012, s. 100-101Konferensbidrag (Övrigt vetenskapligt)
    Ladda ner (pdf)
    sammanfattning
  • 38.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Muszynski, Lech
    Lederer, Wolfgang
    Eberhardsteiner, Josef
    Imaging the Micromechanical Response of Wood in Steel-Dowel Connections2013Konferensbidrag (Övrigt vetenskapligt)
  • 39.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Ormarsson, Sigurdur
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Modeling the Mechanical Behavior of Wood Materials and Timber Structures2023Ingår i: Springer Handbook of Wood Science and Technology / [ed] Niemz, P., Teischinger, A., Sandberg, D., Springer, 2023, s. 507-568Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    This chapter aims at highlighting the benefit of numerical methods and their broad application in the field of wood, engineered wood-based products (EWPs), structural elements including glued-laminated and cross-laminated timber, and engineered timber structures. It focuses on the hygrothermo- viscoelastic material behavior of these elements and structures as a consequence of the behavior of wood materials. After motivating the need for models of wood, different types of numerical models and their application for determination of mechanical properties and dimensional stability of wooden boards, strand- and veneer-based engineered woodbased products, including glued-laminated and crosslaminated timber, as well as of connections in EWPs are reviewed and application examples are given. Methods and application examples are furthermore provided for moisturerelated stresses and deformations in timber structures, the influence of connections on the structural response, instability of structural systems, and modeling of prefabricated frame structures, before modeling of historical structures of wood is discussed. The chapter ends with discussing bottlenecks in modeling of wood materials and timber structures, which might be a starting point for further improvements and novel modeling strategies. © Springer Nature Switzerland AG 2023.

  • 40.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Oscarsson, Jan
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Olsson, Anders
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Schweigler, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Dorn, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Dodoo, Ambrose
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Competitive CLT - Improving the competitive advantage of CLT-based building systems through engineering design andreduced carbon footprint: Final report2024Rapport (Övrigt vetenskapligt)
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  • 41.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY). TU Wien, Austria.
    Schweigler, M.
    TU Wien, Austria.
    Hochreiner, Georg
    TU Wien, Austria.
    Eberhardsteiner, Josef
    TU Wien, Austria.
    Dorn, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Serrano, Erik
    Lund University, Sweden.
    Integrative Research for an Enhanced Design of Dowel Connections2015Ingår i: Proceedings of the EUROMECH Colloquium 556 on Theoretical, Numerical, and Experimental Analyses in Wood Mechanics, 2015Konferensbidrag (Refereegranskat)
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  • 42.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Schweigler, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Numerical modelling of the rope effect in laterally loaded dowel-type connections2018Ingår i: 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK, 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Theory of laterally loaded dowel-type fasteners is well understood in relation to their bending deformation as a consequence of lateral embedment stresses in wood. Modelling of the so- called rope effect has however attracted less attention. The rope effect in laterally loaded connections is evoked by withdrawal resistance of the shank as well as by axial resistance of the head of the fasteners. It describes the development of tensile forces along the axis of the fastener, as a consequence of its bending deformation and axial constrains. Hilson [1] emphasized the pronounced contribution of frictional forces in the shear planes that contribute to increased strength of laterally loaded connections. The axial force component parallel to the shear plane however will only become significant for large relative displacements. Different kind of numerical models have been proposed for the simulation of dowel-type connections, including 3D FEM with elasto-plastic material models, with damage mechanics, or so-called foundation models. In this contribution, calculations with a beam-on-nonlinear foundation method [2] will be presented. The model was extended to account for increased lateral connection strength due to withdrawal resistance of fasteners. This was implemented in terms of axial springs that encompass a withdrawal force-relative displacement relationship, similar to the lateral springs that hold information on the embedment behaviour. Friction between the connected timber members was taken into account by the frictional coefficient times the force component perpendicular to the shear plane, which is a result of the axial force in the fastener.

    Calculations were performed for different types of dowel-type fasteners, including screws, smooth shank nails, annular-ringed shank nails and smooth dowels. Model predictions were compared to experimental data and showed good agreement. This encourages the use of the beam model for the engineering design of dowel-type connections in timber structures based on a deeper understanding of structure-connection relationships [3].

  • 43.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Schweigler, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Anderson, Daniel
    Karlsson, Håkan
    Eriksson, Gabriel
    Sabaa, Stephen
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Larsson, Carl
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Engineering design for anefficient assembly of multi-storycross-laminated timber structures: A survey conducted between November 2020 and November 20212023Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Design for efficient assembly is essential to further enhance the competitiveness of cross-laminated timber building systems for multi-story timber structures. This requires a holistic view from the design of the load bearing structures by structural engineers, over the production, pre-fabrication, and transport to the assembly of the structural elements on-site, which often is done by different companies with input from different stakeholders in the construction process. Especially the design of connections between CLT elements, and CLT and other construction materials and products, as well as the size of CLT elements and possibilities for pre-fabrication are crucial for an efficient assembly process. The paper summarizes findings from expert interviews with a focus on Sweden along the before-mentioned value chain, with the aim to identify current practice and potentials for further improvements. Design for efficient assembly starts at the early-stage design and involves all stakeholders in the design construction process. The reduction of uncertainties in the design and assembly process of multi-storey CLT structures as well as knowledge and experience transfer could lead to more efficient design. The identified requirements for efficient assembly should be combined with a life cycle analysis to quantify the potential for a reduction of the carbon footprint of CLT-based building systems, which is the aim of the ongoing research project ‘Improving the competitive advantage of CLT-based building systems through engineering design and reduced carbon footprint’.

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  • 44.
    Bader, Thomas K.
    et al.
    Technische Universität Wien, Austria.
    Schweigler, Michael
    Technische Universität Wien, Austria.
    Hochreiner, Georg
    Technische Universität Wien, Austria.
    Eberhardsteiner, Josef
    Technische Universität Wien, Austria.
    Berechnungsmodell für das Last-Verformungsverhalten von Stabdübelgruppen im Ingenieurholzbau2014Ingår i: Berichte der Fachtagung Baustatik-Baupraxis 12, München: Technischen Universität, München , 2014, s. 113-121Konferensbidrag (Övrigt vetenskapligt)
    Abstract [de]

    In diesem Beitrag wird ein Berechnungsmodell für das Last-Verformungsverhalten von Stabdübelgruppen vorgestellt, mit dem lokale Verbindungsmittelkräfte und Verbindungsmitteldeformationen mit zugehörigen globale Schnittgrößen und Relativverformungen konsistent berechnet werden können. Grundlage dafür bildet das Last-Verformungsverhalten des Einzeldübels, das mit Hilfe eines baustatischen Modellierungsansatzes hergeleitet wird. Ein wesentlicher Eingangsparameter dieses Modells ist die Lochleibungsfestigkeit von Holz, die für beliebige Kraft-Faserrichtungen experimentell untersucht wurde. Mit Hilfe des vorgestellten Berechnungsmodells für Stabdübelgruppen können die Tragfähigkeit einer Verbindung unter einer beliebigen Kombination von Normalkraft, Querkraft und Momentenbeanspruchung und die zugehörige Relativverformung berechnet werden. Mit dem vorgestellten Berechnungsmodell kann der lastfallabhängige Einfluss einer Verbindung auf Schnittgrößen-Verformungsinteraktionen direkt in der baustatischen Berechnung von Holzkonstruktionen berücksichtigt werden.

  • 45.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Schweigler, Michael
    Technische Universität Wien, Austria.
    Hochreiner, Georg
    Technische Universität Wien, Austria.
    Eberhardsteiner, Josef
    Technische Universität Wien, Austria.
    Ingenieurmodelle für die Strukturmodellierung und Nachweisführung von stiftförmigen Verbindungen im Holzbau: (Engineering models for the structural design and verification of dowel-type connections in timber structures)2017Ingår i: Österreichische Ingenieur- und Architekten-Zeitschrift, ISSN 0721-9415, Vol. 162, nr 1-12, s. 1-9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Connections of elements in timber structures play an important role, not only due to their pronounced effect on the mechanical behavior of structures, but also due to the fact they can be decisive for the economic success of timber structures. Herein, approaches for a calculation of the ductile load-displacement behavior of dowel-type connections, of multi-dowel joints and of stresses in their timber matrix, by means of numerical methods, are presented. With these methods, kinematically compatible relative deformations of joints under arbitrary plane loading conditions and their effect on the mechanical behavior of timber structures can be reasonably predicted. The combination of the presented models and their integration in the structural analysis and the verification of timber structures lead to a more realistic prediction of their behavior (internal forces, stresses and deformations), as well as to a more economic design of timber structures. 

  • 46.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Schweigler, Michael
    Vienna University of Technology, Austria.
    Hochreiner, Georg
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Load Distribution in Multi-Dowel Timber Connections under Moment Loading: Integrative Evaluation of Multiscale Experiments2016Ingår i: Proceedings of the 2016 World Conference on Timber Engineering (WCTE) / [ed] J. Eberhardsteiner, W. Winter, A. Fadai, M. Pöll, Vienna: Vienna University of Technology , 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    The load distribution in multi-dowel timber connections under bending moments was investigated by means of an integrative evaluation of a hierarchically organized test program, which encompassed component tests as well as single dowel and multi-dowel connection tests. It was demonstrated that the anisotropic material behaviour of LVL, and consequently of wood in general, leads to a non-uniform distribution among the dowels.

  • 47.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY). Vienna University of Technology, Austria.
    Schweigler, Michael
    Vienna University of Technology, Austria.
    Hochreiner, Georg
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Serrano, Erik
    Lund University, Sweden.
    Dorn, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Enquist, Bertil
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Experimental Assessment of the Load Distribution in Multi-Dowel Timber Connections2016Ingår i: 17th International Conference on Experimental Mechanics, Rhodes, Greece, July 3-7, 2016, 2016Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    An integrative, hierarchically organized testing procedure for the quantification of the load distribution in multi-dowel timber connections is presented herein. The use of contactless deformation measurement systems allowed the combination of test data from single dowel and multi-dowel connections, which gave access to the loads acting on each dowel over the full loading history. As a consequence of the anisotropic material behavior of wood, a nonuniform and progressively changing load distribution among the dowels was found.

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  • 48.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY). Vienna University of Technology, Austria.
    Schweigler, Michael
    Vienna University of Technology, Austria .
    Hochreiner, Georg
    Vienna University of Technology, Austria .
    Enquist, Bertil
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Dorn, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Serrano, Erik
    Lund University.
    Experimental characterization of the global and local behavior of multi-dowel LVL-connections under complex loading2016Ingår i: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 49, nr 6, s. 2407-2424Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The thorough experimental characterization of a dowel-type connection under various combinations of bending moments and normal forces is presented in this study. Double-shear steel-to-timber connections with 12 and 20 mm steel dowels were tested in a 4-point bending test set-up. The load, between the connected steel and wood beams, was transferred by the dowels themselves and also via an additional (passive) contact device, which introduced an eccentric normal force in the timber beam. The behavior of the connections was studied at the global scale of the connection and at the local scale of the individual dowels. A non-contact deformation measurement system was used to assess the changes of the location of the center of relative rotation over the entire loading. At the same time, the head deformations of the individual dowels could be measured, giving a direct indication about the force distribution among the dowels. Due to reinforcement, connections behaved distinctly ductile with a global relative rotation of up to 3°. Pre-stressing of the contact device by a force of 40 kN yielded an even stiffer behavior. For the particular configurations tested herein, the center of rotation was found to be close to the vertical axis of symmetry of the joint and close to the top row of the dowels. Moreover, the superimposed vertical shift of the center of relative rotation in case of a delayed normal force could be quantified. © 2015 RILEM

  • 49.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY). Vienna University of Technology, Austria.
    Schweigler, Michael
    Vienna University of Technology, Austria.
    Hochreiner, Georg
    Vienna University of Technology, Austria.
    Serrano, Erik
    Lund University, Sweden.
    Enquist, Bertil
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Dorn, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Dowel deformations in multi-dowel LVL-connections under moment loading2015Ingår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, nr 3, s. 216-231Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of the experimental study presented herein is the assessment and quantification of the behavior of individual dowels in multi-dowel connections loaded by a bending moment. For this purpose, double-shear, steel-to-timber connections with nine steel dowels arranged in different patterns and with different dowel diameters were tested in four-point bending. In order to achieve a ductile behavior with up to 7° relative rotation, the connections were partly reinforced with self-tapping screws. The reinforcement did not influence the global load–deformation behavior, neither for dowel diameters of 12 mm nor for 20 mm, as long as cracking was not decisive. The deformation of the individual dowels was studied by means of a non-contact deformation measurement system. Thus, the crushing deformation, that is, the deformation at the steel plate, and the bending deformation of the dowels could be quantified. In the case of 12 mm dowels, the bending deformation was larger than the crushing deformation, while it was smaller in the case of 20 mm dowels. Moreover, dowels loaded parallel to the grain showed larger bending deformations than dowels loaded perpendicular to the grain. This indicates that the loading of the individual dowels in the connection differs depending on their location.

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  • 50.
    Bader, Thomas K.
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY). Vienna University of Technology, Austria.
    Schweigler, Michael
    Vienna University of Technology, Austria.
    Serrano, Erik
    Lund University.
    Dorn, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Enquist, Bertil
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Hochreiner, Georg
    Vienna University of Technology, Austria.
    Integrative experimental characterization and engineering modeling of single-dowel connections in LVL2016Ingår i: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 107, s. 235-246Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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. (c) 2016 Elsevier Ltd. All rights reserved.

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