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Godinho, P. M. .., Jajcinovic, M., Wagner, L., Vass, V., Fischer, W., Bader, T. K., . . . Hellmich, C. (2019). A continuum micromechanics approach to the elasticity and strength of planar fiber networks: Theory and application to paper sheets. European journal of mechanics. A, Solids, 75, 516-531
Open this publication in new window or tab >>A continuum micromechanics approach to the elasticity and strength of planar fiber networks: Theory and application to paper sheets
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2019 (English)In: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 75, p. 516-531Article in journal (Refereed) Published
Abstract [en]

2D materials such as planar fibrous networks exhibit several mechanical peculiarities, which we here decipher through a 3D-to-2D transition in the framework of continuum micromechanics or random mean-field homogenization theory. Network-to-fiber concentration (or “downscaling”) tensors are derived from Eshelby-Laws matrix-inclusion problems, specified for infinitely long, infinitely flat fibers, and for infinitely flat spheroidal pores of vanishing stiffness. Overall material failure is associated with microscopic shear failure orthogonal to the fiber direction. Corresponding structure-property relations between porosity on the one hand, and in-plane stiffness as well as strength on the other hand, appear as linear. This is in good agreement with mechanical experiments carried out on pulp fibers, on pulp fiber-to-pulp fiber bonds, and on corresponding paper sheets.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Continuum micromechanics; Linear elasticity; Strength; Planar fiber networks; Two-dimensional representation; Wood pulp fiber experiments; Wood pulp fiber-to-wood pulp fiber bond experiments; Wood pulp-based paper sheet experiments
National Category
Building Technologies Paper, Pulp and Fiber Technology
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-78700 (URN)10.1016/j.euromechsol.2018.10.005 (DOI)000471361100042 ()2-s2.0-85061483302 (Scopus ID)
Available from: 2018-11-06 Created: 2018-11-06 Last updated: 2019-08-29Bibliographically approved
Lemaitre, R., Bocquet, J.-F., Schweigler, M. & Bader, T. K. (2019). Beam-on-Foundation Modelling as an Alternative Design Method for Timber Joints with Dowel-Type Fasteners: Part 2: Modelling Techniques for Multiple Fastener Connections. In: INTER: International Network on Timber Engineering Research: Proceedings, Meeting 52, 26-29 August 2019, Tacoma, USA. Paper presented at 6th meeting of INTER (International Network on Timber Engineering Research), Tacoma, USA, August 26-29, 2019. Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen, Article ID 52-7-9.
Open this publication in new window or tab >>Beam-on-Foundation Modelling as an Alternative Design Method for Timber Joints with Dowel-Type Fasteners: Part 2: Modelling Techniques for Multiple Fastener Connections
2019 (English)In: INTER: International Network on Timber Engineering Research: Proceedings, Meeting 52, 26-29 August 2019, Tacoma, USA, Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen , 2019, article id 52-7-9Conference paper, Published paper (Refereed)
Abstract [en]

In many design codes for timber structures (e.g. Eurocode 5 and SIA 265), the stiffness of a connection is given by empirical equations for a single dowel-type fastener per shear plane. The global stiffness of the connection is then given by multiplication with the number of dowels and shear planes. In the codes cited above, the empirical equations to estimate stiffness only depend on two parameters, namely the dowel diameter and the wood density. The main difference between different codes and stiffness of different types of fasteners is the choice of the exponent on these two parameters. Development and background of empirical equations for stiffness in different codes were recently reported in Jockwer and Jorissen (2018), who analysed about one thousand double shear timber-to-timber connection tests to evaluate the influence of further parameters on stiffness, such as number of fasteners in a row, number of rows of fasteners and dowel slenderness. From this huge database, they have been able to estimate another empirical stiffness equation, that includes dowel slenderness as an additional parameter. Effects of the latter have even been reported in Lemaître et al. (2018), by using a phenomenological numerical model instead ofexperiments. Sandhaas and van de Kuilen (2017) reported that using the slip modulus Kser, calculated according to Eurocode 5 for stiffness prediction of multiple fastener joints, considerably overestimates the experimentally observed stiffness and they proposed to introduce an effective number of dowels in their design, which was also recommended in Jockwer and Jorissen (2018).

This paper continues the work presented in Lemaître et al. (2018) on strength and stiffness estimations of single-fastener connections using a beam-on-foundation (BOF) modelling. In Lemaître et al (2018), the beam-on-foundation model calculations were compared to design equations of Eurocode 5, i.e. the load-carrying capacity and slip modulus. By these comparisons, the validity of the method for the design of single-fastener connections was highlighted. Moreover, effects that are not explicitly covered in the empirical design equations, namely the influence of the dowel slenderness and the nonlinear dowel diameter on the slip modulus were demonstrated.

In the present paper, the same comparisons are made for multiple dowelled connections. Moreover, load distribution between dowels in this type of connection, which was shown to be non-uniform by Blass (1995), is studied by means of the BOF model. Different approaches to estimate the load distribution have been proposed by Cramer (1968), Lantos (1969) and Wilkinson (1986).

Place, publisher, year, edition, pages
Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen, 2019
Keywords
Dowelled timber connections, Numerical modelling, Beam-on-foundation
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89340 (URN)
Conference
6th meeting of INTER (International Network on Timber Engineering Research), Tacoma, USA, August 26-29, 2019
Available from: 2019-09-29 Created: 2019-09-29 Last updated: 2019-10-01Bibliographically approved
Bader, T. K., Füssl, J. & Olsson, A. (Eds.). (2019). CompWood 2019 - Computational Methods in Wood Mechanics -: From Material Properties to Timber Structures: Book of Abstracts.. Paper presented at CompWood 2019 - Computational Methods in Wood Mechanics - From Material Properties to Timber Structures, June 17-19, 2019, Växjö, Sweden. Växjö: Linnaeus University Press
Open this publication in new window or tab >>CompWood 2019 - Computational Methods in Wood Mechanics -: From Material Properties to Timber Structures: Book of Abstracts.
2019 (English)Conference proceedings (editor) (Refereed)
Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2019. p. 110
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-90446 (URN)978-91-88898-64-7 (ISBN)
Conference
CompWood 2019 - Computational Methods in Wood Mechanics - From Material Properties to Timber Structures, June 17-19, 2019, Växjö, Sweden
Available from: 2019-12-09 Created: 2019-12-09 Last updated: 2019-12-19Bibliographically approved
Schweigler, M. (2019). Database of embedment parameters from soft- and hardwoods. Växjö, Sweden: Linnaeus University
Open this publication in new window or tab >>Database of embedment parameters from soft- and hardwoods
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2019 (English)Data set, Aggregated data
Place, publisher, year
Växjö, Sweden: Linnaeus University, 2019
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-87945 (URN)
Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2019-10-01Bibliographically approved
Schweigler, M., Bader, T. K., Bocquet, J.-F., Lemaitre, R. & Sandhaas, C. (2019). Embedment test analysis and data in the context of phenomenological modeling for dowelled timber joint design. In: INTER: International Network on Timber Engineering Research: Proceedings, Meeting 52, 26-29 August 2019, Tacoma, USA. Paper presented at 6th meeting of INTER (International Network on Timber Engineering Research), Tacoma, USA, August 26-29, 2019. Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen, Article ID 52-7-8.
Open this publication in new window or tab >>Embedment test analysis and data in the context of phenomenological modeling for dowelled timber joint design
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2019 (English)In: INTER: International Network on Timber Engineering Research: Proceedings, Meeting 52, 26-29 August 2019, Tacoma, USA, Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen , 2019, article id 52-7-8Conference paper, Published paper (Refereed)
Abstract [en]

Numerical models, like the phenomenological Beam-On-Foundation (BOF) approach, have proven to be an efficient alternative to the analytical European Yield Model (EYM) for the design of dowelled timber joints according to EN 1995-1-1 (2004) (EC 5) (see e.g. Lemaître et al. (2018), Bader et al. (2016)). In contrast to the EYM, BOF-models allow not only for prediction of the load-carrying capacity, but also for prediction of the load-displacement behavior of single-dowel connections, and thus of their stiffness. This makes BOF-models predestined for the design of joints in advanced modern timber structures, which for reason of their complexity rely on a reliable prediction of the jointload-deformation behavior.

BOF-models are used since the early thirties of the last century (Hager, 1930). Models of different complexity were used from simplified (i) rigid-ideal plastic models, which allow only for strength prediction (cf. Johansen (1949)); to (ii) bi-linear elastic approaches, being able to predict stiffness and strength (Sawata and Yasumura (2003), Cachim and Franssen (2009)), and (iii) nonlinear elastic models, which are optimized for numerical simulations (Lemaître et al., 2018). BOF-models might be even used for earthquake design by application of plastic, or even hysteresis models (Izzi et al. (2018), Girhammar et al. (2017)). Developers and users of such phenomenological models face the challenge to find reliable input data on the load-deformation behavior of steel dowels embedded in wood or wood-based products.

Lack of input data for numerical models, like BOF, is one of the main reasons which hinders application of such models in engineering practice and in research. Since the EYM of EC 5 uses only the embedment strength (fh,EC5) but no stiffness, as input, the related European standard for embedment testing, EN 383 (2007), focuses mainly on the embedment strength determination. However, numerical modeling requires information on the entire load-displacement curve from embedment tests.The aim of this contribution is to

  1. present methods to analyze and parameterize experimental load-displacement curves for BOF-models, with embedment parameters suitable for this purpose;
  2. provide a database of embedment parameters for different wood spieces and wood products, and try to find correlations between parameters;
  3. give recommendations for embedment testing, with the aim to exploit data in numerical models.
Place, publisher, year, edition, pages
Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen, 2019
Keywords
Dowelled timber joints, Embedment tests, Load-displacement curves, Numerical analysis, Database
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89339 (URN)
Conference
6th meeting of INTER (International Network on Timber Engineering Research), Tacoma, USA, August 26-29, 2019
Available from: 2019-09-29 Created: 2019-09-29 Last updated: 2019-10-01Bibliographically approved
Gečys, T., Bader, T. K., Olsson, A. & Kajėnasa, S. (2019). Influence of the rope effect on the slip curve of laterally loaded, nailed and screwed timber-to-timber connections. Construction and Building Materials, 228, 1-13, Article ID 116702.
Open this publication in new window or tab >>Influence of the rope effect on the slip curve of laterally loaded, nailed and screwed timber-to-timber connections
2019 (English)In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 228, p. 1-13, article id 116702Article in journal (Refereed) Published
Abstract [en]

Timber-to-timber connections with different types of screws and nails were experimentally investigated with the aim to quantify the contribution of their axial resistance to their slip and their lateral load bearing capacity, which is the so-called rope effect in dowel-type timber connections. Five different types of screws, including partly threaded and double-threaded screws, as well as three types of nails, including smooth round nails, twisted square-sectioned and grooved nails, were used in the experimental investigations in order to cover a broad range of axial resistance of fasteners. Their behavior was tested in single shear and double shear timber-to-timber connections. In addition to connection testing, system and material properties were experimentally determined. This gave input to design equations and allowed for a comparison of the mechanical model in the European design standard for timber structures, Eurocode 5, with experiments. Experiments indicate that the initial slip modulus in the quasi-elastic domain is not influenced by withdrawal capacity of the fastener, while it shows pronounced influence on load-carrying capacity and the nonlinear shape of the slip curve of the connection at larger deformations. Rope effect strongly depends on fastener properties. High axial resistance of fasteners leads to highly non-linear slip curves and design equations tended to underestimate strength including the rope effect up to a displacement limit of 15 mm. Experimentally observed failure modes were well in line with the theoretical failure modes predicted by the design model. The provided experimental results are motivation for improvement of design models and development of analytical and numerical models that account for nonlinear effects in the complex load transfer mechanism.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Rope effect; Dowel-type connection; Nonlinear slip; Ductility; Stiffness
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89192 (URN)10.1016/j.conbuildmat.2019.116702 (DOI)000497886100010 ()
Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-12-13Bibliographically approved
Akter, S. T., Bader, T. K. & Serrano, E. (2019). Modeling of wood under combination of normal stresses with rolling shear stress. In: Presented at CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from material properties to Timber Structures, Växjö, Sweden, June 17-19, 2019: . Paper 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
Open this publication in new window or tab >>Modeling of wood under combination of normal stresses with rolling shear stress
2019 (English)In: 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, 2019Conference paper, Oral presentation with published abstract (Refereed)
Place, publisher, year, edition, pages
Växjö, Sweden: , 2019
National Category
Wood Science Building Technologies
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology; Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89211 (URN)
Conference
CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from material properties to Timber Structures, Växjö, Sweden, June 17-19, 2019
Available from: 2019-09-20 Created: 2019-09-20 Last updated: 2019-11-04Bibliographically approved
Akter, S. T., Bader, T. K. & Serrano, E. (2019). Modelling of wood under compression perpendicular to the grain with rolling shear in cross-laminated timber. In: Presented at COMPLAS 2019 - XV International Conference on Computational Plasticity: Fundamentals and Applications, Barcelona, Spain, September 3-5, 2019: . Paper 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)
Open this publication in new window or tab >>Modelling of wood under compression perpendicular to the grain with rolling shear in cross-laminated timber
2019 (English)In: 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), 2019Conference paper, Oral presentation with published abstract (Refereed)
Place, publisher, year, edition, pages
Barcelona, Spain: European Community on Computional Methods in Applied Sciences (ECCOMAS), 2019
Keywords
Compression perpendicular to the grain, Rolling shear
National Category
Wood Science Building Technologies
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology; Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89212 (URN)
Conference
COMPLAS 2019 - XV International Conference on Computational Plasticity: Fundamentals and Applications, Barcelona, Spain, September 3-5, 2019
Available from: 2019-09-20 Created: 2019-09-20 Last updated: 2019-11-04Bibliographically approved
Schweigler, M. & Bader, T. K. (2019). Numerical modeling of dowel-type connections in soft- and hardwoods including the rope effect. In: CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures: . Paper presented at CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures, 17-19 June, 2019, Växjö (pp. 10-10). Växjö, Sweden: Lnu Press
Open this publication in new window or tab >>Numerical modeling of dowel-type connections in soft- and hardwoods including the rope effect
2019 (English)In: CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures, Växjö, Sweden: Lnu Press , 2019, p. 10-10Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

In laterally loaded dowel-type connections, forces are not only transferred perpendicular to the fastener axis via contact forces (so-called embedment forces) and shear forces in the fastener, but also by means of forces evoked by displacement along the fastener axis and frictional forces within shear planes. The latter load transfer, the so-called rope effect, is often neglected or simplified in numerical models for laterally loaded connections, but considerably increases strength in case of large bending deformations of the fastener. In partially threaded screws, the rope effect is a result of the withdrawal behavior of the threaded part in combination with the axial resistance of the head of the fasteners. The tensile force along the axis of the fastener causes compression between connected members and frictional forces within the shear planes of the connection, which increase the load bearing capacity [1]. Consideration of the rope effect in numerical models is decisive for valid and suitable prediction of the load-deformation behavior and discussed in this presentation.

Place, publisher, year, edition, pages
Växjö, Sweden: Lnu Press, 2019
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89768 (URN)978-91-88898-64-7 (ISBN)
Conference
CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures, 17-19 June, 2019, Växjö
Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-11-12Bibliographically approved
Muszyński, L., Akter, S. T., Nairn, J. & Bader, T. K. (2019). On the need for reliable rolling shear characteristics in CLT lamellas and for efficient related test methods. In: Bool of abstract: CompWood 2019, International Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber Structures. June 17-19, 2019, Växjö, Sweden.: . Paper presented at CompWood 2019, International Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber Structures. June 17-19, 2019, Växjö, Sweden.. Lnu Press
Open this publication in new window or tab >>On the need for reliable rolling shear characteristics in CLT lamellas and for efficient related test methods
2019 (English)In: Bool of abstract: CompWood 2019, International Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber Structures. June 17-19, 2019, Växjö, Sweden., Lnu Press , 2019Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Effective modeling of structural behavior of cross-laminated timber (CLT) elements requires reliable input on the mechanical properties of its laminations. The cross-lamination of layers provides for dimensional stability of CLT elements. In this arrangement, however, all laminations in shear walls and the layers of floor elements oriented perpendicular to the major strength axis transfer shear stress in the radial–tangential plane, often referred to as rolling shear. It is among the least documented characteristics of wood, since it had been of marginal interest for structural lumber and engineered wood composites until the emergence of CLT. While the numerical models may easily account for the contribution of rolling shear in the immediate and long-term deformations of laminated panels, simulations are charged with wide margins of uncertainty because of shortage of reliable experimental data. Rolling shear is not the easiest property to measure, and it received only limited coverage in the literature [1-7]. What has been documented was that the rolling shear strength and stiffness in the cross-layers in CLT floor panels is related to the species, density, growth ring orientation, and manufacturing parameters, but there is no evidence for a meaningful correlation with the grade of lumber, whether established by visual or machine grading. In the presentation, we will discuss the pressing need for reliable data on rolling shear characteristics in clear wood and in structural lumber, their statistical distributions in species important for CLT industry, as well as for efficient test methods to allow generation of relevant data in timely manner. Prototype methods and preliminary data will be presented.

Place, publisher, year, edition, pages
Lnu Press, 2019
Keywords
CLT, Rolling shear
National Category
Construction Management
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89767 (URN)978-91-88898-64-7 (ISBN)
Conference
CompWood 2019, International Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber Structures. June 17-19, 2019, Växjö, Sweden.
Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-12-04Bibliographically approved
Projects
Hardwood_joint: Innovative joints in hardwoods [2018-04980]; Linnaeus University; Publications
Lemaitre, R., Bocquet, J.-F., Schweigler, M. & Bader, T. K. (2019). Beam-on-Foundation Modelling as an Alternative Design Method for Timber Joints with Dowel-Type Fasteners: Part 2: Modelling Techniques for Multiple Fastener Connections. In: INTER: International Network on Timber Engineering Research: Proceedings, Meeting 52, 26-29 August 2019, Tacoma, USA. Paper presented at 6th meeting of INTER (International Network on Timber Engineering Research), Tacoma, USA, August 26-29, 2019. Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen, Article ID 52-7-9. Schweigler, M., Bader, T. K., Bocquet, J.-F., Lemaitre, R. & Sandhaas, C. (2019). Embedment test analysis and data in the context of phenomenological modeling for dowelled timber joint design. In: INTER: International Network on Timber Engineering Research: Proceedings, Meeting 52, 26-29 August 2019, Tacoma, USA. Paper presented at 6th meeting of INTER (International Network on Timber Engineering Research), Tacoma, USA, August 26-29, 2019. Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen, Article ID 52-7-8. Schweigler, M. & Bader, T. K. (2019). Numerical modeling of dowel-type connections in soft- and hardwoods including the rope effect. In: CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures: . Paper presented at CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures, 17-19 June, 2019, Växjö (pp. 10-10). Växjö, Sweden: Lnu Press
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7829-4630

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