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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
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, 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, 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)
Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-09-26Bibliographically 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: 2019-09-24Bibliographically 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: 2019-09-24Bibliographically approved
Lemaitre, R., Bocquet, J.-F., Schweigler, M. & Bader, T. K. (2018). Beam-on-foundation modelling as an alternative design method for single fastener connections. In: Carmen Sandhaas, Jorgen Munch-Andersen, Philipp Dietsch (Ed.), Design of Connections in Timber Structures: A state-of-the-art report by COST Action FP1402/WG3 (pp. 207-220). Aachen: Shaker Verlag
Open this publication in new window or tab >>Beam-on-foundation modelling as an alternative design method for single fastener connections
2018 (English)In: 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, p. 207-220Chapter in book (Refereed)
Place, publisher, year, edition, pages
Aachen: Shaker Verlag, 2018
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-77871 (URN)978-3-8440-6144-4 (ISBN)
Available from: 2018-09-19 Created: 2018-09-19 Last updated: 2018-10-04Bibliographically approved
Lemaitre, R., Bocquet, J.-F., Schweigler, M. & Bader, T. K. (2018). Beam-on-foundation modelling as an alternative design method for timber joints with dowel-type fasteners: Part 1: Strength and stiffness per shear plane of single-fastener joints.. In: 5th INTER Proceedings, 2018: International Network on Timber Engineering Research 2018. Paper presented at 5th INTER Meeting, 13-16 August, 2018, Tallin. Karlsruher Institut für Technologie, Article ID 51-7-13.
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 1: Strength and stiffness per shear plane of single-fastener joints.
2018 (English)In: 5th INTER Proceedings, 2018: International Network on Timber Engineering Research 2018, Karlsruher Institut für Technologie , 2018, article id 51-7-13Conference paper, Published paper (Refereed)
Abstract [en]

Optimised manufacturing processes made possible the production of larger dimensions timber products, which allow for the design of remarkable structures. In the last version of the EN 1995-1-1, it seemed important to its drafters to propose design formulas to estimate stiffness of joints in accordance with the needs of that time. Aware of the technical jump that had to be managed, the proposed rules remained simple. However, simple design equations became insufficient to cope with present-day challenges, which are, e.g., related to the design of high-rise wooden buildings. In EN 1995-1-1, the resistant capacity of dowel-type timber joints is no longer determined by empirical formulas but it is based on the limit analysis proposed by Johansen (1949). This methodology however shows limits for complex joints even though many improvements have been made since its introduction (Blaß and Laskewitz 2000). In parallel with these analytical approaches, developments in computational mechanics made it possible to develop simple numerical methods (Foschi 1974, Hirai 1983), which taken even into account nonlinear phenomena. These approaches have remained unused in practical design due to their complex implementation and their high running time, at the time of their invention, while todays computational resources strongly reduced corresponding limitations. Thus, numerical modelling of connections can help engineers to fill the gaps of the EN 1995-1-1 and to cope with variability in connection design. For this purpose, dowel-type fasteners are numerically modelled as elastoplastic beams on a nonlinear foundation in engineered in wood-based products (Sawata and Yasumura 2003, Hochreiner et al. 2013). This method is called Beam-On-Foundation (BOF) modelling and shows huge potential for engineering design. The purpose of this paper is to show how this method can substitute and complement limit analysis and empirical stiffness formulas of timber joints with dowel-type fasteners.

Place, publisher, year, edition, pages
Karlsruher Institut für Technologie, 2018
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-77867 (URN)
Conference
5th INTER Meeting, 13-16 August, 2018, Tallin
Available from: 2018-09-19 Created: 2018-09-19 Last updated: 2018-10-04Bibliographically approved
Bocquet, J.-F., Lemaitre, R. & Bader, T. K. (2018). Design recommendations and example calculations for dowel-type connections with multiple shear planes. In: C. Sandhaas, J. Munch-Andersen, P. Dietsch (Ed.), Design of Connections in Timber Structures: A state-of-the-art report by COST Action FP1402/WG3 (pp. 241-295). Aachen: Shaker Verlag
Open this publication in new window or tab >>Design recommendations and example calculations for dowel-type connections with multiple shear planes
2018 (English)In: Design of Connections in Timber Structures: A state-of-the-art report by COST Action FP1402/WG3 / [ed] C. Sandhaas, J. Munch-Andersen, P. Dietsch, Aachen: Shaker Verlag, 2018, p. 241-295Chapter in book (Refereed)
Abstract [en]

Numerical modeling approaches, for the determination of load distribution in later-ally loaded connections, as well as for the assignment of stiffness properties of con-nections 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 connections, even more pronounced when connections 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 connection displacement. Pros and cons of the modeling approaches as well as necessary input data are dis-cussed in relation to the design process and European standardization. 

Place, publisher, year, edition, pages
Aachen: Shaker Verlag, 2018
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-78702 (URN)978-3-8440-6144-4 (ISBN)
Available from: 2018-11-06 Created: 2018-11-06 Last updated: 2018-12-10Bibliographically 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.
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ORCID iD: ORCID iD iconorcid.org/0000-0002-7829-4630

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