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Godinho, P. M. .., Jajcinovic, M., Wagner, L., Vass, V., Fischer, W., Bader, T. K., . . . Hellmich, C. (2018). 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
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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2018 (English)In: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285Article in journal (Refereed) In press
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.

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)
Available from: 2018-11-06 Created: 2018-11-06 Last updated: 2018-12-11
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
Schweigler, M., Bader, T. K. & Hochreiner, G. (2018). Engineering modeling of semi-rigid joints with dowel-type fasteners for nonlinear analysis of timber structures. Engineering structures, 171, 123-139
Open this publication in new window or tab >>Engineering modeling of semi-rigid joints with dowel-type fasteners for nonlinear analysis of timber structures
2018 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 171, p. 123-139Article in journal (Refereed) Published
Abstract [en]

Plastic analysis in engineered structures requires ductility of structural components, which in timber structures is primarily provided by joints made of dowel-type fasteners. A prerequisite for nonlinear analysis is realistic modeling of joint stiffness and load distribution in dowel-type joints. A joint model suitable for structural analysis is presented and validated in this contribution. The semi-analytical joint model is based on kinematic compatibility and equilibrium considerations. It accounts for local fastener slip by means of nonlinear elastic springs. Influences of nonlinearity and orientation dependence of fastener slip are assessed. Elastic deformations of the timber in between dowels are however neglected. The model allows for predicting global joint stiffness, as well as load distribution within the joint, taking explicitly the effect of simultaneously acting internal forces into account. Model validation builds upon an experimental database that spans from embedment testing on the material scale up to joint testing on the structural scale. Application examples demonstrate the broad applic- ability of the model for structural analysis. Moreover, they illustrate effects of assumptions of fastener slip on the joint and structural behavior. Limitations, as well as pros and cons of these assumptions are discussed. Special attention is drawn to load distribution within the joint, since it is important for fastener-based design, currently prescribed by the European design standard. Load distribution in joints is also important for verification against brittle failure modes. As an alternative to fastener-based design, joint-based design, by means of a framework for applying the presented model to plastic design of timber structures with ductile joints, is proposed.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-76149 (URN)10.1016/j.engstruct.2018.05.063 (DOI)000443787000012 ()
Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-09-20Bibliographically approved
Akter, S., Bader, T. K. & Enquist, B. (2018). Failure envelope for interaction of stresses perpendicular to the grain with rolling shear stress in wood. In: 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK: . Paper presented at 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK.
Open this publication in new window or tab >>Failure envelope for interaction of stresses perpendicular to the grain with rolling shear stress in wood
2018 (English)In: 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK, 2018Conference paper, Oral presentation with published abstract (Refereed)
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].

National Category
Building Technologies
Identifiers
urn:nbn:se:lnu:diva-76228 (URN)
Conference
6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK
Available from: 2018-06-20 Created: 2018-06-20 Last updated: 2018-09-11Bibliographically approved
Godinho, P. M., Bader, T. K., Eberhardsteiner, J. & Hellmich, C. (2018). Multiscale modelling of transversely isotropic and anisotropic planar fiber networks: current results for elasticity and strength of paper, and potential applications to related materials. In: Engineering Mechanics Institute Conference 2018 (EMI 2018), Cambridge, Massachusetts, USA: . Paper presented at Engineering Mechanics Institute Conference May 29 - June 1, 2018 (EMI 2018)At: Cambridge, Massachusetts, USA.
Open this publication in new window or tab >>Multiscale modelling of transversely isotropic and anisotropic planar fiber networks: current results for elasticity and strength of paper, and potential applications to related materials
2018 (English)In: Engineering Mechanics Institute Conference 2018 (EMI 2018), Cambridge, Massachusetts, USA, 2018Conference paper, Oral presentation with published abstract (Refereed)
National Category
Building Technologies Wood Science
Identifiers
urn:nbn:se:lnu:diva-76226 (URN)
Conference
Engineering Mechanics Institute Conference May 29 - June 1, 2018 (EMI 2018)At: Cambridge, Massachusetts, USA
Available from: 2018-06-20 Created: 2018-06-20 Last updated: 2018-09-12Bibliographically approved
Bader, T. K., Bocquet, J.-F., Schweigler, M. & Lemaitre, R. (2018). Numerical modeling of the load distribution in multiple 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. 221-239). Aachen: Shaker Verlag
Open this publication in new window or tab >>Numerical modeling of the load distribution in multiple 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. 221-239Chapter 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-77872 (URN)978-3-8440-6144-4 (ISBN)
Available from: 2018-09-19 Created: 2018-09-19 Last updated: 2018-10-04Bibliographically approved
Bader, T. K. & Schweigler, M. (2018). Numerical modelling of the rope effect in laterally loaded dowel-type connections. In: 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK: . Paper presented at 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK.
Open this publication in new window or tab >>Numerical modelling of the rope effect in laterally loaded dowel-type connections
2018 (English)In: 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK, 2018Conference paper, Oral presentation with published abstract (Refereed)
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].

National Category
Building Technologies
Identifiers
urn:nbn:se:lnu:diva-76227 (URN)
Conference
6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11 – 15 June 2018, Glasgow, UK
Available from: 2018-06-20 Created: 2018-06-20 Last updated: 2018-09-11Bibliographically approved
Schweigler, M., Bader, T. K., Hochreiner, G. & Lemaître, R. (2018). Parameterization equations for the nonlinear connection slip applied to the anisotropic embedment behavior of wood. Composites Part B: Engineering, 142, 142-158
Open this publication in new window or tab >>Parameterization equations for the nonlinear connection slip applied to the anisotropic embedment behavior of wood
2018 (English)In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 142, p. 142-158Article in journal (Refereed) Published
Abstract [en]

Nonlinear numerical models for the engineering design of mechanical connections in anisotropic materials require nonlinear material behavior of their components, which are essentially determined by material or structural testing. Herein, a multi-step approach for the parameterization of the nonlinear and anisotropic connection slip behavior is presented and applied to the ductile embedment behavior of steel dowels in wood. For this purpose, previously proposed regression functions for the slip behavior are reviewed, and further possible equations are discussed. Their suitability in the description of typical shapes of slip curves observed in connection testing is assessed before certain combinations are applied to an experimental dataset of embedment tests of steel dowels embedded in Laminated Veneer Lumber. The dependence of the regression parameters on the displacement range in the experimental dataset and the benefit of using parameters with a physical interpretation for being able to exploit connection test data reported in literature is highlighted.

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-70763 (URN)10.1016/j.compositesb.2018.01.003 (DOI)000431157500014 ()
Available from: 2018-02-12 Created: 2018-02-12 Last updated: 2018-07-11Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-7829-4630

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