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  • 1.
    Bader, Thomas K.
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Modeling the Mechanical Behavior of Wood Materials and Timber Structures2023In: Springer Handbook of Wood Science and Technology / [ed] Niemz, P., Teischinger, A., Sandberg, D., Springer, 2023, p. 507-568Chapter in book (Refereed)
    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.

  • 2.
    Blomqvist, Lars
    et al.
    RISE, Sweden.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ziethen, Rune
    RISE, Sweden.
    Stress distribution in veneers under lamination and simultaneously bending: an experimental and numerical investigation2023In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 18, no 3, p. 995-1002Article in journal (Refereed)
    Abstract [en]

    Laminated veneer products (LVPs) are veneers glued together into a predetermined shape. Experimental and numerical investigations were performed under lamination and simultaneously bending of veneer laminate to study the stress distribution in the laminate. Laminates of different thicknesses were made of peeled veneers of European beech. The veneers were coated with adhesive, inserted in a mould which had the shape of a semicircle, and finally pressed at 20 degrees C to a laminate. Two Teflon-polymer films including sensors for measurement of the contact pressure were placed on both sides of the laminate to measure the local contact pressure (contact stress) between the laminate and the mould. At the beginning of the bending process, the contact stresses were locally distributed over the laminate in a similar pattern as in a three-point bending; after the laminate was further bent, the stress distribution rearranged to be as in four-point bending. In the end of the moulding, the local contact stresses increased over the entire laminate and reached a 'peak-value' over bent area in the middle part of the mould. A finite-element model was created to study the bending process. Regarding the overall development of the contact stress variations, the experimental and the numerical results agreed.

  • 3.
    Bolmsvik, Åsa
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vercruysse, Adrien
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Stenberg, Sarah
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vibration Distribution Due to Continous, Intermittent or Half Embedded Elastomer Connections in Wooden Constructions2016In: Proceeding of the 2016 World Conference on Timber Engineering (WCTE), August 22-25, 2016 Vienna / [ed] Josef Eberhardsteiner, Wolfgang Winter, Alireza Fadai, Martina Pöll, Vienna: TU-MV Media Verlag , 2016, p. 2912-2920Conference paper (Refereed)
    Abstract [en]

    Elastomers are commonly used to decrease the sound transmission between apartments in timber framed houses. In previous studies, different types of elastomers have been evaluated experimentally. The wooden assemblies, in which elastomers were used in the connections, showed that elastomers cause the vibrations to increase in the direction perpendicular to the applied load within the low frequency span.

    In this study, the effects on acceleration, depending on how the elastomers are placed are studied. The cases having the elastomer continuous, placed as intermittent pieces or positioned half embedded in the junctions are evaluated.

    The frequency dependent properties of the elastomers are needed in order to model the dynamic behaviour and thereby be able to predict sound- and vibration transmission in wooden houses. Here, the properties of a wooden construction having different elastomers connections are studied to enable simulations of the behaviour of the elastomers in a FE model in the future.

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  • 4.
    Carlsson, Peter
    et al.
    Mid Sweden University.
    Esping, Björn
    Mid Sweden University.
    Dahlblom, Ola
    Lund University.
    Ormarsson, Sigurdur
    Lund University.
    Söderström, Ove
    Royal Institute of Technology.
    Optimization, a tool with which to create an effective drying schedule1998In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 52, no 5, p. 530-540Article in journal (Refereed)
    Abstract [en]

    A method for defining effective schedules for kiln drying of wood is presented. The method is designed in such a way that it proposes an optimized variation of temperature and humidity which yields the minimum total drying time , with the condition that the moisture content and the deformation not exceed specified limits after the drying and that the stress not exceeds a specified level at any time during the drying process in order to avoid crack development. To demonstrate the capability of the optimization method numerical results are presented. It should be noted that ill this first approach, drying starts from moisture content corresponding to the fibre-saturation point, i.e. approximate to 30%).

  • 5.
    Crocetti, Roberto
    et al.
    Lund University.
    Gustafsson, Per Johan
    Lund University.
    Danielsson, Henrik
    Lund University.
    Emilsson, Arne
    Limträtenik AB.
    Ormarsson, Sigurdur
    Technical University of Denmark, Denmark.
    Experimental and numerical investigation on the shear strength of glulam2010In: International Council for Research and Innovation in Building and Construction: Working Commission W18 ‑ Timber Structures — 2010, Nelson: University of Canterbury , 2010Conference paper (Refereed)
    Abstract [en]

    According to EC5, the shear resistance of a structural timber element should be determined on the basis of the characteristic shear strength of the material, along with classical beam theory. For glulam, the characteristic strength values are given by the European standard EN 1194 [3], which assumes a direct relationship between tensile strength and shear strength of the lamination. As an example, the characteristic shear strength of glulam class GL28c, consisting of inner laminations with characteristic tensile strength ft,0,k = 14.5 MPa, would  be fv,k = 0.32·(14.5)^0.8 = 2.9 MPa. However, recent investigations both on glulam members [4] and on timber members [5] have shown that the shear strength of spruce is higher than the shear strength obtained by means of the model proposed by EN1194. Moreover, the studies show that the shear strength is nearly constant, regardless the strength class of the timber material.

  • 6.
    Dahlblom, O.
    et al.
    Lund University.
    Ormarsson, Sigurdur
    Lund University.
    Petersson, H.
    Lund University.
    Simulation of wood deformation processes in drying and other types of environmental loading1996In: Annales des Sciences Forestieres, ISSN 0003-4312, E-ISSN 1878-6545, Vol. 53, no 4, p. 857-866Article in journal (Refereed)
    Abstract [en]

    Deformation processes in wood exposed to drying and other types of environmental loading are simulated by use of the finite element method. In the material model applied, the orthotropic structure of the wood material is considered. The differences of properties in the longitudinal, radial and tangential directions for stiffness parameters as well as for moisture shrinkage parameters are taken into account. As an illustration of possible application areas, the deformation development of boards during drying is simulated. In the analyses, the influence of spiral grain and the variation of wood properties with the distance from the pith are considered. The simulation yields information about unfavourable deformations that develop during the drying process., Le processus de déformation du bois exposé au séchage et autres types de charges environnementales est simulé par la méthode des éléments finis. La structure orthotropique du bois est prise en considération sur le modèle de matériel utilisé. Les différences existant au niveau des propriétés des directions longitudinales, radiales et tangentielles sont prises en compte pour les paramètres de rigidité et de contraction par humidité. Une des possibilités du champ d'applications est illustrée par le fait que l'évolution de la déformation des planches pendant le séchage est simulée. À l'échelon des analyses, l'influence du grain spiral et la variation des propriétés du bois avec la distance depuis la moelle sont pris en compte. La simulation permet d'obtenir des informations concernant l'évolution des déformations défavorables pendant le processus de séchage.

  • 7. Dahlblom, Ola
    et al.
    Lindemann, Jonas
    Ormarsson, Sigurdur
    Software for Numerical Simulation of Drying Induced Deformation of Wooden Products2003In: 8th International IUFRO Wood Drying Conference, TRANSILVANIA University of Brasov, Faculty of Wood Industry , 2003, p. 45-50Conference paper (Refereed)
    Abstract [en]

    A previously developed computational model for 3D finite element simulations of wood during moisture changes is in the present work provided with a special-purpose graphical user interface. The software is designed to use a personal computer for the graphical user interface and to have possibility to use distributed computational resources for the simulation.

  • 8. Dahlblom, Ola
    et al.
    Ormarsson, Sigurdur
    Petersson, Hans
    Prediction of deformations by an extended two-dimensional formulation1996In: Quality wood drying through process modelling and novel technologies / [ed] Alain Cloutier, Yves Fortin, 1996, p. 69-76Conference paper (Refereed)
  • 9.
    Dahlblom, Ola
    et al.
    Lund Institute of Technology, Sweden.
    Persson, Kent
    Lund Institute of Technology, Sweden.
    Ormarsson, Sigurdur
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Experimental investigation of basic wood properties with respect to spatial variation in stem1997In: International Conference on Wood-Water relations, Department of Structural Engineering and Materials, Technical University of Denmark / [ed] P. Hoffmeyer,, 1997, p. 197-212Conference paper (Refereed)
  • 10.
    Dahlblom, Ola
    et al.
    Lund Institute of Technology, Sweden.
    Persson, Kent
    Lund Institute of Technology, Sweden.
    Ormarsson, Sigurdur
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Stiffness and shape stability analysis of sawn timber based on experimentally found variations of wood properties1999In: Connection between Silviculture and Wood Quality through Modelling Approaches and Simulation Softwares, 1999Conference paper (Refereed)
  • 11.
    Dahlblom, Ola
    et al.
    Lund Institute of Technology, Sweden.
    Persson, Kent
    Lund Institute of Technology, Sweden.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Ormarsson, Sigurdur
    Investigation of variation of engineering properties of spruce1999In: Wood Drying Research & Technology for Sustainable Forestry Beyond 2000, 1999Conference paper (Refereed)
  • 12.
    Dahlblom, Ola
    et al.
    Lund Institute of Technology.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Ormarsson, Sigurdur
    Full 3-D FEM-Simulations of Drying Distortion in Spruce Boards based on Experimental Studies2001In: 7th International IUFRO Wood Drying Conference, 2001Conference paper (Refereed)
  • 13.
    Dahlblom, Ola
    et al.
    Lund University, Sweden.
    Petersson, Hans
    Chalmers University of Technology, Sweden.
    Ormarsson, Sigurdur
    Chalmers University of Technology, Sweden.
    Stiffness, strength and shape stability grading analysis of sawn timber based on experimentally found growth characteristics2000In: World Conference on Timber Engineering, 2000Conference paper (Refereed)
    Abstract [en]

    Stiffness, strength and shape stability analysis of sawn timber should be based on how the material properties vary in the stem due to different growth conditions. As part of an EU study, results from investigations of the modulus of elasticity, shrinkage coefficient and spiral grain angle of spruce are presented. The variation in properties with the position in the stem has been investigated. The specimens were sawn from 274 stems in 29 stands in five countries of the European Union. A total of about 7000 small specimens were tested. Results from the modelling of stiffness and moisture-induced deformations of battens are presented. The simulations were based on material data obtained from measurements performed on specimens sawn from the same logs as the battens. The simulation results are compared with experimental results and are of interest for the development of new grading procedures for sawn timber.

  • 14. Dahlblom, Ola
    et al.
    Petersson, Hans
    Persson, Kent
    Ormarsson, Sigurdur
    Experimental investigation of basic properties of spruce1998In: World Conference on Timber Engineering, 1998Conference paper (Refereed)
  • 15. Eriksson, John
    et al.
    Ormarsson, Sigurdur
    Chalmers University of Technology, Sweden.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Adaptive Finite Element Analysis of Non-linear Moisture Flow and Associated Distortion Behaviour in Wood2003In: ADMOS Conference on Adaptive Modelling and Simulation, 2003Conference paper (Refereed)
  • 16.
    Eriksson, John
    et al.
    Chalmers University of Technology.
    Ormarsson, Sigurdur
    Chalmers University of Technology.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    An experimental and numerical study of the shape stability in glued columns2005In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 63, no 6, p. 423-429Article in journal (Refereed)
    Abstract [en]

    The study concerns the question of how the shape stability features of laminated columns of Norway spruce can be improved in terms of twist through optimal orientation of the individual laminates. Both experimental testing and numerical simulations were employed for evaluating twist stability. In all the columns studied, deformations were measured experimentally at different moisture content levels. A number of columns were also selected for numerical analysis in order to obtain a more thorough understanding of the twist behavior involved, their geometries and material properties of interest being determined. The experimental results showed the twist stability of the columns to be highly dependant upon the internal orientation of the individual laminates. It was also found that high quality columns in terms of shape stability could be manufactured, even when the center-core material has a strong twist tendency. The numerical simulations performed were in close agreement with the experimental results.

  • 17.
    Eriksson, John
    et al.
    Chalmers University of Technology.
    Ormarsson, Sigurdur
    Chalmers University of Technology.
    Petersson, Hans
    Chalmers University of Technology.
    Experimental study of shape stability in glued boards2004In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 62, no 3, p. 225-232Article in journal (Refereed)
    Abstract [en]

    An experimental study of shape stability in wooden glued boards was performed to verify certain results of particular interest obtained earlier in numerical simulations. Possibilities for achieving products of good shape stability by gluing boards together in an optimal way are discussed. Since twist is often the most serious form of distortion defects for the user, it was the main type of board deformation considered. Three types of glued products were tested. The experiments show clearly that glued boards can be produced that remain stable in shape when exposed to extreme variations in moisture. The results agree well with the numerical simulations performed earlier. It was found that initial twist could be reduced by proper application of pressure during gluing and that through gluing the occurrence of cracking defects on visible surfaces could be substantially reduced.

  • 18.
    Eriksson, John
    et al.
    Chalmers University of Technology .
    Ormarsson, Sigurdur
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Chalmers University of Technology .
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Finite element analysis of coupled nonlinear heat and moisture transfer in wood2006In: Numerical Heat Transfer, Part A Applications, ISSN 1040-7782, E-ISSN 1521-0634, Vol. 50, no 9, p. 851-864Article in journal (Refereed)
    Abstract [en]

    A nonlinear model for analysing heat and moisture flow in wood during drying below the fiber saturation point is presented. The model used considers wood at a macro level without taking the various moisture transports mechanisms at the microscopic level into account. Based on the finite-element method, a coupled system of equations resulting from the adopted heat and moisture transfer equations is established and an iterative scheme is proposed. The numerical procedure is verified by a test example. In a two-dimensional analysis, the influence of the coupling on the combined heat and moisture transfer is studied for a board subjected to a typical kiln-drying condition. How well the results agree with those obtained by introducing a commonly applied simplification is discussed.

  • 19.
    Florisson, Sara
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    The effect of initial green state moisture gradients on stresses in timber boards during drying2016In: Eccomas 2016 Proceedings, 2016Conference paper (Refereed)
  • 20.
    Florisson, Sara
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    The effect of surface emission, diffusion and initial moisture profiles on stress development in timber boards2017In: CompWood 2017 : Computational Methods in Wood Mechanics – from Material Properties to Timber: Programme & book of abstract, TU Verlag , 2017Conference paper (Refereed)
  • 21.
    Florisson, Sara
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    A numerical study of the effect of green-state moisture content on stress development in timber boards during drying2019In: Wood and Fiber Science, ISSN 0735-6161, Vol. 51, no 1, p. 41-57Article in journal (Refereed)
    Abstract [en]

    Timber boards manufactured with a traditional sawing pattern often contain both heartwood andsapwood. In such boards, internal constraints can occur during drying because of a radial variation in greenstate(GS) MC between the heartwood (30-60%) and sapwood region (120-200%). Despite such knowledge,the initial MC is seldom considered when evaluating kiln-drying schedules. The effect of GS MC on thedevelopment of tangential tensile stress during drying is studied for four types of timber boards. A numericalmodel was developed that can simulate transient nonlinear orthotropic moisture flow and moisture–inducedstress and distortion in wood with the use of the finite element method. The stress analysis considers elastic,hygroscopic, and mechano-sorptive strain. The study shows that the GS MC does not significantly influencethe maximum stress state, but that it does influence the time at which the maximum tangential tensile stressoccurs at different exchange surfaces. This results in several periods in the drying schedule where unfavorablehigh stress situations in the tangential direction arise, which could lead to crack propagation.

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  • 22.
    Florisson, Sara
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Modelling of mechano-sorption in clear wood by using an orthotropic non-linear moisture flow and stress model2018In: WCTE 2018 - World Conference on Timber Engineering: 2018 World Conference on Timber Engineering, WCTE 2018; COEX Convention and Exhibition CenterSeoul; South Korea, 20-23 August 2018, World Conference on Timber Engineering (WCTE) , 2018Conference paper (Refereed)
    Abstract [en]

    The European design standard for timber structures provides, besides obligatory safety requirements, a set of general serviceability requirements. Despite their generality, they have been proven important in design of timber structures, especially in varying climatic conditions, where the time dependent deflection can have a dominant role in long term performance. The total deformation consists of instantaneous elastic deformation, hygroscopic deformation, time dependent creep and mechano-sorptive deformation. The three latter deformations are influenced by climate, and when the change in climate is considerable over time, the deflection will significantly increase. In this paper a test-setup is created to study the effect of mechano-sorption on the global deflection of clear wood samples. The samples are loaded in a three-point bending test subjected to a constant mechanical load combined with a cyclic climatic load. The moisture induced stress and bending distortion were simulated by taking into account elastic, hygroscopic and mechano-sorptive strain. The non-linear moisture flow was simulated using Fick’s law. A parametric study was performed to obtain a better understanding of the constitutive equation, especially the term related to the moisture and temperature dependent diffusion coefficient. In addition to the simulations, an experiment was performed to verify the global deflection and mass change. The obtained results show that the mechano-sorption behaviour of the tested clear wood samples can be modelled, but an improvement of both the experimental setup and the model is required to come to more accurate conclusions on this type of long-term material behaviour.

  • 23.
    Florisson, Sara
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Mmari, Winston
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Three-dimensional orthotropic nonlinear transient moisture simulation for wood: analysis on the effect of scanning curves and nonlinearity2020In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 54, p. 1197-1222Article in journal (Refereed)
    Abstract [en]

    This paper introduces, with the development of user-subroutines in the finite-element software Abaqus FEA (R), a new practical analysis tool to simulate transient nonlinear moisture transport in wood. The tool is used to revisit the calibration of moisture simulations prior to the simulation of mechanical behaviour in bending subjected to climate change. Often, this calibration does not receive sufficient attention, since the properties and mechanical behaviour are strongly moisture dependent. The calibration of the moisture transport simulation is made with the average volumetric mass data experimentally obtained on a paired specimen of Norway spruce (Picea abies) with the dimensions 30x15x640 mm(3). The data, from a 90-day period, were measured under a constant temperature of 60 degrees C and systematic relative humidity cycles between 40 and 80%. A practical method based on analytical expressions was used to incorporate hysteresis and scanning behaviour at the boundary surface. The simulation tool makes the single-Fickian model and Neumann boundary condition readily available and the simulations more flexible to different uses. It also allows for a smoother description of inhomogeneity of material. The analysis from the calibration showed that scanning curves associated with hysteresis cannot be neglected in the simulation. The nonlinearity of the analysis indicated that a coherent set of moisture dependent diffusion and surface emission coefficient is necessary for the correct description of moisture gradients and mass transport.

  • 24.
    Florisson, Sara
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology. Luleå University of Technology, Sweden.
    Vessby, Johan
    Karlstad University, Sweden.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    A three-dimensional numerical analysis of moisture flow in wood and of the wood's hygro-mechanical and visco-elastic behaviour2021In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 55, p. 1269-1304Article in journal (Refereed)
    Abstract [en]

    A three-dimensional numerical model was employed in simulating nonlinear transient moisture flow in wood and the wood's hygro-mechanical and visco-elastic behaviour under such conditions. The model was developed using the finite element software Abaqus FEA, while taking account of the fibre orientation of the wood. The purpose of the study was to assess the ability of the model to simulate the response of wood beams to bending and to the climate of northern Europe. Four-point bending tests of small and clear wood specimens exposed to a constant temperature and to systematic changes in relative humidity were conducted to calibrate the numerical model. A validation of the model was then performed on the basis of a four-point bending test of solid timber beams subjected to natural climatic conditions but sheltered from the direct effects of rain, wind and sunlight. The three-dimensional character of the model enabled a full analysis of the effects of changes in moisture content and in fibre orientation on stress developments in the wood. The results obtained showed a clear distinction between the effects of moisture on the stress developments caused by mechanical loads and the stress developments caused solely by changes in climate. The changes in moisture that occurred were found to have the strongest effect on the stress state that developed in areas in which the tangential direction of the material was aligned with the exchange surface of the beams. Such areas were found to be exposed to high-tension stress during drying and to stress reversal brought about by the uneven drying and shrinkage differences that developed between the outer surface and the inner sections of the beams.

  • 25.
    Gustafsson, Per Johan
    et al.
    Lund University.
    Emilsson, Arne
    Lund University.
    Crocetti, Roberto
    Lund University.
    Ormarsson, Sigurdur
    Lund University.
    Provningar av limträs skjuvhållfasthet hösten 20092010Report (Other academic)
  • 26.
    Johansson, Marie
    et al.
    Chalmers University of Technology, Sweden.
    Ormarsson, Sigurdur
    Chalmers University of Technology, Sweden.
    Effect of residual stresses on performance of sawn timber: Experiments2005In: Fifth IUFRO Workshop on Connection between Forest Resources and Wood Quality : Modelling Approaches and Simulation Software, 2005Conference paper (Refereed)
  • 27.
    Johansson, Marie
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Ormarsson, Sigurdur
    Technical University of Denmark.
    Influence of growth stresses and material properties on distortion of sawn timber – Numerical investigation.2009In: Annals of Forest Science, ISSN 1286-4560, E-ISSN 1297-966X, Vol. 66, no 6, article id 604Article in journal (Refereed)
  • 28.
    Jára, Robert
    et al.
    UCEEB , ČVUT, Czech Republic.
    Ptáček, Petr
    UCEEB , ČVUT, Czech Republic.
    Pošta, Jan
    UCEEB , ČVUT, Czech Republic.
    Sejkot, Petr
    UCEEB , ČVUT, Czech Republic.
    Nechanický, Pavel
    České vysoké učení technické, Czech Republic.
    Kuklík, Petr
    České vysoké učení technické, Czech Republic.
    Machalická, Klára
    České vysoké učení technické, Czech Republic.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Patlakas, Panagiotis
    Southampton Solent University, UK.
    Navrhování spojů dřevěných prvků za pomoci kování2016In: Dřevostavby 2016 / [ed] VOŠ Volyně, Volyně, 2016, p. 187-189Conference paper (Other academic)
    Abstract [cs]

    Článek je zaměřen na řešení problematiky spojů dřevěných prvků za pomoci tenkostěnných ocelových elementů aneb kování, kde jako spojovací prvek jsou použity kolíkové spojovací prostředky.

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  • 29.
    Kliger, Robert
    et al.
    Chalmers University of Technology, Sweden.
    Johansson, Marie
    Chalmers University of Technology, Sweden.
    Ormarsson, Sigurdur
    Chalmers University of Technology, Sweden.
    Bäckström, Magnus
    Chalmers University of Technology, Sweden.
    The Builders'€™ View on Drying Quality and its Consequences2004In: Proceedings of COST E15 - Drying timber for value-added products, Athens, Greece, 22-24 April. 01/01/2004, 2004Conference paper (Refereed)
  • 30.
    Kuai, Le
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Karlstad University, Sweden.
    Modelling and experimental verification of light-frame timber modules loaded in shear2021In: World Conference on Timber Engineering 2021, WCTE 2021, World Conference on Timber Engineering (WCTE) , 2021Conference paper (Refereed)
    Abstract [en]

    Building with prefabricated light-frame modules is an innovative construction method whose market share is increasing in Sweden. It is often used to build low and mid-rise residential buildings where the modules are premanufactured in factories with high efficiency and accuracy. This building method has many advantages, though more research regarding wind stabilization of both individual and assembled modules is still needed. To study the racking stiffness and strength of such timber modules, a numerical model of their shear walls was created and verified based on experimental results from specially prefabricated test modules. A new test facility was built for this work, where several potentiometers and a digital image correlation system collected the data used to verify the simulation model. The results from the simulations agree well with the experimental findings, which indicate that the three-dimensional finite element model works with reasonable accuracy for this application. © WCTE 2021. All rights reserved.

  • 31.
    Kuai, Le
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Karlstad University, Sweden.
    Nonlinear FE-analysis and testing of light-frame timber shear walls subjected to cyclic loading2023In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 362, article id 129646Article in journal (Refereed)
    Abstract [en]

    Light-frame timber shear walls have been used as load-bearing elements in buildings for several decades. To predict the performance of such structural elements under loading, numerous analytical and numerical models have been developed. However, little focus has been on the prediction of the plastic damage behaviour and unloading of the walls. In this paper, a parametric Finite Element (FE) model is further developed by introducing elasto-plastic connectors to simulate the mechanical behaviour of the sheathing-to-framing connections. To verify the accuracy of the elasto-plastic model, full-size walls were tested and compared with results from simulations. The numerical results, from a few loading cycles, indicate that the model achieves reasonable accuracy in predicting both the nonlinear elastic and plastic deformations. Both experimental and simulation results demonstrate the importance of opening locations relating to the external racking force. The results also indicate that for a double-layer wall, its racking strength can be achieved by summation of the separate contribution from each layer. Furthermore, the internal layer was observed to contribute significantly less than the external layer since its nail pattern was based on the sheathing pattern of the external layer.

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  • 32.
    Kuai, Le
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Karlstad University, Sweden.
    Maharjan, Rajan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    A numerical and experimental investigation of non-linear deformation behaviours in light-frame timber walls2022In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 252, article id 113599Article in journal (Refereed)
    Abstract [en]

    In recent decades, there is a trend in Scandinavian countries to build multi-storey residential houses using prefabricated timber modules. It is a highly efficient construction process with less environmental impact and less material waste. A significant building element in the timber modules is the light-frame timber wall, which has to be carefully analysed and optimized in this process. This paper presents a new parametric Finite Element (FE) model that can simulate both in-plane and out-of-plane deformations in the light-frame walls. A new and flexible (Eurocode based) approach to define the properties of the mechanical connections is introduced. A numerical model is presented through simulations of several walls that were verified with full-scale experiments. The results indicate that the numerical model could achieve fairly reasonable accuracy with the new approach. Furthermore, several parametric studies are presented and discussed from global and local points of view, to investigate the effects of certain parameters that are not considered in the design method according to Eurocode 5.

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  • 33.
    Kuklík, Petr
    et al.
    Czech Technical University in Prague, Czech Republic.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Dolejš, Jakub
    Czech Technical University in Prague, Czech Republic.
    Ptáček, Petr
    Czech Technical University in Prague, Czech Republic.
    Jára, Robert
    Czech Technical University in Prague, Czech Republic.
    Pošta, Jan
    Czech Technical University in Prague, Czech Republic.
    Sejkot, Petr
    Czech Technical University in Prague, Czech Republic.
    Leiterman, Zdeněk
    BOVA Březnice spol. s.r.o., Czech Republic.
    Úhelníky s prolisem ve spojích dřevěných prvků2015In: Sympozium Energeticky efektivní budovy 2015 / [ed] Matuška, T., Prague: Společnost pro techniku prostředí , 2015, p. 149-154Conference paper (Other academic)
    Abstract [en]

    The paper presents load-bearing capacity calculation methods for timber elements connections by angle brackets with a rib. As connectors, annular ring nails were used. Paper brings direct comparison of results from full-scale tests, analytical calculations and numerical simulations of connections under the external load using two different versions of brackets.

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  • 34. Larsen, Finn
    et al.
    Ormarsson, Sigurdur
    A numerical and experimental study of stress and crack development in kiln-dried wood2012In: Proceedings of World Conference on Timber Engineering 2012, 2012Conference paper (Refereed)
    Abstract [en]

    Numerical and experimental investigations were carried out on well defined log-disc samples of Norway spruce consisting of both heartwood and sapwood, with the aim of gaining more adequate knowledge of stress and fracture generation during the drying process. Use of thin discs enabled a well-controlled and simplified drying history of the samples to be obtained. Experiments supported by the numerical model showed the heartwood to dry below the fibre saturation point, much earlier than the sapwood, and thus to start shrinking at a much earlier stage.

  • 35.
    Larsen, Finn
    et al.
    Technical University of Denmark, Denmark.
    Ormarsson, Sigurdur
    Technical University of Denmark, Denmark.
    Experimental and finite element study of the effect of temperature and moisture on the tangential tensile strength and fracture behavior in timber logs2014In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 68, no 1, p. 133-140Article in journal (Refereed)
    Abstract [en]

    Timber is normally dried by kiln drying, in the course of which moisture-induced stresses and fractures can occur. Cracks occur primarily in the radial direction due to tangential tensile strength (TSt) that exceeds the strength of the material. The present article reports on experiments and numerical simulations by finite element modeling (FEM) concerning the TSt and fracture behavior of Norway spruce under various climatic conditions. Thin log disc specimens were studied to simplify the description of the moisture flow in the samples. The specimens designed for TS were acclimatized to a moisture content (MC) of 18% before TSt tests at 20°C, 60°C, and 90°C were carried out. The maximum stress results of the disc simulations by FEM were compared with the experimental strength results at the same temperature levels. There is a rather good agreement between the results of modeling and experiments. The results also illustrate the strong decrease of TSt with increasing temperature at a constant MC level.

  • 36.
    Larsen, Finn
    et al.
    Technical University of Denmark, Denmark.
    Ormarsson, Sigurdur
    Technical University of Denmark, Denmark.
    Numerical and experimental study of moisture-induced stress and strain field developments in timber logs2013In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 47, no 4, p. 837-852Article in journal (Refereed)
    Abstract [en]

    When solid wood dries from a green condition to a moisture content used for further processing, moisture-induced fracture and stresses can occur. The drying stresses arise because of internal deformation constraints that are strongly affected by the cross-sectional moisture gradient differential shrinkage and the inhomogeneity of the material. To obtain a better understanding of how stresses develop during climatic variations, the field histories of stresses (and strains) in cross sections in their entirety need to be studied. The present paper reports on experiments and numerical simulations concerned with analysing the development of strains and stresses during the drying of 15-mm-thick discs of Norway spruce timber log. The samples were dried at 23 °C and relative humidity of 64 % from a green condition to equilibrium moisture content. The moisture gradient in the longitudinal direction was minimised by use of thin discs simplifying the moisture history of the samples studied. The strain field history was measured throughout the drying process by use of a digital image correlation system. Numerical simulations of the samples agreed rather well with the experimental strain results obtained. The stress results also indicated where in the cross section and when fractures could be expected to occur during drying. More optimal drying schemes showed markedly reduced stress generation.

  • 37.
    Larsen, Finn
    et al.
    Technical University of Denmark, Denmark.
    Ormarsson, Sigurdur
    Technical University of Denmark, Denmark.
    Olesen, John Forbes
    Technical University of Denmark, Denmark.
    Experimental Investigation of Moisture Driven Fracture in Solid Wood2010In: WCTE - World Conference on Timber Engineering 2010: Conference Proceeding, Riva del Garda: Trees and Timber Institute , 2010, p. 449-450Conference paper (Refereed)
    Abstract [en]

    Solid timber products, containing both heartwood and sapwood, often have a high tendency to crack during the drying process. This can cause severe loss of material for the saw-mills, especially for products with large cross sectional dimensions. The cracks (e.g. end-cracks) arise, in some cases, early in the drying process and close again later in the process. It can be difficult to see the closed cracks with visual grading. This may result in too high grading of the damaged material which may cause problems for customers such as building and furniture industries. Moisture content (MC) in green wood varies within the cross section of a timber log. The MC of heartwood, for example, is considerable lower than the MC of sapwood. Shrinkage starts at different times within different parts of the cross section, which results in a complex state of strains and stresses. The moisture related crack pattern in wood often becomes quite complex because of the annual ring structure and the different MC levels within heartwood and sapwood. The focus of this work represents the cross sectional behaviour of a timber log. The main aim is to accumulate experimental results and data for the development of a finite element model to evaluate the various couplings in the hygro-mechanical problem that govern moisture driven cracking in wood.

  • 38.
    Larsen, Finn
    et al.
    Technical University of Denmark, Denmark.
    Ormarsson, Sigurdur
    Technical University of Denmark, Denmark.
    Olesen, John Forbes
    Technical University of Denmark, Denmark.
    Experimental study of moisture-driven distortion and fracture in solid wood2010In: 11th International IUFRO Wood Drying Conference : Recent Advances in the Field of Wood Drying, Luleå: Luleå tekniska universitet, 2010, p. 137-144Conference paper (Refereed)
    Abstract [en]

    Moisture-induced fracture and lack of shape stability in solid wood products are well known problems to the saw-milling and building industries. Cracks that initiate during the drying process may cause severe material losses and the building industry may be forced to use alternative building materials. The cracking caused by kiln-drying of solid timber (and round wood) is extremely difficult to predict due to the strong orthotropic and non-homogeneous characteristics of the material in combination with considerable amounts of microscopic defects which may act as crack initiators. An experimental study has been performed to reveal the cracking behaviour of Norway spruce during drying from green moisture content down to equilibrium moisture content (EMC) at a temperature of 22-24°C and a RH of 64%. The moisture related strains and crack widths were measured with a digital image correlation system (ARAMIS) on thin discs cut from a timber log. The history of the strain field over the entire cross section of the discs was measured throughout the drying period. The results showed that the thicker discs (30 mm) cracked very early during the drying process. They also cracked significantly more than the thinner ones (15 mm) and the crack patterns developed differently. For the thicker discs the early cracks which may partly be caused by the moisture gradient in the longitudinal direction of the log, closed and became invisible later during the drying process. This indicates that sealing of timber log ends in the green moisture state could significantly reduce the development of end-cracks. It was also recognized that the initial moisture content and the shrinkage properties vary significantly from pith to bark. Based on this experimental finding it can be concluded that modelling of crack propagation in solid wood must take the material inhomogeneities into account.

  • 39.
    Larsen, Finn
    et al.
    University of Denmark.
    Ormarsson, Sigurdur
    University of Denmark.
    Olesen, John Forbes
    University of Denmark.
    Moisture-driven fracture in solid wood2011In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 6, no 1-2, p. 49-57Article in journal (Refereed)
    Abstract [en]

    Moisture-induced fractures in solid timber create considerable problems for both building industries and sawmills. Cracks caused by kiln-drying of solid timber are extremely difficult to predict. This paper reports on experiments concerned with methods of reducing cracks in wood and with the cracking behaviour of Norway spruce discs. The spruce was dried from green moisture content down to equilibrium moisture content at 23°C and 64% relative humidity. Moisture-related strains and crack development were measured using a digital image correlation system, Aramis. The moisture gradient in the longitudinal direction had a major influence on crack behaviour and was quite pronounced in discs more than 30 mm thick, but much more limited in discs only 15 mm thick. Although the thicker discs often cracked very early in the drying process, many of these cracks became invisible later on in the drying process, suggesting that sealing the ends of timber logs while in the green moisture state could considerably reduce the development of end-cracks. The initial moisture content and the shrinkage properties of the wood varied markedly from pith to bark. The importance of taking material inhomogeneities into account when modelling crack propagation in solid wood is emphasized. © 2011 Taylor & Francis.

  • 40.
    Lindemann, Jonas
    et al.
    Lund Institute of Technology, Sweden.
    Ormarsson, Sigurdur
    Dahlblom, Ola
    Sandberg, Göran
    Enabling Access to Distributed Resources in a Software for Simulating Drying Induced Deformation of Wood2003In: 16th Nordic Seminar on Computational Mechanic, 2003Conference paper (Refereed)
  • 41.
    Nilsson, Jonaz
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Moisture-related distortion and damage of lightweight wood panels: experimental and numerical study2017In: Journal of the Indian Academy of Wood Science, ISSN 0972-172X, Vol. 14, no 2, p. 99-109Article in journal (Refereed)
    Abstract [en]

    This study was conducted to increase the knowledge of moisture-related distortion and damage in the field of wood-based lightweight panels. By increasing the possibilities of predicting moisture-related distortion and damage, the possibilities of using lightweight wood materials could increase. The study was performed through experiments and modelling work on a wooden panel product with numerous struts and two thin outer-face sheets of beech-wood glued tightly onto the struts, as well as reference panels of solid wood. During the testing period the results showed the density of the studied lightweight panels to vary from 170 to 290 kg/m3. These panels shrunk and swelled less than the solid wood panels and reacted faster to changes of surrounding humidity and temperature. Moisture related distortions such as twist and bow were not inferior compared to the solid wood panels. Shrinkage or swelling produced moisture related stresses. This may mean that the panel will have a risk of serious damage in the form of cracks or glue release between the outer face sheet and the struts when it is exposed to intense drying. The experimental tests also followed how various damages arose in the panels. Until the damage occurred, the deformation results showed a strong agreement between the experimental and the model findings. Better knowledge of how this type of panel reacts to climate variations is important for the further design and development of this type of product.

  • 42.
    Ormarsson, Sigurdur
    Lund University.
    A Finite Element Study of the Shape Stability of Sawn Timber Subjected to Moisture Variations1995Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Shape instability in timber products exposed to moisture variation is a serious problem since it can make wood products unsuitable for construction purposes. In this thesis the finite element method has been used to simulate deformations during the drying process

    .…

    .…

    .…

    To investigate the influence of different parameters on drying deformations a parameter study was performed, the influence of different material parameters and of different constitutive models being studied. In addition, the influence of the spiral grain angle, the conical angle, the orientation of the growth rings, the cross section dimension and the drying profile was examined.

  • 43.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Moisture-induced stresses in curved statically indeterminate timber structures2015In: Theoretical, Numerical, and Experimental Analyses in Wood Mechanics, 2015Conference paper (Refereed)
  • 44.
    Ormarsson, Sigurdur
    Chalmers University of Technology.
    Numerical Analysis of Moisture-Related Distortion in Sawn Timber1999Doctoral thesis, monograph (Other academic)
    Abstract [en]

    A 3D theory for the numerical simulation of deformations and stresses in wood during moisture variation is described. The constitutive model employed assumes the total strain rate to be the sum of the elastic strain rate, the moisture-induced strain rate, the mechano-sorption strain rate and the creep strain rate. The 3D theory used for analyzing the shape stability of sawn timber was implemented in a finite element program. To illustrate the types of results that can be obtained, the behaviour of boards during drying was simulated. .....

  • 45.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Parameterized and adaptive modelling of structural behaviour of innovative modular-based multi-storey timber buildings of wood2018In: Presented at EMI 2018, Engineering Mechanics Institute Conference, May 29 - June 1, 2018, MIT, Cambridge, USA, 2018Conference paper (Refereed)
  • 46.
    Ormarsson, Sigurdur
    et al.
    Technical University of Denmark, Denmark.
    Blond, Mette
    COWI A/S, Denmark.
    An improved method for calculating force distributions in moment-stiff timber connections2012In: Proceedings of World Conference on Timber Engineering 2012, 2012Conference paper (Refereed)
    Abstract [en]

    An improved method for calculating force distributions in moment-stiff multi-dowel timber connections is presented, a method based on use of three-dimensional finite element simulations of timber connections subjected to moment action. The study that was carried out aimed at determining how the slip modulus varies with the angle between the direction of the dowel forces and the fibres in question, as well as how the orthotropic stiffness behaviour of the wood material affects the direction and the size of the forces. It was assumed that the force distribution generated by the moment action taking place strives to minimize the slip rotation between the separate members of a given timber connection. The results of modified hand calculations and of the corresponding finite element calculations that were performed were found to agree rather closely, and to differ remarkably from the results of conventional hand calculations.

  • 47. Ormarsson, Sigurdur
    et al.
    Cown, Dave
    Wood Quality and Solid Wood Products Forest Research.
    Moisture-Related Distortion of Boards and Wooden Products of Radiata Pine: Comparison with Norway Spruce2003In: IUFRO – All Division 5 Conference, Forest products research – providing for sustainable choices, 2003Conference paper (Refereed)
  • 48.
    Ormarsson, Sigurdur
    et al.
    Chalmers University of Technology.
    Cown, Dave
    Forest Res, Wood Qual & Solid Wood Prod, New Zealand.
    Moisture-Related Distortion of Timber Boards of Radiata Pine: Comparison with Norway Spruce2005In: Wood and Fiber Science, ISSN 0735-6161, Vol. 37, no 3, p. 424-436Article in journal (Refereed)
    Abstract [en]

    Based on material data obtained by several researchers at Forest Research in New Zealand, with respect to variations in the main material properties from pith to bark, the distortion model developed earlier for Norway spruce has been further modified for radiata pine. Numerical simulations were performed for both pine and spruce to investigate how different sawn pattern options affect the shape stability of individual boards. Results for spruce presented earlier have shown clearly that warping of the timber products is strongly influenced by the annual ring patterns within the individual boards. Comparisons between the two species were performed to study how the radial variations in the basic properties such as shrinkage parameters, stiffness parameters, and spiral grain have influence on the warping. Generally, the intrinsic patterns of variation in wood properties within stems were similar, and both species show a tendency to distort with changing moisture environment. There are strong indications that intelligent re-combination of material in glued products may overcome many of the inherent problems in using biological material with predictable variation in material properties. Keyword: Finite element simulations, Pinus radiata, shrinkage, spiral grain, distortions, wood, timber boards

  • 49. Ormarsson, Sigurdur
    et al.
    Cown, Dave
    Wood Quality and Solid Wood Products Forest Research.
    Dahlblom, Ola
    Lund Institute of Technology, Sweden.
    Finite Element Simulations of Moisture Related Distortion in Laminated Timber Products of Norway Spruce and Radiata Pine2003In: 8th International IUFRO Wood Drying Conference, 2003Conference paper (Refereed)
    Abstract [en]

    A three dimensional finite element model has been used to analyse distortion in different laminated products of Norway spruce and Radiata pine such as laminated boards, panels and windows. The results show that twist of the products is strongly influenced by the radial variation in material data (spiral grain, shrinkage coefficients etc), original location of the separate pieces within the log and how they are oriented in the products. The results also indicate that the twist pattern for both the spices are quite similar but the twist values of Radiata pine are significantly higher because of its high spiral grain angle. The shape stability of laminated engineering products of wood can be much improved by combining the material knowledge and simulation technique to find the optimal choice and orientation of the individual pieces in the products.

  • 50. Ormarsson, Sigurdur
    et al.
    Dahlblom, O.
    Nygaard, M. J.
    Finite Element Simulation of Mechanical and Moisture-Related Stresses in Laterally Loaded Multi-Dowel Timber Connections2010In: WCTE - World Conference on Timber Engineering 2010, Riva del Garda: Trees and Timber Institute , 2010Conference paper (Refereed)
    Abstract [en]

    Numerical simulations of stress distribution within a moment stiff timber frame corner have been performed. The frame corner is a multi-dowel connection with two slotted-in steel plates. The interaction between the fasteners and the wood material is modelled as a full contact interaction based on penalty formulation. The wood material is assumed to be an orthotropic material in reference to elastic and shrinkage behaviours. Both mechanical loading (from snow and wind) and moisture loading have been studied. Model adaptivity was used to reduce the computer time and to find suitable coupling conditions between beam and solid elements. The simulation results have been compared with typical hand calculations. The conclusion is that the hand calculations diverge quite a lot from the simulation results and relatively small moisture changes can cause significant stresses in areas adjoining the fasteners.

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