| 1. |
- Bader, Thomas K., 1980-, et al.
(författare)
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Modeling the Mechanical Behavior of Wood Materials and Timber Structures
- 2023
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Ingår i: Springer Handbook of Wood Science and Technology. - : Springer. - 9783030813147 - 9783030813154 ; , s. 507-568
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Bokkapitel (refereegranskat)abstract
- 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.
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| 2. |
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| 3. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Stress distribution in veneers under lamination and simultaneously bending : an experimental and numerical investigation
- 2023
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis Group. - 1748-0272 .- 1748-0280. ; 18:3, s. 995-1002
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Bolmsvik, Åsa, 1975-, et al.
(författare)
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Vibration Distribution Due to Continous, Intermittent or Half Embedded Elastomer Connections in Wooden Constructions
- 2016
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Ingår i: Proceeding of the 2016 World Conference on Timber Engineering (WCTE), August 22-25, 2016 Vienna. - Vienna : TU-MV Media Verlag. - 9783903039001 - 9783903024359 ; , s. 2912-2920
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Konferensbidrag (refereegranskat)abstract
- 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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| 5. |
- Carlsson, Peter, et al.
(författare)
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Optimization, a tool with which to create an effective drying schedule
- 1998
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 52:5, s. 530-540
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Tidskriftsartikel (refereegranskat)abstract
- 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%).
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| 6. |
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| 7. |
- Crocetti, Roberto, et al.
(författare)
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Experimental and numerical investigation on the shear strength of glulam
- 2010
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Ingår i: International Council for Research and Innovation in Building and Construction: Working Commission W18 ‑ Timber Structures — 2010. - Nelson : University of Canterbury.
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 8. |
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| 9. |
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| 10. |
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| 11. |
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| 12. |
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| 13. |
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| 14. |
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| 15. |
- Dahlblom, O., et al.
(författare)
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Simulation of wood deformation processes in drying and other types of environmental loading
- 1996
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Ingår i: Annales des Sciences Forestieres. - : Elsevier. - 0003-4312 .- 1878-6545. ; 53:4, s. 857-866
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 16. |
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| 17. |
- Dahlblom, Ola, et al.
(författare)
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Software for Numerical Simulation of Drying Induced Deformation of Wooden Products
- 2003
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Ingår i: 8th International IUFRO Wood Drying Conference. - : TRANSILVANIA University of Brasov, Faculty of Wood Industry. - 973635198X ; , s. 45-50
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 18. |
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| 19. |
- Dahlblom, Ola, et al.
(författare)
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Stiffness, strength and shape stability grading analysis of sawn timber based on experimentally found growth characteristics
- 2000
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Ingår i: World Conference on Timber Engineering.
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 20. |
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| 21. |
- Eriksson, John, 1973, et al.
(författare)
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An experimental and numerical study of the shape stability in glued columns
- 2005
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Ingår i: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 63:6, s. 423-429
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 22. |
- Eriksson, John, et al.
(författare)
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Experimental study of shape stability in glued boards
- 2004
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Ingår i: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 62:3, s. 225-232
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 23. |
- Eriksson, John, 1973, et al.
(författare)
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Finite element analysis of coupled nonlinear heat and moisture transfer in wood
- 2006
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Ingår i: Numerical Heat Transfer, Part A Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 50:9, s. 851-864
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 24. |
- Florisson, Sara, et al.
(författare)
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A numerical study of the effect of green-state moisture content on stress development in timber boards during drying
- 2019
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Ingår i: Wood and Fiber Science. - : Society of Wood Science and Technology. - 0735-6161. ; 51:1, s. 41-57
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 25. |
- Florisson, Sara, et al.
(författare)
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A three-dimensional numerical analysis of moisture flow in wood and of the wood's hygro-mechanical and visco-elastic behaviour
- 2021
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Ingår i: Wood Science and Technology. - : Springer. - 0043-7719 .- 1432-5225. ; 55:5, s. 1269-1304
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 26. |
- Florisson, Sara, et al.
(författare)
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Modelling of mechano-sorption in clear wood by using an orthotropic non-linear moisture flow and stress model
- 2018
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Ingår i: WCTE 2018 - World Conference on Timber Engineering. - : World Conference on Timber Engineering (WCTE).
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 27. |
- Florisson, Sara
(författare)
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Moisture-induced stress and distortion of wood : A numerical and experimental study of wood's drying and long-term behaviour
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the current advances made in three-dimensional modelling of wood, it is possible to provide an overall picture of moisture flow, and moisture-induced stress and deformations, whereas previously, experiments only provided local measurements. The main aim of the doctoral thesis is to investigate the possibilities of the developed three-dimensional numerical model to predict the behaviour of wood when simultaneously exposed to a mechanical load and a particular climate. Three applications in the fields of wood drying and long-term behaviour of wood are considered: 1) the effect of green-state moisture content on the drying behaviour of timber boards, 2) the calibration of the numerical model based on a long-term four-point bending tests using small wood beams subjected to a constant temperature and systematic relative humidity (RH) changes, and 3) the validation of the numerical model by means of a long-term four-point bending test on solid timber beams subjected to Northern European climate. As part of the second application, an experimental methodology and analytical method were designed. The numerical model was developed in finite element software Abaqus FEA® and consists of several user-subroutines to include material orientation (i.e. annual ring pattern, conical shape and spiral grain), and the selected constitutive behaviour and required boundary conditions. To simulate the moisture flow, a nonlinear single-Fickian approach was combined with a nonlinear Neumann boundary condition, which describes the flux normal to the exchange surface based on a moisture and temperature dependent surface emission coefficient. A strain relation was used that accounts for hygro-expansion, and the elastic, creep and mechano-sorptive behaviour. The analytical method describes the elastic and creep deflection in the constant moment area of the four-point bending setup, and was used to isolate and assess the mechano-sorption deflection in the cumulative moisture content domain. The results show that the three-dimensional character of the numerical model contributed to the analysis and visualisation of the different stress states and deformations that are affected by material properties that vary (i.e. from pith to bark, between heartwood and sapwood, and due to temperature and moisture content), fibre orientation and climate. The simulations made on timber boards clarified phenomena, such as stress reversal and casehardening associated with wood drying, and showed that the green-state moisture content affected the time, size and frequency with which extremes in tangential tensile stress developed inside the timber during drying. The results of the calibration and validation indicated that the numerical model is able to describe moisture change and gradients in the considered temperature and relative humidity ranges (between -2-60℃ and 40-80% RH), as well as the deflection. The experimental methodology and analytical method led to a successful identification of each deflection component and isolation of the mechano-sorptive deflection curves. The experimental methodology benefitted the calibration of the numerical model. In conclusion, the presented three-dimensional numerical model compatible with Abaqus FEA® provides a powerful tool for scientists and timber engineers to study the combined effect of load and climate on stress state and deformations of various timber products in a wide field of applications.
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| 28. |
- Florisson, Sara, et al.
(författare)
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Numerical analysis of wood subjected to bending and northern European climate
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Due to the natural process of sorption, wood constantly interacts with the surrounding climate to establish an equilibrium moisture content, even without the direct influence of rain, solar radiation or wind. However, when wood is subjected to a combination of a change in moisture content and a state of stress brought on by e.g. mechanical load, differential shrinkage or swelling, or differences in material properties, a continuous change in the level of stress and the occurrence of deformations and fracture can be the result.The techniques available for in-situ monitoring of changes in moisture content and hygro-mechanical and viscoelastic behaviour can only be employed in specific locations in or around the wood. Whereas, modern techniques employed in laboratories, such as digital image correlation and computed tomography are laborious and time consuming. With recent developments in three-dimensional modelling, endless predictions can be made both of moisture flow and of the hygro-mechanical and visco-elastic behaviour of wood in three-dimensional space, requiring experimental data only to calibrate and validate the model.A three-dimensional numerical model was created in finite element software Abaqus FEA® to simulate both the transient nonlinear moisture flow and the moisture-dependent distortion and stress, while account is being taken of the fibre orientation (annual ring pattern, conical shape and spiral grain). A nonlinear single-Fickian model in connection with a nonlinear Neumann boundary condition is used to describe the moisture flow. For a moisture-sensitive and visco-elastic material such as wood, it is common to describe the total strain rate as a summation of the elastic, hygro-expansion, visco-elastic creep and mechano-sorptive strain rates.The aim was to determine whether the model was able to simulate in an adequate way the beam bending that occurs under northern European climate conditions. To accomplish this, the following steps were taken: 1) on the basis of experimental data available in literature, a set of expressions was created to describe the moisture- and temperature-dependent diffusion coefficient and surface emission coefficient, 2) experimental results obtained for small beams tested under constant temperature and systematic relative humidity (controlled climatic) conditions were used to calibrate the numerical model, account being taken of the spiral grain that applied and the annual ring curvature, and 3) test results for solid beams tested in northern European (natural) climatic conditions were used to validate the numerical model, account being taken of the fibre orientation.The results obtained showed a clear distinction between the effect of moisture on the stress development caused by mechanical load and the stress development 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 a stress overturn brought about by wetting. The material orientation showed to have a strong effect on the estimated deflection, calibrated material parameters and normative stress states.
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| 29. |
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| 30. |
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| 31. |
- Florisson, Sara, et al.
(författare)
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Three-dimensional orthotropic nonlinear transient moisture simulation for wood : analysis on the effect of scanning curves and nonlinearity
- 2020
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Ingår i: Wood Science and Technology. - : Springer. - 0043-7719 .- 1432-5225. ; 54, s. 1197-1222
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 32. |
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| 33. |
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| 34. |
- Huber, Johannes Albert Josef, 1989-
(författare)
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Modelling Alternative Load Paths in Platform-Framed CLT Buildings : A Finite Element Approach
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Timber has become more popular as a construction material during recent years. Engineered wood products, such as glued laminated timber and cross-laminated timber, have enabled the construction of multi-storey buildings. Tall buildings with many occupants need to resist a disproportional collapse in case of unexpected exposures, e.g. accidents or terrorism. Structural robustness can improve the collapse resistance of a building. The literature about robustness is comprehensive concerning concrete and steel buildings, but it is rather limited regarding timber.A robust building can mobilise alternative load paths in the structure after the removal of bearing building components. Alternative load paths rely primarily on the connections between components. For timber buildings, few investigations exist to evaluate the alternative load paths after a removal. Analyses usually do not take into account non-linear effects which could influence the capacity of alternative load paths, such as damage of single fasteners, friction, timber crushing and brittle failure. In particular, the alternative load paths in platform-framed cross-laminated timber buildings are not well understood. The goals of this thesis are to i) review the concept of robustness in general and determine the state of the art concerning timber buildings in particular, ii) develop a method to analyse the alternative load paths in a platform-framed CLT building taking into account relevant non-linearities, iii) use the method to elicit the alternative load paths in a building after a wall removal, and iv) study the effects of probabilistic variations of model parameters. The thesis first introduces tall timber buildings and then presents a summary of structural robustness in a collapse resistance framework. The summary includes established analysis methods and specific considerations for timber, whereof a detailed review is provided in Paper I. Paper III additionally provides results of a survey on contemporary practices of professionals around the world concerning robustness. In the subsequent chapter, the studied 8-storey case building made of platform-framed cross-laminated timber is described including the modelling abstractions. Additionally, the setup of a validation experiment for the modelling approach is described. The following chapter introduces the modelling approach for an alternative load path analysis after a wall removal. The approach is based on the finite element method using the commercial software Abaqus. The deterministic part of the approach includes a non-linear static pushdown analysis of single storeys in a bay and elicits the alternative load paths and their capacity. Finite connector elements in the model substitute single fasteners including their elastic, plastic, damage and rupture behaviour. The 3D models of the walls and floors account for timber crushing, brittle failure and contact friction. A simplified non-linear dynamic model of the entire bay uses the pushdown results as inputs and evaluates the collapse progression among storeys after a sudden element removal. The probabilistic part of the approach models the uncertainty of the input parameters of the dynamic model by varying the parameter values in a Monte Carlo simulation, to evaluate the probability of a collapse. Paper II applies the approach for a simple pushdown of a single storey and Paper IV applies the pushdown and the dynamic analysis to elicit the alternative load paths after a single wall removal. The thesis shows furthermore the results of a double wall removal in the example building and the results of the Monte Carlo analysis for the single and double wall removal. For the assumed removals, the developed approach could identify the alternative load paths, determine their capacities and estimate the probability of a collapse under probabilistic variations. The approach might be used to classify various removal scenarios in platform-framed multi-storey cross-laminated timber buildings specifically and predetermine design solutions which could provide a desired level of robustness. The approach might be generalised for multi-storey timber buildings of various construction types.
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| 35. |
- Huč, Sabina
(författare)
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Moisture-Induced Strains and Stresses in Wood
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To design safe, reliable and durable timber structures subjected to varying natural outdoor or indoor climates, understanding the long-term behavior of wood when mechanically loaded or restrained to deform is crucial. The present thesis focuses on the numerical modeling of the long-term mechanical behavior of wood. The numerical analysis is divided in the moisture transport and the mechanical analyses. In the moisture analysis, the multi-Fickian moisture transport model is used to determine spatial and temporal moisture content fields over the analyzed domain due to changing relative humidity (RH) of the ambient air. The obtained moisture contents are taken into the mechanical analysis where a new mechanical model is applied for predicting rheological response of wood in three orthotropic directions simultaneously. Experimental results of different authors are used to support numerous numerical analyses performed for various wood species, deformation and loading modes in constant or changing RH conditions. The performed analyses show that the new mechanical model adequately predicts the viscoelastic behavior of hardwood and softwood species in two orthotropic directions simultaneously under a sustained load or deformation. A significant influence of grain orientation in relation to the applied mechanical load on the viscoelastic creep behavior of wood is observed. The mechanical model is also able to predict accurately the rheological behavior of hardwood subjected to a sustained compressive mechanical load and changing moisture content. Applying the moisture and the mechanical models to the glued-laminated timber specimens during wetting and drying shows good agreement with the experimental results. The magnitudes of moisture-induced stresses perpendicular to the grain indicate a possibility of crack initiation during drying. The influence of characteristic material parameters required in the models on the mechanical state of the analyzed specimens is also determined. A quantification of the viscoelastic and the mechanosorptive material parameters required in the mechanical model is the additional outcome of the performed numerical analyses. The mechanical model presented in this thesis in combination with the multi-Fickian moisture transport model enables a full two- or three-dimensional long-term mechanical analysis of timber members exposed to natural climate with RH variations.
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| 36. |
- Jára, Robert, et al.
(författare)
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Navrhování spojů dřevěných prvků za pomoci kování
- 2016
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Ingår i: Dřevostavby 2016. - Volyně. - 9788086837840 ; , s. 187-189
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 37. |
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| 38. |
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| 39. |
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| 40. |
- Kuai, Le, et al.
(författare)
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A numerical and experimental investigation of non-linear deformation behaviours in light-frame timber walls
- 2022
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Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 252
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 41. |
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| 42. |
- Kuai, Le, et al.
(författare)
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Modelling and experimental verification of light-frame timber modules loaded in shear
- 2021
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Ingår i: World Conference on Timber Engineering 2021, WCTE 2021. - : World Conference on Timber Engineering (WCTE).
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 43. |
- Kuai, Le, et al.
(författare)
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Nonlinear FE-analysis and testing of light-frame timber shear walls subjected to cyclic loading
- 2023
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Ingår i: Construction and Building Materials. - : Elsevier. - 0950-0618 .- 1879-0526. ; 362
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Tidskriftsartikel (refereegranskat)abstract
- 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. © 2022 The Authors
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| 44. |
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| 45. |
- Kuai, Le, et al.
(författare)
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Numerical and experimental investigations of prefabricated light-frame timber modules
- 2024
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Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 303
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Tidskriftsartikel (refereegranskat)abstract
- Structures built with prefabricated timber modules have been recognised as an innovative construction method and have been implemented in several countries and regions. In recent years, there have been considerable research activities directed towards these types of structures. However, most of the studies have focused on modules made of steel and concrete in their load-bearing structures and only a few of them are exploring light-frame timber modules. This study focuses on the racking behaviour of light-frame timber modules through experimental and numerical investigations. Full-size tests were performed to examine the global and local structural behaviours of several test modules. A novel finite element model of the modules is also presented. It is a parameterised structural model with high flexibility concerning the generation of different module geometries, materials, fastener types and assembly methods etc. The numerical model was developed in the commercial finite element software ABAQUS, and the numerical results obtained were validated against results from experimental tests. The validation results indicate that the model is capable of achieving satisfactory accuracy in predicting both the global and local structural behaviour of light-frame timber modules. Furthermore, several parametric studies are conducted and discussed to examine how certain parameters affect the structural response of the modules.
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| 46. |
- Kuai, Le
(författare)
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Parametric FE-modelling of non-linear racking behaviour of light-frame shear walls and modules used for multi-storey timber buildings
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood is a sustainable material from nature that has a longstanding traditionas a building material. Compared to other construction materials, such as steeland concrete, the significance of using structural timber and engineered wood products has increased in recent years because they are regarded as a renewable source and require a low carbon footprint and less energy consumption during production. In Scandinavia, the European design standard EN 1995-1-1 (EC5) is extensively used to guide structural engineers in the design of timber structures, while addressing safety and service ability issues. However, this standard relieson multiple simplifications to achieve simple semi empirical hand calculations. In addition to these simplified expressions, engineers and researchers need reliable numerical models to study the racking behaviour of light-frame timber structures with arbitrary geometry under complex loading conditions. Such modelling tools must be computationally effective, easy to use and able to simulate the global structural behaviour as well as the local fastener force distributions and the crack growth in the sheathing panels.The main aim of this doctoral thesis is to develop a numerical model to analyse the complex structural behaviour of prefabricated light-frame timber modules. The model is developed in the commercial finite element software ABAQUS® with the assistance of the parametric Python scripting method. This thesis work also includes development of a graphical user interface in Python for user-friendly inputs, outputs, and visualisation of the numerical results. The simulation tool was used to study two different structural applications, firstly light-frame timber walls and then light-frame timber modules. For these applications, the modelling of the mechanical sheathing-to-framing joints is very important. In the first paper application, oriented and uncoupled elastic spring-based connectors were used to simulate the sheathing-to-framing joints. To define the material parameters for the connector, new Eurocode-based expressions were also presented. To simulate the permanent displacements in the sheathing-to-framing joints a coupled elasto-plastic spring-based connector model was proposed in papers II and III for both isotropic and orthotropic joint properties.To validate the accuracy of the numerical model, full-scale experimental tests were conducted for light-frame timber walls and modules. The validation indicates that by using effective 3D structural elements, the model achieves a satisfying balance between computational efficiency and reasonable accuracy. The numerical results presented for the applications agreed well with experimental results, regarding the global and local displacements and crack growth in the sheathing panels. The simulation results also increased the understanding of local joint behaviour in terms of fastener forces and their directions. The developed model was used to perform numerous parametric studies and thus investigate how different geometries, sheathing panels, connection types orboundary conditions affect the global and local structural behaviour of light-frame timber structures. These studies demonstrate how the parametric modelling can easily be used to analyse how different parameters have influence on these types of structures and significantly reduce the number of experimental tests necessaryto perform.The parametric model has also the potential to be further developed for the structural design of more complex modular-based multi-storey timber buildings. Furthermore, the proposed orthotropic elasto-plastic spring-based connector model can be further calibrated to simulate the performance of dowel-type connections in wood-based materials.
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| 47. |
- Kuklík, Petr, et al.
(författare)
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Úhelníky s prolisem ve spojích dřevěných prvků
- 2015
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Ingår i: Sympozium Energeticky efektivní budovy 2015. - Prague : Společnost pro techniku prostředí. - 9788002026150 ; , s. 149-154
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 48. |
- Källander, Björn, et al.
(författare)
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Fuktförändringar, klimat och mögelpåväxt vid lagring av granvirke : Kalibrering av Finit Elementmodell för fuktförändringar
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A diffusion based Finite Element- model designed to calculate changes in moisture content distribution in packages of wood during storage has been calibrated by means of combined measurements of climate and moisture content in a test package. Moisture content distribution before and after storage has been determined by dry mass measurements and X- ray Computer Tomography (CT- scanning). CT- scanning was done on individual planks to reduce interference from surrounding material. As a complement to the measurements of climate and moisture content, the test material was inspected visually after storage to determine if mould growth had occurred.The results from the study show that the moisture flux within a package of wood is slower than the moisture flux theoretically estimated based on published diffusion coefficients of wood. The moisture flux from the interior of a plank to the surface is slower than the removal of moisture from the surface, also when the plank is within a closed package covered with plastic on five surfaces.The calibration of the Finite Element model makes it ready for calculations of changes in moisture content in wood with high accuracy.
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| 49. |
- Källander, Björn, et al.
(författare)
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Fuktförändringar, klimat och mögelpåväxt vid lagring av granvirke : Laboratoriestudie och modellering av industriellt torkat virke
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Studien avsåg att bestämma hur fuktkvoten i virke förändras under lagring i paket och vid vilka klimat och fuktkvoter mögelpåväxt uppkommer. Fyra satser virke med medelfuktkvoter mellan 18 % och 24 % skulle studeras för att säkerställa att studien omfattade virke både över och under fuktnivåer där mögel kan uppkomma. En Finit Element- modell som kan beräkna förändringar i fuktkvot i virke under lagring utvecklas och kalibreras mot mätdata för att resultaten ska kunna tillämpas på industriell produktion.Studien avsåg komplettera den tidigare studien i industrimiljö genom att dels oförstörande mäta förändringar i fuktkvotens fördelning under lagringen, dels bestämma fuktens fördelning med större noggrannhet än torrviktsmätningar för att ge underlag till kalibrering av FE-modellen.
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| 50. |
- Landel, Pierre, 1981-
(författare)
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Wind-induced vibrations in tall timber buildings : Design standards, experimental and numerical modal analyses
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate change and densification of cities are two major global challenges. Inthe building and construction industry, there are great expectations that tall timberbuildings will constitute one of the most sustainable solutions. First, verticalurban growth is energy and resource-efficient. Second, forest-based productsstore carbon and have one of the highest mechanical strength to density ratios.If the structural substitution of concrete and steel with wood in high-rise buildingsawakens fears of fire safety issues, engineers and researchers are particularlyworried about the dynamic response of the trendy tall timber buildings.Indeed, due to the low density of wood, they are lighter, and for the same height,they might be more sensitive to wind-induced vibrations than traditional buildings.To satisfy people’s comfort on the top floors, the serviceability design oftall timber buildings must consider wind-induced vibrations carefully. Architectsand structural engineers need accurate and verified calculation methods,useful numerical models and good knowledge of the dynamical properties oftall timber buildings.Firstly, the research work presented hereby attempts to increase the understandingof the dynamical phenomena of wind-induced vibration in tall buildings andevaluate the accuracy of the semi-empirical models available to estimate alongwindaccelerations in buildings. Secondly, it aims at, experimentally and numerically,studying the impact of structural parameters – masses, stiffnesses anddamping – on the dynamics of timber structures. Finally, it suggests how talltimber buildings can be modeled to correctly predict modal properties and windinducedresponses.This research thesis confirms the concerns that timber buildings above 15-20stories are more sensitive to wind excitation than traditional buildings with concreteand steel structures, and solutions are proposed to mitigate this vibrationissue. Regarding the comparison of models from different standards to estimatewind-induced accelerations, the spread of the results is found to be very large.From vibration tests on a large glulam truss, the connection stiffnesses are foundto be valuable for predicting modal properties, and numerical reductions withsimple spring models yield fair results. Concerning the structural models of conceptualand real tall timber buildings, numerical case studies emphasize the importanceof accurately distributed masses and stiffnesses of structural elements,connections and non-structural building parts, and the need for accurate dampingvalues.
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