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Florisson, S., Ormarsson, S. & Vessby, J. (2019). A numerical study of the effect of green-state moisture content on stress development in timber boards during drying. Wood and Fiber Science, 51(1), 41-57
Open this publication in new window or tab >>A numerical study of the effect of green-state moisture content on stress development in timber boards during drying
2019 (English)In: Wood and Fiber Science, ISSN 0735-6161, Vol. 51, no 1, p. 41-57Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Society of Wood Science and Technology, 2019
Keywords
Green state, Nonlinear, Numerical, Moisture transport, Transient, Timber drying, Tangential stress
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-80214 (URN)
Available from: 2019-02-05 Created: 2019-02-05 Last updated: 2019-02-25Bibliographically approved
Florisson, S., Ormarsson, S. & Vessby, J. (2018). Modelling of mechano-sorption in clear wood by using an orthotropic non-linear moisture flow and stress model. In: 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. Paper presented at 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)
Open this publication in new window or tab >>Modelling of mechano-sorption in clear wood by using an orthotropic non-linear moisture flow and stress model
2018 (English)In: 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, Published 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.

Place, publisher, year, edition, pages
World Conference on Timber Engineering (WCTE), 2018
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-80218 (URN)2-s2.0-85058165472 (Scopus ID)
Conference
2018 World Conference on Timber Engineering, WCTE 2018; COEX Convention and Exhibition CenterSeoul; South Korea, 20-23 August 2018
Available from: 2019-02-05 Created: 2019-02-05 Last updated: 2019-05-27Bibliographically approved
Sejkot, P., Ormarsson, S. & Vessby, J. (2018). Numerical and experimental study of punched metal plate connection used for long-span pitched timber roof truss structure. In: WCTE 2018 - World Conference on Timber Engineering: . Paper presented at WCTE 2018, World Conference on Timber Engineering, August 20-23, 2018, Seoul, Rep. of Korea. World Conference on Timber Engineering (WCTE)
Open this publication in new window or tab >>Numerical and experimental study of punched metal plate connection used for long-span pitched timber roof truss structure
2018 (English)In: WCTE 2018 - World Conference on Timber Engineering, World Conference on Timber Engineering (WCTE) , 2018Conference paper, Published paper (Refereed)
Abstract [en]

According to the harmonized European design code for timber structures, Eurocode 5, all pitched timber trusses used in load bearing roofs are designed as in-plane structures which means that a bracing system must be designed and put in place to prevent the out-of-plane instability. Results from numerical 3D stability analyses of the whole roof structure indicate that the out of plane stability is often the critical factor. Therefore, influence of stiffness properties of that system is studied in detail herein for long-span timber roofs. Focus is put on how the stiffness of the mechanical connections in the roof structure influences the load carrying capacity of the roof. The punched metal plate connections are modelled as non-coupled spring elements connecting the various beam elements in the timber truss respectively. The spring stiffness of the connections is derived from full-scale tests, which were made for all in- and out-of-plane degrees of freedom. To evaluate the experimental testing, a digital image correlation method was used. The results from the digital image correlation tests were compared with numerical simulations of the experimentally tested connections to check the potential of using the numerical simulations instead of the experimental testing to get the stiffness properties of various connections used in the whole roof stability analysis. Based on such analysis, punched metal plate fasteners showed to be an important contributor to the roof stability because of its relatively high stiffness in all six degrees of freedom.

Place, publisher, year, edition, pages
World Conference on Timber Engineering (WCTE), 2018
Keywords
Timber truss structures, punched metal plate connections, numerical analysis, top chord buckling length
National Category
Construction Management
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-82136 (URN)2-s2.0-85058165120 (Scopus ID)
Conference
WCTE 2018, World Conference on Timber Engineering, August 20-23, 2018, Seoul, Rep. of Korea
Available from: 2019-04-24 Created: 2019-04-24 Last updated: 2019-05-27Bibliographically approved
Habite, T., Florisson, S. & Vessby, J. (2018). Numerical Simulation of Moisture-Induced Crack Propagation in Dowelled Timber Connection Using XFEM. In: 2018 World Conference on Timber Engineering (WCTE), August 20-23, 2018, Seoul, Republic of Korea: . Paper presented at 2018 World Conference on Timber Engineering (WCTE), August 20-23, 2018, Seoul, Republic of Korea. World Conference on Timber Engineering (WCTE)
Open this publication in new window or tab >>Numerical Simulation of Moisture-Induced Crack Propagation in Dowelled Timber Connection Using XFEM
2018 (English)In: 2018 World Conference on Timber Engineering (WCTE), August 20-23, 2018, Seoul, Republic of Korea, World Conference on Timber Engineering (WCTE) , 2018Conference paper, Published paper (Refereed)
Abstract [en]

At times dowelled glulam timber connections experience crack development in the fibre direction. The main reason for this is moisture variation in the timber elements which induces a stress perpendicular to the fibre direction. The aim of this paper is to study the influence of different moisture conditions and vertical dowel spacing on crack development through numerical simulations by use of the finite element method in three dimensions. A transient non-linear Fickian moisture diffusion model is implemented to simulate the moisture state within the glulam beam. The moisture gradient in the diffusion model was created by adopting a physical scenario by assuming what conditions the considered glulam beam will go through, from the factory up to installation. Further, an extended finite element method (XFEM) for two different vertical dowel spacing, 100 mm and 300 mm, with a linear elastic fracture mechanics (LEFM) approach was applied for the crack simulation. The results reveal that the moisture variation in combination with unfavourable placement of dowels can cause a crack to develop in the glulam timber beam. Moreover, it was shown that a moisture induced crack development may be modelled successfully by use of an Extended Finite Element Method (XFEM) approach.

Place, publisher, year, edition, pages
World Conference on Timber Engineering (WCTE), 2018
Keywords
Transient moisture flow, XFEM, LEFM, dowelled connection, fracture
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-81114 (URN)2-s2.0-85058166537 (Scopus ID)
Conference
2018 World Conference on Timber Engineering (WCTE), August 20-23, 2018, Seoul, Republic of Korea
Available from: 2019-03-15 Created: 2019-03-15 Last updated: 2019-03-21Bibliographically approved
Bader, T. K., Vessby, J. & Enquist, B. (2018). Path dependence in OSB sheathing-to-framing nailed connection revealed by biaxial testing. Journal of Structural Engineering, 144(10), Article ID 04018197.
Open this publication in new window or tab >>Path dependence in OSB sheathing-to-framing nailed connection revealed by biaxial testing
2018 (English)In: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 144, no 10, article id 04018197Article in journal (Refereed) Published
Abstract [en]

OSB sheathing-to-wood framing connection, as typically used in light-frame shear walls, was experimentally examined in a novel biaxial test setup with respect to possible path dependence of the load-displacement relation. The connection with an annular-ringed shank nail was loaded under displacement control following nine different displacement paths within the sheathing plane, which coincided at a number of points. In intersection points, resultant connection force, its orientation and work performed on the connection system to reach the specific point were calculated and compared. Evaluation of experiments revealed significant path dependence with respect to orientation of force resultants at path intersection points. However, magnitude of the forces and the work carried out showed relatively small dependence of the displacement path undertaken. Comparison of uniaxial connection tests with the European yield model demonstrated strong contribution of withdrawal resistance of the ringed shank nail to its lateral strength. Results of this type are a valuable basis to build better models when simulating such connections in wood structures.

Place, publisher, year, edition, pages
Reston, VA: American Society of Civil Engineers (ASCE), 2018
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-70762 (URN)10.1061/(ASCE)ST.1943-541X.0002112 (DOI)000441685500001 ()2-s2.0-85051250090 (Scopus ID)
Available from: 2018-02-12 Created: 2018-02-12 Last updated: 2019-08-29Bibliographically approved
Schweigler, M., Bader, T. K., Vessby, J. & Eberhardsteiner, J. (2017). Constrained displacement boundary condition in embedment testing of dowel-type fasteners in LVL. Strain, 53(6), Article ID e12238.
Open this publication in new window or tab >>Constrained displacement boundary condition in embedment testing of dowel-type fasteners in LVL
2017 (English)In: Strain, ISSN 0039-2103, E-ISSN 1475-1305, Vol. 53, no 6, article id e12238Article in journal (Refereed) Published
Abstract [en]

The influence of the loading orientation with respect to the grain direction of wood and the influence of the lateral dowel displacement boundary condition on the embedment behaviour of steel dowels in laminated veneer lumber (with parallel-laminated veneers) are investigated in this study. For limit states of the lateral boundary condition, the load-displacement behaviour was experimentally studied by means of full-hole embedment tests on screw-reinforced laminated veneer lumber, for two dowel diameters and up to large dowel displacements. A novel biaxial test set-up is proposed for embedment tests with constrained lateral dowel displacement boundary condition, in order to quantify laterally evoked reaction forces. Corresponding forces were found to change orientation with increasing dowel displacement and amounted to about 20% and 40% of the vertical reaction force for dowel displacements of 5 mm and twice the dowel diameter, respectively. The influence of the lateral displacement boundary condition was highlighted by comparison of the test data with a previously established data set for unconstrained embedment testing. Constrained loading showed a stiffer response and higher nominal embedment stresses, as well as a more pronounced displacement hardening, compared to unconstrained loading.

Place, publisher, year, edition, pages
John Wiley & Sons, 2017
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-68122 (URN)10.1111/str.12238 (DOI)000415339000001 ()2-s2.0-85033779512 (Scopus ID)
Available from: 2017-09-28 Created: 2017-09-28 Last updated: 2019-08-29Bibliographically approved
Bader, T. K. & Vessby, J. (2017). Modeling displacement path dependence in nailed sheathing-to-framing connections. In: Josef Füssl, Thomas K. Bader, Josef Eberhardsteiner (Ed.), CompWood 2017 - Computational Methods in Wood Mechanics - from Material Properties to Timber Structures: Programme & Books of Abstracs. Paper presented at CompWood 2017 - ECCOMAS Thematic Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures, 7-9 June, 2017, Vienna, Austria. Vienna: TU verlag
Open this publication in new window or tab >>Modeling displacement path dependence in nailed sheathing-to-framing connections
2017 (English)In: CompWood 2017 - Computational Methods in Wood Mechanics - from Material Properties to Timber Structures: Programme & Books of Abstracs / [ed] Josef Füssl, Thomas K. Bader, Josef Eberhardsteiner, Vienna: TU verlag , 2017Conference paper, Oral presentation with published abstract (Refereed)
Place, publisher, year, edition, pages
Vienna: TU verlag, 2017
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-65874 (URN)978-3-903024-49-6 (ISBN)
Conference
CompWood 2017 - ECCOMAS Thematic Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures, 7-9 June, 2017, Vienna, Austria
Available from: 2017-06-27 Created: 2017-06-27 Last updated: 2017-08-25Bibliographically approved
Sejkot, P., Ormarsson, S. & Vessby, J. (2017). Numerical and experimental study of punched metal plate connections to obtain spring stiffness needed for 3D buckling analysis of long-span timber trusses. In: Presented at CompWood 2017 – ECCOMAS Thematic Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber, June 7-9, 2017, Vienna, Austria: . Paper presented at CompWood 2017 – ECCOMAS Thematic Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber, June 7-9, 2017, Vienna, Austria..
Open this publication in new window or tab >>Numerical and experimental study of punched metal plate connections to obtain spring stiffness needed for 3D buckling analysis of long-span timber trusses
2017 (English)In: Presented at CompWood 2017 – ECCOMAS Thematic Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber, June 7-9, 2017, Vienna, Austria, 2017Conference paper, Oral presentation with published abstract (Refereed)
National Category
Construction Management
Identifiers
urn:nbn:se:lnu:diva-68219 (URN)
Conference
CompWood 2017 – ECCOMAS Thematic Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber, June 7-9, 2017, Vienna, Austria.
Available from: 2017-10-05 Created: 2017-10-05 Last updated: 2017-10-19Bibliographically approved
Vessby, J., Florisson, S. & Habite, T. (2017). Numerical simulation of moisture driven fracture in mechanical timber connection using XFEM. In: CompWood 2017 ECCOMAS Thematic Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber Structures, Vienna, Austria, June 7-9, 2017: . Paper presented at CompWood 2017 ECCOMAS Thematic Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber Structures, Vienna, Austria, June 7-9, 2017 (pp. 25-25). TuVerlag
Open this publication in new window or tab >>Numerical simulation of moisture driven fracture in mechanical timber connection using XFEM
2017 (English)In: CompWood 2017 ECCOMAS Thematic Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber Structures, Vienna, Austria, June 7-9, 2017, TuVerlag , 2017, p. 25-25Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Structural timber and glulam elements are an appealing alternative when it comes to choosing between structural elements as load bearing parts in e.g. halls, arenas and residential buildings. The wooden material is relatively strong in respect to its weight and its stiffness is sufficient enough to allow its use in a wide range of applications. However, there are also challenges associated with handling the material, one of which is the dimensional instability associated with moisture changes. The effect of climate variations on moisture induced deformations, stresses and failure in timber structures has already been addressed by several researchers, see e.g. [1] and [2]. A numerical model developed in the finite element package Abaqus is proposed herein to simulate crack propagation caused by variation in climate. In mechanical connections moisture induced strains in combination with boundary conditions that introduces constraints can lead to crack development and in turn weakening of wooden structures. Previous application of fracture mechanics typically focused on crack development caused by pure mechanical loading, see e.g. [3] for methods summarized and typical applications. Within the scope of the current work a numerical model is presented to simulate moisture driven crack growth within the beam/column dowel group connection shown in Figure 1. The model consists of two dimensional hygro-mechanical plane stress and XFEM analysis coupled to a nonlinear transient moisture flow analysis. A visualization of the considered problem is given in Figure 1. This figure shows a beam to column connection, which is exposed to natural climate variation (a). A schematic description of the problem is shown in Figure 1 (b). Figure 1 (c) shows simulated moisture content gradient and significant cracked beam because of the deformation constraints imposed by the dowels. The transient non-linear moisture flow was modelled using Fick’s law of orthotropic diffusion, using different diffusion coefficient in the two main directions, the length direction of the beam (assumed parallel to the fibers) and the direction perpendicular to that. The moisture transport in parallel direction was taken to be dominant. The shrinkage coefficients experience different values in perpendicular and parallel direction, αperp and αpar, respectively. For the fracture model, the critical energy release rate, GIC, is set to 300 J/m2, the strength in the perpendicular direction, ft,perp, to 2.5 MPa and the stiffness perpendicular and parallel to the length directions of the fibres are Eperp= 500 MPa and Epar= 10 000 MPa respectively.

Place, publisher, year, edition, pages
TuVerlag, 2017
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering)
Identifiers
urn:nbn:se:lnu:diva-89352 (URN)978-3-903024-49-6 (ISBN)
Conference
CompWood 2017 ECCOMAS Thematic Conference on Computational Methods in Wood Mechanics – from Material Properties to Timber Structures, Vienna, Austria, June 7-9, 2017
Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2019-10-08Bibliographically approved
Ormarsson, S. & Vessby, J. (2016). Geometric nonlinear analysis of a pitched roof structure of wood. In: Eccomas 2016 Proceedings: . Paper presented at ECCOMAS Congress 2016 VII European Congress on Computational Methods in Applied Sciences and Engineering, June 5–10, 2016 Crete Island, Greece..
Open this publication in new window or tab >>Geometric nonlinear analysis of a pitched roof structure of wood
2016 (English)In: Eccomas 2016 Proceedings, 2016Conference paper, Oral presentation with published abstract (Refereed)
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-68215 (URN)
Conference
ECCOMAS Congress 2016 VII European Congress on Computational Methods in Applied Sciences and Engineering, June 5–10, 2016 Crete Island, Greece.
Available from: 2017-10-05 Created: 2017-10-05 Last updated: 2017-10-16Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1638-1023

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