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  • 1.
    Florisson, Sara
    et al.
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Ormarsson, Sigurdur
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Vessby, Johan
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    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.

  • 2.
    Florisson, Sara
    et al.
    Linnéuniversitetet, Växjö.
    Ormarsson, Sigurdur
    Linnéuniversitetet, Växjö.
    Vessby, Johan
    Linnéuniversitetet, Växjö.
    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, 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.

  • 3.
    Ormarsson, Sigurdur
    et al.
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Vessby, Johan
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Geometric nonlinear analysis of a pitched roof structure of wood2016In: Eccomas 2016 Proceedings, 2016Conference paper (Refereed)
  • 4.
    Ormarsson, Sigurdur
    et al.
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Vessby, Johan
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Källsner, Bo
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Filchev, Ivan
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Numerical analysis of failure modes and force distribution in a pitched roof structure of wood2016In: Proceedings of the 2016 World Conference on Timber Engineering (WCTE) / [ed] J. Eberhardsteiner, W. Winter, A. Fadai, M. Pöll, Vienna: Vienna University of Technology , 2016Conference paper (Refereed)
    Abstract [en]

    Instability failures of timber elements and timber structures are reported relatively frequently although there are some suggestions available how to prevent such failures. These types of failures are characterized by sudden deformations that typically lead to failure in a single loadbearing element or collapse of the entire structure. This paper deals with buckling analysis and geometric nonlinear stress analysis of pitched roof structures of wood. A FE- model has been developed and used to study how different parameters influence the buckling modes and force distribution in the lateral bracing system of the roof structure. The simulated forces in the bracing system are also compared with results based on a simple design method given in Eurocode 5 (EC5) and a method where the compressed top chord is treated as a beam on a continuous elastic foundation. The buckling simulations showed the out-of-plane buckling to be the critical failure mode for the truss structure studied and the geometric nonlinear analysis showed the bracing stiffness and the bracing forces to be significant lower than those calculated by hand according to EC5.

  • 5.
    Sejkot, Petr
    et al.
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Ormarsson, Sigurdur
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Vessby, Johan
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Numerical and experimental study of punched metal plate connection used for long-span pitched timber roof truss structure2018In: WCTE 2018 - World Conference on Timber Engineering, World Conference on Timber Engineering (WCTE) , 2018Conference 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.

  • 6.
    Sejkot, Petr
    et al.
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Ormarsson, Sigurdur
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Vessby, Johan
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Numerical and experimental study of punched metal plate connections to obtain spring stiffness needed for 3D buckling analysis of long-span timber trusses2017In: 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 (Refereed)
  • 7.
    Sejkot, Petr
    et al.
    Czech Tech Univ, Czech Republic.
    Ormarsson, Sigurdur
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Vessby, Johan
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Kuklik, P.
    Czech Tech Univ, Czech Republic.
    Determination of Load Bearing Capacity for Spatial Joint with Steel Angle Brackets2015In: 2ND INTERNATIONAL CONFERENCE ON INNOVATIVE MATERIALS, STRUCTURES AND TECHNOLOGIES / [ed] Sahmenko, G; Rucevskis, S; Bajare, D, Institute of Physics Publishing (IOPP), 2015, article id UNSP 012070Conference paper (Refereed)
    Abstract [en]

    The design of spatial connections in load bearing timber structures with steel angle brackets has insufficient support in the existing design standards. Therefore, research has been necessary to improve this state of the art. In the current paper an experimental study on two designs of angle brackets is presented and the results from full-scale experiments are compared to numerical and analytical computational models.

  • 8.
    Vessby, Johan
    et al.
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Källsner, Bo
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Ormarsson, Sigurdur
    Linnéuniversitetet, Institutionen för byggteknik (BY).
    Stabilisering av takkonstruktioner i trä: arbetet med ny handbok2016In: Bygg & teknik, ISSN 0281-658X, no 4, p. 60-63Article in journal (Other (popular science, discussion, etc.))
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