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  • 1.
    Bader, Thomas K.
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Modeling displacement path dependence in nailed sheathing-to-framing connections2017In: 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 (Refereed)
  • 2.
    Bader, Thomas K.
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Path dependence in OSB sheathing-to-framing nailed connection revealed by biaxial testing2018In: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 144, no 10, article id 04018197Article in journal (Refereed)
    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.

  • 3.
    Caprolu, Giuseppe
    et al.
    Luleå Tekniska Universitet.
    Källsner, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Girhammar, Ulf Arne
    Luleå Tekniska Universitet.
    Vessby, Johan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Analytical and experimental evaluation of the capacity of the bottom rail in partially anchored timber shear walls2012In: WCTE World Conference on Timber Engineering, Auckland, New Zealand, 15-19 July, 2012, 2012, p. 157-166Conference paper (Refereed)
    Abstract [en]

    Källsner and Girhammar have developed plastic design methods for light-frame timber shear walls that can be used fordetermining the load-carrying capacity when the shear walls are partially anchored. For such walls, the leading stud isnot fully anchored against uplift and tying down forces are developed in the sheathing-to-framing joints. Since theforces in the anchor bolts and the sheathing-to-framing joints do not act in the same vertical plane, the bottom rail willbe subjected to cross-wise bending, leading to possible splitting along the bottom side of the rail. Another possiblebrittle failure mode is splitting along the edge of the bottom rail in line with the sheathing-to-framing fasteners. Anexperimental program has been conducted using different anchor bolt locations, washer sizes and pith orientations. Afracture mechanics approach for the two failure modes is used to evaluate the experimental results. The comparisonshows a good agreement between the experimental and analytical results. The failure mode is largely dependent on thedistance between the edge of the washer and the edge of the bottom rail. The size of the washer seems also to havesome influence on the failure load. The fracture mechanics models seem to capture the essential behaviour of thesplitting modes and to include the decisive parameters. These parameters can easily be adjusted to experimental resultsand be used in design equations for bottom rails in partially anchored shear walls.

  • 4.
    Florisson, Sara
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    A numerical study of the effect of green-state moisture content on stress development in timber boards during drying2019In: Wood and Fiber Science, ISSN 0735-6161, Vol. 51, no 1, p. 41-57Article in journal (Refereed)
    Abstract [en]

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

  • 5.
    Florisson, Sara
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Modelling of mechano-sorption in clear wood by using an orthotropic non-linear moisture flow and stress model2018In: WCTE 2018 - World Conference on Timber Engineering: 2018 World Conference on Timber Engineering, WCTE 2018; COEX Convention and Exhibition CenterSeoul; South Korea, 20-23 August 2018, World Conference on Timber Engineering (WCTE) , 2018Conference paper (Refereed)
    Abstract [en]

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

  • 6.
    Gustafsson, Åsa
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Vessby, Johan
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Rask, Lars-Olof
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Erfarenheter av logistik- och montageprocessen vid byggandet av höga flerbostadshus med trästomme: Del 2 : Faktorer som påverkat tidseffektiviteten vid projekt Limologen, Växjö 20072008Report (Other academic)
    Abstract [sv]

    Föreliggande rapport är den andra av tre avrapporteringar kring erfarenheter av att bygga höga flerbostadshus med trästomme. Forskningsprojektet har sin empiriska bas i Midroc´s bygge av fyra åttavåningars hus för bostadsrätter vid Trummens strand i Växjö.

    Data samlades in under 2007 och analys och diskussion är gjord på detta material. De problem och förbättringsbehov som identifierats hänför sig alltså till det system som användes under 2007 och som i huvudsak kommer att användas för de efterföljande byggnaderna i kvarteret Limnologen. Erfarenheterna som gjorts under byggtiden har lett till att leverantören för kommande byggprojekt vidareutvecklat byggsystemet främst avseende en högre prefabriceringsnivå och ett effektivare och flexiblare system för väderskydd och traverslyft.

    Projektet är en del av insatser från Nationella Träbyggstrategin och Centrum för Byggande och Boende med Trä (CBBT) för att öka kunskapen om modernt stort träbyggande.

    Projektet har finansierats av Nationella Träbyggstrategin, CBBT, Växjö universitet och SP Trätek.

  • 7.
    Gustafsson, Åsa
    et al.
    Linnaeus University, Faculty of Business, Economics and Design, Linnaeus School of Business and Economics.
    Vessby, Johan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Rask, Lars-Olof
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Identification of potential improvement areas in industrial housing: A case study of waste2012In: Lean Construction Journal, ISSN 1555-1369, E-ISSN 1555-1369, p. 61-77Article in journal (Refereed)
  • 8.
    Habite, Tadios
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Florisson, Sara
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Numerical Simulation of Moisture-Induced Crack Propagation in Dowelled Timber Connection Using XFEM2018In: 2018 World Conference on Timber Engineering (WCTE), August 20-23, 2018, Seoul, Republic of Korea, World Conference on Timber Engineering (WCTE) , 2018Conference 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.

  • 9.
    Jarnerö, Kirsi
    et al.
    SP Sveriges Tekniska forskningsinstitut.
    Johan, Vessby
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Gustafsson, Åsa
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Rask, Lars-Olof
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Erfarenheter av logistik- och montageprocessen vid byggande av höga flerbostadshus med trästomme: Del 1 : Probleminventering vid projekt Limnologen, Växjö, 20072008Report (Other academic)
    Abstract [sv]

    Föreliggande rapport är den första av tre planerade avrapporteringar kring erfarenheter av att bygga höga flerbostadshus med trästomme. Forskningsprojektet har sin empiriska bas i Midroc´s bygge av fyra åttavåningars hus för bostadsrätter vid Trummens strand i Växjö.

    Projektet är en del av insatser från Nationella Träbyggstrategin och Centrum för Byggande och Boende med Trä (CBBT) för att öka kunskapen om modernt stort träbyggande.

    Projektet har finansierats av Nationella Träbyggstrategin, CBBT, Växjö universitet och SP Trätek.

  • 10.
    Johansson, Marie
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Mahapatra, Krushna
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Blom, Åsa
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Expert competence for sustainable timber engineering: a master program in close cooperation between industry and academia2014In: WCTE 2014 - World Conference on Timber Engineering, Proceedings, 2014Conference paper (Refereed)
    Abstract [en]

    From a legislative point of view it has been possible to build timber buildings with arbitrary number of storeys in Sweden during almost two decades. Several buildings up to eight storeys have been completed during that time, but the competence for planning and building such structures are limited to a handful of actors. This fact has been recognized by funders of research/education and an educational program for spreading the knowledge within the industry led by Linnaeus University is financed since about two years. Particularly interesting in the programme is that the courses are developed in cooperation between the industry and the academia. The courses are to fulfil needs with respect to knowledge, but also with respect to format so that the main target group, skilled engineers within the industry, can find the motivation to follow a course or lager parts of the program.

  • 11.
    Källsner, Bo
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Girhammar, Ulf Arne
    Luleå Tekniska Universitet.
    Vessby, Johan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Evaluation of two analytical plastic design models for light-frame shear walls2012In: WCTE, World Conference on Timber Engineering, New Zealand, 15-19 July, 2012: Final Papers, Poster Papers / [ed] Pierre Quenneville, 2012, p. 479-488Conference paper (Refereed)
    Abstract [en]

    The objective of this paper is to clarify the difference between two analytical models for plastic design ofshear walls and evaluate their potential for hand calculation by comparing calculated load-bearing capacities of differentwall configurations with the corresponding ones obtained by finite element analyses. The first analytical model is basedon a true plastic lower bound concept, i.e. always fulfilling the conditions of equilibrium. The second model is based onthe assumption that the full vertical shear capacity of the wall is utilized, considering that the vertical equilibrium isalways fulfilled but disregarding that the horizontal equilibrium of the wall is not always satisfied. If the shear capacityof the stud-to-rail joints is sufficiently large, then the second model is also a true plastic lower bound method. The ratiosbetween the calculated load-carrying capacities of the two analytical models are in the range between 1.00 – 1.24 with amean value of 1.12 for the wall and load configurations studied. Results from FE simulations show that the firstanalytical method underestimates the load-carrying capacity by about 10 %, but that the method gives very stablecapacity values relative to the FE simulations. It is further evident that there is a good agreement between the secondanalytical model and the results of the FE calculations at the mean level, but that this method has a considerably highervariation in the capacity values relative to the FE-simulations. Performed tests of different wall and load configurationsshow about 30 % higher measured capacities than calculated ones. The large deviations are mainly due to differences inthe manufacturing of the specimens for the sheathing-to-framing joint tests and the specimens for the wall tests.

  • 12.
    Källsner, Bo
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Girhammar, Ulf Arne
    Umeå universitet, Institutionen för tillämpad fysik och elektronik.
    Vessby, Johan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Some design aspects on anchoring of timber frame shear walls by transverse walls2010In: Proceedings of the 11th World Conference on Timber Engineering / [ed] Ario Ceccotti, 2010Conference paper (Refereed)
  • 13.
    Ormarsson, Sigurdur
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Geometric nonlinear analysis of a pitched roof structure of wood2016In: Eccomas 2016 Proceedings, 2016Conference paper (Refereed)
  • 14.
    Ormarsson, Sigurdur
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Källsner, Bo
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Filchev, Ivan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    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.

  • 15.
    Petersson, Hans
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Källsner, Bo
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Influence of structural stability and material property variations on bending strength of solid timber2015In: Theoretical, Numerical, and Experimental Analyses in Wood Mechanics, 2015Conference paper (Refereed)
  • 16.
    Reynolds, Thomas
    et al.
    University of Bath, UK.
    Bolmsvik, Åsa
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Chang, Wen-Shao
    University of Bath, UK.
    Harris, Richard
    University of Bath, UK.
    Bawcombe, Jonathan
    Cambridge Unviersity, UK.
    Bregulla, Julia
    Building Research Establishment (BRE), UK.
    Ambient vibration testing and modal analysis of multi-storey cross-laminated timber buildings2014In: World conference on timber engineering (WCTE), 2014Conference paper (Refereed)
    Abstract [en]

    The ambient movement of three multi-storey cross-laminated timber (CLT) buildings have been measured and used to determine natural frequencies, mode shapes and damping ratios. This information, obtained by a simple, unobtrusive series of tests, can give insights into the structural performance of this form of building, as well as providing information for the design of future, taller timber buildings for dynamic loads. For two of the buildings, the natural frequency has been related to the lateral stiffness of the structure, and compared with the stiffness based on simple calculation. In future tall timber buildings, a new design criterion is expected to become important: deflection and vibration serviceability under wind load. Design standards give techniques for prediction and mitigation of wind-induced movement, but require an estimate of the mass, stiffness and damping ratio of the structure to make an accurate prediction. For multi-storey timber buildings there is no empirical basis to use for damping estimation, and there is little information for stiffness. This study therefore provides an insight into the modal properties for lateral vibration of multi-storey CLT construction which could inform the design of taller buildings in the future.

  • 17.
    Schweigler, Michael
    et al.
    Vienna University of Technology, Austria.
    Bader, Thomas K.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Constrained displacement boundary condition in embedment testing of dowel-type fasteners in LVL2017In: Strain, ISSN 0039-2103, E-ISSN 1475-1305, Vol. 53, no 6, article id e12238Article in journal (Refereed)
    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.

  • 18.
    Sejkot, Petr
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    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.

  • 19.
    Sejkot, Petr
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    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)
  • 20.
    Sejkot, Petr
    et al.
    Czech Tech Univ, Czech Republic.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    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, 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.

  • 21.
    Serrano, Erik
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology. Lund University, Sweden;SP Technical Research Institute of Sweden, Sweden.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vessby, Johan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Long term in-situ measurements of displacement, temperature and relative humidity in a multi storey residential CLT building2014In: WCTE 2014 - World Conference on Timber Engineering, Proceedings, 2014Conference paper (Refereed)
    Abstract [en]

    In a multi-storey residential housing project comprising of four 8-storey timber buildings, the bottom storeybeing designed with concrete and storeys 2-8 in timber, the vertical relative displacement, the temperature and the relativehumidity (RH) along one vertical channel in the external wall of one building has been monitored. Measurements startedduring construction and presented herein are results of 6.5 years of in-situ measurements. Displacement data was monitoredstorey-by-storey, with a sampling frequency of 1 measurement every 10-60 minutes. In another of the four buildingsadditional temperature and relative humidity measurements have been ongoing for about 5.5 years. These temperature andRH measurements were performed at six different locations in the building, at each location in eight positions through theexterior wall with a sampling frequency of 1 measurement every 15 minutes. The results show that the total verticaldisplacement over six storeys after 6.5 years of service life is approximately 23 mm as a yearly average, and over the yearthe displacement varies from this value by approximately ±2 mm. The main cause for the relative displacement is thedecrease of moisture content in the wood material leading to shrinkage after completion of the building. The resultsobtained show also that the exterior wall design of the building behaves well in terms of not comprising a general risk fordamp or mould in the timber core of the external walls.

  • 22.
    Serrano, Erik
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Vessby, Johan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Vertical relative displacements in a medium-rise CLT-building.2010In: Structures and Architecture / [ed] Paulo J.S. Cruz, 2010Conference paper (Refereed)
  • 23.
    Serrano, Erik
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Vessby, Johan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Modeling of fracture in the sill plate in partially anchored shear walls2012In: Journal of Structural Engineering, ISSN 0733-9445, E-ISSN 1943-541X, Vol. 138, no 10, p. 1285-1288Article in journal (Refereed)
    Abstract [en]

    This study relates to the topic of anchorage of shear walls. At times, eccentric forces between the sheathing and the anchoring devices may be introduced in the sill plate. In severe cases, such forces may cause the sill plate to split and to fail in a brittle manner. In this study, fracture mechanics are applied to develop a simple closed-form hand-calculation expression for estimation of the ultimate load capacity of the sill plate. Finite-element analyses using both linear elastic fracture mechanics (LEFM) theory and a nonlinear fictitious crack model are also used to predict the ultimate load-bearing capacity of the sill plate. The hand-calculation model is compared with the finite-element models, and good agreement is obtained. The results obtained with the various fracture mechanics models are compared with results available from previously performed experimental tests, and again good agreement is obtained. A general conclusion is that the LEFM theory is an adequate approach for the case studied and that the hand-calculation expression developed could be useful for structural design.

  • 24.
    Serrano, Erik
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Vessby, Johan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Girhammar, Ulf Arne
    Luleå Tekniska Universitet.
    Källsner, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Design of Bottom Rails in Partially Anchored Shear Walls Using Fracture Mechanics2011In: Proc. CIB-W18, Meeting 44, Alghero, Italy / [ed] Blass, 2011Conference paper (Other academic)
  • 25.
    Vessby, Johan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Analysis of shear wallsfor multi-storey timber buildings2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This doctoral thesis addresses questions of how wind loads acting on multistoreytimber buildings can be dealt with by structural design of such buildings.The conventional use of sheathing either nailed or screwed to a timberframework is considered, together with other stabilizing structures such ascross-laminated timber panels.The finite element method was employed in simulating the structuralbehaviour of stabilizing wall units. A series of studies was carried out of walls inwhich the sheathing was nailed to a timber frame. Different structural levelswere studied starting with modelling the performance of single sheathing-toframingconnections, to the use of models for studying the overall structuralbehaviour of walls. The results of calculations using models for simulation ofwalls subjected to different loading agree reasonably well with experimentalresults. The structural properties of the connections between the sheathing andthe frame, as well as of the connections between the members of the frame,were shown to have a substantial effect on the simulated behaviour of shearwall units. Both these types of connections were studied and described inappended papers.Regarding cross-laminated timber wall panels, it was concluded that walls witha high level of both stiffness and strength can be produced by the use of suchpanels, and also that the connections between the solid wall panels can bedesigned in such a way that the shear forces involved are transmitted from onepanel to the next in an efficient manner.Other topics in the thesis include the properties of connections between shearwalls and the rest of the building. Typically high tension forces occur at specificpoints in a timber structure. These forces need to be transmitted downwards inthe structure, ultimately connecting them to the substrate. A lap-joint that maybe used for this purpose has been studied using generalized Volkersen theory.Finally the maximum capacity of a conventional rail to substrate connection hasbeen examined using linear and nonlinear fracture mechanics.

  • 26.
    Vessby, Johan
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Shear walls for multi-storey timber buildings2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wind loads acting on wooden building structures need to be dealt with adequately in order to ensure that neither the serviceability limit state nor the ultimate limit state is exceeded. For the structural designer of tall buildings, avoiding the possibly serious consequences of heavy wind loading while taking account at the same time of the effects of gravitation can be a real challenge. Wind loads are usually no major problem for low buildings, such as one- to two-storey timber structures involving ordinary walls made by nailing or screwing sheets of various types to the frame, but when taller structures are designed and built, serious problems may arise.

    Since wind speed and thus wind pressure increases with height above the ground and the shear forces transmitted by the walls increase accordingly, storey by storey, considerable efforts can be needed to handle the strong horizontal shear forces that are exerted on the bottom floor in particular. The strong uplift forces that can develop on the wind side of a structure are yet another matter that can be critical. Accordingly, a structure needs to be anchored to the substrate or to the ground by connections that are properly designed. Since the calculated uplift forces depend very much upon the models employed, the choice of models and simplifications in the analysis that are undertaken also need to be considered carefully.

    The present licentiate thesis addresses questions of how wind loads acting on multi-storey timber buildings can be best dealt with and calculated for in the structural design of such buildings. The conventional use of sheathing either nailed or screwed to a timber framework is considered, together with other methods of stabilizing timber structures. Alternative ways of using solid timber elements for stabilization are also of special interest.

    The finite element method was employed in simulating the structural behaviour of stabilizing units. A study was carried out of walls in which sheathing was nailed onto a timber frame. Different structural levels were involved, extending from modelling the performance of a single fastener and of the connection of the sheathing to frame, to the use of models of this sort for studying the overall structural behaviour of wall elements that possess a stabilizing function. The results of models used for simulating different load cases for walls agreed reasonably well with experimental test results. The structural properties of the fasteners binding the sheathing to the frame, as well as of the connections between the members of the frame were shown to have a strong effect on the simulated behaviour of shear wall units.

    Regarding solid wall panels, it was concluded that walls with a high level of both stiffness and strength can be produced by use of such panels, and also that the connections between the solid wall panels can be designed in such a way that the shear forces involved are effectively transmitted from one panel to the next.

  • 27.
    Vessby, Johan
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Källsner, Bo
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Directional dependency in an OSB sheathing-to-framing mechanical connection2014Conference paper (Refereed)
    Abstract [en]

    Nailed connections are commonly employed for connecting sheathings to the framing used in shear walls. Although many aspects of such connections have been investigated thoroughly within the research community generally, the effect the loading direction has on connections of this sort has been much less investigated. In the present study experimental tests were carried out for determining in detail the effects the loading has on different sheathing-to-framing connections. The results obtained indicated the degree of loading to which a nail fastened to an oriented strand board (OSB) sheathing is subjected to not be strongly affected by which of the two main loading directions is involved, but that the effects of loading direction are found to be much greater if the timber element in question is also included in the testing carried out. The dependency of the loading effect on the loading direction at different loading stages and for different directions - parallel to the fibres, perpendicular to them, at some angle between these two main directions - was investigated here.

  • 28.
    Vessby, Johan
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Enquist, Bertil
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Alsmarker, Tomas
    Experimental study of cross-laminated timber wall panels2009In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 67, no 2, p. 211-218Article in journal (Refereed)
    Abstract [en]

    The use of cross-laminated structural timber elementsis becoming increasingly popular. The number of layersvaries normally from three upwards. The structural performanceof five-layer cross-laminated timber elements was investigated.The five layers consisted of 19mm thick boards,laid successively at right angles to each other and gluedtogether with PU-adhesive, layers 1, 3 and 5 lying in onedirection and layers 2 and 4 in the other. The stiffness andstrength of four cross-laminated timber elements (4955mmlong, 1250mm wide and 96mm thick) were studied duringin-plane bending. Two of the elements were first partitionedinto two parts that were reconnected in two different waysprior to testing. The influence of the way in which the crosslaminatedtimber elements were reconnected was studied,the behaviour observed being compared with the test resultsfor the unpartitioned specimens with respect to both strengthand stiffness. The experimental tests performed showed thecross-laminated timber elements to possess a high degree ofstiffness and strength. There was also found to be a markeddifference in behaviour between the two different ways inwhich the elements were connected to each other. One of thetwo connecting methods studied, being of less good designbut earlier frequently used in Sweden, showed as expectedpoor structural performance, whereas the other one appliedas a safer alternative performed well.

  • 29.
    Vessby, Johan
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Florisson, Sara
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Habite, Tadios
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Numerical simulation of moisture driven fracture in mechanical timber connection using XFEM2017In: 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 (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.

  • 30.
    Vessby, Johan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Källsner, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Girhammar, Ulf Arne
    Umeå universitet, Institutionen för tillämpad fysik och elektronik.
    Influence of contact stress between sheets on strength and stiffness of timber frame shear walls2010In: Proceedings of the 11th World Conference on Timber Engineering / [ed] Ario Ceccotti, 2010Conference paper (Refereed)
  • 31.
    Vessby, Johan
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Byggteknik.
    Källsner, Bo
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Byggteknik.
    Olsson, Anders
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Byggteknik.
    Influence of initial gap between timber members on stiffness and capacity of shear walls2008In: 10:th World Conference on Timber Engineering, 2008Conference paper (Refereed)
  • 32.
    Vessby, Johan
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Källsner, Bo
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Girhammar, Ulf Arne
    Luleå Univ Technol.
    Evaluation of softening behaviour of timber light-frame walls subjected to in-plane forces using simple FE models2014In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 81, p. 464-479Article in journal (Refereed)
    Abstract [en]

    The present investigation focuses on evaluating the entire load displacement relationship, especially the softening part, of light-frame wall segments subjected to in-plane monotonic forces when the load-slip curves of the individual sheathing-to-framing fasteners are considered. Different sheathing-to-framing joint characteristics, including unloading behaviour, and stud-to-rail joint characteristics are incorporated in the analyses. Two loading cases are investigated: Horizontal loading resulting in uplift of the leading stud and diagonal loading representing a fully anchored wall. Two common types of finite element (FE) models for the sheathing-to-framing joints are used for the analyses: A single spring model and a spring pair model, where the joint characteristics valid for the timber properties perpendicular and parallel to the grain are used. The maximum capacity of the wall segments is somewhat overestimated when using the spring pair model compared to that of the single spring model. The softening parts of the load displacement curves are significantly affected, regardless of whether the perpendicular or parallel characteristics of the joints are used. The results from FE simulations using models with perpendicular and parallel characteristics are compared with full scale test results for walls with a single segment loaded horizontally and diagonally. The behaviour of the wall segments subjected to horizontal loading is dominated by fastener displacements perpendicular to the bottom rail. Hence, FE models including perpendicular characteristics should be used. For diagonal loading the behaviour of the wall segments is dominated by displacements parallel to the framing members, and FE models including parallel characteristics should therefore be used. The analyses were extended to multiple segment walls resulting in the same type of behaviour as single segment walls. (C) 2014 Elsevier Ltd. All rights reserved.

  • 33.
    Vessby, Johan
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Källsner, Bo
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Stabilisering av takkonstruktioner i trä: arbetet med ny handbok2016In: Bygg & teknik, ISSN 0181-658X, no 4, p. 60-63Article in journal (Other (popular science, discussion, etc.))
  • 34.
    Vessby, Johan
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Olsson, Anders
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Byggteknik.
    Stabilizing strategies for multi-story timber frame structures2006In: 9th World Conference on Timber Engineering, Oregon State University, Portland, OR 97331, U.S.A 2006. , 2006Conference paper (Refereed)
  • 35.
    Vessby, Johan
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Byggteknik.
    Olsson, Anders
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Byggteknik.
    Enquist, Bertil
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Byggteknik.
    Contact-free strain measurement of bi-axially loaded sheathing-to-framing connection2008In: 10:th World Conference on Timber Engineering, 2008Conference paper (Refereed)
  • 36.
    Vessby, Johan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Serrano, Erik
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Contact-free measurement and numerical and analytical evaluation of the strain distribution in a wood-FRP lap-joint2010In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 43, no 8, p. 1085-1095Article in journal (Refereed)
    Abstract [en]

    Wood specimens to each of which alaminate of carbon fibre reinforcement polymers(FRP) was glued (creating a lap joint in each case)were loaded to failure. A total of 15 specimens ofthree types differing in the glued length (anchoragelength) of the FRP laminate (50, 150 and 250 mmrespectively) were tested, their strength, stiffness andstrain distribution being evaluated. Synchronizeddigital cameras (charge-coupled devices) used intesting enabled strain fields on surfaces they weredirected at during the loading procedure to bemeasured. These results were also evaluated bothanalytically on the basis of generalized Volkersentheory and numerically by use of the finite elementmethod. The lap joints showed a high level ofstiffness as compared with mechanical joints. A highdegree of accuracy in the evaluation of stiffness wasachieved through the use of the contact-free evaluationsystem. The load-bearing capacity of joints ofthis type was found to be dependent upon theanchorage length in a non-linear fashion. The experimental,analytical and numerical results were shownto be in close agreement with respect to the strengthand the strain distribution obtained.

  • 37.
    Vessby, Johan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Serrano, Erik
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Coupled and uncoupled nonlinear elastic finite element models formonotonically loaded sheathing-to-framing joints in timber based shear walls2010In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 32, no 11, p. 3433-3442Article in journal (Refereed)
    Abstract [en]

    Four different elastic models for sheathing-to-framing connections are presented and evaluated on asingle connection level and on a shear wall level. Since the models are elastic in their nature they aresuitable mainly for cases where the sheathing-to-framing connections are subjected to monotonicallyincreasing displacements. Of the four models one is uncoupled and the others are coupled with respect tothe two perpendicular displacement directions in a two-dimensional model. Two of the coupled modelsare non-conservative, while the third is conservative, indicating a path independency with respect to thework done to reach a defined state of deformation. When the different models are compared it is obviousthat the uncoupled model gives strength and stiffness values higher than the others; however it is notobvious which of the models to use in a shear wall analysis, each of the models having its advantages anddisadvantages. For the experimental data used as input in the analyses of this study however, a couplednon-conservative model seems the most appropriate.

  • 38.
    Vessby, Johan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Serrano, Erik
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Girhammar, Ulf Arne
    Luleå University of Technology.
    Källsner, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Simulation of bottom rail fracture in partially anchored shear walls using XFEM2012In: INTERNATIONAL COUNCIL FOR RESEARCH AND INNOVATIONIN BUILDING AND CONSTRUCTION, WORKING COMMISSION W18 - TIMBER STRUCTURES (CIB-W18): Meeting forty-five, Växjö, Sweden, August 2012, 2012Conference paper (Refereed)
1 - 38 of 38
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