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Blomqvist, L., Berg, S. & Sandberg, D. (2019). Distortion in laminated veneer products exposed to relative-humidity variations: Experimental studies and finite-element modelling. BioResources, 14(2), 3768-3779
Open this publication in new window or tab >>Distortion in laminated veneer products exposed to relative-humidity variations: Experimental studies and finite-element modelling
2019 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, no 2, p. 3768-3779Article in journal (Refereed) Published
Abstract [en]

A shortcoming of the laminated bending process is that the product may become distorted after moulding. This study focused on the influence of fibre orientation deviation for individual veneers on the distortion of a moulded shell. The distortion of 90 cross-laminated shells of the same geometrical shape, consisting of seven peeled birch veneers, were studied under relative humidity variation. All the veneers were straight-grained in the longitudinal-tangential plane, but to simulate a deviation in fibre orientation, some of the individual veneers were oriented at an angle of 7° relative to the main orientation of the other veneers in the laminate. A finite element model (FEM) was applied to study the possibility of predicting the results of a practical experiment. The study confirms the well-known fact that deviation in fibre orientation influences shape stability. The results also show how the placement of the abnormal veneer influences the degree of distortion. From this basic knowledge, some improvements in the industrial production were suggested. However, the FE model significantly underestimated the results, according to the empirical experiment, and it did not show full coherence. The survey shows the complexity of modelling the behaviour of laminated veneer products under changing climate conditions and that there is a great need to improve the material and process data to achieve accurate simulations. Examples of such parameters that may lead to distortion are density, annual ring orientation in the cross section of the veneer, the orientation of the loose and tight sides of the veneer, and parameters related to the design of the moulding tool.

Place, publisher, year, edition, pages
North Carolina State Univ Dept Wood & Paper Sci, 2019
Keywords
Birch, Cup, FEM, Veneer, Wood, Twist
National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-73340 (URN)10.15376/biores.14.2.3768-3779 (DOI)000466449000091 ()2-s2.0-85071081837 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-04-10 (oliekm)

Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-09-09Bibliographically approved
Berg, S., Turesson, J., Ekevad, M. & Huber, J. A. (2019). Finite element analysis of bending stiffness for cross-laminated timber with varying board width. Wood Material Science & Engineering
Open this publication in new window or tab >>Finite element analysis of bending stiffness for cross-laminated timber with varying board width
2019 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Article in journal (Refereed) Epub ahead of print
Abstract [en]

ross laminated timber (CLT) is a wood panelling building system that is used in construction, e.g. for floors, walls and beams. Because of the increased use of CLT, it is important to have accurate simulation models. CLT systems are simulated with one-dimensional and two-dimensional (2D) methods because they are fast and deliver practical results. However, because non-edge-glued panels cannot be modelled under 2D, these results may differ from more accurate calculations in three dimensions (3D). In this investigation, CLT panels with different width-to-thickness ratios for the boards have been simulated using the finite element method. The size of the CLT-panels was 3.0 m × 3.9 m and they had three and five laminate layers oriented 0°–90°–0° and 0°–90°–0°–90°–0°. The thicknesses of the boards were 33.33, 40.0, and 46.5 mm. The CLT panel deformation was compared by using a distributed out-of-plane load. Results showed that panels with narrow boards were less stiff than wide boards for the four-sided support setup. The results also showed that 2D models underestimate the displacement when compared to 3D models. By adjusting the stiffness factor k88, the 2D model displacement became more comparable to the 3D model.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
Cross laminated timber, finite element analysis, board width, out-of-plane loading
National Category
Wood Science Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-73140 (URN)10.1080/17480272.2019.1587506 (DOI)2-s2.0-85062711678 (Scopus ID)
Available from: 2019-03-08 Created: 2019-03-08 Last updated: 2019-03-20
Turesson, J., Berg, S. & Ekevad, M. (2019). Impact of board width on in-plane shear stiffness of cross-laminated timber. Engineering structures, 196, Article ID 109249.
Open this publication in new window or tab >>Impact of board width on in-plane shear stiffness of cross-laminated timber
2019 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 196, article id 109249Article in journal (Refereed) Published
Abstract [en]

Board width-to-thickness ratios in non-edge-glued cross laminated timber (CLT) panels influence the in-plane shear stiffness of the panel. The objective is to show the impact of board width-to-thickness ratios for 3- and 5-layer CLT panels. Shear stiffnesses were calculated using finite element analysis and are shown as reduction factors relative to the shear stiffnesses of edge-glued CLT panels. Board width-to-thickness ratios were independently varied for outer and inner layers. Results show that the reduction factor lies in the interval of 0.6 to 0.9 for most width-to-thickness ratios. Results show also that using boards with low width-to-thickness ratios give low reduction factors. The calculated result differed by 2.9% compared to existing experimental data.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
CLT, In-plane shear modulus, In-plane shear stiffness, Finite element method, CLT board width, CLT layer thickness, CLT shear modulus, Board gap
National Category
Building Technologies Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-75098 (URN)10.1016/j.engstruct.2019.05.090 (DOI)000482518700013 ()2-s2.0-85067851120 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-07-05 (johcin)

Available from: 2019-06-27 Created: 2019-06-27 Last updated: 2019-09-13Bibliographically approved
Berg, S., Turesson, J., Ekevad, M. & Björnfot, A. (2019). In-plane Shear Modulus of Cross-laminated Timber by Diagonal Compression Test. BioResources, 14(3), 5559-5572
Open this publication in new window or tab >>In-plane Shear Modulus of Cross-laminated Timber by Diagonal Compression Test
2019 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, no 3, p. 5559-5572Article in journal (Refereed) Published
Abstract [en]

Cross-laminated timber (CLT) is an engineered wood material that is used in the construction industry, e.g., for floors, walls, and beams. In cases where CLT-elements are used as shear walls, the in-plane-stiffness is an important property. For non-edge glued CLT, in-plane shear stiffness is lower than for edge-glued CLT. To evaluate the non-edge glued CLT panel’s in-plane shear modulus, the diagonal compression test and finite element (FE) simulation was used. FE-models with both isotropic and orthotropic material models were used to calculate the shear stiffness. The FE models using pure shear loads were used as a reference to determine the correct value of the shear modulus. To verify the FE simulations, diagonal compression tests were conducted on 30 CLT samples. A calibration formula was derived using the least square method for calculation of shear modulus. The formula gave accurate results. The results showed that FE simulations can reproduce the same shear stiffness as tests of non-edge glued 3-layer and 5-layer CLT panels.

Place, publisher, year, edition, pages
NC State University, 2019
Keywords
Cross-laminated timber, Finite element analysis, In-plane shear stiffness, Diagonal compression test, Shear modulus
National Category
Other Engineering and Technologies not elsewhere specified Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-74597 (URN)10.15376/biores.14.3.5559-5572 (DOI)000473204700043 ()2-s2.0-85066306339 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-06-24 (svasva)

Available from: 2019-06-17 Created: 2019-06-17 Last updated: 2019-08-16Bibliographically approved
Turesson, J., Björnfot, A., Berg, S., Ekevad, M. & Tomasi, R. (2019). Picture frame and diagonal compression testing of cross-laminated timber. Materials and Structures, 52(4), Article ID 66.
Open this publication in new window or tab >>Picture frame and diagonal compression testing of cross-laminated timber
Show others...
2019 (English)In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 52, no 4, article id 66Article in journal (Refereed) Published
Abstract [en]

Currently, no appropriate standard exists that describes how to determine the in-plane shear stiffness for cross-laminated timber (CLT) panels, meaning that, there is a lack of appropriate and reliable test methods. In this paper, two gross shear test methods are evaluated: a picture frame test and a diagonal compression test, which are intended to measure the shear stiffness of a whole CLT panel. This evaluation aimed to compare the shear modulus, the amount of compression/tension in the diagonal directions of the panels and the deformations of both sides of the panels. The picture frame test and diagonal compression test provides a bi- and uniaxial pre-stress, respectively. A total of 30 non-edge glued CLT panels were tested, 17 3-layer and 13 5-layer panels. The shear modulus for the 3- and 5-layer non-edge-glued panels were measured as 418 and 466 MPa, respectively, in the picture frame test. In the diagonal compression test, the shear modulus was measured to substantially higher values of 530 and 626 MPa for the 3- and 5-layer panels, respectively. In the picture frame test, panels were equally stretched along one of the diagonals as they were compressed along the other diagonal, which was not the case for panels in the diagonal compression test. The test results also showed that measuring only one side incurs a risk of over- or under-estimating the in-plane shear modulus. Compared with results from the literature, the picture frame test seems to be a more reliable test method than the diagonal compression test.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
In-plane shear stiffness, Picture frame method, CLT, Shear modulus, Diagonal compression
National Category
Building Technologies Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-74874 (URN)10.1617/s11527-019-1372-7 (DOI)000472221500001 ()2-s2.0-85067616889 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-06-24 (svasva)

Available from: 2019-06-23 Created: 2019-06-23 Last updated: 2019-07-10Bibliographically approved
Huber, J. A., Ekevad, M., Girhammar, U. A. & Berg, S. (2019). Simulation of Alternative Load Paths After a Wall Removal in a Platform-Framed Cross-Laminated Timber Building. In: Tomas K. Bader, Josef Füssl, Anders Olsson (Ed.), CompWood 2019 Book of Abstracts: . Paper presented at CompWood 2019 - International Conference on Computational Methods in Wood Mechanics- from Material Properties to Timber Structures, June 17-19, 2019.
Open this publication in new window or tab >>Simulation of Alternative Load Paths After a Wall Removal in a Platform-Framed Cross-Laminated Timber Building
2019 (English)In: CompWood 2019 Book of Abstracts / [ed] Tomas K. Bader, Josef Füssl, Anders Olsson, 2019Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

An increasing number of multi-storey timber buildings use cross-laminated timber (CLT) for their bearing structure. Platform-framed CLT buildings consist of vertical repetitions of floors resting upon one-storey tall walls, squeezing-in the floor panels between the walls. Tall buildings need to be structurally robust because many lives would be at stake in case of a disproportionate collapse. Robustness is the ability of a system to survive the loss of components. For collapse resistance, it poses the last line of defence, after an unforeseen exposure (e.g. accident, terrorism) has already occurred and after the exposed components could not resist failure. A robust building offers alternative load paths (ALPs) which come into action when a part of the bearing structure has been removed [1].

Many alternative load path analyses (ALPA) have been conducted for tall concrete and steel buildings using the finite element method (FEM), but for timber, ALPA are still scarce. ALPs depend on the behaviour of the connections after a loss [1]. Studies on timber so far have accounted for connections in a simplified manner by lumping their aggregate behaviour into single points. Our goal is to elicit the ALPs after a wall removal in a platform-framed CLT building, study their development and quantify their capacity, to determine whether they can prevent a collapse.

We investigated a corner bay of an 8-storey platform-framed CLT building (see Figure 1) and removed a wall at the bottom storey. We studied the ALPs of each storey by pushing down the walls above the gap in a non-linear quasi-static analysis in the FE software Abaqus. We accounted for contact and friction, considered plastic timber crushing, and accounted for brittle cracking in the panels. We modelled single fasteners with connector elements which simulated the elastic, plastic, damage and rupture behaviour. We recorded the force-displacement curves, i.e. pushdown curves, for each storey and used them to conduct a dynamic analysis of the entire bay in a simplified model, as suggested by [2].

The results show that the structure could engage the following ALPs after a wall removal: I) arching action in the outer floor panels, II) arching action of the walls, III) quasi-catenary action in the floor panels, and IV) hanging action from the roof panels. The ALPs were limited by various parameters, but they sufficed to resist a collapse of the bay. We observed that the inter-storey stiffness influenced the load-sharing among storeys, which affected the structural robustness. In the compressed connections, friction, and not the fasteners, transferred most of the horizontal loads. Future research should test the squeezed-in platform joint experimentally, to quantify its capacity for transverse shear loads. We also advise to assess the inter-storey stiffness to estimate the capacity for load-sharing among storeys.

National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-74893 (URN)978-91-88898-64-7 (ISBN)
Conference
CompWood 2019 - International Conference on Computational Methods in Wood Mechanics- from Material Properties to Timber Structures, June 17-19, 2019
Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2019-09-06
Huber, J. A., Ekevad, M., Girhammar, U. A. & Berg, S. (2018). A Review of Structural Robustness with Focus on Timber Buildings. In: 40th IABSE Symposium: Tomorrow’s Megastructures. Paper presented at 40th IABSE Symposium in Nantes 2018: Tomorrow's Megastructures; Nantes; France; 19 - 21 September 2018. International Association for Bridge and Structural Engineering (IABSE), Article ID S32-17.
Open this publication in new window or tab >>A Review of Structural Robustness with Focus on Timber Buildings
2018 (English)In: 40th IABSE Symposium: Tomorrow’s Megastructures, International Association for Bridge and Structural Engineering (IABSE) , 2018, article id S32-17Conference paper, Published paper (Refereed)
Abstract [en]

With an increasing number of storeys, timber buildings require closer attention to structuralrobustness. If a building can survive unforeseen events (e.g. accidents, terrorism), lives can be saved.The literature appears to be rather limited concerning robustness of timber buildings. This paperaims to give a brief review on robustness in general and design guidelines for timber in specific. Theresults indicate that connection design is a key aspect for robustness. Like in seismic design, by usingthe ductile capacity of connectors, the brittleness of timber can be controlled. For light timber-framebuildings, more guidelines exist than for posts and beams and cross-laminated timber, which bothseem to be similar to steel frames and precast concrete respectively regarding robustness.

Place, publisher, year, edition, pages
International Association for Bridge and Structural Engineering (IABSE), 2018
Keywords
robustness, timber, disproportionate collapse, progressive collapse, alternative load path
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-70959 (URN)9783857481611 (ISBN)
Conference
40th IABSE Symposium in Nantes 2018: Tomorrow's Megastructures; Nantes; France; 19 - 21 September 2018
Funder
VINNOVA, Bioinnovation 4.4
Available from: 2018-09-24 Created: 2018-09-24 Last updated: 2019-01-14Bibliographically approved
Huber, J. A., Ekevad, M., Berg, S. & Girhammar, U. A. (2018). Assessment of Connections In Cross-Laminated Timberbuildings Regarding Structural Robustness. In: : . Paper presented at 2018 World Conference on Timber Engineering, Seoul, Republic of Korea, August 20-23 2018.
Open this publication in new window or tab >>Assessment of Connections In Cross-Laminated Timberbuildings Regarding Structural Robustness
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Cross-laminated timber makes timber buildings with an increasing number of storeys achievable. Withmore storeys, structural robustness needs more attention to make a building survive unforeseen events (e.g. accidents,terrorism) and save lives. For steel and concrete buildings, design methods for robustness focus on connection details.The assessment of joints in cross-laminated timber buildings regarding robustness is rather limited in the literature. Theobjective of this paper is to conduct an initial assessment of the connectors after the removal of a wall in a platformcross-laminated timber building. We used the finite element method and the component method for the analysis of acase building. The results indicate that the wall-to-wall and the floor-to-floor connectors may fail at low deflectionlevels leading to high shear loads in the floor panel above the removed wall, which might induce cracking. The removalanalysis was only partially completed, but we identified an indication of the deformation behaviour of the case building.Testing and refined modelling of the connections is needed in the future to verify the results. This study may facilitatefuture investigations regarding robustness of multi-storey cross-laminated timber buildings.

Keywords
Robustness, Connection, Component method, Cross-laminated timber, Finite element method, Disproportionate collapse
National Category
Other Civil Engineering Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-70599 (URN)
Conference
2018 World Conference on Timber Engineering, Seoul, Republic of Korea, August 20-23 2018
Projects
Bioinnovation 4.4
Funder
VINNOVA
Available from: 2018-08-27 Created: 2018-08-27 Last updated: 2019-03-27Bibliographically approved
Huber, J. A., Ekevad, M., Girhammar, U. A. & Berg, S. (2018). Structural Robustness of Timber Buildings. In: : . Paper presented at 2018 World Conference on Timber Engineering, Seoul, Republic of Korea, August 20-23 2018.
Open this publication in new window or tab >>Structural Robustness of Timber Buildings
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The number of storeys in timber buildings are increasing. With more storeys, structural robustness needsmore attention, to make a building survive unforeseen events (e.g. accidents, terrorism) and save lives. The state of theart regarding robustness of concrete and steel buildings seems to be rather refined, but for timber buildings, theliterature appears to be quite limited. This study aims to review the design methods for robustness of timber buildings.First, the terminology and definitions are introduced. Then, the state of the art for design methods for robustness ingeneral are presented. Finally, the design methods for timber buildings are discussed and compared to those from otherbuilding materials. The results indicate that the guidelines for light timber-frame buildings are more refined than thosefor post and beam and cross-laminated timber buildings. Regarding robustness, the latter two construction types exhibitcertain similarities to steel frames and precast concrete buildings respectively. For timber, ductile connections can beused to avoid brittle timber failure after local damages, which resembles the approach of seismic design. Future researchin robustness should focus on the connection details in multi-storey timber buildings.

Keywords
Robustness, Timber buildings, Disproportionate collapse, Progressive collapse, Alternative load paths
National Category
Other Civil Engineering Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-70593 (URN)
Conference
2018 World Conference on Timber Engineering, Seoul, Republic of Korea, August 20-23 2018
Projects
Bioinnovation 4.4
Funder
VINNOVA
Available from: 2018-08-27 Created: 2018-08-27 Last updated: 2018-08-31Bibliographically approved
Turesson, J., Ekevad, M. & Berg, S. (2017). Comparison of Cross- and Stress-Laminated Timber Bridge Decks. In: : . Paper presented at 3rd International conference on timber bridges 2017, ICTB2017, June 26-29 2017 in Skellefteå, Sweden..
Open this publication in new window or tab >>Comparison of Cross- and Stress-Laminated Timber Bridge Decks
2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Simply supported bridge decks made of cross-laminated timber (CLT) and stress-laminated timber (SLT) are compared. The decks have a constant axle load and varying span and thickness. CLT in the form of a plate is built up from an uneven number of layers of boards with crosswise varying fibre directions. SLT is built up from glulam beams with the same fibre direction placed side by side to form a plate. Both CLT and SLT have homogenised mechanical and physical properties and can be produced as large elements. This study was conducted by comparing results from finite element simulations of bridge decks made up from SLT and CLT for various bridge spans. The ratio of timber volume needed to fulfil deflection limits for CLT and SLT increased as the bridge span increased. The ratio was 1.3 for 24 m span and width 3.2 m. The transverse displacement curve was flatter for CLT compared to SLT. Longitudinal displacement curves were similar for CLT and SLT.

Keywords
stress-laminated, cross-laminated, timber bridge deck, FEM, finite element method
National Category
Engineering and Technology Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-63066 (URN)
Conference
3rd International conference on timber bridges 2017, ICTB2017, June 26-29 2017 in Skellefteå, Sweden.
Available from: 2017-04-19 Created: 2017-04-19 Last updated: 2017-11-24Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-4686-4010

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