| 1. |
- Berg, Sven, et al.
(författare)
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Finite element analysis of bending stiffness for cross-laminated timber with varying board width
- 2019
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis. - 1748-0272 .- 1748-0280. ; 14:6, s. 392-403
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Tidskriftsartikel (refereegranskat)abstract
- Cross 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.
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| 2. |
- Berg, Sven, et al.
(författare)
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In-plane Shear Modulus of Cross-laminated Timber by Diagonal Compression Test
- 2019
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Ingår i: BioResources. - : NC State University. - 1930-2126. ; 14:3, s. 5559-5572
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Nziengui, Claude Feldman Pambou, et al.
(författare)
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Experimental assessment of the annual growth ring’s impact on the mechanical behavior of temperate and tropical species
- 2020
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Ingår i: BioResources. - : NC State University. - 1930-2126. ; 15:2, s. 4282-4293
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Tidskriftsartikel (refereegranskat)abstract
- An innovative experimental protocol is presented, linking a nondestructive (on computed tomography scanner) and destructive approach (bending test on electrostatic press). This study aimed to evaluate the annual growth ring’s impact on the mechanical behavior of wood. The tests were carried out on temperate specimens (Pseudotsuga menziesii and Abies alba Mill) from the Massif Central Region of France and tropical specimens (Aucoumea klaineana Pierre, Milicia excelsa, and Pterocarpus soyauxii) from Gabon. The connection between the mechanical parameters, taken from these tests and their structural characteristics, are also highlighted. Based on these results, a database was formed of the annual growth ring’s impact on the mechanical characteristics of these species. A link was found between the annual growth ring and the mechanical and physical characteristics of the species. The number and width of the earlywood ring and its mechanical properties were also investigated for each type of species. This comparison and the link highlighted was possible due to the study of the impact of dry density’s specimens, considered in this work as an adjustment parameter on the study of the mechanical behavior of these species.
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| 4. |
- Pambou Nziengui, C.F, et al.
(författare)
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Détermination des principales caractéristiques physiques et mécaniques du sapin blanc du massif central et de l’okoumé du Gabon.
- 2018
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Ingår i: Actes de la conference. - : Association Universitaire de Génie Civil (AUGC). ; , s. 559-562
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Konferensbidrag (refereegranskat)abstract
- The following study, shows on the basis of a series of tests carried out on samples of White fir species of the central massif and okume of Gabon, a database of the different physical and mechanical properties of these species. The tests are carried out indoors at room temperature, on specimens sized according to the French standard [AFN 06]. These specimens, whose physical properties are previously determined, are loaded in 4-point static bending on an electrostatic press. Then, using standardized calculation methods, a determination of the main mechanical parameters of these species is made. The results of the various comparative analyzes carried out show that there are no significant differences between the parameters highlighted in this study for these different species despite the difference between their growth areas.
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| 5. |
- Turesson, Jonas, 1991-, et al.
(författare)
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Comparison of Cross- and Stress-Laminated Timber Bridge Decks
- 2017
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 6. |
- Turesson, Jonas, 1991-, et al.
(författare)
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Impact of board width on in-plane shear stiffness of cross-laminated timber
- 2019
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Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 196
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Turesson, Jonas, 1991-, et al.
(författare)
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Impact of laminate directions on inplane shear stiffness of crosslaminated timber
- 2016
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Ingår i: Annual Meeting of the Northern European Network for Wood Science and Engineering WSE.
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Konferensbidrag (refereegranskat)abstract
- Twenty-three finite element models of cross-laminated timber (CLT) with different laminate directions were studied. Simulations with quadratic orthotropic linear elastic finite elements were conducted. One goal was to compare in-plane shear stiffnesses for CLT blocks made up from Norway Spruce (Picea abies) boards. 3- and 5-layer CLT were studied with board sizes 25x150x1200 mm. Bloc sizes were 75x1200x1200 and 125x1200x1200 mm for 3-layer and 5-layer blocs, respectively. The first and last layers laminate directions were assumed to be in direction 0○. The second and fourth layers laminate directions for 5-layer models were assumed equal and were 5○, 10○, 15○, 30○, 45○, 60○, 75○ and 90○. The middle layer was in direction 0○ or 90○. For 3-layer models the middle layers laminate directions were 5○, 10○, 15○, 30○, 45○, 60○, 75○ and 90○. No edge gluing was assumed and thus all side edges were allowed to separate or overlap. Glued contact surfaces were assumed to be perfectly glued with rigid glue. The results for 5-layer models showed that all models with angled second and fourth layers were stiffer than the models with 90○ layers. Stiffnesses for models with angled second and fourth layers were higher when the middle layer laminate direction was 90○ compared to 0○. The stiffest 5-layer model was the one with laminate directions 0/45/90/45/0. This stiffness was 1.5 times the shear stiffness of a reference block with 1-layer and solid timber shear stiffness. The stiffest 3-layer model was the one with laminate directions 0/30/0. This stiffness was 0.99 times the shear stiffness of the reference bloc.
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| 8. |
- Turesson, Jonas, 1991-, et al.
(författare)
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Influence of laminate direction and glue area on in-plane shear modulus of cross-laminated timber
- 2020
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Ingår i: SN Applied Sciences. - : Springer. - 2523-3963 .- 2523-3971. ; 2:12
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Tidskriftsartikel (refereegranskat)abstract
- The use of cross-laminated timber (CLT) in constructing tall buildings has increased. So, it has become crucial to get a higher in-plane stiffness in CLT panels. One way of increasing the shear modulus, G, for CLT panels can be by alternating the layers to other angles than the traditional 0° and 90°. The diagonal compression test can be used to measure the shear stiffness from which G is calculated. A general equation for calculating the G value for the CLT panels tested in the diagonal compression test was established and verified by tests, finite element simulations and external data. The equation was created from finite element simulations of full-scale CLT walls. By this equation, the influence on the G value was a factor of 2.8 and 2.0 by alternating the main laminate direction of the mid layer from the traditional 90° to 45° and 30°, respectively. From practical tests, these increases were measured to 2.9 and 1.8, respectively. Another influence on the G value was studied by the reduction of the glue area between the layers. It was shown that the pattern of the contact area was more important than the size of the contact area.
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| 9. |
- Turesson, Jonas, 1991-, et al.
(författare)
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Picture frame and diagonal compression testing of cross-laminated timber
- 2019
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Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873. ; 52:4
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Turesson, Jonas, 1991-, et al.
(författare)
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Shear modulus analysis of cross-laminated timber using picture frame tests and finite element simulations
- 2020
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Ingår i: Materials and Structures. - : Springer Nature. - 1359-5997 .- 1871-6873. ; 53:4
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Tidskriftsartikel (refereegranskat)abstract
- Determining the mechanical properties of cross-laminated timber (CLT) panels is an important issue. A property that is particularly important for CLT used as shear walls in buildings is the in-plane shear modulus. In this study, a method to determine the in-plane shear modulus of 3- and 5-layer CLT panels was developed based on picture frame tests and a correction factor evaluated from finite element simulations. The picture frame test is a biaxial test where a panel is simultaneously compressed and tensioned. Two different testing methods are simulated by finite elements: theoretical pure shear models as a reference cases and picture frame models to simulate the picture frame test setup. An equation for calculating the shear modulus from the measured shear stiffnesses in the picture frame tests is developed by comparisons between tests and finite element simulations of the CLT panels. The results show that pure shear conditions are achieved in the central region of the panels. No influence from the size of the tested panels is observed in the finite element simulations.
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