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Mechanics of Cross-Laminated Timber
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0001-7091-6696
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing awareness of sustainable building materials has led to interest in enhancing the structural performance of engineered wood products. Wood is a sustainable, renewable material, and the increasing use of wood in construction contributes to its sustainability. Multi-layer wooden panels are one type of engineered wood product used in construction.

There are various techniques to assemble multi-layer wooden panels into prefabricated, load-bearing construction elements. Assembly techniques considered in the earliest stages of this research work were laminating, nailing, stapling, screwing, stress laminating, doweling, dovetailing, and wood welding. Cross-laminated timber (CLT) was found to offer some advantages over these other techniques. It is cost-effective, not patented, offers freedom of choice regarding the visibility of surfaces, provides the possibility of using different timber quality in the same panel at different points of its thickness, and is the most well-established assembly technique currently used in the industrial market.

Building upon that foundational work, the operational capabilities of CLT were further evaluated by creating panels with different layer orientations. The mechanical properties of CLT panels constructed with layers angled in an alternative configuration produced on a modified industrial CLT production line were evaluated. Timber lamellae were adhesively bonded in a single-step press procedure to form CLT panels. Transverse layers were laid at a 45° angle instead of the conventional 90° angle with respect to the longitudinal layers’ 0° angle.

Tests were carried out on 40 five-layered CLT panels, each with either a ±45° or a 90° configuration. Half of these panels were evaluated under bending: out-of-plane loading was applied in the principal orientation of the panels via four-point bending. The other twenty were evaluated under compression: an in-plane uniaxial compressive loading was applied in the principal orientation of the panels. Quasi-static loading conditions were used for both in- and out-of-plane testing to determine the extent to which the load-bearing capacity of such panels could be enhanced under the current load case. Modified CLT showed higher stiffness, strength, and fifth-percentile characteristics, values that indicate the load-bearing capacity of these panels as a construction material. Failure modes under in- and out-of-plane loading for each panel type were also assessed.

Data from out-of-plane loading were further analysed. A non-contact full-field measurement and analysis technique based on digital image correlation (DIC) was utilised for analysis at global and local scales. DIC evaluation of 100 CLT layers showed that a considerable part of the stiffness of conventional CLT is reduced by the shear resistance of its transverse layers. The presence of heterogeneous features, such as knots, has the desirable effect of reducing the propagation of shear fraction along the layers. These results call into question the current grading criteria in the CLT standard. It is suggested that the lower timber grading limit be adjusted for increased value-yield.

The overall experimental results suggest the use of CLT panels with a ±45°-layered configuration for construction. They also motivate the use of alternatively angled layered panels for more construction design freedom, especially in areas that demand shear resistance. In addition, the design possibility that such 45°-configured CLT can carry a given load while using less material than conventional CLT suggests the potential to use such panels in a wider range of structural applications. The results of test production revealed that 45°-configured CLT can be industrially produced without using more material than is required for construction of conventional 90°-configured panels. Based on these results, CLT should be further explored as a suitable product for use in more wooden-panel construction.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keyword [en]
CLT assembly, CLT manufacture, Crosslam, DIC analysis, Digital speckle photography, Full-field mechanics, Laminated wood product, Mass timber engineering, Non-contact measurement, Non-destructive, Optical measurement, Panel configuration, Strain localization, X-lam
Keyword [sv]
Alternativ byggmetod, Bildkorrelation, Hållbart byggande, KL- trä, Korslimmat trä, Skjuvtöjning, Massivträ, Träkonstruktion
National Category
Mechanical Engineering Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-68729ISBN: 978-91-7790-150-1 (print)ISBN: 978-91-7790-151-8 (electronic)OAI: oai:DiVA.org:ltu-68729DiVA, id: diva2:1205877
Presentation
2018-06-20, Hörsal A, Luleå tekniska universitet, Skellefteå, 10:00 (English)
Opponent
Supervisors
Note

External cooperation: Martinson Group AB and Research Institutes of Sweden (RISE)

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-06-13Bibliographically approved
List of papers
1. Comparison of Different Assembling Techniques Regarding Cost, Durability, and Ecology: A Survey of Multi-layer Wooden Panel Assembly Load-Bearing Construction Elements
Open this publication in new window or tab >>Comparison of Different Assembling Techniques Regarding Cost, Durability, and Ecology: A Survey of Multi-layer Wooden Panel Assembly Load-Bearing Construction Elements
2015 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 10, no 4, p. 8378-8396Article in journal (Refereed) Published
Abstract [en]

Wood is a pure, sustainable, renewable material. The increasing use of wood for construction can improve its sustainability. There are various techniques to assemble multi-layer wooden panels into prefabricated, load-bearing construction elements. However, comparative market and economy studies are still scarce. In this study, the following assembling techniques were compared: laminating, nailing, stapling, screwing, stress laminating, doweling, dovetailing, and wood welding. The production costs, durability, and ecological considerations were presented. This study was based on reviews of published works and information gathered from 27 leading wood product manufacturing companies in six European countries. The study shows that the various techniques of assembling multi-layer wooden construction panel elements are very different. Cross laminated timber (CLT) exhibited the best results in terms of cost and durability. With regard to ecological concerns, dovetailing is the best. Taking into account both durability and ecological considerations, wooden screw-doweling is the best. These alternatives give manufacturers some freedom of choice regarding the visibility of surfaces and the efficient use of lower-quality timber. CLT is the most cost-effective, is not patented, and is a well-established option on the market today.

National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-6194 (URN)10.15376/biores.10.4.8378-8396 (DOI)000366990800160 ()2-s2.0-85011309055 (Scopus ID)46395d70-95a9-4286-9834-bb37c6c45a47 (Local ID)46395d70-95a9-4286-9834-bb37c6c45a47 (Archive number)46395d70-95a9-4286-9834-bb37c6c45a47 (OAI)
Note

Validerad; 2015; Nivå 2; 20150827 (aliwan)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-05-15Bibliographically approved
2. Further Development of Cross-Laminated Timber (CLT): Mechanical Tests on 45° Alternating Layers
Open this publication in new window or tab >>Further Development of Cross-Laminated Timber (CLT): Mechanical Tests on 45° Alternating Layers
2016 (English)In: WCTE 2016 : Proceedings, Vienna: Vienna University of Technology, Austria , 2016Conference paper, Published paper (Refereed)
Abstract [en]

 

In this paper, a series of experimental bending and compression tests were performed on cross-laminated timber (CLT) products with ±45° alternating layers, to evaluate their performance against conventional panels of 90° orientation. Engineered wood products, such as CLT with ±45° alternating layers can provide opportunities for greater use in larger and more sustainable timber constructions. A total of 40 panels, manufactured in an industrial CLT production line with either of these two configurations, were tested and compared. Panels were evaluated in bending tests n=20 and the remaining ones in compression tests. Results showed that 35% increased the strength in the four-point bending tests for panels containing ±45° alternating layers compared with the 90° alternating layers. Compression strength was increased by 15%. Stiffness increased by 15% in the four-point bending and 30% in the compression. The results indicate that CLT containing ±45° alternating layers has increased strength and stiffness compared to 90° alternating layers. These findings suggest that further developments in CLT are feasible in advanced building applications.

Place, publisher, year, edition, pages
Vienna: Vienna University of Technology, Austria, 2016
National Category
Infrastructure Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-60093 (URN)978-3-903039-00-1 (ISBN)
Conference
World Conference on Timber Engineering (WCTE 2016), Vienna, August 22-25 2016
Available from: 2016-11-02 Created: 2016-11-01 Last updated: 2018-05-15Bibliographically approved
3. Bending Properties of Cross Laminated Timber (CLT) with a 45° Alternating Layer Configuration
Open this publication in new window or tab >>Bending Properties of Cross Laminated Timber (CLT) with a 45° Alternating Layer Configuration
2016 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 11, no 2, p. 4633-4644Article in journal (Refereed) Published
Abstract [en]

Bending tests were conducted with cross laminated timber (CLT) panels made using an alternating layer arrangement. Boards of Norway spruce were used to manufacture five-layer panels on an industrial CLT production line. In total, 20 samples were tested, consisting of two CLT configurations with 10 samples of each type: transverse layers at 45° and the conventional 90° arrangement. Sample dimensions were 95 mm × 590 mm × 2000 mm. The CLT panels were tested by four point bending in the main load-carrying direction in a flatwise panel layup. The results indicated that bending strength increased by 35% for elements assembled with 45° layers in comparison with 90° layers. Improved mechanical load bearing panel properties could lead to a larger span length with less material.

National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-11156 (URN)10.15376/biores.11.2.4633-4644 (DOI)a1093b71-f2f8-4b06-9af1-b46a7c406aa8 (Local ID)a1093b71-f2f8-4b06-9af1-b46a7c406aa8 (Archive number)a1093b71-f2f8-4b06-9af1-b46a7c406aa8 (OAI)
Note

Validerad; 2016; Nivå 2; 20160331 (aliwan)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-05-15Bibliographically approved
4. Production and In-Plane Compression Mechanics of Alternatively Angled Layered Cross-Laminated Timber
Open this publication in new window or tab >>Production and In-Plane Compression Mechanics of Alternatively Angled Layered Cross-Laminated Timber
2018 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 13, no 2, p. 4029-4045Article in journal (Refereed) Published
Abstract [en]

 Increasing awareness of sustainable building materials has led to interest in enhancing the structural performance of engineered wood products. This paper reports mechanical properties of cross-laminated timber (CLT) panels constructed with layers angled in an alternative configuration on a modified industrial CLT production line. Timber lamellae were adhesively bonded together in a single-step press procedure to form CLT panels. Transverse layers were laid at an angle of 45°, instead of the conventional 90° angle with respect to the longitudinal layers’ 0° angle. Tests were carried out on 20 five-layered CLT panels divided into two matched groups with either a 45° or a 90° configuration; an in-plane uniaxial compressive loading was applied in the principal orientation of the panels. These tests showed that the 45°-configured panels had a 30% higher compression stiffness and a 15% higher compression strength than the 90° configuration. The results also revealed that the 45°-configured CLT can be industrially produced without using more material than is required for conventional CLT 90° panels. In addition, the design possibility that the 45°-configured CLT can carry a given load while using less material also suggests that it is possible to use CLT in a wider range of structural applications.

Place, publisher, year, edition, pages
University of North Carolina Press, 2018
Keyword
CLT manufacturing; Crosslam; Cross-ply; Diagonal-laminated lumber; Impact of laminate orientation; In-plane rotation; Grain inclination angle; Mass timber engineering; Solid wood panel; X-lam
National Category
Building Technologies Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-68424 (URN)
Note

Validerad;2018;Nivå 2;2018-04-26 (andbra)

Available from: 2018-04-20 Created: 2018-04-20 Last updated: 2018-05-15Bibliographically approved

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