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Further Development of Cross-Laminated Timber (CLT): Mechanical Tests on 45° Alternating Layers
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0001-7091-6696
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0001-8404-7356
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0001-5872-2792
SP Technical Research Institute of Sweden, SP Sustainable Built Environment, Skellefteå.
Number of Authors: 42016 (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: urn:nbn:se:ltu:diva-60093ISBN: 978-3-903039-00-1 (print)OAI: oai:DiVA.org:ltu-60093DiVA, id: diva2:1044173
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
In thesis
1. Mechanics of Cross-Laminated Timber
Open this publication in new window or tab >>Mechanics of Cross-Laminated Timber
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
Keywords
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, 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:nbn:se:ltu:diva-68729 (URN)978-91-7790-150-1 (ISBN)978-91-7790-151-8 (ISBN)
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

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Buck, DietrichHagman, OlleWang, Alice

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