| 1. |
- Buck, Dietrich, 1990-
(author)
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Mechanics of Cross-Laminated Timber
- 2018
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Licentiate thesis (other academic/artistic)abstract
- 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.
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| 2. |
- Björngrim, Niclas, et al.
(author)
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Factory Mounted and Retrofit Passive Resistance Sensors Adapted to Monitor Moisture Content in Timber Bridges
- 2017
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In: BioResources. - : North Carolina State University. - 1930-2126. ; 12:4, s. 7218-7227
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Journal article (peer-reviewed)abstract
- The biggest threats to the longevity of a timber bridge are rot and decay. Wood protection by design, inspections, and monitoring of the bridge for elevated moisture content will ensure that the full service life of the structure can be achieved. Today's sensors for moisture content measurements are limited in their functionality and range. This paper presents a sensor that can be both factory installed and retrofitted, which can measure the moisture content through the cross-section of the member in a timber bridge. The sensor has been mounted on Sundbron bridge during manufacturing and retrofitted on Gislaved bridge. The ensuing measurements helped to adjust a design flaw on Gislaved bridge. Monitoring of Sundbron showed that the bridge deck dried up after the bridge had been exposed to sleet and snow during the on-site assembly of the stress laminated bridge deck
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| 3. |
- Björngrim, Niclas, et al.
(author)
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Multivariate Screening of the Weather Effect on Timber Bridge Movements
- 2016
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In: BioResources. - : BioResources. - 1930-2126. ; 11:4, s. 8890-8899
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Journal article (peer-reviewed)abstract
- Monitoring displacements and weather impact of complex structures such as a large cable stayed footbridge generates large amount of data. In order to extract, visualize and classify health-monitoring data to get a better comprehension multivariate statistical analysis is a powerful tool. This paper is a screening to evaluate if principal component analysis is useful on health monitoring data. Principal component analysis (PCA) and projections to latent structures by means of partial least squares (PLS) modeling were used to achieve a better understanding of the complex interaction between bridge dynamics and weather effects. The results show that principal component analysis (PCA) give good overview of the collected data, and PLS modeling show that winds from east and west best explain bridge movements.
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| 4. |
- Björngrim, Niclas, et al.
(author)
-
Resistance measurements to find high moisture content inclusions adapted for large timber bridge cross-sections
- 2017
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In: BioResources. - : North Carolina State University. - 1930-2126. ; 12:2, s. 3570-3582
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Journal article (peer-reviewed)abstract
- One challenge of monitoring and inspecting timber bridges is the difficulty of measuring the moisture content anywhere other than close to the surface. Damage or design mistakes leading to water penetration might not be detected in time, leading to costly repairs. By placing electrodes between the glulam beams, the moisture content through the bridge deck can be measured. Due to the logarithmic decrease of the resistance in wood as a function of electrode length, the model must be calibrated for measurement depth. Two models were created: one for electrode lengths of 50 mm and one for electrode lengths up to 1355 mm. The model for short electrodes differed by no more than 1 percentage points compared with the oven dry specimens. The model for long electrodes differed up to 2 percentage points for lengths up to 905 mm, and over that it could differ up to 4 percentage points.
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| 5. |
- Buck, Dietrich, 1990-, et al.
(author)
-
Full-Field Correlated Mechanics of Cross-Laminated Timber
- 2019
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In: International Digital Image Correlation Society Conference And Workshop (iDICs 2019). - : International Digital Image Correlation Society.
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Conference paper (other academic/artistic)abstract
- This work evaluated the effect of timber quality features on the full-field mechanics of cross-laminated timber (CLT) panels. Panels were individuallysubjected to destructive out-of-plane loading in the principal panel orientation. A digital image correlation (DIC)-based technique was applied fornon-contact full-field measurement and analysis of panel mechanics. The results for 50 layers show that the stiffness of conventional CLT is largelyreduced by the shear resistance of transverse layers. Notably, heterogeneous timber features, such as knots, can reduce the propagation of shear.These results suggest an optimized panel assembly strategy that can be generalized: If shear is dimensioning in an area, e.g. the transverse or thecentral longitudinal layer, the use of knotty timber in that layers can reduce shear propagation. Knots in the compression zone in longitudinal layershave some negative impact, but knots have the largest negative impact in areas of longitudinal layers under tension. Therefore, it is suggested thecurrent grading criteria in the CLT standard be revised to allow the use of more knotty timber in the transverse layers of CLT; doing so could allowa more profitable use of otherwise low-grade timber while producing a stiffer product. The potential of panels constructed according to such anapproach may allow new applications for CLT in timber construction and should be further explored
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| 6. |
- Buck, Dietrich, et al.
(author)
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Further Development of Cross-Laminated Timber (CLT) : Mechanical Tests on 45° Alternating Layers
- 2016
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In: WCTE 2016 : Proceedings. - Vienna : Vienna University of Technology, Austria. - 9783903039001 ; , s. 1107-1114
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Conference paper (peer-reviewed)abstract
- 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.
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| 7. |
- Buck, Dietrich, 1990-, et al.
(author)
-
Mechanical Performance of Cross-Laminated Timber Panels with Alternated Layers
- 2017
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Conference paper (other academic/artistic)abstract
- This research assessed the mechanics of cross-laminated timber (CLT) panels with different alternating layer directions. A total of 20 industrially produced panels, configured with 0° longitudinal layers and transverse layers alternating at either ±45° or at 90° were subjected to destructive testing in bending. Four-point bending tests showed higher stiffness and strength for panels with ±45° alternating layers compared with the conventional 90° crosswise configuration. A noncontact numerical cross-correlation full-field measurement technique based on digital image correlation (DIC) was used as the main method of analysis for determining the mechanics in different scales. The results of the DIC analysis showed that the shear strain in bending was a more critical parameter in 90° layers than in adjacent 0° longitudinal layers of conventional configurations. Results infer that the use of CLT panels with ±45° can be beneficial to timber engineering construction and can induce an increase in the use of alternating layer laminates, especially in areas with shear.
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| 8. |
- Buck, Dietrich, 1990-, et al.
(author)
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Mechanics of diagonally layered cross-laminated timber
- 2018
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In: WCTE 2018 - World Conference on Timber Engineering. - : World Conference on Timber Engineering (WCTE).
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Conference paper (peer-reviewed)abstract
- This research evaluated the mechanics of cross-laminated timber (CLT) panels with different layer orientations. A total of 20 industrially produced panels, configured with 0° longitudinal layers and transverse layers alternating at either ±45° or the conventional 90°, were tested. Each panel was subjected to destructive out-of-plane testing in the principal panel orientation to evaluate stiffness and strength in bending. Four-point bending tests showed higher stiffness and strength for panels with ±45° alternating layers compared to 90°. A non-contact full-field measurement and analysis technique based on digital image correlation (DIC) was utilised for the main mechanical analysis at different scales. DIC evaluations of 100 CLT panel layers showed that a considerable part of the stiffness of conventional CLT is reduced by the shear resistance of transverse layers. Heterogeneous wooden features, such as knots, reduce the propagation of shear fraction along the layers. These results call into question the present grading criteria in the CLT standard: It is suggested that the current lower grading limit be adjusted for increased value-yield. The overall experimental results suggest the use of CLT panels with a ±45° layered configuration would be beneficial for timber engineering construction. They also motivate the use of alternatively angled layered laminates in design and construction, especially in areas subjected to shear. Based on these results, CLT should be further explored as a suitable product to potentially facilitate the use of wooden panels in more construction applications.
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| 9. |
- Buck, Dietrich, 1990-, et al.
(author)
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Multivariate Image Analysis Applied to Cross-Laminated Timber: Combined Hyperspectral Near-Infrared and X-ray Computed Tomography
- 2023
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In: Journal of Spectroscopy. - : Hindawi Publishing Corporation. - 2314-4920 .- 2314-4939.
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Journal article (peer-reviewed)abstract
- Engineered wood products, such as cross-laminated timber (CLT), are becoming more popular in the designs of modern sustainable buildings. This increased production of CLT requires more robust, yet less labour-intensive means to assess the material characteristics of whole CLT panels. In exploring ways of improving efficiency, this study explores multivariate image analysis (MIA) via partial least squares discriminant analysis (PLS-DA) machine learning as a means to classify CLT material features. CLT panels underwent nondestructive testing using near-infrared (NIR) hyperspectral imaging and X-ray computed tomography (CT) analysis. MIA was performed on these results to build predictive models for wood features, such as fibre alignment and knot type. The models showed that it was possible to classify material features on the surface of CLT using NIR alone; whilst when combined with X-ray data, it enhanced the predictive ability of material features throughout the CLT volume. These first results from such modelling have the potential to help map the chemical and physical material properties of CLT, improving the manufacturing efficiency of the product and allowing greater sustainability of engineered wood products.
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| 10. |
- Buck, Dietrich, 1990-, et al.
(author)
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Production and In-Plane Compression Mechanics of Alternatively Angled Layered Cross-Laminated Timber
- 2018
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In: BioResources. - : University of North Carolina Press. - 1930-2126. ; 13:2, s. 4029-4045
-
Journal article (peer-reviewed)abstract
- 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.
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