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Compressive Strength Properties Perpendicular to the Grain of Larch Cross-laminated Timber

https://research.thinkwood.com/en/permalink/catalogue2410
Year of Publication
2019
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Application
Wood Building Systems

Makerjoint, a New Concept for Joining Members in Timber Engineering – Strength Test and Failure Analyses

https://research.thinkwood.com/en/permalink/catalogue260
Year of Publication
2015
Topic
Connections
Mechanical Properties
Material
LVL (Laminated Veneer Lumber)
Author
Rebstock, Florian
Bomark, Peter
Sandberg, Dick
Year of Publication
2015
Format
Journal Article
Material
LVL (Laminated Veneer Lumber)
Topic
Connections
Mechanical Properties
Keywords
CNC
Prefabrication
Failure Modes
Tensile Strength
Compressive Strength
Joints
Research Status
Complete
Series
Pro Ligno
Summary
The wood construction industries are becoming more focused on climate change and resource depletion, and individual and industrial consumption must reflect a greater degree of concern for the climate and environmental wellbeing. This paper presents a new concept for timber engineering, the purpose being to acquire information about the failure modes and the tensile and compressive strengths of two types of joint, the Simple Gooseneck and Thick Gooseneck, that can be used in a new concept for joining members in timber structures. This Makerjoint concept uses laminated veneer lumber (LVL) as nodes in regions with a pronounced non-uniform stress distribution and sawn timber in regions with a more uniform stress distribution. No metal fasteners or adhesives are used in the joint between timber and LVL. The concept is intended for joints using 3-axis CNC machinery and to be a system for on-site- and pre-fabrication of e.g. small houses, emergency shelters and exhibition stands. The joints have a higher compressive than tensile strength. The joints exhibited brittle failure in tension (beam and/or node failure) and buckling occurred in compression around the thinnest cross section of the beams. Suggestions are made for how the mechanical properties of the joints can be improved.
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A Post-tensioned Cross-Laminated Timber Core for Buildings

https://research.thinkwood.com/en/permalink/catalogue2700
Year of Publication
2020
Topic
Connections
Mechanical Properties
Design and Systems
Material
CLT (Cross-Laminated Timber)
Application
Cores
Walls
Author
Znabei, Tigist
Year of Publication
2020
Format
Thesis
Material
CLT (Cross-Laminated Timber)
Application
Cores
Walls
Topic
Connections
Mechanical Properties
Design and Systems
Keywords
Prestress
Post-Tensioning
Bending
Shear Stiffness
Core Structure
Compressive Strength
Research Status
Complete
Summary
This master thesis is on post-tensioning cross-laminated timber stability cores for multiple story buildings. When designing a CLT core, significantly larger core sections will be needed than when designing a stabilizing core in concrete. This is for one part due to the limited stiffness of the CLT compared to concrete. For another part it is due to the limited stiffness of connectors in CLT. Sliding and uplift can occur in connections in CLT loaded in tension and shear respectively. The CLT panels behave like rigid bodies, with most of the displacement occurring at the connections. In addition, cooperation between flange and web may be limited, depending on the stiffness of the corner connection and the occurrence of shear lag. Post-tensioning is suggested as a solution to diminish uplift and sliding in the connectors. In this way, with the same core section, a taller building may be realized compared to the non-post-tensioned case. In the thesis also the long-term effects on the prestress level is assessed, as estimating these effects is important for the safety of the system.This thesis adds to the body of knowledge on post-tensioned CLT structures. Firstly, previous studies on post-tensioned CLT focus on individual shear walls and on seismic design situations. This thesis explores how beneficial post-tensioning is from the perspective of serviceability limit state governed design. Furthermore, though post-tensioning as a prestressing method has been applied often in concrete structures, prestressing of CLT is a novel research subject. Especially the estimation of long-term force loss is a topic that still requires research. This thesis provides the designer with a straightforward calculation method (using python) for estimation of prestress force loss in the long-term.The research was carried out with a literature study and a case-study. The literature research comprised of studies on structural design with CLT loaded in-plane; the effective flange of a CLT core; stiffness of connections in CLT; prestressing of CLT; a design approach for post-tensioning; time dependent losses in post-tensioned CLT. The case study was based on a fictitious floorplan including a “minimal core”, and at expressing the benefit of post-tensioning in terms of height gain.The degree to which the flange and the web cooperate showed highly dependent on the connection between flange and web and the core height. In the case study, the effective flange width showed to depend highly on the height of the core and the stiffness of the connection between flange and web.In the case-study, without post-tensioning, approximately half of the displacements could be attributed to the connections. With post-tensioning, the uplift and sliding displacements in the horizontal joints was eliminated. Consequently, the attainable height was significantly increased: from 5 storeys in the un-post-tensioned case, to 8 storeys in the post-tensioned case. Long-term effects on the prestress loss were considerable. In the case-study, approximately 40% loss of post-tension force in the lifetime of the building was predicted and included in the design. Largest causeof force loss was due to changes of moisture content during construction. The remaining lateral displacements after post-tensioning were due to bending and shear.Post-tensioning of CLT cores is a powerful method for reducing lateral displacements in cases where uplift and sliding are dominant contributors to the lateral displacements. This is especially the case in light-weight buildings. Uplift and sliding displacements can be eliminated altogether with post-tensioning. The designer should realize that post-tensioning does not increase the bending and shear stiffness of the core. The thesis also concludes that with the post-tensioning of CLT walls, the compressive strength of the CLT in the so-called “compression-toe” might be exceeded. It is an important check in design. Furthermore, depending on the decision to re-tighten the rods at some point or not, the post-tension force loss should be calculated and included in finding the right prestress level. For this estimation of the moisture level of the CLT proved to be an important but difficult step. It is likely that the 40% force loss in the case-study is on the conservative side, since a large change in moisture content has been assumed. In practice, the moisture content can be measured on site. This can help verify the assumptions on the moisture content used in force loss calculations. This can help in assuring the structure is safe in the long-term.
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Predicting the Average Compression Strength of CLT by Using the Average Density or Compressive Strength of Lamina

https://research.thinkwood.com/en/permalink/catalogue3020
Year of Publication
2022
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Tian, Zhaopeng
Gong, Yingchun
Xu, Junhua
Li, Mingyue
Wang, Zhaohui
Ren, Haiqing
Organization
Chinese Academy of Forestry
Editor
Elustondo, Diego
Publisher
MDPI
Year of Publication
2022
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Topic
Mechanical Properties
Keywords
Compressive Strength
Density
Linear Regression Analysis
Monte Carlo Simulation
Plated Larch
Prediction Model
Research Status
Complete
Series
Forests
Summary
The compressive strength in the major direction of cross-laminated timber CLT is the key to supporting the building load when CLT is used as load-bearing walls in high-rise wood structures. This study mainly aims to present a model for predicting the average compressive strength of CLT and promoting the utilization of CLT made out of planted larch. The densities and compressive strengths of lamina specimens and CLT samples with widths of 89 and 178 mm were evaluated, and their relationship was analyzed to build a prediction model by using Monte Carlo simulation. The results reveal that the average density of the lamina and CLT were about equal, whereas the average compressive strength of the CLT was just about 72% of that of the lamina. Width exerted no significant effect on the average compressive strength of the CLT, but homogenization caused the wider CLT to have a smaller variation than that of the lamina. The average compressive strength of the lamina could be calculated by using the average density of lamina multiply by 103.10, and the average compressive strength of the CLT could be calculated according to the compression strength of lamina in major and minor direction, therefore, a new prediction model is determined to predict the average compression strength of CLT by using the average density of lamina or CLT, the average compression strength of CLT made in this study is about 74.23 times of the average density of the lamina. The results presented in this study can be used to predict the average compressive strength of CLT by using the average density of lamina and provide a fundamental basis for supporting the utilization of CLT as load-bearing walls.
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Free
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Prediction of Compressive Strength of Cross-Laminated Timber Panel

https://research.thinkwood.com/en/permalink/catalogue517
Year of Publication
2015
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Application
Walls
Author
Oh, Jung-Kwon
Lee, Jun-Jae
Hong, Jung-Pyo
Publisher
Springer Japan
Year of Publication
2015
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Application
Walls
Topic
Mechanical Properties
Keywords
Lamina
Monte Carlo
Compressive Strength
Research Status
Complete
Series
Journal of Wood Science
Summary
Compressive strength of cross-laminated timber (CLT) is one of the important mechanical properties which should be considered especially in design of mid-rise CLT building because it works to resist a vertical bearing load from the upper storeys. The CLT panel can be manufactured in various combinations of the grade and dimension of lamina. This leads to the fact that an experimental approach to evaluate the strength of CLT would be expensive and time-demanding. In this paper, lamina property-based models for predicting the compressive strength of CLT panel was studied. A Monte Carlo simulation was applied for the model prediction. A set of experimental compression tests on CLT panel (short column) was conducted to validate the model and it shows good results. Using this model, the influence of the lamina’s width on the CLT compressive strength was investigated. It reveals that the CLT compressive strength increases with the increase in the number of lamina. It was thought that repetitive member effect (or dispersion effect) is applicable for the CLT panel, which was explained by the decrease of the variation in strength. This dependency of the number of lamina needs further study in development of reference design values, CLT wall design and CLT manufacturing.
Online Access
Free
Resource Link
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