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43 records – page 1 of 5.

Bending, Shear, and Compressive Properties of Three- and Five-Layer Cross-Laminated Timber Fabricated with Black Spruce

https://research.thinkwood.com/en/permalink/catalogue2589
Year of Publication
2020
Topic
Design and Systems
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
He, Minjuan
Sun, Xiaofeng
Li, Zheng
Feng, Wei
Publisher
SpringerOpen
Year of Publication
2020
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Topic
Design and Systems
Mechanical Properties
Keywords
Black Spruce
Panels
Bending
Thickness
Language
English
Research Status
Complete
Series
Journal of Wood Science
Summary
Cross-laminated timber (CLT) is an innovative engineering wood product made by gluing layers of solid-sawn lumber at perpendicular angles. The commonly used wood species for CLT manufacturing include spruce-pine-fir (SPF), douglas fir-larch, and southern pine lumber. With the hope of broadening the wood species for CLT manufacturing, the purposes of this study include evaluating the mechanical properties of black spruce CLT and analyzing the influence of CLT thickness on its bending or shear properties. In this paper, bending, shear, and compressive tests were conducted respectively on 3-layer CLT panels with a thickness of 105 mm and on 5-layer CLT panels with a thickness of 155 mm, both of which were fabricated with No. 2-grade Canadian black spruce. Their bending or shear resisting properties as well as the failure modes were analyzed. Furthermore, comparison of mechanical properties was conducted between the black spruce CLT panels and the CLT panels fabricated with some other common wood species. Finally, for both the CLT bending panels and the CLT shear panels, their numerical models were developed and calibrated with the experimental results. For the CLT bending panels, results show that increasing the CLT thickness whilst maintaining identical span-to-thickness ratios can even slightly reduce the characteristic bending strength of the black spruce CLT. For the CLT shear panels, results show that increasing the CLT thickness whilst maintaining identical span-to-thickness ratios has little enhancement on their characteristic shear strength. For the CLT bending panels, their effective bending stiffness based on the Shear Analogy theory can be used as a more accurate prediction on their experiment-based global bending stiffness. The model of the CLT bending specimens is capable of predicting their bending properties; whereas, the model of the CLT shear specimens would underestimate their ultimate shear resisting capacity due to the absence of the rolling shear mechanism in the model, although the elastic stiffness can be predicted accurately. Overall, it is attested that the black spruce CLT can provide ideal bending or shear properties, which can be comparable to those of the CLT fabricated with other commonly used wood species. Besides, further efforts should focus on developing a numerical model that can consider the influence of the rolling shear mechanism.
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Edge Connection Technology for Cross Laminated Timber (CLT) Floor Slabs Promoting Two-Way Action

https://research.thinkwood.com/en/permalink/catalogue2718
Year of Publication
2020
Topic
Connections
Material
CLT (Cross-Laminated Timber)
Application
Floors
Author
Asselstine, Julian
Publisher
University of British Columbia
Year of Publication
2020
Country of Publication
Canada
Format
Thesis
Material
CLT (Cross-Laminated Timber)
Application
Floors
Topic
Connections
Keywords
Bending
Two-Way
Self-Tapping Screws
Stiffness
Modulus of Elasticity
Language
English
Research Status
Complete
Summary
Cross-laminated timber (CLT) is a class of engineered wood product with the ability to act as a flat plate floor system transferring loads in two-directions due to the orthogonally crossed layers. Currently, dimensional limitations from manufacturing and transportation limit the minor span to about 3.0 m. This results in under utilization of the bending properties of the cross-layers or the choice of a different product because of the common use of one-way bending support conditions such as drop beams simply supporting the ends of the longer span. This study investigates the performance of a newly developed edge connection system to maintain continuity in the minor direction span of CLT and promote two-way bending action. Three connections utilizing a tension splice fastened to the underside of the panel edges with self-tapping screws are investigated, with experimental results showing promise to maintain a high level of stiffness. This connection system was placed in the maximum moment location of the minor span - attaining a connected span modulus of elasticity up to 1.17 times the intact span modulus of elasticity, indicating a reinforcing effect created by the connection. Further, the minor direction span is additionally stiffened through the use of parallel-strand lumber rim beams fixed to the edges of the CLT in the minor direction span and hidden within the cross-section of the CLT. ANSYS finite element modelling calibrated and validated from the experimental results show the potential of this flat-plate system using 5-layer CLT to reach column spacing of 6.0 m by 6.0 m limited by deflection under a serviceability limit state uniformly distributed load of 3.25 kPa. This claim maintains a high degree of conservatism, as the boundary stress obtained from the minimum observed failure load is greater than 6 times the maximum stress at an ultimate limit state load of 4.67 kPa. This system has the ability to expand the flexibility for designers to utilize CLT more efficiently and create large open floor spaces uninhibited by drop-beams.
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Evaluation of Fire-Retardant Treated Laminated Veneer Lumber

https://research.thinkwood.com/en/permalink/catalogue2471
Year of Publication
2020
Topic
Fire
Mechanical Properties
Material
LVL (Laminated Veneer Lumber)

Evaluation of Fire-Retardant Treated Laminated Veneer Lumber: Final Report — Part 1 of 2

https://research.thinkwood.com/en/permalink/catalogue2502
Year of Publication
2020
Topic
Fire
Mechanical Properties
Material
LVL (Laminated Veneer Lumber)
Application
Wood Building Systems

Experimental and Numerical Analysis of Mixed I-214 Poplar/Pinus Sylvestris Laminated Timber Subjected to Bending Loadings

https://research.thinkwood.com/en/permalink/catalogue2592
Year of Publication
2020
Topic
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Author
Rescalvo, Francisco
Timbolmas, Cristian
Bravo, Rafael
Gallego, Antolino
Publisher
MDPI
Year of Publication
2020
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
Topic
Mechanical Properties
Keywords
Poplar
Pine
Bending
Numerical Modelling
Non-Destructive Testing
Language
English
Research Status
Complete
Series
Materials
Summary
The structural use of timber coming from fast growing and low-grade species such as poplar is one of the current challenges in the wood value chains, through the development of engineering products. In this work, a qualitative comparison of the behavior of mixed glued laminated timber made of pine in their outer layers and of poplar in their inner layers is shown and discussed. Single-species poplar and pine laminated timber have been used as control layouts. The investigation includes destructive four-point bending tests and three non-destructive methodologies: finite elements numerical model; semi-analytical model based on the Parallel Axes theorem and acoustic resonance testing. An excellent agreement between experimental and numerical results is obtained. Although few number of samples have been tested, the results indicate that the use of poplar as a low-grade species in the inner layers of the laminated timber can be a promising technology to decrease the weight of the timber maintaining the good mechanical properties of pine. Likewise, the need for the use of the shear modulus in both experimental measurements and numerical analysis is suggested, as well as the need to reformulate the vibration methodology for non-destructive grading in the case of mixed timber.
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Experimental Research on Structural Behaviors of Glulam I-Beam with a Special-Shaped Section

https://research.thinkwood.com/en/permalink/catalogue2447
Year of Publication
2020
Topic
Design and Systems
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Author
Yang, Ruyuan
Hong, Chaokun
Zhang, Xiaofeng
Yuan, Quan
Sun, Youfu
Publisher
Tech Science Press
Year of Publication
2020
Country of Publication
United States
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Topic
Design and Systems
Mechanical Properties
Keywords
Flange Thickness
Shear Pan Ratio
Stiffener
Stiffness
Bending
Failure
Language
English
Research Status
Complete
Series
Journal of Renewable Materials
Online Access
Free
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Flexural Performance of Novel Nail-Cross-Laminated Timber Composite Panels

https://research.thinkwood.com/en/permalink/catalogue2649
Year of Publication
2020
Topic
Mechanical Properties
Design and Systems
Material
CLT (Cross-Laminated Timber)
Application
Floors
Walls
Author
Zhang, Yannian
Nehdi, Moncef
Gao, Xiaohan
Zhang, V. Lei
Organization
Western University
Shenyang Jianzhu University
Publisher
MDPI
Year of Publication
2020
Country of Publication
Canada
China
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Application
Floors
Walls
Topic
Mechanical Properties
Design and Systems
Keywords
Panels
Flexural Performance
Nails
Bending
Model
Prediction
Fracture
Nail-Cross-Laminated Timber
Language
English
Research Status
Complete
Series
Applied Sciences
Summary
Cross-laminated timber (CLT) is an innovative wood panel composite that has been attracting growing interest worldwide. Apart from its economic benefits, CLT takes full advantage of both the tensile strength parallel to the wood grain and its compressive strength perpendicular to the grain, which enhances the load bearing capacity of the composite. However, traditional CLT panels are made with glue, which can expire and lose effectiveness over time, compromising the CLT panel mechanical strength. To mitigate such shortcomings of conventional CLT panels, we pioneer herein nail-cross-laminated timber (NCLT) panels with more reliable connection system. This study investigates the flexural performance of NCLT panels made with different types of nails and explores the effects of key design parameters including the nail incidence angle, nail type, total number of nails, and number of layers. Results show that NCLT panels have better flexural performance than traditional CLT panels. The failure mode of NCLT panels depends on the nail angle, nail type, and quantity of nails. A modified formula for predicting the flexural bearing capacity of NCLT panels was proposed and proven accurate. The findings could blaze the trail for potential applications of NCLT panels as a sustainable and resilient construction composite for lightweight structures.
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Geopolymer-Bonded Laminated Veneer Lumber as Environmentally Friendly and Formaldehyde-Free Product: Effect of Various Additives on Geopolymer Binder Features

https://research.thinkwood.com/en/permalink/catalogue2484
Year of Publication
2020
Topic
Connections
Mechanical Properties
Material
LVL (Laminated Veneer Lumber)
Author
Shalbafan, Ali
Thoemen, Heiko
Publisher
MDPI
Year of Publication
2020
Country of Publication
Switzerland
Format
Journal Article
Material
LVL (Laminated Veneer Lumber)
Topic
Connections
Mechanical Properties
Keywords
Bonding Quality
Geopolymer
Shear
Bending
Compression
Language
English
Research Status
Complete
Series
Applied Sciences
Online Access
Free
Resource Link
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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
Language
English
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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Refined Zigzag Theory: An Appropriate Tool for the Analysis of CLT-Plates and Other Shear-Elastic Timber Structures

https://research.thinkwood.com/en/permalink/catalogue2725
Year of Publication
2020
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Wimmer, Heinz
Hochhauser, Werner
Nachbagauer, Karin
Publisher
Springer
Year of Publication
2020
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Topic
Mechanical Properties
Keywords
Stress
Load
Refined Zigzag Theory
Bending
Gamma Method
Shear Analogy
First Order Shear Deformation Theory
Plates
Language
English
Research Status
Complete
Series
European Journal of Wood and Wood Products
Summary
Cross laminated timber (CLT), as a structural plate-like timber product, has been established as a load bearing product for walls, floor and roof elements. In a bending situation due to the transverse shear flexibility of the crossing layers, the warping of the cross section follows a zigzag pattern which should be considered in the calculation model. The Refined Zigzag Theory (RZT) can fulfill this requirement in a very simple and efficient way. The RZT, founded in 2007 by A. Tessler (NASA Langley Research Center), M. Di Sciuva and M. Gherlone (Politecnico Torino) is a very robust and accurate analysis tool, which can handle the typical zigag warping of the cross section by introducing only one additional kinematic degree of freedom in case of plane beams and two more in case of biaxial bending of plates. Thus, the RZT-kinematics is able to reflect the specific and local stress behaviour near concentrated loads in combination with a warping constraint, while most other theories do not. A comparison is made with different methods of calculation, as the modified Gamma-method, the Shear Analogy method (SA) and the First Order Shear Deformation Theory (FSDT). For a test example of a two-span continuous beam, an error estimation concerning the maximum bending stress is presented depending on the slenderness L/h and the width of contact area at the intermediate support. A stability investigation shows that FSDT provides sufficiently accurate results if the ratio of bending and shear stiffness is in a range as stated in the test example. It is shown that by a simple modification in the determination of the zigzag function, the scope can be extended to beams with arbitrary non-rectangular cross section. This generalization step considerably improves the possibilities for the application of RZT. Furthermore, beam structures with interlayer slip can easily be treated. So the RZT is very well suited to analyze all kinds, of shear-elastic structural element like CLT-plate, timber-concrete composite structure or doweled beam in an accurate and unified way.
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43 records – page 1 of 5.