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Advanced Modelling of Cross Laminated Timber (CLT) Panels in Bending

https://research.thinkwood.com/en/permalink/catalogue1796
Year of Publication
2015
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Application
Wood Building Systems
Author
Franzoni, Lorenzo
Lebée, Arthur
Lyon, Florent
Forêt, Gilles
Publisher
HAL archives-ouvertes.fr
Year of Publication
2015
Format
Presentation
Material
CLT (Cross-Laminated Timber)
Application
Wood Building Systems
Topic
Mechanical Properties
Keywords
Bending
Model
Panels
Shear
Stiffness
Failure Behavior
Shear Force
Reference Test
Conference
Euromech Colloquim 556 Theoretical Numerical and Experimental Analyses of Wood Mechanics
Research Status
Complete
Notes
May 2015, Dresde, Germany
Summary
Cross Laminated Timber (CLT) panels are more and more common in timber construction. When submitted to out-of-plane loads, they can be considered as multi-layer plates with anisotropic behaviour. Their main structural issue is the low transverse shear strength of cross layers which leads to rolling shear failure. In addition the fabrication process can include or not lateral boards’ gluing. The resulting discontinuities can be considered as weakly heterogeneous and influence the mechanical response. Moreover the timber construction market requires new technical solutions for CLT, like periodic voids within the panel. This solution leads to lighter and more thermally efficient floors. However, the spaced voids between boards increase the heterogeneity of the panel and therefore the complexity of stresses’ distribution.
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Air-Coupled Ultrasound Propagation and Novel Non-Destructive Bonding Quality Assessment of Timber Composites

https://research.thinkwood.com/en/permalink/catalogue13
Year of Publication
2012
Topic
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Author
Martín, Sergio
Organization
ETH Zurich
Year of Publication
2012
Format
Thesis
Material
Glulam (Glue-Laminated Timber)
Topic
Mechanical Properties
Keywords
Adhesives
Bonding
Delamination
Failure
Non-Destructive Testing
Air-coupled Ultrasound (ACU)
Finite-Difference Time-Domain (FDTD) model
Research Status
Complete
Summary
Glued laminated timber (glulam) is manufactured by gluing and stacking timber lamellas, which are sawn and finger-jointed parallel to the wood grain direction. This results in a sustainable and competitive construction material in terms of dimensional versatility and load-carrying capacity. With the proliferation of glued timber constructions, there is an increasing concern about safety problems related to adhesive bonding. Delaminations are caused by manufacturing errors and in service climate variations simultaneously combined with long-sustained loads (snow, wind and gravel filling on flat roofs). Several recent building collapses were related to bonding failure, which should be prevented in the future with a timely defect detection. As an outlook, the feasibility of air-coupled ultrasound tomography was demonstrated with numerical tests and preliminary experiments on glulam. The FDTD wave propagation model was excited by the difference of the time-reversed sound fields transmitted through a test and a reference (defect-free) glulam cross-section. Both datasets were obtained with the same SLT setup. Wave convergences then provided a map of bonding defects along the height and width of the inspected glulam cross-sections. Further research is envisaged in this direction
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Analyses of cracking failure in curved laminated lumber due to transverse stress under a curvature-decreasing moment

https://research.thinkwood.com/en/permalink/catalogue3066
Year of Publication
2020
Topic
Mechanical Properties
Material
LVL (Laminated Veneer Lumber)
Author
Huang, Yan-San
Hsu, Fu-Lan
Organization
National Chung Hsing University
Taiwan Forestry Research Institute
Publisher
Elsevier
Year of Publication
2020
Format
Journal Article
Material
LVL (Laminated Veneer Lumber)
Topic
Mechanical Properties
Keywords
Laminated Lumber
Cracking Failure
Curved Beam
Transverse Stress
Research Status
Complete
Series
Results in Engineering
Summary
Cracking failure of a curved laminated lumber might occur due to transverse stress under a curvature-decreasing bending moment. From both safety and cost perspectives, it is essential to understanding the failure moments and failure modes of curved laminated lumber. While the existing equation to calculate the transverse stress of a curved laminated lumber under a bending moment applied in most literatures is approximate and may cause considerable errors when the initial curvature of beam is small. This is detrimental to the design of curved laminated timber. To solve this problem, we proposed a new equation of bending moment Mc at which the cracking failure is initiated. Mc calculated from this new equation is accurate and larger than Mc-approx calculated from the existing approximate equation. We also derived a novel equation to calculate the minimum ch (cminh) below which cracking failure will not occur. Besides, a novel equation to calculate the critical ch (ccrih) which represents equal opportunities for cracking and bending failure of the beam to occur was further derived. The model proposed in this article are valuable and practical in the design of curved laminated lumber. To exert our model to practice, the equations derived in this paper are applied to literature data (Wood handbook, 1999) and the results showed that hardwoods have statistically significantly larger average values of three parameters, Mc, cminh and ccrih, than softwoods which means hardwoods are more resistant to cracking failure than softwoods. This information is quite useful since lots of laminated lumber for building or furniture are made of hardwoods in Asia.
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Analysis of Mechanical Properties of Cross-Laminated Timber (CLT) with Plywood using Korean Larch

https://research.thinkwood.com/en/permalink/catalogue1806
Year of Publication
2018
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Choi, Chul
Kojima, Erina
Kim, Kyung-Jung
Yamasaki, Mariko
Sasaki, Yasutoshi
Kang, Seog-Goo
Publisher
North Carolina State University
Year of Publication
2018
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Topic
Mechanical Properties
Keywords
Korean Larch
Bending Strength
Hybrid Wooden-Core Laminated Timber (HWLT)
Lamina
Compression
Tensile Strength
Korea
In-Plate Shear Failure
Research Status
Complete
Series
BioResources
Summary
The bending strength of hybrid wooden-core laminated timber (HWLT), a composite material made from existing cross-laminated timber (CLT) and plywood, was analyzed. Using plywood makes it possible to decrease the bending strength of the starting material. Korea Larch (Larix kaempferi Carr.) was used as plywood because of its popularity in Korea. To analyze HWLT’s bending properties, each component (lamina, plywood) was tested for bending, compression, and tensile strengths. The results showed that the HWLT’s bending strength depended on the plywood’s number of plies. With an increased number of plies, plywood’s bending strength decreased, and also HWLT’s bending strength decreased. Most of the failure showed in-plate shear failure of plywood. This result meant that use of reinforced plywood made it possible to increase HWLT’s bending strength for structural material.
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Analysis of Shear Transfer and Gap Opening in Timber–Concrete Composite Members with Notched Connections

https://research.thinkwood.com/en/permalink/catalogue1399
Year of Publication
2017
Topic
Connections
Mechanical Properties
Material
Timber-Concrete Composite
Author
Boccadoro, Lorenzo
Steiger, René
Zweidler, Simon
Frangi, Andrea
Publisher
Springer Netherlands
Year of Publication
2017
Format
Journal Article
Material
Timber-Concrete Composite
Topic
Connections
Mechanical Properties
Keywords
Notched Connections
Analytical Model
Shear Stress
Failure
Research Status
Complete
Series
Materials and Structures
Summary
In timber–concrete composite members with notched connections, the notches act as the shear connections between the timber and the concrete part, and have to carry the shear flow necessary for composite action. The shear transfer through the notches generates shear and tensile stresses in both parts of the composite member, which may lead to brittle failure and to an abrupt collapse of the structure. Although simplified design formulas already exist, some structural aspects are still not clear, and a reliable design model is missing. This paper summarizes current design approaches and presents analytical models to understand the shear-carrying mechanism, to estimate the shear stresses acting in the timber and concrete, and to predict failure. The analysis concentrates on three problems: the shearing-off failure of the timber close to the notch, the shear failure of the concrete, and the influence of the shear flow on the gap opening between the timber and concrete. Parts of the model calculations could be compared to experimental observations. The conclusions of this paper contribute to improving current design approaches.
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Analytical and experimental evaluation of the effect of knots on rolling shear properties of cross-laminated timber (CLT)

https://research.thinkwood.com/en/permalink/catalogue1942
Year of Publication
2019
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Cao, Yawei
Organization
Mississippi State University
Year of Publication
2019
Format
Thesis
Material
CLT (Cross-Laminated Timber)
Topic
Mechanical Properties
Keywords
Rolling Shear
Southern Pine
Center Point Bending Test
Two-Plate Shear Test
Knots
Strength
Failure Mechanism
Research Status
Complete
Summary
Knots are usually regarded as defects when grading lumber. In order to evaluate a member under out-of-plane loading, shear strength is one of the major mechanical properties, specifically, rolling shear (RS) strength is one of the critical mechanical properties of Cross-Laminated Timber (CLT), which determines the flexural strength of CLT under short-span bending loads. Lower grade lumber with a higher percentage of knots is recommended to be utilized for the cross-layer laminations which are mainly responsible for resisting shear stresses. Firstly, shear tests were performed in order to evaluate the effect of knots on longitudinal shear strength using shear blocks. After that, the effect of knots on the RS strength of 3-ply southern yellow pine CLT were investigated by experimental tests and an analytical model. Center-point bending tests with a span-to-depth ratio of 6 and two-plate shear tests with a loading angle of 14° were conducted on six CLT configurations composed of different types of cross layer laminations: clear flatsawn lumber with/without pith, lumber with sound knots with/without pith, and lumber with decayed knots with/without pith. The shear analogy method was implemented to evaluate the RS strength values from the bending test results, which were also compared against the results from the two-plate shear tests. It was found that: (1) The shear blocks containing sound knots had higher shear strength than matched clear shear blocks, the shear blocks containing unsound knots had lower shear strength than the matched clear shear blocks. (2) CLT specimens with cross-layer laminations with either sound knots or decayed knots had higher RS strength. (3) In general, the shear analogy method underestimated the RS strength of CLT specimens containing knots and pith.
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An Analytical Model for Design of Reinforcement around Holes in Laminated Veneer Lumber (LVL) Beams

https://research.thinkwood.com/en/permalink/catalogue135
Year of Publication
2013
Topic
Design and Systems
Mechanical Properties
Material
LVL (Laminated Veneer Lumber)
Application
Beams
Author
Ardalany, Manoochehr
Fragiacomo, Massimo
Moss, Peter
Deam, Bruce
Publisher
Springer Netherlands
Year of Publication
2013
Format
Journal Article
Material
LVL (Laminated Veneer Lumber)
Application
Beams
Topic
Design and Systems
Mechanical Properties
Keywords
Failure
Glued-In Rods
Model
Reinforcement
Screws
Tensile
Research Status
Complete
Series
Materials and Structures
Summary
Openings are usually required to allow services like plumbing, sewage pipes and electrical wiring to run through beams. This prevents an extra depth of the floor/ceiling, while preserving architectural considerations. The introduction of large opening causes additional tension perpendicular to grain in timber beams. The low tensile strength perpendicular to grain of wood allows crack formation. Crack propagation around the hole considerably decreases the load-carrying capacity of the beam. However, in most cases, crack formation and propagation around the hole can be prevented by the use of an appropriate reinforcement. Screw, glued-in rods, and plywood are alternative options for the reinforcement. Design of the reinforcement requires that the working mechanism of the reinforcement is fully understood and properly addressed. In addition, reinforcement should be designed for actions produced in the section of the beam weakened by the hole. The current paper uses a simple truss model around the opening to calculate the tensile force in the reinforcement. Two simple formulations for design of the reinforcement are derived and compared with numerical and experimental results, showing an overall good correspondence. The proposed truss model can be considered for incorporation in future codes of practice.
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Application of Quasi-Brittle Material Model for Analysis of Timber Members

https://research.thinkwood.com/en/permalink/catalogue925
Year of Publication
2014
Material
Solid-sawn Heavy Timber
Author
Khorsandnia, Nima
Crews, Keith
Publisher
Taylor&Francis Online
Year of Publication
2014
Format
Journal Article
Material
Solid-sawn Heavy Timber
Keywords
ultimate load
Finite Element Model
Load-Deflection Response
Failure Load
Four Point Bending Test
Research Status
Complete
Series
Australian Journal of Structural Engineering
Summary
Over the last two decades many constitutive models with different degrees of accuracy have been developed for analysis of sawn timber and engineered wood products. However, most of the existing models for analysis of timber members are not particularly practical to implement, owing to the large number of material properties (and associated testing) required for calibration of the constitutive law. In order to overcome this limitation, this paper presents details of 1D, 2D and 3D non-linear fi nite element (FE) models that take advantage of a quasi-brittle material model, requiring a minimum number of material properties to capture the load-defl ection response and failure load of timber beams under 4-point bending. In order to validate the model, four tapered timber piles with circular cross-section (two plains and two retrofi tted with steel jacket) were tested and analysed with the proposed 3D FE modelling technique; and a good correlation between experimentally observed and numerically captured ultimate load was observed. Consequently, it was concluded that the developed FE models used in conjunction with the quasi-brittle constitutive law were able to adequately capture the failure load and load-defl ection response of the fl exural timber elements.
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Basis of Design Principles for Timber Structures

https://research.thinkwood.com/en/permalink/catalogue1939
Year of Publication
2018
Topic
Serviceability
Design and Systems
Material
CLT (Cross-Laminated Timber)
Author
Abeysekera, Ishan
Baravalle, Michele
Brandner, Reinhard
Colling, François
Fink, Gerhard
Hamm, Patricia
Hochreiner, Georg
Honfi, Dániel
Ilharco, Tiago
Jockwer, Robert
Kleinhenz, Miriam
Kohler, Jochen
Lawrence, Andrew
Marcroft, Julian
Mikoschek, Michael
Toratti, Tomi
Editor
Fink, Gerhard
Honfi, Dániel
Kohler, Jochen
Dietsch, Philipp
Publisher
COST (European Cooperation in Science and Technology)
Year of Publication
2018
Format
Book/Guide
Material
CLT (Cross-Laminated Timber)
Topic
Serviceability
Design and Systems
Keywords
Eurocode
Deflection
Vibrations
Serviceability Limit States
Eurocode 5
Dowel Type Fastener
Failure Behavior
Research Status
Complete
Summary
This report represents the results of the activities performed in working group 1, Basis of Design. The most important task of working group 1 was the defragmentation and harmonization of techniques and methods that are necessary to prove the reliable, safe and economic application of timber materials or products in the construction industry. This report is structured into five parts. At first general principles regarding the design formats are addressed (Part I). Afterwords timber specific aspects regarding code calibration (Part II) and serviceability (Part III) are summarized. In Part IV other demanding issues for the implementation into Eurocode 5 are addressed. Here also summaries of joint activities with other working groups on cross laminated timber and timber connections are presented. The report concludes with a guideline for data analysis (Part V).
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Behavior of Strengthened Timber Concrete Composite Under Axial Loads

https://research.thinkwood.com/en/permalink/catalogue2778
Year of Publication
2021
Topic
Mechanical Properties
Material
Timber-Concrete Composite
Author
El-Salakawy, Tarek
Gamal, Amr
Publisher
ScienceDirect
Year of Publication
2021
Format
Journal Article
Material
Timber-Concrete Composite
Topic
Mechanical Properties
Keywords
Axial Loading
Strengthening
Wire Mesh
Epoxy
Modulus of Elasticity
Failure Mode
Ductility
Post Failure Behavior
Research Status
Complete
Series
Case Studies in Construction Materials
Summary
The research study focuses on different strengthening techniques for timber concrete composites (TCC) using different types of wire and wire mesh integrated with a layer of epoxy on a timber core embedded in concrete using experimental and analytical procedure. The impact of TCC on axial compression performance, modulus of elasticity, failure mode and post failure behavior and ductility were compared to reference concrete specimens. Different types of wire and wire mesh used in strengthening of the timber core, timber core size and reinforcement in the concrete cylinder were all parameters considered in this study. Timing of application of the epoxy on the wire strengthened timber core was very important. For structural applications, where the weight reduction and ductility as well as post failure endurance are essential, the development of this composite is recommended. The ratio of the ductility index to the weight is discussed. The light weight of the timber composite, and the increased ductility were noted in this study. An equation to estimate the axial compression capacity of the strengthened timber concrete composite was developed in this study. This study will pave the way for further applications for timber concrete composite aiming at reducing dead weight of concrete and the reducing the amount of concrete and steel in construction.
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150 records – page 1 of 15.