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Characterizing Influence of Laminate Characteristics on Elastic Properties of Cross Laminated Timber

https://research.thinkwood.com/en/permalink/catalogue221
Year of Publication
2014
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Niederwestberg, Jan
Chui, Ying Hei
Year of Publication
2014
Country of Publication
Canada
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Topic
Mechanical Properties
Keywords
Modal Testing
Laminates
Language
English
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 10-14, 2014, Quebec City, Canada
Summary
Properties of CLT panels are influenced by the properties of their layers and the layer properties are in turn influenced by the structural characteristics of the laminate material. In order to realize the mechanical property potential of CLT panels it is necessary to understand the effects of laminate properties on the performance of the final product. This paper presents the approach and outcomes of an on-going study dealing with the evaluation of material and structural characteristics of laminates and their effects on overall characteristics of CLT using modal testing. Characteristics of “homogenised” layers and CLT panels were evaluated using modal and static testing. The suitability of test methods was established for single-layer panels and CLT panels. Relationships between overall single-layer properties and laminate characteristics were established. Differences in CLT properties calculated by different calculation models were discussed.
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Diagrams for Stress and Deflection Prediction in Cross-Laminated Timber (CLT) Panels with Non-Classical Boundary Conditions

https://research.thinkwood.com/en/permalink/catalogue2719
Year of Publication
2020
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Obradovic, Nikola
Todorovic, Marija
Marjanovic, Miroslav
Damnjanovic, Emilija
Year of Publication
2020
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Topic
Mechanical Properties
Keywords
Stress
Deflection
Eurocode 5
Layerwise Plate Theory
Panels
Language
English
Conference
International Conference on Contemporary Theory and Practice in Construction
Research Status
Complete
Summary
Invention of cross-laminated timber (CLT) was a big milestone for building with wood. Due to novelty of CLT and timber’s complex mechanical behavior, the existing design codes cover only rectangular CLT panels, simply supported along 2 parallel or all 4 edges, making numerical methods necessary in other cases. This paper presents a practical engineering tool for stress and deflection prediction of CLT panels with non-classical boundary conditions, based on the software for the computational analysis of laminar composites, previously developed by the authors. Diagrams applicable in engineering practice are developed for some common cases. The presented methodology could be a basis for more detailed design handbooks and guidelines for various layouts of CLT panels and different types of loadings.
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Reinforcing the Mechanical Properties of Poplar LVL with Hardwood Veneer Layers, Part I.: Non-Destructive Testing and Modelling the Elastic Properties

https://research.thinkwood.com/en/permalink/catalogue1097
Year of Publication
2014
Topic
Mechanical Properties
Material
LVL (Laminated Veneer Lumber)
Author
Vilpponen, Edit
Komán, Szabolcs
Bejó, László
Year of Publication
2014
Country of Publication
Hungary
Format
Journal Article
Material
LVL (Laminated Veneer Lumber)
Topic
Mechanical Properties
Keywords
Modulus of Elasticity
Reinforcement
Laminate Theory
Deterministic Modeling
Language
Hungarian
Research Status
Complete
Series
Faipar
ISSN
2064-9231
Summary
One opportunity for the value-added utilisation of domestic poplar hybrids is manufacturing LVL products. The mechanical properties of poplar LVL are somewhat inferior to those of traditional Spruce/Pine LVL products. These characteristics may be improved by reinforcing the product using hardwood veneer layers. In this study, the mechanical properties of poplar LVL were improved using beech, turkey oak and tree-of-heaven as reinforcement layers. The mechanical properties of the experimental LVL were determined using vibration testing and destructive ramp testing. The MOE was also estimated using a deterministic model based on the elastic properties and densification of the veneer layers. In this article, the non-destructively measured and model-predicted elastic properties are described. The reinforcement layers improved the MOE significantly. Beech reinforcement performed as anticipated, while turkey oak and tree-of-heaven veneers increased the MOE more drastically than expected. This indicates that these veneers are especially suitable for this purpose. The theoretical model predicted the MOE of the control and beech-reinforced specimen reasonably well, but provided a conservative estimate for the effect of turkey oak and tree-of-heaven.
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Non Destructive Evaluation of Elastic Material Properties of Cross-Laminated Timber (CLT)

https://research.thinkwood.com/en/permalink/catalogue2315
Year of Publication
2008
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Application
Wood Building Systems

Efficient Measurement of Elastic Constants of Cross Laminated Timber using Modal Testing

https://research.thinkwood.com/en/permalink/catalogue117
Year of Publication
2014
Topic
Acoustics and Vibration
Material
CLT (Cross-Laminated Timber)
Author
Zhou, Jianhui
Chui, Ying Hei
Year of Publication
2014
Country of Publication
Canada
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Topic
Acoustics and Vibration
Keywords
Elasticity
Modal Testing
Modulus of Elasticity
Natural Frequency
Testing
Vibrations
Language
English
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 10-14, 2014, Quebec City, Canada
Summary
It has been shown that measurement of elastic constants of orthotropic wood-based panel products can be more efficiently measured by modal testing technique. Identification of vibration modes and corresponding natural frequencies is key to the application of modal testing technique. This process is generally tedious and requires a number of measurement locations for mode shape identification. In this study, a simplified method for frequency identification was developed which will facilitate the adoption of the vibration-based testing technique for laboratory and industrial application. In the method, the relationship between frequency order and mode order is first studied considering the boundary condition, elastic properties of the orthotropic panel. An algorithm is proposed to predict the frequency values and mode indices based on corresponding normalized sensitivity to elastic constants, initial estimates of orthotropic ratios and measured fundamental natural frequency. The output from the algorithm can be used for identification of sensitive natural frequencies from up to three frequency spectra. Then the algorithm is integrated with the elastic calculation algorithm to extract the elastic constants from the sensitive frequencies. The elastic constants of cross laminated timber panels were measured by the proposed method. The moduli of elasticity agree well with static testing results. The calculated in-plane shear modulus was found to be within the expected range.
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Effect of Realistic Boundary Conditions on the Behaviour of Cross-Laminated Timber Elements Subjected to Simulated Blast Loads

https://research.thinkwood.com/en/permalink/catalogue2361
Year of Publication
2017
Topic
Seismic
Material
CLT (Cross-Laminated Timber)
Application
Floors
Walls
Author
Cote, Dominic
Publisher
University of Ottawa
Year of Publication
2017
Country of Publication
Canada
Format
Thesis
Material
CLT (Cross-Laminated Timber)
Application
Floors
Walls
Topic
Seismic
Keywords
Connections
Seismic Load
Blast Loads
Fasteners
Language
English
Research Status
Complete
Summary
Cross-laminated timber (CLT) is an emerging engineered wood product in North America. Past research effort to establish the behaviour of CLT under extreme loading conditions has focussed CLT slabs with idealized simply-supported boundary conditions. Connections between the wall and the floor systems above and below are critical to fully describing the overall behaviour of CLT structures when subjected to blast loads. The current study investigates the effects of “realistic” boundary conditions on the behaviour of cross-laminated timber walls when subjected to simulated out-of-plane blast loads. The methodology followed in the current research consists of experimental and analytical components. The experimental component was conducted in the Blast Research Laboratory at the University of Ottawa, where shock waves were applied to the specimens. Configurations with seismic detailing were considered, in order to evaluate whether existing structures that have adequate capacities to resist high seismic loads would also be capable of resisting a blast load with reasonable damage. In addition, typical connections used in construction to resist gravity and lateral loads, as well as connections designed specifically to resist a given blast load were investigated. The results indicate that the detailing of the connections appears to significantly affect the behaviour of the CLT slab. Typical detailing for platform construction where long screws connect the floor slab to the wall in end grain performed poorly and experienced brittle failure through splitting in the perpendicular to grain direction in the CLT. Bearing type connections generally behaved well and yielding in the fasteners and/or angles brackets meant that a significant portion of the energy was dissipated there reducing the energy imparted on the CLT slab significantly. Hence less displacement and thereby damage was observed in the slab. The study also concluded that using simplified tools such as single-degree-of-freedom (SDOF) models together with current available material models for CLT is not sufficient to adequately describe the behaviour and estimate the damage. More testing and development of models with higher fidelity are required in order to develop robust tools for the design of CLT element subjected to blast loading.
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Influence of Orientation and Number of Layers on the Elastic Response and Failure Modes on CLT Floors: Modeling and Parameter Studies

https://research.thinkwood.com/en/permalink/catalogue1418
Year of Publication
2016
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Franzoni, Lorenzo
Lebée, Arthur
Lyon, Florent
Forêt, Gilles
Publisher
Springer Berlin Heidelberg
Year of Publication
2016
Country of Publication
Germany
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Topic
Mechanical Properties
Keywords
Failure Modes
Bending
Elastic Behavior
Language
English
Research Status
Complete
Series
European Journal of Wood and Wood Products
ISSN
1436-736X
Summary
In the present paper, the bending behavior of Cross Laminated Timber panels is investigated by means of the linear elastic exact solution from Pagano (1970; 1969). The resulting stresses are the input for a wood failure criterion, which can point out the first-crack load and the respective dominant failure mode. Heterogeneous layers are modeled as equivalent and homogeneous layers. This simplified and deterministic modeling gives results in good agreement with a reference experimental test. A comparison is made with respect to the panel’s global stiffness and failure stages within the apparent elastic stage. Finally, parameter studies are carried out, in order to quantify CLT limitations and advantages. The effect of varying properties like the panel’s slenderness, orientation of transverse layers and number of layers for a fixed total thickness are investigated.
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Influence of Steel Properties on the Ductility of Doweled Timber Connections

https://research.thinkwood.com/en/permalink/catalogue2789
Year of Publication
2021
Topic
Connections
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
LVL (Laminated Veneer Lumber)
Author
Geiser, Martin
Bergmann, M.
Follesa, Maurizio
Publisher
ScienceDirect
Year of Publication
2021
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
LVL (Laminated Veneer Lumber)
Topic
Connections
Mechanical Properties
Keywords
Ductility
Strength
Monotonic Test
Cyclic Tests
Dowel Type Fastener
Serial Yielding
Doweled Connections
Capacity Design
Strain Hardening Ratio
Steel
Seismic
Language
English
Research Status
Complete
Series
Construction and Building Materials
Summary
In the seismic design of structures according to the dissipative structural behaviour, the connection ductility is crucial in order to ensure the desired level of energy dissipation of the overall structure. Therefore, in case of ductile zones composed of dowel-type fasteners arranged in series, it is important to ensure that all the fasteners can fully develop their energy dissipation capacity by plastic deformations. However, when different types of connections made of two symmetrical and serially arranged assemblies of dowel-type fasteners are tested, it often appears that only few fasteners fully work in the plastic region while most of the remaining ones exhibit very low yielding. Looking at the causes of this dysfunction, a possible explanation is due to the fact that the rules for the seismic design of dissipative zones in timber structures given in international codes and used in common practice often make reference only to the steel quality of the dowel-type fasteners specifying a minimum tensile strength or sometime, like is the case of the current version of Eurocode 8, only to maximum values of the dowel-type fastener diameter and of the thickness of the connected timber or wood-based members. Also, the research conducted so far about the ductile behaviour of serially arranged connections was not focused on the post-elastic properties of steel. However, for the seismic design of ductile zones of other materials, such as for example is the case of reinforced concrete walls, post-elastic characteristics of steel are required for the reinforcing bars, in order to achieve the desired dissipative behaviour. Inspired by this fact, timber connections composed of serially arranged dowels made of steel grades with different hardening ratio and elongation at maximum tensile stress were fabricated and tested. The purpose of this work is to understand if the use of steel with significant post-elastic properties may help to solve the problem of limited yielding in serially arranged dowel-type connections. The tested specimens were composed of two symmetrical timber members made of Glulam and LVL connected to two 6 mm thick slotted-in steel plates by means of 9 steel dowels with a diameter of 6.0 mm, which were subjected to monotonic and cyclic tests carried out by implementing dowels made of steel with favourable post-elastic properties. The results showed that the simultaneous yielding of two serially arranged dowelled assemblies is possible, although not fully. Moreover, assuming as reference the steel grade with the lowest post-elastic properties, the connection ductility and strength measured through monotonic and cyclic tests increased by about 30% for the steel grades with the highest hardening ratio and elongation at maximum tensile stress, whereas the displacement at maximum strength was about five times higher. In addition, it was found that confinement of the timber members and shaping of holes were crucial in order to avoid undesired and premature brittle failures and to increase the connection strength and ductility. The results obtained may be useful in order to bring a reassessment of the code requirements regarding the steel properties of ductile connections as well as of certain principles of dimensioning and detailing.
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Influence of Layer and Laminate Characteristics on Shear Properties of Cross Laminated Timber and Hybrids

https://research.thinkwood.com/en/permalink/catalogue1543
Year of Publication
2016
Topic
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
LSL (Laminated Strand Lumber)
OSL (Oriented Strand Lumber)
Application
Floors
Author
Niederwestberg, Jan
Chui, Ying Hei
Gong, Meng
Year of Publication
2016
Country of Publication
Austria
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
LSL (Laminated Strand Lumber)
OSL (Oriented Strand Lumber)
Application
Floors
Topic
Mechanical Properties
Keywords
Shear Tests
Aspect Ratio
Growth Ring Orientation
Edge-Gluing
Static Test
Modal Test
Language
English
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 22-25, 2016, Vienna, Austria p. 1113-1122
Summary
In-plane shear and planar shear due to out-of-plane bending are important properties for the design of CLT-type floor systems. Properties of CLT-type panels are influenced by the orientation of the layer’s major stiffness directions and the properties of their layers. The layers are influenced by their characteristics, laminate aspect ratio, growth ring orientation and edge-gluing. In order to utilize the mechanical potential of CLT-type panels, it is necessary to understand the effects of layer and laminate properties on CLT performance. CLT and CLT-hybrid panels were tested in planar and in-plane shear tests. The shear properties were evaluated using static and modal test procedures, the accuracy of non-destructive test methods was evaluated. Relationships between specimen properties and the characteristics of laminates and layers, such as aspect ratio, growth ring orientation and edge-gluing, were established.
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Influence of Varying Material Properties on the Load-Bearing Capacity of Glued Laminated Timber

https://research.thinkwood.com/en/permalink/catalogue173
Year of Publication
2014
Topic
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Author
Fink, Gerhard
Organization
ETH Zurich
Year of Publication
2014
Country of Publication
Switzerland
Format
Thesis
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Topic
Mechanical Properties
Keywords
Knot Clusters
Non-Destructive
Tensile tests
Load Carrying Capacity
Joints
Model
Language
English
Research Status
Complete
Summary
Glued laminated timber (GLT) is a structural product composed of several layers of timber boards glued together. GLT components have many advantages, such as the larger range of available component dimensions to choose from, the environmental sustainability or the e- cient ratio between weight and load-bearing capacity. Because of that, GLT beams have been established as one of the most important products in timber engineering in the last decades. As a natural grown material, timber properties exhibit higher variability, compared with other building materials. The variability is pronounced not only between dierent structural elements but also within single elements, the latter being highly related to the occurrence of knot clusters. Due to the highly inhomogeneous structure of timber, the prediction of the material properties of GLT beams is aected by large uncertainties. In the presented thesis, the in uence of varying material properties on the load-bearing capacity of GLT beams was investigated. Thus the thesis contributes to develop the quality of GLT beams, in terms of reliability and eciency. Detailed, non-destructive investigations of altogether 400 timber boards were performed. Thereby, dierent strength and stiness related indicators, such as the position and characteristic of knots, or the eigenfrequency, were assessed. Furthermore, non-destructive tensile test were performed to estimate the stiness properties of knot clusters. Out of the investigated timber boards, GLT beams having a precisely-known beam setup were fabricated. As a result, the exact position of each particular timber board (and each particular knot cluster) within the GLT beams was known. Afterwards, bending tests were performed to estimate the load-bearing capacity of these GLT beams. Thereby, the in uence of knot clusters and nger joint connections on the deformation and failure behaviour was investigated. In addition to the experimental investigations, a probabilistic approach for modelling GLT beams (referred to as GLT model ) was developed. Thereby, at rst, timber boards are simulated according to their natural growth characteristics. Afterwards, out of the simulated timber boards, virtual GLT beams are fabricated. Finally, the load-bearing behaviour of these GLT beams is estimated by using a numerical model. To assure the quality of the numerical model, it was validated with the test results. Using the GLT model, the in uence of dierent parameters, such as the position and characteristics of knots, or the quality of nger joint connections, on the load-bearing capacity of GLT beams was investigated. One further goal of this thesis was the investigation of machine-grading indicators, that are measured during the grading process. Therefore, all the investigations presented in this thesis are conducted for indicators measured in laboratory and machine-grading indicators. The same applies for the GLT model, which was also developed for both types of indicators
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10 records – page 1 of 1.