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32 records – page 1 of 4.

Adhesive Bonding of Structural Hardwood Elements

https://research.thinkwood.com/en/permalink/catalogue75
Year of Publication
2015
Topic
Mechanical Properties
Serviceability
Moisture
Material
Glulam (Glue-Laminated Timber)
CLT (Cross-Laminated Timber)
Author
Hassani, Mohammad
Organization
ETH Zurich
Year of Publication
2015
Format
Thesis
Material
Glulam (Glue-Laminated Timber)
CLT (Cross-Laminated Timber)
Topic
Mechanical Properties
Serviceability
Moisture
Keywords
Abaqus
Adhesives
Beech
Bonding
Delamination
Finite Element Model
Fracture
Long-term
Model
Hardwood
Research Status
Complete
Summary
The current research investigated the delamination process of adhesively bonded hardwood (European beech) elements subject to changing climatic conditions. For the study of the long-term fracture mechanical behavior of gluedlaminated components under varying moisture content, the role of moisture development, time- and moisture-dependent responses are absolutely crucial. For this purpose, a 3D orthotropic hygro-elastic, plastic, visco-elastic, mechano-sorptive wood constitutive model with moisture-dependent material constants was presented in this work. Such a comprehensive material model is capable to capture the true historydependent stress states and deformations which are essential to achieve reliable design of timber structures. Besides the solid wood substrates, the adhesive material also influences the interface performance considerably. Hence, to gain further insight into the stresses and deformations generated in the bond-line, a general hygro-elastic, plastic, visco-elastic creep material model for adhesive was introduced as well. The associated numerical algorithms developed on the basis of additive decomposition of the total strain were formulated and implemented within the Abaqus Finite Element (FE) package. Functionality and performance of the proposed approach were evaluated by performing multiple verification simulations of wood components, under different combinations of mechanical loading and moisture variation. Moreover, the generality and efficiency of the presented approach was further demonstrated by conducting an application example of a hybrid wood element.
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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. The goal of the thesis was the development of novel non-destructive testing methodologies capable of imaging the position and geometry of delaminations within the bonding planes of glulam. An ACU system prototype capable of detecting an ultrasound beam transmitted through up to 500mm thick glulam was developed, consisting of off-the-shelf ACU transducers, high-power pulsed excitation electronics and a low-noise amplification chain. A five-axes computerized scanning system and a low-cost micro-electromechanic sensors (MEMS) linear array design allowed ultrasound imaging with fix or independent transmitter and receiver transducer units. The bonding assessment was fundamentally based on the evaluation of the attenuation of the ultrasound beam, which significantly increases when transmitted through a material discontinuity (delamination) with respect to a defect-free glue line.
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Analysis of Hygroscopic Self-Shaping Wood at Large Scale for Curved Mass Timber Structures

https://research.thinkwood.com/en/permalink/catalogue2162
Year of Publication
2019
Topic
Design and Systems
Material
CLT (Cross-Laminated Timber)
Author
Grönquist, Philippe
Wood, Dylan
Hassani, Mohammad
Wittel, Falk
Menges, Achim
Rüggeberg, Markus
Organization
ETH Zurich
University of Stuttgart
Publisher
American Association for the Advancement of Science
Year of Publication
2019
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Topic
Design and Systems
Keywords
Moisture Content
Architecture
Self-Shaping
Research Status
Complete
Series
Science Advances
Summary
The growing timber manufacturing industry faces challenges due to increasing geometric complexity of architectural designs. Complex and structurally efficient curved geometries are nowadays easily designed but still involve intensive manufacturing and excessive machining. We propose an efficient form-giving mechanism for large-scale curved mass timber by using bilayered wood structures capable of self-shaping by moisture content changes. The challenge lies in the requirement of profound material knowledge for analysis and prediction of the deformation in function of setup and boundary conditions. Using time- and moisture-dependent mechanical simulations, we demonstrate the contributions of different wood-specific deformation mechanisms on the self-shaping of large-scale elements. Our results outline how to address problems such as shape prediction, sharp moisture gradients, and natural variability in material parameters in light of an efficient industrial manufacturing.
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An Improved Model for the Fire Design of Cross Laminated Timber in Bending

https://research.thinkwood.com/en/permalink/catalogue1940
Year of Publication
2018
Topic
Fire
Material
CLT (Cross-Laminated Timber)
Author
Schmid, Joachim
Klippel, Michael
Fahrni, Reto
Frangi, Andrea
Tiso, Mattia
Just, Alar
Werther, Norman
Organization
ETH Zurich
Tallinn University of Technical
Technical University Munich
Year of Publication
2018
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Topic
Fire
Keywords
Fire Resistance
Model
Zero-Strength Layer
Cross-Section
Bending
Strength
Stiffness
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 20-23, 2018, Seoul, Republic of Korea
Summary
In this study, new design models for cross-laminated timber (CLT) are developed to verify the fire resistance up to 120 minutes. This is done aiming for the popular Effective Cross-Section Method using a so-called zero-strength layer (ZSL) to account for losses in strength and stiffness. This was done using a method earlier presented at WCTE 2010 and discussed with the European industry. To allow for improvements, (a) the current CLT product portfolio was analysed and thermal and mechanical simulations were done accordingly for initially unprotected and unprotected members. Further, (b) new definitions for the ZSL were used to allow for a higher accuracy of the simplified models. As anoutcome, a model with (1) tabulated data between 7.0 and 12.0 mm for the effective ZSL only considering longitudinal layers and (2) a simplified model “twelve and two” is proposed for CLT members in bending.
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Assessing the Adhesive Performance in CLT Exposed to Fire

https://research.thinkwood.com/en/permalink/catalogue1945
Year of Publication
2018
Topic
Connections
Fire
Material
CLT (Cross-Laminated Timber)
Application
Floors
Walls
Author
Klippel, Michael
Schmid, Joachim
Fahrni, Reto
Frangi, Andrea
Organization
ETH Zurich
Year of Publication
2018
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Application
Floors
Walls
Topic
Connections
Fire
Keywords
Adhesive
Fire Tests
Polyurethane
1C PUR
Melamine Urea Formaldehyde
Conference
World Conference on Timber Engineering
Research Status
Complete
Summary
Cross-laminated timber (CLT) became a popular engineered wood product in recent years for highquality and innovative timber buildings. As for any building product, the fire behaviour of CLT panels requires careful evaluation in the design of such buildings. The adhesive used in the bond lines of CLT plays an important role in the fire design. However, currently, European standards do not provide a test method to assess the adhesive performance in CLT exposed to fire. This paper presents a series of fire tests performed with CLT panels glued with different adhesives. It is shown how the mass loss of the CLT panels in standard fire resistance tests can be used to assess the adhesive performance in CLT exposed to fire.
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Bending Resistance and Deformation Capacity of Fibre Reinforced Glulam Beams

https://research.thinkwood.com/en/permalink/catalogue2208
Year of Publication
2018
Topic
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Application
Beams

Bending Tests on Glued Laminated Timber Beams with Well-Known Material Properties

https://research.thinkwood.com/en/permalink/catalogue186
Year of Publication
2013
Topic
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Author
Fink, Gerhard
Kohler, Jochen
Frangi, Andrea
Organization
ETH Zurich
Year of Publication
2013
Format
Report
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Topic
Mechanical Properties
Keywords
Bending Strength
Failure
Load Bearing Capacity
Four Point Bending Test
Density
Model
Bending Stiffness
Research Status
Complete
Summary
At the Institute of Structural Engineering at the ETH Zurich numerous of investigations are conducted to analyse the load bearing capacity of glued laminated timber beams. The investigations are part of the research project ’Influence of varying material properties on the load bearing capacity of glued laminated timber (glulam)’. The investigations are taking place on 24 glulam beams with well-known material properties. The glulam beams are fabricated out of 400 timber boards. From those boards the material properties are investigated non-destructively within a former research project. During the glulam fabrication it is particularly focused to keep the information of the timber boards; i.e. after the glulam fabrication the position of each particular timber board within the glulam beam and thus the position of each particular knot is still known. The glulam beams are investigated during a 4-point bending test. On the glulam members the load bearing capacity, the bending stiffness and the density is measured. Furthermore local strains within the glulam beams are investigated using an optical coordinate-measurement device. Following the test the failure is investigated in detail. Hereby the type of failure (knot cluster, finger joint, clear wood) and the amount of failure (number of damaged lamellas) is documented. Afterwards the failed glulam beams are loaded again to analyse the remaining bending strength and the corresponding remaining bending stiffness. The major aim of the experimental analysis is the investigation of the load bearing capacity of glulam beams with well-known local material properties. The gained results can be used for an investigation of the influence of local weak zones, such as knot clusters or finger joints, on the load bearing capacity of glulam. In addition a data basis is produced to develop a new model (or to evaluate existing models) for the estimation of the load bearing capacity of glulam.
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Bending Tests with Glulam Columns under Eccentric Normal Force Stress

https://research.thinkwood.com/en/permalink/catalogue1138
Year of Publication
2015
Topic
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Author
Frangi, Andrea
Theiler, Matthias
Organization
ETH Zurich
Year of Publication
2015
Format
Thesis
Material
Glulam (Glue-Laminated Timber)
Topic
Mechanical Properties
Keywords
Load Bearing Capacity
Axial Compression
Buckling Tests
Spruce
Research Status
Complete
Summary
The force-displacement behaviour of structural timber members subjected to axial compression or combined axial compression and bending is distinctively non-linear. This behaviour is caused by the non-linear increase of the deformation due to the increasing eccentricity of the axial load as well as by the non-linear material behaviour of timber when subjected to compression. The present report describes experimental investigations on glued laminated timber members subjected to eccentric compression. The aim of these experimental investigations was to create a data base, which can be used to validate theoretical calculation models and to assess the accurateness of the design approaches given in the design codes for timber structures. The specimens for the main bunch of experiments were produced using lamellas made of Norway spruce grown in Switzerland. For this purpose, a total of 336 lamellas were available. In the first step, non-destructive tests on the lamellas were performed. These tests aimed at the collection of data in order to characterise the raw material. In the second step, the lamellas were strength graded. The aim of the grading process was to select two classes of lamellas for the production of the test specimens. The lamellas were selected so that they were suitable to produce glued laminated timber of strength classes GL24h and GL32h. Within the grading process, visual grading criteria as well as machine grading criteria were used. In the third step, the graded lamellas were used to produce glued laminated timber members. Five tests series were produced. Each of the test series consisted of ten specimens. Three series were made of glued laminated timber GL24h and two series were made of glued laminated timber GL32h. The length of the timber members was varied between the different test series. The lengths were L = 1’400 mm, L = 2’300 mm and L = 3’200 mm respectively. During the production, the setup of the test specimens was recorded. Hence, the position and the orientation of every lamella within the test specimen were documented. Additionally, some non-destructive tests were performed using the test specimens. In the last step, the glued laminated timber members were subjected to buckling tests. The test specimens were loaded with an eccentric compression force up to failure. During the tests, different measurements were carried out in order to document the experimental investigations as accurate as possible. Amongst others, the applied loads as well as horizontal and vertical deformations were recorded. For a subsample of 20 test specimens, additional local deformation measurements were performed using an optical measurement device.
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Correct Temperature Measurements in Fire Exposed Wood

https://research.thinkwood.com/en/permalink/catalogue2025
Year of Publication
2018
Topic
Fire
Material
CLT (Cross-Laminated Timber)
Author
Fahrni, Reto
Schmid, Joachim
Klippel, Michael
Frangi, Andrea
Organization
ETH Zurich
Year of Publication
2018
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Topic
Fire
Keywords
Temperature
Thermocouples
Charring
Conference
World Conference on Timber Engineering
Research Status
Complete
Summary
The performance of timber in fire is often assessed by measuring the temperature at different positions in the specimen. As timber is a low conductive material, it can be difficult to measure the correct temperature.Therefore, this paper shows how to correctly measure the temperature in timber members and how to describe temperature measurements of fire tests and experiments non-ambiguously.Typical temperature measurement setups used in tests and experiments were experimentally assessed under ISO/EN fire exposure and a constant incident radiant heat flux. By comparing the charring depth and the thermocouple readings(charring temperature 300°C) it was found that only the wire thermocouples inlaid parallel to the isotherms deliver correct temperature readings. For other temperature measurement setups, the underestimation was between 5 and 20 minutes.Due to the numerous factors influencing the measurement error, no correction factor could be defined.
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Experimental analysis of cross-laminated timber rib panels at normal temperature and in fire

https://research.thinkwood.com/en/permalink/catalogue2933
Year of Publication
2021
Topic
Fire
Material
CLT (Cross-Laminated Timber)
Glulam (Glue-Laminated Timber)
Application
Floors
Author
Kleinhenz, Miriam
Just, Alar
Frangi, Andrea
Organization
ETH Zurich
Tallinn University of Technology
Publisher
Elsevier
Year of Publication
2021
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Glulam (Glue-Laminated Timber)
Application
Floors
Topic
Fire
Keywords
Timber Composite Structures
Massive Timber Rib Panel
Fire Resistance
ISO Fire Exposure
Glue Line Quality
Effective Width
Research Status
Complete
Series
Engineering Structures
Summary
The results of an experimental programme on the structural behaviour, fire behaviour, and fire resistance of CLT rib panels are presented. The floor system consists of cross-laminated timber (CLT) plates rigidly bonded to glued-laminated timber ribs by means of screw-press gluing. The experimental programme comprised ultimate-load tests at normal temperature as reference tests and full-scale fire resistance tests on four cross-sections. In addition to the reference tests, shear tests of the glue line between CLT plate and glued-laminated timber rib were performed for analysis of the cross-sections’ composite action. The results of the reference tests show good agreement with results based on the simplified method according to EN 1995-1-1 [1] and its final draft of CLT design [2]. The importance of the glue line’s quality was confirmed. The fire resistance tests show results on the safe side compared to predictions of the fire behaviour according to EN 1995-1-2 [3] and its actual draft [4]. However, the fire resistance was underestimated due to conservative assumptions about the composite cross-section’s structural behaviour. The experimental programme addressed the fire behaviour and fire resistance of CLT rib panels currently not covered in standards. The project’s overall aim is the development of design rules in fire for EN 1995-1-2.
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32 records – page 1 of 4.