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Influence of Moisture Content and Gaps on the Withdrawal Resistance of Self Tapping Screws in CLT

https://research.thinkwood.com/en/permalink/catalogue299
Year of Publication
2014
Topic
Connections
Mechanical Properties
Moisture
Material
CLT (Cross-Laminated Timber)
Author
Silva, Catarina
Ringhofer, Andreas
Branco, Jorge
Lourenço, Paulo
Schickhofer, Gerhard
Organization
National Congress of Experimental Mechanics
Year of Publication
2014
Country of Publication
Portugal
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Topic
Connections
Mechanical Properties
Moisture
Keywords
Self-Tapping Screws
Withdrawal
Gaps
Moisture Content
Language
English
Conference
9th National Congress of Experimental Mechanics
Research Status
Complete
Notes
October 15-17, 2014, Aveiro, Portugal
Summary
Self-tapping screws (STS) have been proclaimed as the easiest solution for structural timber connections, in special for cross laminated timber (CLT) constructions. In order to understand deeply the composite model “CLT-STS”, an experimental campaign which comprised 270 withdrawal tests was carried out. Maximum withdrawal load capacity of self-tapping screws inserted in plane side of a three layered CLT panel was evaluated considering three main parameters: moisture levels of CLT (i), number of gaps (ii) and the width of gaps (iii). Regarding (i), connections were tested with CLT at 8%, 12% and 18% of moisture content. Concerning (ii) and (iii), different test configurations with 1, 2 and 3 gaps, with 0 or 4mm, were tested. The influences of moisture content and number of gaps were modeled. Further a correlation between test results and a prediction model developed by Uibel and Blaß (2007) has been proposed.
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The Influences of Moisture Content Variation, Number and Width of Gaps on the Withdrawal Resistance of Self Tapping Screws inserted in Cross Laminated Timber

https://research.thinkwood.com/en/permalink/catalogue1359
Year of Publication
2016
Topic
Connections
Moisture
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Author
Silva, Catarina
Branco, Jorge
Ringhofer, Andreas
Lourenço, Paulo
Schickhofer, Gerhard
Publisher
ScienceDirect
Year of Publication
2016
Country of Publication
Netherlands
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Topic
Connections
Moisture
Mechanical Properties
Keywords
Withdrawal Tests
Withdrawal Resistance
Self-Tapping Screws
Moisture Content
Gaps
Language
English
Research Status
Complete
Series
Construction and Building Materials
Summary
A large experimental campaign comprised of 470 withdrawal tests was carried out, aiming to quantify the withdrawal resistance of self-tapping screws (STS) inserted in the side face of cross laminated timber (CLT) elements. In order to deeply understand the “CLT-STS” composite model, the experimental tests considered two main parameters: (i) simple and cyclic changes on moisture content (MC) and (ii) number and width of gaps. Regarding (i), three individual groups of test specimens were stabilized with 8%, 12% and 18% of moisture content and one group was submitted to a six month RH cycle (between 30% and 90% RH). Concerning (ii), different test configurations with 0 (REF), 1, 2 and 3 gaps, and widths equal to 0mm (GAP0) or 4mm (GAP4), were tested. The influences of MC and number of gaps were modeled by means of least square method. Moreover, a revision of a prediction model developed by Uibel and Blaß (2007) was proposed. The main findings of the experimental campaign were: the decrease of withdrawal resistance for specimens tested with MC=18% in most configurations; the unexpected increase of withdrawal resistance as the number of gaps with 0mm increased; and, the surprising increase of withdrawal resistance for REF specimens submitted to the RH cycle.
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Finite Element Modelling of Moisture Related and Visco-Elastic Deformations in Inhomogeneous Timber Beams

https://research.thinkwood.com/en/permalink/catalogue425
Year of Publication
2013
Topic
Mechanical Properties
Moisture
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Author
Ormarsson, Sigurdur
Dahlblom, Ola
Publisher
ScienceDirect
Year of Publication
2013
Country of Publication
Netherlands
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Topic
Mechanical Properties
Moisture
Keywords
Inhomogeneous
Finite Element Model
Axial Deformation
Lateral Deformation
Shrinkage
Mechanosorption
Visco-Elastic
Language
English
Research Status
Complete
Series
Engineering Structures
Summary
Wood is a hygro-mechanical, non-isotropic and inhomogeneous material concerning both modulus of elasticity (MOE) and shrinkage properties. In stress calculations associated with ordinary timber design, these matters are often not dealt with properly. The main reason for this is that stress distributions in inhomogeneous glued laminated members (glulams) and in composite beams exposed to combined mechanical action and variable climate conditions are extremely difficult to predict by hand. Several experimental studies of Norway spruce have shown that the longitudinal modulus of elasticity and the longitudinal shrinkage coefficient vary considerably from pith to bark. The question is how much these variations affect the stress distribution in wooden structures exposed to variable moisture climate. The paper presents a finite element implementation of a beam element with the aim of studying how wooden composites behave during both mechanical and environmental load action. The beam element is exposed to both axial and lateral deformation. The material model employed concerns the elastic, shrinkage, mechano-sorption and visco-elastic behaviour of the wood material. It is used here to simulate the behaviour of several simplysupported and continuous composite beams subjected to both mechanical and environmental loading to illustrate the advantages this can provide. The results indicate clearly both the inhomogeneity of the material and the variable moisture action occurring to have had a significant effect on the stress distribution within the cross-section of the products that were studied.
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Elastic Properties of Thermo-Hydro-Mechanically Modified Bamboo (Guadua Angustifolia Kunth) Measured in Tension

https://research.thinkwood.com/en/permalink/catalogue164
Year of Publication
2014
Topic
Mechanical Properties
Moisture
Material
Other Materials
Author
Archila-Santos, Hector
Ansell, Martin
Walker, Pete
Publisher
Scientific.net
Year of Publication
2014
Country of Publication
Switzerland
Format
Journal Article
Material
Other Materials
Topic
Mechanical Properties
Moisture
Keywords
Bamboo
Modulus of Elasticity
Thermo-hydro-mechanical (THM) treatments
Poissons Ratio
Dimensional Stability
Language
English
Research Status
Complete
Series
Key Engineering Materials
Notes
DOI:10.4028/www.scientific.net/KEM.600.111
Summary
Guadua angustifolia Kunth (Guadua) was subjected to thermo-hydro-mechanical (THM) treatments that modified its microstructure and mechanical properties. THM treatment was applied to Guadua with the aim of tackling the difficulties in the fabrication of standardised construction materials and to gain a uniform fibre density profile that facilitates prediction of mechanical properties for structural design. Dry and water saturated Guadua samples were subjected to THM treatment. A densified homogenous flat sheet material was obtained. Mechanical properties of small clear specimens of THM modified Guadua were evaluated by testing in tension and compared to the results of the same test on a control specimen. Samples were tested in the elastic range to determine values for Modulus of Elasticity (MOE) and Poisson’s ratio. There was a significant increase in the tensile MOE values (parallel to the direction of the fibres) for densified samples. MOE values measured were 16.21 GPa, 22.80 GPa and 31.04 GPa for control, densified dry and densified water saturated samples respectively. Oven dry densities for these samples were 0.54 g/cm3, 0.81 g/cm3 and 0.83 g/cm3. Despite a 50 % reduction in the radial Poisson’s ratio for the water saturated sample, no further variation in the Poisson’s ratio as a result of densification was observed for control and densified dry samples. This paper presents the results of the first phase of a study focussed on the manufacturing of flat Guadua sheet (FGS) by THM treatment and the characterization of its mechanical properties. The achievement of a dimensionally stable FGS by THM modification, with a uniform density and achieved with reduced labour effort during manufacture, will be of key importance for the development of structural applications, and could have a significant impact in the bamboo industry. The final aim of the research at the University of Bath is the development of Cross Laminated Guadua (CLG) panels using THM modified and laminated FGS glued with a high performance resin.
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Checking in CLT Panels: An Exploratory Study

https://research.thinkwood.com/en/permalink/catalogue2625
Year of Publication
2011
Topic
Moisture
Material
CLT (Cross-Laminated Timber)
Author
Casilla, Romulo
Lum, Conroy
Pirvu, Ciprian
Wang, Brad
Organization
FPInnovations
Year of Publication
2011
Country of Publication
Canada
Format
Report
Material
CLT (Cross-Laminated Timber)
Topic
Moisture
Keywords
Panels
Testing Methods
Surface Checks
Moisture Content
Gaps
Language
English
Research Status
Complete
Summary
A study was conducted with the primary objective of gathering information for the development of a protocol for evaluating the surface quality of cross-laminated timber (CLT) products. The secondary objectives were to examine the effect of moisture content (MC) reduction on the development of surface checks and gaps, and find ways of minimizing the checking problems in CLT panels. The wood materials used for the CLT samples were rough-sawn Select grade Hem-Fir boards 25 x 152 mm (1 x 6 inches). Polyurethane was the adhesive used. The development of checks and gaps were evaluated after drying at two temperature levels at ambient relative humidity (RH). The checks and gaps, as a result of drying to 6% to 10% MC from an initial MC of 13%, occurred randomly depending upon the characteristics of the wood and the manner in which the outer laminas were laid up in the panel. Suggestions are made for minimizing checking and gap problems in CLT panels. The checks and gaps close when the panels are exposed to higher humidity. Guidelines were proposed for the development of a protocol for classifying CLT panels into appearance grades in terms of the severity of checks and gaps. The grades can be based on the estimated dimensions of the checks and gaps, their frequency, and the number of laminas in which they appear.
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Durable Solutions for Balconies and Decks in Midrise Buildings

https://research.thinkwood.com/en/permalink/catalogue2536
Topic
Design and Systems
Moisture
Material
Light Frame (Lumber+Panels)
Application
Balconies
Organization
Forest Products Laboratory
Home Innovation Research Labs
Country of Publication
United States
Material
Light Frame (Lumber+Panels)
Application
Balconies
Topic
Design and Systems
Moisture
Research Status
In Progress
Notes
Project contacts are John B. Peavey at Home Innovation Research Labs and Xiping Wang at the Forest Products Laboratory
Summary
The proposed study will evaluate the moisture performance of balconies and decks in midrise multifamily and mixed-use wood-frame buildings with various types of exterior cladding materials. The study will culminate in recommended best practices for balcony and deck construction in midrise wood-frame buildings, with the focus on water management and integration with the primary building enclosure systems. A broad range of finishes and balcony configurations will be evaluated for applications across various construction markets and climatic conditions. The outcome will include a set of specific details and solutions for durable wood-frame deck and balconies with focus on the interface with the exterior wall systems.
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Impact of Air-Gap Design to Hygro-thermal Properties and Mould Growth Risk Between Concrete Foundation and CLT Frame

https://research.thinkwood.com/en/permalink/catalogue1327
Year of Publication
2017
Topic
Serviceability
Moisture
Material
CLT (Cross-Laminated Timber)
Application
Hybrid Building Systems
Author
Fedorik, Filip
Haapala, Antti
Publisher
ScienceDirect
Year of Publication
2017
Country of Publication
Netherlands
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Application
Hybrid Building Systems
Topic
Serviceability
Moisture
Keywords
Hygrothermal
Mould
Concrete
Multi-Storey
Moisture Content
Airflow
Language
English
Research Status
Complete
Series
Energy Procedia
Summary
The presented work deals with hygro-thermal numerical simulation and mould growth risk evaluation between concrete foundation and frame of multi-story building made of CLT element modules. Structural CLT modules represent an approach towards wood material utilization in construction as its strength achieves markedly higher values then common structural wooden elements and makes rapid erection of the building possible. Although there are great promises that the novel CLT structures will gain ground in high-rise buildings market with apparent benefits in sustainability and inhabitant comments regarding ambience and acoustics, it is important to analyse their structural health and hygro-thermal conditions. The highest risk of unfavourable hygro-thermal conditions is usually presented in location characterized by thermal bridge, such as foundation, window-wall, wall-roof and wall-floor junctions. It is also of significant importance to analyse junctions between materials, whether wood, composite, mortar or concrete. A certain combination of thermal and humidity conditions in exposed time causes mould growth initiation that may lead to deterioration of structural material and unhealthy indoor environment. In this case study, the moisture content and air-flow in the junction and open space in structural design details between the first floor (of concrete) housing joint warehouse and technical spaces and the residential upper floors made of CLT modules is analysed. Conditions leading to probable moisture-derived mould issues and design parameters leading to sufficient ventilation according to Mould Index modelling are presented.
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Effect of Cold Temperatures on the Shear Behavior of Glued Laminated Beams

https://research.thinkwood.com/en/permalink/catalogue100
Year of Publication
2015
Topic
Mechanical Properties
Moisture
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Author
Drake, Garrett
Berry, Michael
Schroeder, David
Publisher
ScienceDirect
Year of Publication
2015
Country of Publication
Netherlands
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Topic
Mechanical Properties
Moisture
Keywords
Moisture Content
Shear Behaviour
Temperature
Four Point Bending Test
Failure Mechanisms
Language
English
Research Status
Complete
Series
Cold Regions Science and Technology
Summary
This study evaluated the effects of subfreezing temperatures and moisture content on the shear behavior of glulam beams. Full-scale glulam beams (79 mm by 229 mm deep) at two moisture contents (12 and 28%) and three temperatures (20 °C, 0 °C, and - 40 °C) were tested in four-point bending until failure. Temperature was observed to affect the failure mechanism of the beams, with the beams tested at 0 °C and 20 °C failing in shear and the beams tested at - 40 °C failing in tension. Further, the strengths of the beams and their stiffnesses were observed to increase with decreasing temperature, with these effects being more pronounced in the higher moisture content beams. Over the temperature range of 20 °C to - 40 °C, the 12 percent moisture content beams observed strength and stiffness gains of 17 and 22%, while the 28 percent moisture content beams observed respective gains of 37% and 66%.
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Creep Behavior of Laminated Veneer Lumber from Poplar Under Cyclic Humidity Changes

https://research.thinkwood.com/en/permalink/catalogue2480
Year of Publication
2019
Topic
Mechanical Properties
Moisture
Material
LVL (Laminated Veneer Lumber)
Author
Li, Chao
Huang, Yuxiang
Publisher
North Carolina State University
Year of Publication
2019
Country of Publication
United States
Format
Journal Article
Material
LVL (Laminated Veneer Lumber)
Topic
Mechanical Properties
Moisture
Keywords
Mechanosorption Creep
Humidity
Four Point Bending Test
Adsorption
Language
English
Research Status
Complete
Series
BioResources
ISSN
1930-2126
Online Access
Free
Resource Link
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Moisture Uptake Testing for CLT Floor Panels in a Tall Wood Building in Vancouver

https://research.thinkwood.com/en/permalink/catalogue2343
Year of Publication
2017
Topic
Moisture
Material
CLT (Cross-Laminated Timber)
Application
Floors
Author
Lepage, Robert
Higgins, James
Finch, Graham
Year of Publication
2017
Country of Publication
Canada
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Application
Floors
Topic
Moisture
Keywords
Water Resistance
Coatings
Hygrothermal Models
Moisture Content
Sensors
Biodegradation
Funghi
Language
English
Conference
Canadian Conference on Building Science and Technology
Research Status
Complete
Summary
Cross laminated timber (CLT) and mass timber construction is a promising structural technology that harnesses the advantageous structural properties of wood combined with renewability and carbon sequestering capacities not readily found in other major structural materials. However, as an organic material, mass timber is susceptible to biodeterioration, and when considered in conjunction with increased use of engineered wood materials, particularly in more extreme environments and exposures, it requires careful assessments to ensure long-term performance. A promising approach towards reducing construction moisture in CLT and other mass timber assemblies is to protect the surfaces with a water-resistant coating. To assess this approach, a calibrated hygrothermal model was developed with small and large scale CLT samples, instrumented with moisture content sensors at different depths, and treated with different types of water resistant coatings exposed to the Vancouver climate. The models were further validated with additional moisture content sensors installed in a mock-up floor structure of an actual CLT building under construction. Biodeterioration studies assessing fungal colonization were undertaken using the modified VTT growth method and a Dose-Response model for decay potential. The research indicates that CLT and mass timber is susceptible to dangerously high moisture contents, particularly when exposed to liquid water in horizontal applications. However, a non-porous, vapour impermeable coating, when applied on dry CLT, appears to significantly reduce the moisture load and effectively eliminate the risk of biodeterioration. This work strongly suggests that future use of CLT consider applications of a protective water-resistant coating at the manufacturing plant to resist construction moisture. The fungal study also highlights the need for a limit state design for biodeterioration to countenance variance between predicted and observed conditions.
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10 records – page 1 of 1.