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Preliminary Assessment of Hygrothermal Performance of Cross-Laminated Timber Wall Assemblies Using Hygrothermal Models

https://research.thinkwood.com/en/permalink/catalogue2628
Year of Publication
2010
Topic
Moisture
Design and Systems
Serviceability
Material
CLT (Cross-Laminated Timber)
Light Frame (Lumber+Panels)
Application
Walls
Author
Wang, J.
Baldracchi, P.
Organization
FPInnovations
Year of Publication
2010
Format
Report
Material
CLT (Cross-Laminated Timber)
Light Frame (Lumber+Panels)
Application
Walls
Topic
Moisture
Design and Systems
Serviceability
Keywords
Hygrothermal
Moisture Performance
Rainscreen
Research Status
Complete
Summary
Preliminary simulation was carried out using hygIRC and WUFI, both 1-D hygrothermal models, to analyze moisture performance of rainscreened wood-frame walls and cross-laminated timber (CLT) walls for the climates in Vancouver and Calgary. The major results are as follows. In order to provide baseline knowledge, preliminary comparisons between hygIRC and WUFI were conducted to investigate the effects of climate data, wall orientations and rain intrusion on the performance of the rainscreened wood-frame walls based on Vancouver’s climate. hygIRC tended to produce almost constant moisture content (MC) of the plywood sheathing throughout a year but WUFI showed greater variations, particularly when the ventilation of the rainscreen cavity was neglected. Rainscreen cavity ventilation provided dramatic drying potentials for wall assemblies based on the WUFI simulation. hygIRC indicated that east-facing walls had the highest moisture load, but the differences between orientations seemed negligible in WUFI when the rainscreen cavity ventilation was taken into account. When 1% of wind-driven rain was simulated as an additional moisture load, hygIRC suggested that the rainscreen walls could not dry out in Vancouver, WUFI, however, indicated that they could dry to a safe MC level in the summer. The discrepancies in material property data between the two models and between different databases in WUFI (even for the same wood species) were found to be very large. In terms of wood sorption data, large differences existed at near-saturated RH levels. This is a result of using pressure-plate/membrane methods for measuring material equilibrium moisture content (EMC) under high RH conditions. The EMC of wood at near-100% RH conditions measured with these methods can be higher than 200%, suggesting wood in construction would decay without liquid water intrusion or severe vapour condensation. The pressure-plate/membrane methods also appeared to be highly species-dependent, and have higher EMC at a certain RH level for less permeable species, from which it is relatively difficult to remove water during the measurement. The hygrothermal simulation in this work suggested that such a species bias caused by testing methods could put impermeable species (most Canadian species) at a disadvantage to permeable species like southern pine during related durability design of building assemblies. In terms of using CLT for construction in Vancouver and Calgary, the WUFI simulations suggested that the use of less permeable materials such as EPS (expanded polystyrene insulation), XPS (extruded polystyrene insulation), self-adhered bituminous membrane and polyethylene in wall assemblies reduced the ability of the walls to dry. On the other hand, permeable assemblies such as those using relatively permeable insulation like semi-rigid mineral wool (rock wool) as exterior insulation, instead of less permeable exterior insulation materials, would help walls dry. The simulation also suggested that using CLT products with initially low MC would significantly reduce moisture-related risks, which indicated the importance of protecting CLT and avoiding wetting during transportation and construction. In addition, the simulation found that indoor relative humidity (RH) conditions generated by the indoor RH prediction models included in hygIRC and WUFI varied greatly under the same basic climate and building conditions. The intermediate method specified in ASHRAE Standard 160 P resulted in long periods of saturated RH conditions throughout a year for the Vancouver climate, which may not be representative of ordinary residential buildings in Vancouver. The simulation in this study is preliminary and exploratory. It would be arbitrary to recommend one model over the other based on this report or use the simulation results directly for CLT wall assembly design without consultation with building science specialists. However, this work revealed more opportunities for close collaborations between the wood science and the building science communities. More work should be carried out to develop appropriate testing methods and assemble material property data for hygrothermal simulation of wood-based building assemblies. Model improvement and field verification are also strongly recommended, particularly for new building systems such as CLT constructions.
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Moisture Response of Wall Assemblies of Cross-Laminated Timber Construction in Cold Canadian Climates

https://research.thinkwood.com/en/permalink/catalogue143
Year of Publication
2012
Topic
Serviceability
Moisture
Material
CLT (Cross-Laminated Timber)
Application
Walls
Author
Lepage, Robert
Organization
University of Waterloo
Year of Publication
2012
Format
Thesis
Material
CLT (Cross-Laminated Timber)
Application
Walls
Topic
Serviceability
Moisture
Keywords
Canada
Climate
Decay
Durability
Hem-Fir
Hygrothermal
Mold
Relative Humidity
Rot
Simulation
SPF
Water Vapour Permeability
Research Status
Complete
Summary
Wood is a highly versatile renewable material (with carbon sequestering properties), that is light in weight, has good strength properties in both tension and compression while providing good rigidity and toughness, and good insulating properties (relative to typical structural materials). Engineered wood products combine the benefits of wood with engineering knowledge to create optimized structural elements. Cross-laminated timber (CLT), as one such engineered wood product, is an emerging engineering material which provides great opportunities for the building industry. While building with wood has many benefits, there are also some concerns, particularly decay. Should wood be exposed to elevated amounts of moisture, rots and moulds may damage the product or even risk the health of the occupants. As CLT panels are a relatively new engineered wood product, the moisture characteristics have yet to be properly assessed.
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Damage Problems in Glued Laminated Timber

https://research.thinkwood.com/en/permalink/catalogue165
Year of Publication
2012
Topic
Serviceability
Material
Glulam (Glue-Laminated Timber)
Author
Vanya, Csilla
Year of Publication
2012
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
Topic
Serviceability
Keywords
Construction
Damage
Delamination
Loads
Manufacturing
Service Life
Stress
Tension
Research Status
Complete
Series
Drewno
Summary
On a number of occasions glued laminated timber breaks apart before the end of their service life. Examples in Germany (Frese M., Blaß H. J. [2011]) and Denmark (Hansson, Larsen [2005] ) show that this problem is real. In order to find the causes of the problem, extensive tests were conducted: 16 buildings with glued laminated timber were examined on the spot, calculations and laboratory work were carried out. These examinations told us that not only did the properties of the wooden material cause the damage, but the problems were also due to the wood used and the method of construction. In the calculations, the external load and residual stresses occurring in the glued laminated timber were included. Residual tensions in this timber were generated by climatic stresses and also due to the method of construction. These stresses also accumulated along with the stresses of the external load. Laboratory work was carried out to measure the delamination. We examined whether these analyses and calculations prove or disprove the results of the on- the- spot examinations.
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Development of Steel-Wood Hybrid Systems for Buildings Under Dynamic Loads

https://research.thinkwood.com/en/permalink/catalogue845
Year of Publication
2012
Topic
Seismic
Design and Systems
Serviceability
Application
Hybrid Building Systems
Author
Stiemer, Siegfried
Tesfamariam, Solomon
Karacabeyli, Erol
Popovski, Marjan
Year of Publication
2012
Format
Conference Paper
Application
Hybrid Building Systems
Topic
Seismic
Design and Systems
Serviceability
Keywords
Dynamic Loads
Timber-Steel Hybrid
Strength
Conference
International Specialty Conference on Behaviour of Steel Structures in Seismic Areas
Research Status
Complete
Notes
January 9-11, 2012, Santiago, Chile
Summary
A steel-wood hybrid system furnishes not only aesthetically pleasing and sustainable hybrid structures but is superior in seismic applications due to the light weight, high resistance, and adjustable ductility. Such hybrid structural systems are not covered by any material and structural design standards that hinder the general implementation. For light structures, a builder’s guide to hybrid wood and steel connection details already exists in North America. Despite the obvious advantages, however, today’s applications of steel-wood hybrid structures have been limited. Rare hybrid buildings with a concentrically braced frame used for lateral load resistance with a glulam timber floor slab have been built as prototypes. The use of glulam floor slab led to a substantially reduced self-weight, compared with the reinforced concrete slab option. The lighter structure behaves superior in seismic events and has made wind loads the governing design case. The next generation steel-wood hybrid structures should optimally utilize each material. This paper describes a research program of the next generation wood-steel hybrid structures should optimally utilize each material. In detail the following development issues will be addressed: innovative hybrid steel-wood building systems, technical tools to predict structural responses of hybrid systems, design principles underpinning the definition of key code provisions related to strength and serviceability performance of hybrid buildings. It will be highlighted that potential structural problems at the design stage result from material incompatibilities. The constitutive properties of each material, hybrid-material, and joint properties reported in the literature will be used, or supplemented by findings from experimental work.
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Investigations on the Serviceability Limit State of Dowel-Type Timber Connections

https://research.thinkwood.com/en/permalink/catalogue911
Year of Publication
2012
Topic
Serviceability
Connections
Author
Dorn, Micheal
Organization
Vienna University of Technology
Year of Publication
2012
Format
Thesis
Topic
Serviceability
Connections
Keywords
dowel-type connection
Steel-to-Timber
Failure Modes
Ductility
Eurocode 5
Strength
Stiffness
contact behavior
finite element method
Research Status
Complete
Summary
The aim of this thesis is to study the load-carrying behaviour of dowel-type steel-to-timber connections in detail. This is achieved by performing experimental tests on single-dowel connections. A large variety of influencing parameters is assessed, which include wood density, connection width, the dowel roughness, and the application of reinforcements in order to prevent brittle behaviour. Separate stages in the loading history are identified, starting from an initial consolidation phase, the region of maximum stiffness during load increase, and the point of maximum connection strength. The results of the experiments are compared to the design practice in Eurocode 5 for strength and stiffness estimation. Strength prediction is conservative except for slender connections, while stiffness prediction complied with experimental results only for connections of intermediate width.
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Assessment of Structural Performance of Accoya® Wood for Glulam Fabrication

https://research.thinkwood.com/en/permalink/catalogue1199
Year of Publication
2012
Topic
Mechanical Properties
Serviceability
Material
Glulam (Glue-Laminated Timber)
Author
Crawford, David
Hairstans, Robert
Alexander, John
Bongers, Ferry
Year of Publication
2012
Format
Conference Paper
Material
Glulam (Glue-Laminated Timber)
Topic
Mechanical Properties
Serviceability
Keywords
Durability
Long-term Performance
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
July 15-19, 2012, Auckland, New Zealand
Summary
Accoya® GluLam beams were specified for use as an external foundation support detail for an innovative low carbon affordable home in the Scottish Highlands. This detail was identified in collaboration with Neil Sutherland Architects (NSA) LLP where the use of Accoya® GluLam would result in enhanced performance in exposed conditions. The Accoya® GluLam provides support to the superstructure formed from offsite fabricated closed panels therefore reduced movement over time due to moisture fluctuations was identified as a key design consideration in order to ensure serviceability criteria are met. Due to the nature of Accoya® (acetylated timber) a test programme was developed to determine its mechanical properties for specification as a structural component both in isolation and in combination. In order to assess the long term performance of acetylated GluLam a number of beams are currently being monitored using in-situ monitoring equipment over a minimum period of 12 months.
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Free
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Factors Affecting Distribution of Borate to Protect Building Envelope Components from Biodegradation

https://research.thinkwood.com/en/permalink/catalogue1586
Year of Publication
2012
Topic
Moisture
Serviceability
Material
CLT (Cross-Laminated Timber)
Application
Wood Building Systems
Author
Saadat, Nazmus
Cooper, Paul
Organization
University of Toronto
Year of Publication
2012
Format
Thesis
Material
CLT (Cross-Laminated Timber)
Application
Wood Building Systems
Topic
Moisture
Serviceability
Keywords
Preservatives
Borate
Building Envelope
Moisture Content
Spruce
Douglas-Fir
Research Status
Complete
Summary
Borate can be a potential candidate to protect building envelope components from biodegradation as it has low toxicity and can penetrate wood without pressure treatment, even in the refractory species commonly used in construction industries as structural components. In this research, wood moisture content, grain direction, formulation and species that affect the diffusion of borate in refractory species were investigated. Two highly concentrated formulations were applied and a novel approach (borate bandage) was used to keep the preservative on the surface and enhance the diffusion by reducing surface drying. From ANOVA test for different diffusion periods and depths of penetration, it was found that grain directions and moisture content are significant factors. A mould test was performed, the diffusion co-efficients were calculated and some recommendations were made about the quantity required to protect a specific volume of wood considering the distance moved by diffusion and volume treated in different directions.
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Long Term Monitoring of Timber Bridges - Assessment and Results

https://research.thinkwood.com/en/permalink/catalogue2124
Year of Publication
2013
Topic
Moisture
Serviceability
Application
Bridges and Spans
Author
Franke, Bettina
Franke, Steffen
Müller, Andreas
Vogel, Mareike
Scharmacher, Florian
Tannert, Thomas
Publisher
Scientific Net
Year of Publication
2013
Format
Journal Article
Application
Bridges and Spans
Topic
Moisture
Serviceability
Keywords
Monitoring
Bridge
Moisture Content
Climate
Research Status
Complete
Series
Advanced Materials Research
Summary
Timber bridges have been built for decades all around the world. The hygroscopic material behavior of wood leads to the change of the moisture content of the wood and the dimensions depending on the climate. Therefore in regular inspections following questions arise: what happens with the wood due to the climate changes? Are there major changes of the moisture content? Are there differences between the natural material axes or within the cross section of the structural members? To answer these questions, traffic timber bridges with big cross sections are long-term monitored within a research project. The results of the moisture contents measured and a comparison between the different measuring groups and positions are presented. The analyses confirm that the moisture content in the wood follows the climate changes delayed and with smaller amplitude against the calculated equilibrium moisture content. In first steps, a different behavior of the change of the moisture content could be determined over the cross-section and along the span of the member.
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Field Performance of Timber Bridges: A National Study

https://research.thinkwood.com/en/permalink/catalogue2127
Year of Publication
2013
Topic
Design and Systems
Serviceability
Application
Bridges and Spans
Author
Brashaw, Brian
Wacker, James
Jalinoos, Frank
Year of Publication
2013
Format
Conference Paper
Application
Bridges and Spans
Topic
Design and Systems
Serviceability
Keywords
Timber Construction
Inspection
Non-Destructive Evaluation
Service Life
Conference
International Conference on Timber Bridges
Research Status
Complete
Summary
As many engineers begin to implement life cycle cost analyses within the preliminary bridge design phase, there is a significant need for more reliable data on the expected service life of highway bridges. Many claims are being made about the expected longevity of concrete and steel bridges being 75 years or more, but few are based on actual performance data. Because engineers are least familiar with timber bridges, their expected longevity is often unfairly estimated at 20 years. A national scale project has been developed for the United States, headed by the USDA Forest Products Laboratory and the U.S. Federal Highway Administration. In this project, national cooperators including Federal Highway Administration, the U.S. Forest Service, Louisiana Department of Transportation, University of Minnesota Duluth, Iowa State University, Mississippi State University, Laminated Concepts, Inc. and Tom Williamson Timber Engineering, LLC will each inspect 15-25 timber bridges, using visual, probing, stress wave, and resistance microdrilling. The study results will help to provide a better understanding of the design, performance, and durability characteristics of timber bridge structures, which can improve future bridge design and preservation practices and ultimately extend service life. Lastly, the findings should assist with timber bridge service life expectancy when compared with alternative bridge materials.
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Free
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Numerical Modelling of the Hygro-Thermal Response of Timber Bridges During their Service Life: A Monitoring Case-Study

https://research.thinkwood.com/en/permalink/catalogue2167
Year of Publication
2013
Topic
Serviceability
Moisture
Application
Bridges and Spans
Author
Fortino, Stefania
Genoese, Alessandra
Genoese, Andrea
Nunes, Lina
Palma, Pedro
Organization
VTT Technical Research Centre of Finland
University of Calabria
Universidade dos Açores
Publisher
Elsevier
Year of Publication
2013
Format
Journal Article
Application
Bridges and Spans
Topic
Serviceability
Moisture
Keywords
Bridge
Variable Environment
Monitoring Techniques
Moisture Induced Stress
Multi-Fickian Theory
Finite Element Method
Abaqus Code
Research Status
Complete
Series
Construction and Building Materials
Summary
The monitoring of timber bridges during their service life is important for the maintenance plans of these structures. Numerical modelling can integrate the monitoring techniques by reducing the needed inspections and the maintenance costs. In this paper a 3D computational model based on a well assessed multi-Fickian theory is implemented in Abaqus FEM code. The hygro-thermal response of a timber pedestrian bridge is simulated during a period of its service life. The numerical results are in agreement with measurements taken by a sensor-based technique. Conclusions are given on the moisture gradients which could generate the so-called moisture induced stresses (MIS).
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139 records – page 1 of 14.