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18 records – page 1 of 2.

Review and Survey on Differential Movement in Wood Frame Construction

https://research.thinkwood.com/en/permalink/catalogue2627
Year of Publication
2010
Topic
Design and Systems
Material
Light Frame (Lumber+Panels)
Application
Wood Building Systems
Author
Wang, J.
Ni, Chun
Organization
FPInnovations
Year of Publication
2010
Format
Report
Material
Light Frame (Lumber+Panels)
Application
Wood Building Systems
Topic
Design and Systems
Keywords
Deformation
Mid-Rise
Shrinkage
Movement
Research Status
Complete
Summary
This report summarizes the existing knowledge on building movement related to wood-frame construction. This knowledge includes fundamental causes and characteristics of wood shrinkage, instantaneous and time-dependent deformations under load, major wood-based materials used for construction and their shrinkage characteristics, movement amounts in publications based on limited field measurement, and movement estimations by construction practitioners based on their experience with wood-frame construction. Movement analysis and calculations were also demonstrated by focusing on wood shrinkage based on common engineering design assumptions, using six-storey platform buildings as examples. The report then provides engineering solutions for key building locations where differential movement could occur, based on the literature review as well as a small-scale survey of the construction industry. The report emphasizes the importance of comprehensive analysis during design and construction to accommodate differential movement. Most building materials move when subjected to loading or when environmental conditions change. It is always good practice to detail buildings so that they can accommodate a certain range of movement, whether due to structural loading, moisture or temperature changes. For wood-frame buildings, movement can be reduced by specifying materials with lower shrinkage rates, such as engineered wood products and drier lumber. However, this may add considerable costs to building projects, especially when specifications have to be met through customized orders. Producing lumber with a lower moisture content adds significant costs, given the additional energy consumption, lumber degrade and sorting requirements during kiln drying. Specifying materials with lower moisture content at time of delivery to job site does not guarantee that wood will not get wet during construction, and excessive shrinkage could still be caused by excessively long time of exposure to rain during construction. On the other hand, effective drying can occur during the period between lumber delivery and lumber closed into building assemblies. Appropriate measures should be taken to ensure lumber protection against wetting, protected panel fabrication on site, good construction sequence to facilitate air drying, and supplementary heating before closing in to improve wood drying. This report also provides recommendations for future work, including field measurement of movement and construction sequencing optimization, in order to provide better information for the design and construction of wood buildings, five- and six-storey platform frame buildings in particular.
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Accommodating Movement in High-Rise Wood-Frame Building Construction

https://research.thinkwood.com/en/permalink/catalogue1875
Year of Publication
2011
Topic
Design and Systems
Connections
Material
Steel-Timber Composite
Other Materials
LVL (Laminated Veneer Lumber)
Application
Wood Building Systems
Floors
Walls
Author
Howe, Richard
Publisher
Forest Products Society
Year of Publication
2011
Format
Journal Article
Material
Steel-Timber Composite
Other Materials
LVL (Laminated Veneer Lumber)
Application
Wood Building Systems
Floors
Walls
Topic
Design and Systems
Connections
Keywords
Detailing
Shrinkage
Differential Movement
Research Status
Complete
Series
Wood Design Focus
Summary
Ease of construction and favorable overall costs relative to other construction types are making high-rise (i.e., 4- and 5-story) wood frame construction increasingly popular. With these buildings increasing in height, there is a greater impetus on designers to address frame and finishes movement in such construction. As we all know, buildings are dynamic creatures experiencing a variety of movements during construction and over their service life. In wood frame construction, it is important to consider not only absolute movement but also differential movement between dissimilar materials. This article focuses on differential movement issues and how to recognize their potential and avoid problems by effective detailing.
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Characteristics of the Radio-Frequency/Vacuum Drying of Heavy Timbers for Post and Beam of Korean Style Housings Part II: For Korean Red Pine Heavy Timbers with 250 × 250 mm, 300 × 300 mm in Cross Section and 300 mm in Diameter, and 3,600 mm in Length

https://research.thinkwood.com/en/permalink/catalogue1508
Year of Publication
2011
Topic
Moisture
Material
Solid-sawn Heavy Timber
Application
Wood Building Systems
Author
Lee, Nam-Ho
Zhao, Xue-Feng
Shin, Ik-Hyun
Park, Moon-Jae
Park, Jung-Hwan
Park, Joo-Saeng
Publisher
The Korean Society of Wood Science Technology
Year of Publication
2011
Format
Journal Article
Material
Solid-sawn Heavy Timber
Application
Wood Building Systems
Topic
Moisture
Keywords
Radio-Frequency/Vacuum Drying
Moisture Gradient
Shrinkage
Case Hardening
Surface Checks
Compressive Load
Research Status
Complete
Series
Journal of the Korean Wood Science and Technology
Summary
This study examined the characteristics of radio-frequency/vacuum dried Korean red pine (Pinus densoflora heavy timbers with 250 × 250 mm (S), 300 × 300 mm (L) in cross section and 300 mm in diameter, and 3,600 mm in length, which were subjected to compressive loading after a kerf pretreatment. The following results were obtained : The drying time was short and the drying rate was high in spite of the large cross section of specimens. The moisture gradient inall specimens was gentle in both longitudinal and transverse directions owing to dielectric heating. The shrinkage of the width in the direction perpendicular to was 21 percent ~ 76 percent of that of the thickness of square timbers in the direction parallel to the mechanical pressure. The casehardening for all specimens was very slight because of significantly reduced ratio of the tangential to radial shrinkage of specimens and kerfing. The surface checks somewhat severely occurred although the occurrence extent of the surface checks on the kerfed specimens was slight compared withthat on the control specimen.
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Quantifying the Impacts of Moisture and Load on Vertical Movement in a Simulated Bottom Floor of a 6-Storey Platform Frame Building

https://research.thinkwood.com/en/permalink/catalogue2619
Year of Publication
2013
Topic
Moisture
Design and Systems
Material
Light Frame (Lumber+Panels)
Application
Wood Building Systems
Author
Wang, J.
King, L.
Organization
FPInnovations
Year of Publication
2013
Format
Report
Material
Light Frame (Lumber+Panels)
Application
Wood Building Systems
Topic
Moisture
Design and Systems
Keywords
Mid-Rise
Vertical Movement
Moisture Content
Shrinkage
Load-Induced Movement
Research Status
Complete
Summary
Vertical movement of wood frame buildings has become an important consideration in recent years with the increase of building height in Europe, North America, and Asia up to 6-storeys. This movement is composed of wood shrinkage and load-induced movement including initial settlement and creep. It is extremely difficult to identify the relative contributions of these components while monitoring full size buildings. A laboratory test was therefore designed to do this under controlled environmental and loading conditions. Two identical small-scale platform frame structures with dimensional lumber floor joists were designed and constructed, with built-in vertical movement and moisture content monitoring systems. The two structures were first conditioned in a chamber to achieve an initial moisture content (MC) about 20% to simulate typical MC on exposed construction sites in wintertime in Coastal BC. After the two structures were moved from the conditioning chamber into the laboratory environment, using a unique cantilever system, Structure No. 1 was immediately loaded to measure the combined shrinkage and deformation in the process of drying. Structure No. 2 was not loaded until after the wood had dried to interior equilibrium moisture content to observe the shrinkage and load-induced movement separately. The load applied on the two structures simulated a dead load experienced by the bottom floor of a six-storey wood frame building. The vertical movement and MC changes were monitored over a total period of six months. Meanwhile, shrinkage coefficients were measured by using end-matched lumber samples cut from the plate members of the two structures to predict the shrinkage amounts of the horizontal members of the two structures. The results suggested that a load must be applied for movement to “show up” and occur in a downward direction. Without loads other than the wood weight, even shrinkage could show as upward movement. Monitoring of Structure No. 1 appeared to separate the contributions of wood shrinkage, initial settlement (bedding-in movement), and creep reasonably well. The entire movement amount reached about 19 mm after six months, which was comparable to the vertical movement measured from the bottom floor of a 4-storey wood-frame building in BC. Shrinkage accounted for over 60% of the vertical movement, with the other 40% contributed by load-induced movement including initial settlement and creep (when elastic compression was neglected); the magnitude of creep was similar to the initial settlement amount. Structure No. 2 showed less vertical movement but an increased settlement amount at the time of loading, indicating the presence of larger gaps between members when the wood was dry (with an estimated MC of 11%) before loading. Depending on construction sequencing, such settlement should occur with increase in loads during construction and can therefore be ignored in design. However, this test suggested that there may be a need to consider the impact of creep, in wet climates in particular, in addition to wood shrinkage. This laboratory test will be maintained for a longer period to observe any further vertical movement and the relative contributions of shrinkage and creep. Similar tests should be conducted for structures built with engineered wood floor joists, given the fact that most mid-rise platform buildings use engineered wood floor joists instead of lumber joists.
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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
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
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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Vertical Movement in Wood Platform Frame Structures: Movement Prediction

https://research.thinkwood.com/en/permalink/catalogue737
Year of Publication
2013
Topic
Serviceability
Moisture
Material
Glulam (Glue-Laminated Timber)
Application
Wood Building Systems
Author
Doudak, Ghasan
Lepper, Peggy
Ni, Chun
Wang, Jasmine
Organization
Canadian Wood Council
FPInnovations
Year of Publication
2013
Format
Report
Material
Glulam (Glue-Laminated Timber)
Application
Wood Building Systems
Topic
Serviceability
Moisture
Keywords
Moisture Content
Shrinkage
Swelling
Adhesives
Differential Movement
Research Status
Complete
Summary
It is not possible or practical to precisely predict the vertical movement of wood structures due to the many factors involved in construction. It is, however, possible to obtain a good estimate of the vertical movement to avoid structural, serviceability, and building envelope problems over the life of the structure. Typically “S-Dry” and “S-Grn” lumber will continue to lose moisture during storage, transportation and construction as the wood is kept away from liquid water sources and adapts to different atmospheric conditions. For the purpose of shrinkage prediction, it is usually customary to assume an initial moisture content (MC) of 28% for “S-Green” lumber and 19% for “S-Dry” lumber. “KD” lumber is assumed to have an initial MC of 15% in this series of fact sheets. Different from solid sawn wood products, Engineered Wood Products (EWP) are usually manufactured with MC levels close to or even lower than the equilibrium moisture content (EMC) in service. Plywood, Oriented Strand Board (OSB), Laminated Veneer Lumber (LVL), Laminated Strand Lumber (LSL), and Parallel Strand Lumber (PSL) are usually manufactured at MC levels ranging from 6% to 12%. Engineered wood I-joists are made using kiln dried lumber (usually with moisture content below 15%) or structural composite lumber (such as LVL) flanges and plywood or OSB webs, therefore they are usually drier and have lower shrinkage than typical “S-Dry” lumber floor joists. Glued-laminated timbers (Glulam) are manufactured at MC levels from 11% to 15%, so are the recently-developed Cross-laminated Timbers (CLT). For all these products, low shrinkage can be achieved and sometimes small amounts of swelling can be expected in service if their MC at manufacturing is lower than the service EMC. In order to fully benefit from using these dried products including “S-Dry” lumber and EWP products, care must be taken to prevent them from wetting such as by rain during shipment, storage and construction. EWPs may also have lower shrinkage coefficients than solid wood due to the adhesives used during manufacturing and the more mixed grain orientations in the products, including the use of cross-lamination of veneers (plywood) or lumber (CLT). The APEGBC Technical and Practice Bulletin emphasizes the use of EWP and dimension lumber with 12% moisture content for the critical horizontal members to reduce differential movement in 5 and 6-storey wood frame buildings.
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Monitoring Building Climate and Timber Moisture Gradient in Large-Span Timber Structures

https://research.thinkwood.com/en/permalink/catalogue108
Year of Publication
2014
Topic
Serviceability
Moisture
Material
Glulam (Glue-Laminated Timber)
Application
Wood Building Systems
Author
Gamper, Andreas
Dietsch, Philipp
Winter, Stefan
Editor
Bettina Franke Steffen Franke
Year of Publication
2014
Format
Conference Paper
Material
Glulam (Glue-Laminated Timber)
Application
Wood Building Systems
Topic
Serviceability
Moisture
Keywords
Cracks
Damage
Equilibrium Moisture Content
Internal Climate
Lamellas
Large Span
Long-term
Relative Humidity
Shrinkage
Swelling
Temperature
Conference
COST Workshop – Highly Performing Timber Structures: Reliability, Assessment, Monitoring and Strengthening
Research Status
Complete
Summary
The evaluation of damages in large-span timber structures indicates that the predominantly observed damage pattern is pronounced cracking in the lamellas of glued-laminated timber elements. A significant proportion of these cracks is attributed to the seasonal and use-related variations of the internal climate within large buildings and the associated inhomogeneous shrinkage and swelling processes in the timber elements. To evaluate the significance of these phenomena, long-term measurements of climatic conditions and timber moisture content were taken within large-span timber structures in buildings of typical construction type and use. These measurements were then used to draw conclusions on the magnitude and time necessary for adjustment of the moisture distribution to changing climatic conditions. A comparison of the results for different types of building use confirms the expected large range of possible climatic conditions in buildings with timber structures. Ranges of equilibrium moisture content representative of the type and use of building were obtained. These ranges can be used in design to condition the timber to the right value of moisture content, in this way reducing the crack formation due to moisture variations. The results of this research also support the development of suitable monitoring systems which could be applied in form of early warning systems on the basis of climate measurements. Based on the results obtained, proposals for the practical implementation of the results are given.
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Effect of Reserve Air-Drying of Korean Pine Heavy Timbers on High-Temperature and Low-Humidity Drying Characteristics

https://research.thinkwood.com/en/permalink/catalogue1506
Year of Publication
2014
Topic
Moisture
Material
Solid-sawn Heavy Timber
Author
Lee, Chang-Jin
Lee, Nam-Ho
Park, Moon-Jae
Park, Joo-Saeng
Eom, Chang-Deuk
Publisher
The Korean Society of Wood Science Technology
Year of Publication
2014
Format
Journal Article
Material
Solid-sawn Heavy Timber
Topic
Moisture
Keywords
Moisture Content
Temperature
Humidity
Pine
Air Drying
Shrinkage
Internal Checks
Twist
Case Hardening
Research Status
Complete
Series
Journal of the Korean Wood Science and Technology
Summary
The pre-air-drying of Korean pine before the high-temperature and low-humidity drying was shown to be effective in uniform moisture content distribution and prevention of surface check. Our results suggest that initial moisture content of the timber also plays important role in high-temperature and low-humidity drying method. The pre-air-drying also helps in the reduction of surface checks in Korean pine when compared to the Korean pine dried by only high-temperature and low-humidity. End-coating was not effective in the prevention of twist, shrinkage, case hardening and internal checks. The pre-air-drying reduces the internal tension stresses which occur during high-temperature and low-humidity drying thus decreasing case hardening and also preventing internal checks. The pre-air-drying decreases the moisture content and causes shrinkage which leads to increased twist in the Korean pine.
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Field Measurement of Vertical Movement and Roof Moisture Performance of the Wood Innovation and Design Centre: Instrumentation and First Year's Performance

https://research.thinkwood.com/en/permalink/catalogue102
Year of Publication
2015
Topic
Design and Systems
Serviceability
Material
CLT (Cross-Laminated Timber)
Glulam (Glue-Laminated Timber)
Application
Wood Building Systems
Author
Wang, Jieying
Organization
FPInnovations
Year of Publication
2015
Format
Report
Material
CLT (Cross-Laminated Timber)
Glulam (Glue-Laminated Timber)
Application
Wood Building Systems
Topic
Design and Systems
Serviceability
Keywords
Differential Movement
Long-term
Moisture
Plywood
Roofs
Shrinkage
Tall Wood
Vertical Movement
Research Status
Complete
Summary
Two of the major topics of interest to those designing taller and larger wood buildings are the susceptibility to differential movement and the likelihood of mass timber components drying slowly after they are wetted during construction. The Wood Innovation and Design Centre in Prince George, British Columbia provides a unique opportunity for non-destructive testing and monitoring to measure the ‘As Built’ performance of a relatively tall mass timber building. Field measurements also provide performance data to support regulatory and market acceptance of wood-based systems in tall and large buildings. This report first describes instrumentation to measure the vertical movement of selected glulam columns and cross-laminated timber (CLT) walls in this building. Three locations of glulam columns and one CLT wall of the core structure were selected for measuring vertical movement along with the environmental conditions (temperature and humidity) in the immediate vicinity. The report then describes instrumentation to measure the moisture changes in the wood roof structure. Six locations in the roof were selected and instrumented for measuring moisture changes in the wood as well as the local environmental conditions.
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Accommodating Shrinkage in Multi-Story Wood-Frame Structures

https://research.thinkwood.com/en/permalink/catalogue712
Year of Publication
2017
Topic
Design and Systems
Moisture
Material
Light Frame (Lumber+Panels)
Application
Wood Building Systems
Author
McLain, Richard
Steimle, Doug
Organization
WoodWorks
Year of Publication
2017
Format
Report
Material
Light Frame (Lumber+Panels)
Application
Wood Building Systems
Topic
Design and Systems
Moisture
Keywords
Shrinkage
Mid-Rise
Multi-Story
Moisture Content
Research Status
Complete
Summary
In wood-frame buildings of three or more stories, cumulative shrinkage can be significant and have an impact on the function and performance of finishes, openings, mechanical/electrical/plumbing (MEP) systems, and structural connections. However, as more designers look to wood-frame construction to improve the cost and sustainability of their mid-rise projects, many have learned that accommodating wood shrinkage is actually very straightforward. This publication will describe procedures for estimating wood shrinkage and provide detailing options that minimize its effects on building performance.
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18 records – page 1 of 2.