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Chapter 6: Fire Damage of Wood Structures

https://research.thinkwood.com/en/permalink/catalogue897
Year of Publication
2012
Topic
Fire
Mechanical Properties
Material
Solid-sawn Heavy Timber
LSL (Laminated Strand Lumber)
LVL (Laminated Veneer Lumber)
Author
Kukay, Brian
White, Robert
Woeste, Frank
Publisher
International Code Council
Year of Publication
2012
Format
Book/Guide
Material
Solid-sawn Heavy Timber
LSL (Laminated Strand Lumber)
LVL (Laminated Veneer Lumber)
Topic
Fire
Mechanical Properties
Keywords
Bending Tests
Withdrawal Tests
Load Bearing Capacity
Charring
Reduced Cross Section Method
Research Status
Complete
Series
Inspection, Testing, and Monitoring of Buildings and Bridges
Summary
Depending on the severity, fire damage can compromise the structural integrity of wood structures such as buildings or residences. Fire damage of wood structures can incorporate several models that address (1) the type, cause, and spread of the fire, (2) the thermal gradients and fire-resistance ratings, and (3) the residual load capacity. The investigator should employ engineering judgment to identify those in-service members that are to be replaced, repaired, or can remain in-service as they are. Suchjudgment will likely be based on the visual inspection of damaged members, connections, and any protective membranes.
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Fire Resistance of Cross-Laminated Timber in Japan

https://research.thinkwood.com/en/permalink/catalogue1776
Year of Publication
2016
Topic
Fire
Connections
Material
CLT (Cross-Laminated Timber)
Application
Floors
Walls
Author
Naruse, Tomohiro
Suzuki, Jun-ichi
Mizukami, Tensei
Yasui, Noboru
Kawai, Makoto
Hasemi, Yuji
Year of Publication
2016
Format
Conference Paper
Material
CLT (Cross-Laminated Timber)
Application
Floors
Walls
Topic
Fire
Connections
Keywords
Japan
Charring Rate
Failure Modes
Reduced Cross Section Method
Fire Tests
Fire Resistance
Load Bearing Capacity
Insulation
Bolts
Self-Tapping Screws
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 22-25, 2016, Vienna, Austria p. 5409-5417
Summary
Fire-testing data, such as charring rates and failure modes of structural elements exposed to ISO-standard fires, for unprotected cross-laminated timber (CLT) panels made of domestic timber were investigated to apply the reduced-cross-section method to CLT panels. For the charring rates, a series of fire tests without loading was conducted...
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Predicting the thickness of zero-strength layer in timber beam exposed to parametric fires

https://research.thinkwood.com/en/permalink/catalogue2916
Year of Publication
2021
Topic
Fire
Application
Beams
Author
Huc, Sabina
Pecenko, Robert
Hozjan, Tomaž
Organization
University of Ljubljana
Publisher
Elsevier
Year of Publication
2021
Format
Journal Article
Application
Beams
Topic
Fire
Keywords
Charring Depth
Fire Resistance
Hygro-thermal Analysis
Numerical Model
Parametric Fire
Reduced Cross-section Method
Zero-Strength Layer
Research Status
Complete
Series
Engineering Structures
Summary
In the design of timber structures, the mechanical resistance in fire conditions has to be ensured among others. In the European standards, Eurocodes, the reduced cross-section method is given to determine mechanical resistance of timber structural elements in fire conditions. The reduced cross-section method is based on an effective cross-section that is determined by two key parameters, namely the charring depth and the thickness of zero-strength layer where the latter accounts for the reductions of the stiffness and the strength of timber due to elevated temperatures. Although, the thickness of zero-strength layer of 7 mm is only prescribed for the ISO 834 standard fire exposure longer than 20 min in the Eurocodes, the same value is often used for non-standard fire exposures as well, which might not always be correct. Thus, in the present paper the thickness of zero-strength layer is investigated for a timber beam exposed to 44 different parametric fires by means of advanced numerical models and a simple design method. A hygro-thermal model and a mechanical model are applied to determine the temperature field over a timber beam cross-section and the mechanical resistance of the beam during fire exposure, respectively. The simple design method is based on the reduced cross-section method. The obtained results show that the thickness of zero-strength layer varies between 8.4 mm and 30.5 mm, which are substantially higher values than the value of 7 mm suggested in the Eurocodes for the standard fire exposure. The results also indicate that the thickness of zero-strength layer is not a constant value and should be written as a function of the parameters defining a parametric fire curve. Alternatively, the effective cross-section could be simply determined by finding the combined thickness of zero-strength layer and charring depth at temperature of about 90 °C.
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Structural Response of Cross-Laminated Timber Compression Elements Exposed to Fire

https://research.thinkwood.com/en/permalink/catalogue1338
Year of Publication
2017
Topic
Fire
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Application
Walls
Author
Wiesner, Felix
Randmael, Fredrik
Wan, Wing
Bisby, Luke
Hadden, Rory
Publisher
ScienceDirect
Year of Publication
2017
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Application
Walls
Topic
Fire
Mechanical Properties
Keywords
Reduced Cross-Section Method
Axial Load
Compressive Load
Deformation
Temperature
Zero-Strength Layer
Research Status
Complete
Series
Fire Safety Journal
Summary
A set of novel structural fire tests on axially loaded cross-laminated timber (CLT) compression elements (walls), locally exposed to thermal radiation sufficient to cause sustained flaming combustion, are presented and discussed. Test specimens were subjected to a sustained compressive load, equivalent to 10 % or 20 % of their nominal ambient axial compressive capacity. The walls were then locally exposed to a nominal constant incident heat flux of 50 kW/m2 over their mid height area until failure occurred. The axial and lateral deformations of the walls were measured and compared against predictions calculated using a finite Bernoulli beam element analysis, to shed light on the fundamental mechanics and needs for rational structural design of CLT compression elements in fire. For the walls tested herein, failure at both ambient and elevated temperature was due to global buckling. At high temperature failure results from excessive lateral deflections and second order flexural effects due to reductions the walls’ effective crosssection and flexural rigidity, as well as a shift of the effective neutral axis in bending during fire. Measured average one-dimensional charring rates ranged between 0.82 and 1.0 mm/min in these tests. As expected, the lamellae configuration greatly influenced the walls’ deformation responses and times to failure; with 3- ply walls failing earlier than those with 5-plies. The walls’ deformation response during heating suggests that, if a conventional reduced cross section method (RCSM), zero strength layer analysis were undertaken, the required zero strength layer depths would range between 15.2 mm and 21.8 mm. Deflection paths further suggest that the concept of a zero strength layer is inadequate for properly capturing the mechanical response of fire-exposed CLT compression elements.
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Structural Response of Fire-Exposed Cross-Laminated Timber Beams under Sustained Loads

https://research.thinkwood.com/en/permalink/catalogue1364
Year of Publication
2016
Topic
Fire
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Application
Beams
Author
Lineham, Sean
Thomson, Daniel
Bartlett, Alastair
Bisby, Luke
Hadden, Rory
Publisher
ScienceDirect
Year of Publication
2016
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Application
Beams
Topic
Fire
Mechanical Properties
Keywords
Flexural Loading
Reduced Cross-Section Method
Zero-Strength Layer
Char Depth
Eurocode
Load Bearing Capacity
Deflection
Heat Flux
Research Status
Complete
Series
Fire Safety Journal
Summary
Cross-laminated timber (CLT) is a popular construction material for low and medium-rise construction. However an architectural aspiration exists for tall mass timber buildings, and this is currently hindered by knowledge gaps and perceptions regarding the fire behaviour of mass timber buildings. To begin to address some of the important questions regarding the structural response of fire-exposed CLT structures in real fires, this paper presents a series of novel fire tests on CLT beams subjected to sustained flexural loading, coincident with non-standard heating using an incident heat flux sufficient to cause continuous flaming combustion. The load bearing capacities and measured time histories of deflection during heating are compared against predicted responses wherein the experimentally measured char depths are used, along with the Eurocode recommended reduced cross section method and zero-strength layer thickness. The results confirm that the current zero-strength layer value (indeed the zero-strength concept) fails to capture the necessary physics for robust prediction of structural response under non-standard heating. It is recommended that more detailed thermo-mechanical cross-sectional analyses, which allow the structural implications of real fire exposures to be properly considered, should be developed and that the zero-strength layer concept should be discarded in these situations. Such a novel approach, once developed and suitably validated, could offer more realistic and robust structural fire safety design.
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