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THE UNIVERSITY of EDINBURGH
United Kingdom
Xu DaiAuthors: Xu Dai, Stephen Welch, Asif Usmani
A critical review of “travelling fire”
scenarios for performance-based
structural engineering
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Motivation
Fire uncertainties to large spaces architecture
for structural design?
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IntroductionWindsor Tower in Madrid in 2005 World Trade Center Tower 1
in New York City in 2001
(source: https://www.metabunk.org/)
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WTC 7
2:57 p.m. 3:05 p.m.
3:13 p.m. 3:44 p.m.
Fire visible inside Not visibleWindow glass intact Window open
(source: NIST NCSTAR 1-9, Structural Fire Response and Probable Collapse
Sequence of World Trade Centre Building 7, 2008)
Facade map summarizing observations of fire spread
and window breakage on the north face of WTC 7
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Introduction
What is a travelling fire?
It is a way of approximating fire impact on structures
in large open-plan spaces for structural design.
Large compartment fires may burn locally and tend to
move across floor plates over a period of time.
Alternative names:
moving fires, spreading fires, real fires, natural fires, non-uniform fires…
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Travelling fire experiments
Experiments
Kirby & Cooke, 1993
LBTF – Demonstration Furniture, 1995–1996
Thomas et al., 2005
NFSC - BRE Cardington, 1999–2000
St. Lawrence Burns project, 1958
Veselí Travelling Fire Test, 2011
BRE Travelling Fire Test, 2013
Tisová Travelling Fire Test, 2015
• Labelled as ‘travelling fire tests’
• Fire tests that have a ‘spreading’ nature
before 2010
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Veselí travelling fire test
Experimental building during travelling fire test
(source: photo provided by Horová K., CVUT in Prague)
Fuel load scheme, in hatched, on the upper floor of the
experimental building
(source: F. Wald et al., CVUT in Prague)
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Veselí travelling fire test
5 minutes10 minutes15 minutes20 minutes25 minutes30 minutes35 minutes40 minutes
Development of the fire during the test(source:photos provided by Horová K., CVUT in Prague)
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Travelling fire experiments
Experiments
Kirby & Cooke, 1993
LBTF – Demonstration
Furniture, 1995–1996
Thomas et al., 2005
NFSC - BRE Cardington,
1999–2000
St. Lawrence Burns
project, 1958
Veselí Travelling Fire
Test, 2011
BRE Travelling Fire
Test, 2013
Tisová Travelling Fire
Test, 2015
Categories
Dimensions
22.8 m × 5.6 m × 2.75 m
135 𝐦𝟐
230 𝐦𝟐× 4.4 m
5 m × 18 m × 2 m
10.4 m × 13.4 m × 4 m
11.2 m × 12.8 m, and
13 m × 9 m
8.m × 2.m × 0.6 m
12 m × 12 m × 3 m
Fuel load
Wood cribs
Furniture
Commercial grade
methylated spirits
Wood waste
Wood waste
Gas burners,
or wood cribs
Wood cribs +
Hydrocarbon accelerant
Wood cribs, or 80% wood
cribs + 20% plastic
Thermal
response
Gas and steel
temperatures
Gas and steel
temperatures
Gas and steel
temperatures
Gas temperatures
Gas, steel, and
concrete temperatures
Gas temperatures
Gas and concrete
temperatures
Gas and steel
temperatures
Structural
response
None
Strain and
deflections
None
None
Strain and
deflections
N/A
Deflections
None
Mass loss
measurement
Yes
No
Yes
No
No
Yes
No
Yes
Summaries of the experiments reviewed for travelling fires
Fire
Engineering
Structural
Engineering
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Fire ‘hierarchy’ for structural design
Fire Structural Design
Inc
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rtai
nti
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for
app
lic
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n Standard fire curve
Parametric fire curves
Zone models
Localised fire models
CFD models
Travelling fires
Prescriptive design
Performance-based
design
Thermal loading
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Travelling fire analytical models
How to bring travelling fires into
structural design ?
• Clifton’s travelling fire model
• Rein’s travelling fire model
• Extended Travelling Fire Method (ETFM) framework
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Travelling fire analytical models
Clifton’s travelling fire model
60m
36m
0 min 20 min
40 min 60 min
Fire Preheating Cooling
Conceptual illustration of Clifton’s model
(source: adapted from Y. Wang et al., 2012)
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Travelling fire analytical models
Rein’s travelling fire model
Illustration of a travelling fire and distribution
of gas temperatures
(source: E. Rackauskaite et al., 2015)
Near field:
Far field :
Alpert’s ceiling jetFlapping angle and reduced near field temperature
(source: E. Rackauskaite et al., 2015)
800℃ −1200℃, flapping angle1200℃
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Travelling fire analytical models
Ceiling‘Combination’ of localized fire model & zone model0
heat flux
local fire
Smoke layer depth d = d (t)
Steel Beam
Pre-heating Post-heatingDirect exposure
Extended Travelling Fire Method (ETFM) framework
e.g. - Hasemi’s localised fire external heat flux ሶℎ (W/m2) : e.g. - FIRM zone model:
Based on M. Janssens’ book, 2000
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Travelling fire analytical models
Far field temperature
(i.e. smoke)
Fire path
Smoke accumulation
Spread rate
Non-uniform fuel
Fire size
HRR consideration
Mass conservation
Energy conservation
Compartment boundary
Ventilation/fuel controlled
Firecell to neighboured ones
No
From observation
No
Decided by fuel load density
No
No
No
Yes
Ventilation controlled
Not defined
No
From observation
No
Decided by fuel & fire spread
Yes
Yes
No
No
Fuel controlled
Alpert’s ceiling jet model
Categories Models
Clifton’s Travelling Fire Model
Summaries of the travelling fire analytical models
Rein’s Travelling Fire Model ETFM Framework
Near field
temperature
Time-temperature
curve for firecells800℃ −1200℃, flapping angle Localised fire model (e.g. Hasemi)
Predefined trajectory
Yes
From observation
Yes
Decided by fuel & fire spread
Yes
Yes
Yes
Yes
Fuel & ventilation controlled
Simple zone model (e.g. FIRM)
Flashover Yes No Yes
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Fire ‘hierarchy’ for structural design
Fire Structural Design
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for
app
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Standard fire curve
CFD models
Prescriptive design
Performance-based
design
Parametric fire curves
Localised fire models
Zone models
Clifton’s travelling fire
model
Rein’s travelling fire
model
ETFM framework
Structural AnalysisThermal loading
Heat Transfer
Tabulated results
‘Lumped mass’
calculations
1-D uncoupled
heat transfer
Coupled heat transfer
- mechanical analyses
2-D or 3-D uncoupled
heat transfer
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Case study using ETFM framework
An idealised steel composite building with a core
Visualization output of OpenSees-SIFBuilder during heat transfer analysis
x direction: 6m – 9m – 9m – 6m z direction: 6m – 9m – 6my direction: 5m – 4m
y
xz
Building dimensions:Fire spread rate: 10 mm/s
Fuel load density: 570 MJ/m2HRR per area: 500 kW/m2
Base line fire scenario: Net floor area: 468 m2 Clear floor height: 3.85 mLarge compartment dimensions:
Total vent width: 28 m Soffit height: 3 m Sill height: 1 mFire starts on the first floor
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100 MJ/m2
230 MJ/m2
300 MJ/m2
420 MJ/m2
600 MJ/m2
780 MJ/m2
Case study using ETFM framework
Two key input variables for ETFM: fire spread rates, and fuel load densitiesTravelling fires with changing fuel load densities
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Fire ‘hierarchy’ for structural design
Fire
Inc
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un
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rtai
nti
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for
app
lic
atio
n Standard fire curve
CFD models
Prescriptive design
Performance-based
design
Parametric fire curves
Localised fire models
Zone models
Clifton’s travelling fire
model
Rein’s travelling fire
model
ETFM framework
Structural AnalysisThermal loading
Heat Transfer
Tabulated results
‘Lumped mass’
calculations
1-D uncoupled
heat transfer
Coupled heat transfer
- mechanical analyses
2-D or 3-D uncoupled
heat transfer
Tabulated results
Limiting temperature
or strength
Simplified methods
Dynamic analyses
Static and quasi-static
analyses
(source: adapted from Y. Wang et al., ‘Performance-Based Fire Engineering of Structures’, 2012)
Progress so far…
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Consistent level of complexities/crudeness/efficiency
for
fire – heat transfer – structural analysis
Fire uncertainties to large spaces architecture
for structural design?
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Future work
TRAFIR ProjectCharacterization of TRAvelling FIRes in large compartments
• testing (isolated elements and simplified fire
progression, as well as a full-scale large compartment)
Eight work packages (1/07/2017 → 31/12/2020):
• modelling (both simplified analytical/phenomenological
models and CFD).
Project partners:
Funding from the Research Fund for Coal and Steel (RFCS) - European Commission