travelling fires in building structural design (madrid 2011)
DESCRIPTION
Presentation I gave on Travelling Fires at the 6th International Congress on Performance-Based Design for Fire, Madrid, on 24 Feb 2011.Relates paper are:- A Law, M Gillie, J Stern-Gottfried, G Rein, JL Torero, The Influence of Travelling Fires on a Concrete Frame, Engineering Structures, (in press) 2011. doi:10.1016/j.engstruct.2011.01.034 - A Jonsdottir, G Rein, J Stern-Gottfried, Comparison of Steel Temperatures using Travelling Fires and Traditional Methods: the Case Study of the Informatics Forum Building, Proceedings of the 12th International Interflam Conference, Nottingham, July 2010.- A Jonsdottir, G Rein, Out of Range, Fire Risk Management, Dec 2009, pp. 14-17. http://hdl.handle.net/1842/3204- J Stern-Gottfried, G Rein, JL Torero, Travel Guide, Fire Risk Management, Nov 2009, pp. 12-16. http://hdl.handle.net/1842/3184- G. Rein, X. Zhang, P. Williams, B. Hume, A. Heise, A. Jowsey, B. Lane, and JL. Torero, “Multi-story Fire Analysis for High-Rise Buildings”, 11th Interflam, London, September 2007, p 605-616. http://hdl.handle.net/1842/3184- J Stern-Gottfried, G Rein, L Bisby, JL Torero, Experimental Review of the Homogeneous Temperature Assumption in Post-Flashover Compartment Fires, Fire Safety Journal 45, pp. 249–261, 2010. doi:10.1016/j.firesaf.2010.03.007. http://hdl.handle.net/1842/3866TRANSCRIPT
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Dr Guillermo Rein
University of Edinburgh
Travelling Fires in
Structural Design
6th Int Conf Fire Safety Eng
APICI Madrid, Feb 2011
Contributions from J Stern-Gottfried, A Law,
A Jonsdottir, M Gillie and J Torero
Structural Design for Fire Safety
�Fire is a source of heat that
weakens the structure
�Assessment of structural
response to avoid collapse
� In order to determine structural
detailing and fire protection
requirements
�Enhancement of:� Integral safety
� Robustness
� Safe innovation
� Cost savings
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GI -> GO
�Cold behaviour ≠ Hot behaviour
�Fire dynamics and resulting environment
are the input and boundary condition to
subsequent Fire & Structures Analysis
�If the input is incomplete, the
subsequent analysis cannot be
trusted
Traditional Methods
0
200
400
600
800
1000
1200
1400
0 30 60 90 120 150 180 210 240
Time (minutes)
Temperature (°C)
EC - Short
EC - Long
Standard
� Standard Fire ~1917
� Swedish Curves ~1972
� Eurocode Parametric Curve ~1995
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Buildings are Different
Then… …and Now
� Architecture is always seeking out of bound
– higher, larger, new shapes
TraditionsTraditions
�Traditional methods assume uniform fires
that lead to uniform fire temperatures
�Traditional methods are based on
experiments conducted in small
compartment experiments (~3 m3)
�Traditional methods have been said to be
conservative (?)
Stern-Gottfried et al, Fire Risk Management 2009
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Size MattersSurface Area to Volume Ratio vs Floor Area for a 3m High Square Compartment
0
0.5
1
1.5
2
2.5
3
0 500 1000 1500 2000 2500 3000
Floor Area (m²)
Sur
face
Are
a/V
olum
e (1
/m)
Fire Tests
Real Buildings
Stern-Gottfried et al, Fire Risk Management 2009
Limitations in Traditional Methods Limitations in Traditional Methods
For example, limitations according Eurocode:
�Near rectangularrectangular enclosures
� Floor areas < 500 m< 500 m22
�Heights < 4 m< 4 m
�No ceilings openingsopenings
�No low or high thermal-inertia lininglining
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Sydney Opera HouseSydney Opera House
Near rectangular?Near rectangular?
© KPF Architects
Pompidou CentrePompidou Centre
Proposed WTC Transit HubProposed WTC Transit Hub
< 500 m< 500 m22 floor?floor?
<4 m high?<4 m high?
Excel, LondonExcel, London
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London Bridge TowerLondon Bridge Tower
Only insulating lining?Only insulating lining?
The Gherkin TowerThe Gherkin Tower
© Renzo Piano
©
Proposed WTC MemorialProposed WTC Memorial
No ceiling opening?No ceiling opening?
Arup CampusArup Campus
© Arup/Peter Cook/VIEW
©
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Edinburgh Survey: 3,080 compartments� 19-20th Century buildings:
66% of volume within limitations
� 2008 building: 8%
� Suggests modern architecture increasingly produces buildings out of range
Jonsdottir et alFire Risk Management 2009
Travelling Fires Methodology
� Real fires have been observed to travel
�WTC Towers 2001
�Torre Windsor 2005
�Delft Faculty 2008
� Experimental data indicate fires travel
in large compartments
� In larger compartments, the fire does
not burn uniformly but burns locally
and spreads
Rein et al, Interflam 2007, London
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Fire environment split
into two:
Near-field ≈ 1000-1200 ºC
Far-field ≈ 200-1200 ºC
(Alper’s correlation)
Te
mp
er
atu
re
Distance
Travelling Fires
Fire environment split
into two:
Near-field ≈ 1000-1200 ºC
Far-field ≈ 200-1200 ºC
(Alper’s correlation)
Te
mp
er
atu
re
Distance
Total burning
duration is a function
of the area of the fire
Travelling Fires
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Far Field Temperature
�Maximum temperature at ceiling jet. Average
calculated over the correlation with the distance
from the fire (Alpert’s correlation)
( )H
rQ38.5TT
32
max
&
=− ∞
nfff
r
r
4
4
ffrr
drTT
ff
nfmax
−=∫
�Burning at average heat release per unit area
where tb is the burning time, m” is the fuel load density (kg/m2),
∆Hc is the effective heat of combustion and Q’’ is the heat release
rate per unit area (MW/m2)
Q
Hmt cb & ′′
∆′′=
� 50 MW fire on 200 m2 burns for 30 min� 50 MW fire on 1000 m2 burns for 15 min
Conservation of Mass – burning time
Rein et al, Interflam 2007, London
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�Each structural element sees a combination
of Near Field and Far Field temperatures
as the fire travels
Travelling Fires
Stern-Gottfried et al, SPFE PBD, 2010, Lund
Example – 25% Floor Area fire in a 1000 m2
�Near field temperature 1200ºC for 19 min
� Far field temperature ~ 800ºC for 76 min
Structural
Element
Core
0200
400600800
100012001400
0 50 100 150 200 250 300 350 400Time (min)
Te
mp
era
ture
(ºC
)
Point B, Rebar temperature
Point B, Gas temperature
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Family of possible fires
Stern-Gottfried et al, SPFE PBD, 2010, Lund
Case Study:
Generic Multi-Storey Concrete Structure
Law et al, Engineering Structures 2011
Stern-Gottfried et al, SPFE PBD, 2010, Lund
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50% burn area
400ºC
0ºC600 minutes 1200 minutes
Tem
pera
ture
Time
2.5% burn area5% burn area10% burn area
25% burn area
100% burn area
Rebar Temperature
Law et al, Engineering Structures 2011
Max Rebar Temperatures vs. Fire Size
1h 18 min
Law et al, Engineering Structures 2011
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Max Deflection vs. Fire Size
1h 54 min
Law et al, Engineering Structures 2011
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0% 50% 100%
Fire area
No
rmal
ize
d s
tres
s_
Reb ar temperatureStandard FireParametric - Short hotParametric - Long co ol
00.1
0.20.3
0.40.50.6
0.70.8
0.91
0% 50% 100%
Fire area
No
rma
lized
def
lect
ion_
Deflect ionStand ard FireParametric - Sho rt ho tParametric - Long cool
0
0.01
0.02
0.03
0.04
0.05
0.06
0% 50% 100%
Fire area
No
rmal
ize
d s
trai
n_
Sagg ing strainStandard FireParametric - Short hotParametric - Lo ng coo l
00.02
0.040.06
0.080.1
0.12
0.140.16
0.180.2
0% 50% 100%
Fire area
No
rma
lized
str
ain_
Hog ging strain
Stand ard FireParametric - Sho rt hot
Parametric - Long co ol
Structural Behaviour
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Results for Insulated Steel:
Parametric vs. Travelling firesJonsdottir et al, Interflam 2010, Nottingham
� Compared to parametric fire, 110% higher temperatures
for a protected steel with 39 mm-gypsum
Conclusions
� In large compartments, a post flashover fire
is not likely to occur, but a travelling fire
�Novel framework developed to compliment
traditional methods
�Provides range of possible fire dynamics
�Travelling fires give more onerous conditions
for the structure
�Strengthens collaboration between fire and
structural fire engineers
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ThanksThanksThanksThanks
Collaborators:
J Stern-Gottfried
A Law
A Jonsdottir
M Gillie
J Torero
Sponsors:
ARUP
Jonsdottir et al, Interflam 2010, Nottingham
Law et al, Engineering Structures 2011
Rein et al, Interflam 2007, London
Stern-Gottfried et al, SPFE PBD, 2010, Lund
Stern-Gottfried et al, Fire Risk Management 2009
Jonsdottir et al, Fire Risk Management 2009