Post on 22-May-2018
Performance-Based Fire Safety Engineering:
Challenges and Opportunities
Dr. Thomas Gernay
Gustave Magnel International Award – New activities
SECO – Brussels, Belgium, 1st June 2017
F.R.S.-FNRS, University of Liege, Belgium
Fire safety: a major issue
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The Great Fire of London in 1666 (unknown artist, c. 1700)
T. Gernay, 2017
Fire safety: a major issue
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L’Innovation Fire, Brussels, 1967 World Trade Center attacks, NYC, 2001
T. Gernay, 2017
Fire safety: a major issue
First and foremost: life safety
But also: property protection, infrastructure protection
Total cost of fire: ≈ 1% of GDP in developed countries1
- Cost of direct fire losses (casualties, property losses, etc.)
- Cost of indirect fire losses (rehousing, business interruption, etc.)
- Cost of fire fighting organizations
- Cost of fire protection to buildings
- Cost of fire insurance administration
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1Geneva Association World Fire Statistics Centre (WFSC)
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Fire Safety Engineering: a multidisciplinary field
Structural fire engineering is a key component
Design the structures for adequate response under fire
→ compartmentation and structural stability
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To achieve the goal in Fire Safety Engineering, it requires implementation
of multiple objectives based on various disciplines
↘ proba of ignition ↘ proba of fire spread allow safe evacuation
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Prescriptive vs Performance-Based approach
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Prescribes methods to build vs Prescribes a result (performance)
→ Simplicity vs → Flexibility
PRESCRIPTIVEfollowing codes and standards
PERFORMANCE-BASEDbased on the physics of the problem
DESIGN APPROACHFor a structure against fire hazard
PBD: opportunity for more efficient, economic and elegant design solutions,
but requires a more advanced understanding of the physics of the problem
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Performance-Based: Why it matters? What can we gain?
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Realistic fire scenarios
q
0
600
1200
0 60
[°C]
120 180Time [min]
T. Gernay, 2017
Performance-Based: Why it matters? What can we gain?
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Realistic fire scenarios
Robustness and whole building behavior
Cardington fire test, UK, 1997
T. Gernay, 2017
Performance-Based: Why it matters? What can we gain?
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Realistic fire scenarios
Robustness and whole building behavior
Consideration of specific risk associated with the building
Input variable
𝑔 𝐷𝑉 = 𝑝 𝐷𝑉|𝐷𝑀 𝑝 𝐷𝑀|𝐸𝐷𝑃 𝑝 𝐸𝐷𝑃|𝐼𝑀 𝑔 𝐼𝑀 𝑑𝐷𝑀 𝑑𝐸𝐷𝑃 𝑑𝐼𝑀
T. Gernay, 2017
Performance-Based: Why it matters? What can we gain?
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Realistic fire scenarios
Robustness and whole building behavior
Consideration of specific risk associated with the building
Cost effective fire resistance designs
The Shard, London
T. Gernay, 2017
Research goal: Develop Performance-Based design in SFE
Comprehend the behavior of building materials and structures in fire
Propose models to accurately capture this behavior
Develop numerical tools for structural fire engineering analysis
11T. Gernay, 2017
Example of research project: How to model concrete in fire?
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Challenges
numerically robust applicable to large structuresmaterial behavior + at elevated temperature
Need
Concrete is one of the most used materials
Its behavior is affected by fire
There was no satisfying model available for concrete at elevated temperature
T. Gernay, 2017
A model for concrete in fire: Theory
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Plasticity Damage Plastic-damage
Modeling
Traditional plasticity approach
Damage proposed at ambient temperature
Actually concrete exhibits a combination of both
T. Gernay, 2017
A model for concrete in fire: Theory
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-5.00
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
-0.00020 -0.00010 0.00000 0.00010 0.00020 0.00030
str
ess [M
Pa]
strain [-]
Model
Ramtani [test 1990]
Tension
Compression
Crack closure
Modeling
Different in tension and in compression
Can handle the shift from one to the other
Essential because of thermal stresses
T. Gernay, 2017
A model for concrete in fire: Theory
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Effects of temperature on stress-strain relationships
Compression Tension
-30
-25
-20
-15
-10
-5
0
-0.03-0.025-0.02-0.015-0.01-0.0050
stress [MPa]
strain [-]
Uniaxial behavior in compression
20°C
200°C
400°C
600°C
800°C
0
1
2
3
0 0.0002 0.0004 0.0006 0.0008 0.001
stress [MPa]
strain [-]
Uniaxial behavior in tension
20°C
200°C
400°C
500°C
T. Gernay, 2017
A model for concrete in fire: Implementation
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To achieve the greatest impact in practice and be useful to the community:
The model is implemented in a Finite Element software
SAFIR®: non linear FE software for modeling structures in fire
Widely available to the SFE community (+200 licensees)
Compatibility is ensured with the different types of FE:
Model formulated in fully triaxial stress (SOLID FE)
Algorithm for solving in plane stress (SHELL FE)
Also a uniaxial formulation (BEAM FE)
X Y
Z
Diamond 2009.a.5 for SAFIR
FILE: joint9p
NODES: 31502
ELEMENTS: 25411
SOLIDS PLOT
FRONTIERS PLOT
CONTOUR PLOT
TEMPERATURE PLOT
TIME: 120 sec154.40
141.95
129.49
117.04
104.58
92.13
79.67
67.22
54.76
42.31
29.85
17.40
T. Gernay, 2017
A model for concrete in fire: Validation
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At the material scale
ft
0.0
1.0
2.0
3.0
4.0
0.00 0.02 0.03 0.05 0.06
Str
ess [
MP
a]
Strain [%]
Gopalaratnam [test]
Model
Uniaxial tension
Softening
Stiffness reduction
Permanent strains
Axial strain
Volumetric strain
-40
-30
-20
-10
0
-0.50-0.40-0.30-0.20-0.100.000.10
Str
ess [M
Pa]
Strain [%]
Kupfer et al. [test 1969]
Model
Uniaxial compression
Post-peak
Dilatancy
T. Gernay, 2017
A model for concrete in fire: Validation
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At the structural scale
Reinforced concrete slab in fire
Slab 4.30m x 3.30m
Applied load 3.0 kN/m²
ISO fire during 180 minutes
from Lim et al., Eng. Struct. (2004)
T. Gernay, 2017
A model for concrete in fire: Validation
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At the structural scale
Reinforced concrete slab in fire: Thermal model
0
200
400
600
800
1000
1200
0 30 60 90 120 150 180
Tem
pera
ture
[C
]
Time [min]
Heated surface
55 mm depth
Unheated surface
SAFIR heated surface
SAFIR 55 mm
SAFIR unheated surface
T. Gernay, 2017
A model for concrete in fire: Validation
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At the structural scale
Reinforced concrete slab in fire: Mechanical model
XY
Z
5.0 E-01 m
Diamond 2011.a.2 for SAFIR
FILE: dalle_etc
NODES: 484
BEAMS: 0
TRUSSES: 0
SHELLS: 441
SOILS: 0
DISTRIBUTED LOADS PLOT
DISPLACEMENT PLOT ( x 2)
TIME: 3596 sec
-350
-300
-250
-200
-150
-100
-50
0
0 30 60 90 120 150 180
Ce
ntr
al d
efl
ecti
on
[m
m]
Time [min]
Test data [Lim et al. 2004]
Model
T. Gernay, 2017
• Compartment 15m x 9m
• Composite structure with cellular steel beams
• Two central steel beams are unprotected
• Mechanical load: 3.25 kN/m²
• Fire load: 700 MJ/m² (wood cribs)
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European project to investigate tensile membrane action
A model for concrete in fire: Simulation of a large-scale fire test
T. Gernay, 2017
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A model for concrete in fire: Simulation of a large-scale fire test
T. Gernay, 2017
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A model for concrete in fire: Simulation of a large-scale fire test
T. Gernay, 2017
1. Fire model to get the gas temperature evolution in the compartment
2. Thermal analysis of the sections of the structural components
3. Structural analysis of the composite floor and beams system
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0
200
400
600
800
1000
1200
0 20 40 60 80 100 120 140 160
Tem
pera
ture
[°C
]
Time [min]
Middle
Lef t bottom corner
Lef t top corner
Right bottom corner
Right top corner
OZone model
111 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 1 1
11
111
11 11 1111 11111 1
11
11
11
11
1 11111
111
1 11 11 111 11 11 11 11 11 11 11 11 11 11 11 11 11 11 111 111 1
1 11 1 1 1
1 11 1
1 1
1
1
1
1
1
2
1
2
1
2
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2
1
2
1
2
1
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1
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2222222222222222222
1
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1
2
1
2
1
2
1
2
X
Y
Z
Diamond 2011.a.2 for SAFIR
FILE: unpr1
NODES: 793
ELEMENTS: 683
FRONTIERS PLOT
CONTOUR PLOT
TEMPERATURE PLOT
TIME: 3600 sec848.90
747.33
645.75
544.18
442.60
341.03
239.45
137.88
36.30
F0
F0
F0 F0
F0
F0
F0
F0 F0
F0
F0
F0
F0 F0
F0
F0
F0
F0
F0
F0
F0
F0
F0
F0 F0
F0
F0F0
F0
F0 F0
F0
F0F0
F0
F0
F0F0
F0
F0 F0
F0
F0F0
F0
F0 F0
F0
F0F0
F0
F0
F0F0
F0
F0 F0
F0
F0
F0 F0
F0
F0
F0
F0
F0 F0
F0
F0
F0 F0
F0
F0
F0
F0
F0 F0
F0
F0
F0 F0
F0
F0
F0
F0
F0 F0
F0
F0
F0 F0
F0
F0
F0
F0
F0 F0
F0
F0
F0 F0
F0
F0
F0
F0
F0 F0
F0
F0
F0 F0
F0
F0
F0
F0
F0 F0
F0
F0
F0
F0 F0
F0
F0
F0
F0
F0
F0
F0
F0
F0
F0 F0
F0
F0
F0
F0 F0
F0
F0
F0
F0 F0
F0
X Y
Z
Diamond 2009.a.5 for SAFIR
FILE: UlsterH1
NODES: 2031
BEAMS: 260
TRUSSES: 0
SHELLS: 1664
SOILS: 0
BEAMS PLOT
SHELLS PLOT
IMPOSED DOF PLOT
prot1.tem
prot2.tem
prot3.tem
unpr1.tem
slab_side.tsh
slab_center.tsh
1 2
3
A model for concrete in fire: Simulation of a large-scale fire test
T. Gernay, 2017
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F0
F0
F0F0
F0
F0
F0
F0F0
F0
F0
F0
F0F0
F0
F0
F0
F0
F0
F0
F0
F0
F0
F0F0
F0
F0 F0
F0
F0F0
F0
F0 F0
F0
F0
F0 F0
F0
F0F0
F0
F0 F0
F0
F0F0
F0
F0 F0
F0
F0
F0 F0
F0
F0F0
F0
F0
F0F0
F0
F0
F0
F0
F0F0
F0
F0
F0F0
F0
F0
F0
F0
F0F0
F0
F0
F0F0
F0
F0
F0
F0
F0F0
F0
F0
F0F0
F0
F0
F0
F0
F0F0
F0
F0
F0F0
F0
F0
F0
F0
F0F0
F0
F0
F0F0
F0
F0
F0
F0
F0F0
F0
F0
F0
F0F0
F0
F0
F0
F0
F0
F0
F0
F0
F0
F0F0
F0
F0
F0
F0F0
F0
F0
F0
F0F0
F0
XY
Z
1.0 E+00 m
Diamond 2012.a.0 for SAFIR
FILE: ulsterft1b
NODES: 2031
BEAMS: 260
TRUSSES: 0
SHELLS: 1664
SOILS: 0
SOLIDS: 0
IMPOSED DOF PLOT
DISPLACEMENT PLOT ( x 2)
DISPLACEMENT PLOT ( x 2)
N1-N2 MEMBRANE FORCE PLOT
TIME: 3603.4 sec
- Membrane Force
+ Membrane Force
Results
Evolution of the vertical deflection Deflected shape and forces
A model for concrete in fire: Simulation of a large-scale fire test
T. Gernay, 2017
A model for concrete in fire: Implications for the field
Example: composite building design taking advantage of tensile membrane action
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Protect all elements individually
Performance-based design
40-55% of steel beams can be left unprotected
Prescriptive design
The target performance (stability) can be achieved with the PBD
→ significant cost reduction
→ but to demonstrate it, advanced analysis tools are needed
T. Gernay, 2017
Conclusion
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Performance based design in Structural Fire Engineering
Challenge: not a simple recipe… but a physically-based, specific solution
Opportunities: flexibility, efficiency and cost reduction for safe design
To understand the physics: models and numerical methods are crucial
New concrete model
For multiaxial stress states and elevated temperature
Successfully applied in a large range of applications
Impact
Better understanding of the behavior of materials and structures
Enables advanced analyses of structures in fire for innovative solutions
Implemented in SAFIR® thus available to the SFE community
T. Gernay, 2017
References
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Concrete constitutive model
Gernay, T., Franssen, J.-M. (2012). “A formulation of the Eurocode 2 concrete model at elevated temperature that includes an explicit term for transient creep”. Fire Safety J, 51, 1-9.
Gernay T., Millard A., Franssen J.M. (2013). “A multiaxial constitutive model for concrete in the fire situation: Theoretical formulation”. Int J Solids Struct, 50(22-23), 3659-3673.
Gernay, T., & Franssen, J.-M. (2015). “A plastic-damage model for concrete in fire: Applications in structural fire engineering”. Fire Safety J, 71, 268–278.
SAFIR® software
Franssen, J.-M., Gernay, T. (2017). “Modeling structures in fire with SAFIR®: Theoretical background and capabilities”. Journal of Structural Fire Engineering, 8(3).
Fire tests simulated
Lim, L., Buchanan, A., Moss, P., Franssen, J.-M. (2004). “Numerical modelling of two-way reinforced concrete slabs in fire”. Engineering Structures, 26, 1081-1091.
Vassart, O., Bailey, C. G., Hawes, M., Nadjai, A., Simms, W. I., Zhao, B., Gernay, T., Franssen, J.-M. (2012). “Large-scale fire test of unprotected cellular beam acting in membrane action”. Proc. ICE: Structures and Buildings, 165(7), 327–334.
T. Gernay, 2017
Thank you !
Performance-Based Fire Safety Engineering: Challenges and Opportunities
Dr. Thomas Gernay
Gustave Magnel International Award – New activities
SECO – Brussels, Belgium, 1st June 2017
F.R.S.-FNRS, University of Liege, Belgium