Performance-based Fire Safety Engineering: Challenges and Opportunities

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Performance-Based Fire Safety Engineering:

Challenges and Opportunities

Gustave Magnel International Award – New activities SECO – Brussels, Belgium, 1st _{June 2017}

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Fire safety: a major issue

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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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Fire Safety Engineering: a multidisciplinary field

Structural fire engineering is a key component

Design the structures for adequate response under fire

To achieve the goal in Fire Safety Engineering, it requires implementation of multiple objectives based on various disciplines

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Prescriptive vs Performance-Based approach

Prescribes methods to build vs Prescribes a result (performance)

→ Simplicity vs → Flexibility

PRESCRIPTIVE

following codes and standards

PERFORMANCE-BASED

based on the physics of the problem

DESIGN APPROACH

For 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?

 Realistic fire scenarios

q 0 600 1200 0 60 [°C] 120 180 Time [min]

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Performance-Based: Why it matters? What can we gain?

 Robustness and whole building behavior

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Performance-Based: Why it matters? What can we gain?

 Consideration of specific risk associated with the building

Input variable

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Performance-Based: Why it matters? What can we gain?

 Consideration of specific risk associated with the building  Cost effective fire resistance designs

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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

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Example of research project: How to model concrete in fire?

Challenges

numerically robust applicable to large structures material behavior

+ at elevated temperature

Need

 Concrete is one of the most used materials  Its behavior is affected by fire

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A model for concrete in fire: Theory

Plasticity Damage Plastic-damage

Modeling

 Traditional plasticity approach

 Damage proposed at ambient temperature

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A model for concrete in fire: Theory

-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 s tr e s s [M Pa ] 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

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A model for concrete in fire: Theory

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 -0.005 0 stress

[MPa] 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] Uniaxial behavior in tension

20°C 200°C 400°C 500°C

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A model for concrete in fire: Implementation

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)

X Y Z

Diamond 2009.a.5 for SAFIR

FILE: joint9p NODES: 31502 ELEMEN TS: 25411 SOLIDS PLOT FRONTIERS PLOT CONTOUR PLOT TEMPERATURE PLOT TIME: 120 s ec 154.40 141.95 129.49 117.04 104.58 92.13 79.67 67.22 54.76 42.31 29.85 17.40

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A model for concrete in fire: Validation

At the material scale

f_t 0.0 1.0 2.0 3.0 4.0 0.00 0.02 0.03 0.05 0.06 S tre s s [ M P a ] Strain [%] Gopalaratnam [test] Model Uniaxial tension  Softening  Stiffness reduction  Permanent strains -40 -30 -20 Str e s s [M Pa ] Kupf er et al. [test 1969] Model Uniaxial compression  Post-peak  Dilatancy

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A model for concrete in fire: Validation

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

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A model for concrete in fire: Validation

Reinforced concrete slab in fire: Thermal model

200 400 600 800 1000 1200 T e m p e ra tu re [ C]

Heated surf ace 55 mm depth Unheated surf ace SAFIR heated surf ace SAFIR 55 mm

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A model for concrete in fire: Validation

Reinforced concrete slab in fire: Mechanical model

X Y

Z

5.0 E-01 m

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 C e n tr a l d e fl e c ti o n [ m m ] Time [min]

Test data [Lim et al. 2004] Model

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• 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)

European project to investigate tensile membrane action

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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

0 200 400 600 800 1000 1200 0 20 40 60 80 100 120 140 160 T e m p e ra tu re [ °C] Time [min] Middle Lef t bottom corner Lef t top corner Right bottom corner Right top corner OZone model 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11111111111111 1 1 11 1 1 11 1 111 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 2 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 2 1 2 1 2 1 2 1 2 1 2 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 sec 848.90 747.33 645.75 544.18 442.60 341.03 239.45 137.88 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 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

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

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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 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 1 .0 E +0 0 m Dia mo nd 2 01 2.a .0 fo r S A F IR FIL E : u ls te rft 1b NO DES : 2 0 31 BE AM S: 260 TR US SE S: 0 SH E LL S: 1 66 4 SO I LS : 0 SO LID S: 0 IM PO SE D D OF P LO T DIS PL AC E M E N T P LO T ( x 2 ) DIS PL AC E M E N T P LO T ( x 2 ) N1-N2 ME MB RA NE FO RC E P LO T TIM E : 3 60 3 .4 s ec - M em bra n e Fo rc e + M em bra n e Fo rc e Results

Evolution of the vertical deflection Deflected shape and forces

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A model for concrete in fire: Implications for the field

Example: composite building design taking advantage of tensile membrane action

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

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Conclusion

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

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References

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.

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Thank you !

Performance-Based Fire Safety Engineering: Challenges and Opportunities

Gustave Magnel International Award – New activities SECO – Brussels, Belgium, 1st _{June 2017}