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Linking Fire Severity and Fire Resistance for the Assessment of Structural Performance José L. Torero School of Civil Engineering The University of Queensland Australia
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  • Linking Fire Severity and Fire Resistance for the Assessment of Structural Performance

    José L. Torero School of Civil Engineering The University of Queensland Australia

  • Structural Behaviour in Fire

    • Fire Resistance • A regulatory terminology defining compliance

    with required rules established to implicitly define performance of structural systems in fire

    • Fire Severity • A quantitative, physically based, assessment of

    structural solicitation (can and should be linked to performance)

  • Building Code of Australia

    • Most critical design load in accordance with AS 1170.0 (clause B.11(b));

    • Actions include thermal effects (clause B1.2(e,vii)). • Resistance of steel structures in accordance with AS

    4100 (clause B1.4(c,i)

    AS 1170.0

    • Structural will not be damaged disproportionally to the original cause (e.g. events like fire) (clause 3.2(b));

    • Structural design in accordance with clause 2.2 (clause 3.2);

    • Design in accordance with combination actions in section 4 (clause 2.2(g));

    • Combination factors include thermal actions arising from the fire (clause 4.2.4)

    • In terms of FRL adequate loadbearing capacity as determined by AS 1530.4 (definitions)

    D.T.S. Language

  • Base

    d on

    Fur

    nace

    Test

    Dat

    a ad

    opte

    d in

    the

    Euro

    code

    s (20

    08)

    • D

  • True Performance Assessment: The Fire

    Fire Dynamics

    Heat Transfer

    𝜌𝜌𝐶𝐶𝑝𝑝𝜕𝜕𝜕𝜕𝜕𝜕𝜕𝜕

    = 𝑘𝑘𝜕𝜕2𝜕𝜕𝜕𝜕𝑥𝑥2

    −𝑘𝑘𝜕𝜕𝜕𝜕𝜕𝜕𝑥𝑥�𝑥𝑥=0

    = �̇�𝑞"𝑁𝑁𝑁𝑁𝑁𝑁

    𝜕𝜕𝜕𝜕𝜕𝜕𝑥𝑥�𝑥𝑥=𝑥𝑥𝑆𝑆

    = 0

    𝜕𝜕 𝜕𝜕 = 0 = 𝜕𝜕0

    Structural Analysis

  • Challenge 1 How does thermal expansion effect a

    structure?

    Structural Analysis

    Challenge 2 How does thermal curvature effect a

    structure?

    Challenge 3 Preventing failure

    due to strength degradation

    Challenge 4 Limiting deflections

    due to loss of stiffness

  • Wood Cribs

  • Fire: Heat Fluxes evolve in space and time

    0 1 2 3 4 5 6 7 8 9 10 11 120

    1

    2

    3

    80

    8080

    80

    60 6060

    4040

    40

    20 20 20

    100

    100100

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    120

    120

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    120140

    160

    160160140160

    140160140

    140

    180

    180

    160140

    140

    18016

    060

    0 1 2 3 4 5 6 7 8 9 10 11 120

    1

    2

    3

    2020

    60 60 60

    40 40 40

    80 80 80

    2020

    20

    20

    20

    60

    4060

    40

    40 80100

    120100

    20

    20

    0 1 2 3 4 5 6 7 8 9 10 11 120123456789

    101112 120

    120

    80

    120

    120

    120

    120

    120

    120

    160

    120

    80

    160

    160

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    200

    200160

    120

    200200

    120200

    200

    240

    160

    200

    160

    120

    160

    8012

    080

    8080

    228kW2

    Time

    Space

  • Regime II: Fuel Controlled

    Thomas and The Compartment Fire

    Regime I: Ventilation Controlled

  • F,rq ′′

    W,rq ′′

    g,rq ′′S,rq ′′)TT(hq SgC −=′′

  • Fire Dynamics – The Compartment Fire

    Regime I Regime II

    Regime I

    Regime II

    Theory

    Theory

    A0 H0

    A

    𝐴𝐴𝐴𝐴0 𝐻𝐻0

  • Fire Dynamics – Thermal Load

    T [oC]

    t [min] tBO

    Heating

    Cooling

    R = 0.1 AwH1/2 (kg/s)

    Kawagoe (1958) Thomas (1960)

    𝜕𝜕𝐵𝐵𝐵𝐵 =𝑀𝑀𝐹𝐹𝑅𝑅

    𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘/𝑠𝑠

    = 𝑠𝑠

  • Parametric Fires - Eurocodes MF

  • Real Fire

    Thomas

    Parametric

    Standard: Fire Resistance

  • The Origins

    • Regulations and Fire Service are born after the great fires of New York (1835), London (1861), Chicago (1871), Boston (1872) and San Francisco (1906), etc.

    • Rules stem from the experience of fire fighters, architects and engineers

    • Very poor understanding of human behaviour, fire dynamics and structural behaviour

  • 1850-1940 • Building Separation Distances • Compartmentalization • Size and separation of windows • Maximum Egress distances • Sprinklers • Passive fire protection – fire proofing • 1st Professional Fire Brigade – James

    Braidwood (1824)

    http://upload.wikimedia.org/wikipedia/commons/0/03/Distillery_3.jpg

  • Fire Resistance

    • Developed in the 19th Century as a result of the introduction of steel in construction

    • Based on numerous test conducted prior to 1930 • Semi-formalized in the 1920’s • Formalized in 1928 (Ingberg S.H., “Fire loads:

    Guide to the application of fire safety engineering principles,” Quarterly Journal of the National Fire Protection Association, 1, 1928.)

  • Standard Fire + Rating • Worst Case Scenario • Curve is defined by an envelope to all fires • Rating is defined by total fuel consumption

    0

    250

    500

    750

    1000

    1250

    0 30 60 90 120 150 180time [minutes]

    Tem

    pera

    ture

    [oC

    ]

    Fire (BS-476-Part 8)

    Increasing Fuel Load

  • Restraint + Compartmentation • Allows to approximate global structural

    behaviour to single element – Restraint enables effective load transfer

    Restraint

    http://www.google.ch/imgres?q=flame+sketches&hl=en&sa=G&biw=1366&bih=571&gbv=2&tbm=isch&tbnid=bvt-Gf4aLDPDyM:&imgrefurl=http://monsterguide.net/how-to-draw-flames&docid=KgIZn7y1ucU37M&imgurl=http://monsterguide.net/images/flameStage-4.gif&w=147&h=160&ei=vCaxTqS0OuXe4QT5s6W8AQ&zoom=1

  • Furnace Testing

    • Single elements can be tested within a controlled environment

    • The environment has to create “worst case scenario” condition

  • Standard Fire

    0

    250

    500

    750

    1000

    1250

    0 30 60 90 120 150 180time [minutes]

    Tem

    pera

    ture

    [oC

    ]

    Fire (BS-476-Part 8)

    Critical Temperature

    Rating

    Structural Element

  • Critical Temperature • Based on material properties – steel

    – Steel structural element (steel design) – Reinforcement - prestressing (concrete design)

    𝑁𝑁𝐹𝐹𝑁𝑁𝑈𝑈

    = 0.7

    𝑁𝑁𝐹𝐹𝑁𝑁𝑈𝑈

    = 0.5

    𝑁𝑁𝐹𝐹𝑁𝑁𝑈𝑈

    = 0.2

  • Importance • The building will be designed in a

    manner that allows the test to be a scenario worse than any possible fire

    • Fire protection will guarantee that the failure conditions described in the test will never be attained

    • Architects will prescribe fire protection

    • Separated structural analysis from fire safety through the development of a standardized testing procedure

    • Enabled structural engineers to design tall buildings

  • What is Equivalent?

    • Energy input – Equivalence Methods? • If we provide the same amount of energy – will

    the outcome be the same?

  • The Objective is not an – Equivalent level of energy but an Equivalent structural

    behaviour?

    Broadgate Phase 8 Furnace Recreation

  • Linking Severity to Resistance

    Time (s)

    0 10 20 30 40 50 60 70 80 90 100 110 120

    Ver

    tical

    Def

    lect

    ion

    (mm

    )

    -1000

    -750

    -500

    -250

    0

    Central deflect ion - Parametric Heat ingCentral deflect ion - Heat Flux Model

    δ

    Simple

    Detailed

  • Time (s)

    0 10 20 30 40 50 60 70 80 90 100 110 120

    Ver

    tical

    Def

    lect

    ion

    (mm

    )

    -1000

    -750

    -500

    -250

    0

    Central deflect ion - Parametric Heat ingCentral deflect ion - Heat Flux Model

    Linking Severity to Resistance

    δ

    Simple

    Detailed

  • Summary • Fire Resistance is a regulatory definition – Many

    issues with this implicit form of performance • Fire Severity is an explicit physical solicitation of

    the structure due to fire – Can be defined at many levels of precision

    • Equivalency means equal desired outcomes – Desired outcome is adequate Structural Behaviour

    • Outcome: Equal Explicit Structural Performance

    Slide Number 1Structural Behaviour in FireD.T.S. LanguageBased on Furnace Test Data adopted in the Eurocodes (2008)True Performance Assessment: The FireStructural AnalysisSlide Number 7Fire: Heat Fluxes evolve in space and timeThomas and The Compartment FireSlide Number 10Fire Dynamics –�The Compartment FireFire Dynamics –�Thermal LoadParametric Fires - EurocodesSlide Number 14The Origins1850-1940Fire ResistanceStandard Fire + RatingRestraint + CompartmentationFurnace TestingStandard FireCritical TemperatureImportanceWhat is Equivalent?The Objective is not an – Equivalent level of energy but an Equivalent structural behaviour?Linking Severity to ResistanceLinking Severity to ResistanceSummary


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