Workshop at Indian Institute of ScienceWorkshop at Indian Institute of Science9-13 August, 20109-13 August, 2010

BangaloreBangaloreIndiaIndia

Fire Safety Engineering & Structures Fire Safety Engineering & Structures in Firein Fire

Organisers:Organisers: CS Manohar and Ananth RamaswamyCS Manohar and Ananth RamaswamyIndian Institute of ScienceIndian Institute of Science

Speakers:Speakers: Jose Torero, Asif Usmani and Martin GillieJose Torero, Asif Usmani and Martin GillieThe University of EdinburghThe University of Edinburgh

Funding and Funding and Sponsorship:Sponsorship:

Structural Fire Engineering –

Design Approaches

Structural design for fireStructural design for firePRESCRIPTIVE APPROACHPRESCRIPTIVE APPROACH

Structural elements protected to remain Structural elements protected to remain under a certain temperature under a certain temperature

Fire scenario so that they retain adequate Fire scenario so that they retain adequate strength and stiffness to continue to carry strength and stiffness to continue to carry loads. This has been the traditional approach.loads. This has been the traditional approach.

PERFORMANCE BASED DESIGN APPROACHPERFORMANCE BASED DESIGN APPROACHEngineer must show structure meets certain Engineer must show structure meets certain

criteriacriteriaRequires understanding of behaviourRequires understanding of behaviour

Schematic of design methodsSchematic of design methods

Conventionaldesign

SCI Level-1Design guide

Advancedmethods

E.g. EurocodeParametric fire

Standard fire Natural fires

Singlememberbehaviour

Wholestructurebehaviour

EurocodesEurocodes

Replacing British (and other) Standards (for all Replacing British (and other) Standards (for all structural design)structural design)

9 Codes9 Codes Eurocode 1 - actionsEurocode 1 - actions Eurocode 2 - concreteEurocode 2 - concrete Eurocode 3 - steelEurocode 3 - steel Eurocode 4 - compositeEurocode 4 - composite EtcEtc All available online via the library websiteAll available online via the library website

Eurocode 1Eurocode 1 Covers “actions” for all designCovers “actions” for all design

– Various parts and sectionsVarious parts and sections Part 1-2 covers fire actionsPart 1-2 covers fire actions Allows forAllows for

– Standard fire curveStandard fire curve– Natural firesNatural fires– Computer analysis of firesComputer analysis of fires

Provides background information onProvides background information on– Parametric firesParametric fires– Fire load densitiesFire load densities– etcetc

Procedure for Fire Engineering Procedure for Fire Engineering Design (1)Design (1)

1.1. Obtain compartment sizeObtain compartment size– From geometry/use of structureFrom geometry/use of structure– Ventilation openings also neededVentilation openings also needed

2.2. Estimate loads on structureEstimate loads on structure– Fire load based on use of structureFire load based on use of structure– Mechanical load with low safety factorsMechanical load with low safety factors

3.3. Estimate gas temperaturesEstimate gas temperatures– Swedish curvesSwedish curves– Parametric curvesParametric curves– Zone modelsZone models– CFDCFD

Procedure for Fire Engineering Procedure for Fire Engineering Design (1)Design (1)

4.4. Estimate structural temperaturesEstimate structural temperatures– Simple calculationSimple calculation– Computer analysisComputer analysis

5.5. Check resistance of structure to fireCheck resistance of structure to fire– Calculation on single elementsCalculation on single elements– SCI style design guidesSCI style design guides– Computer analysisComputer analysis

Loads for Fire DesignLoads for Fire Design

Mechanical Loads for Fire Mechanical Loads for Fire DesignDesign

Dead loads always presentDead loads always present– γγ (safety factor) normally taken as 1 (safety factor) normally taken as 1

Imposed loads taken as less than design Imposed loads taken as less than design loadload– γγ typically taken as 0.4-0.9 typically taken as 0.4-0.9

Eurocode 1 hasEurocode 1 has– 1 x dead load +0.9 x permanent live load 1 x dead load +0.9 x permanent live load

+0.5 x temporary live load+0.5 x temporary live load

Fire LoadsFire Loads

Measure of the combustible material in a fire Measure of the combustible material in a fire compartmentcompartment– Normally measured in MJ/mNormally measured in MJ/m2 2 floor areafloor area– REMEMBER temperature calculations often use total REMEMBER temperature calculations often use total

surface area of compartmentsurface area of compartment In design adjusted forIn design adjusted for

– Compartment areaCompartment area– ““Fire activation risk”Fire activation risk”– EtcEtc

Extract from Eurocode availableExtract from Eurocode available

Estimating Compartment Estimating Compartment TemperaturesTemperatures

Temperatures in compartment Temperatures in compartment firesfires

Need to know atmosphere temperatures in Need to know atmosphere temperatures in order to estimate structural temperaturesorder to estimate structural temperatures

Simple approach uses energy balance in a Simple approach uses energy balance in a compartmentcompartment

Swedish method the most common (from Swedish method the most common (from physics)physics)

Similar curves in parametric form in the Similar curves in parametric form in the Eurocode 1 Part 2 (curve fire to Swedish Eurocode 1 Part 2 (curve fire to Swedish method)method)

Compartment FiresCompartment Fires

Energy balance for a Energy balance for a compartmentcompartment

openinghrough t

radiatedEnergy

t wallscompartmen

gh lost throuEnergy

gases of exchange

by lost Energy

combustionby

releasedEnergy

R

w

l

c

Q

Q

Q

Q

RQwQ

LQcQ

Qc

QW

QW

QL

QR

Assumptions in Swedish methodAssumptions in Swedish method

No heat built-up in pre-flashover phase of No heat built-up in pre-flashover phase of firefire

Temperature uniform in the compartmentTemperature uniform in the compartment Uniform heat transfer coefficient in Uniform heat transfer coefficient in

compartment boundariescompartment boundaries All combustion takes place in the All combustion takes place in the

compartmentcompartment

Evaluation of terms - QEvaluation of terms - Qcc

Heat release rate given by Kawagoe equation Heat release rate given by Kawagoe equation asas

Assumes all fuel is woodAssumes all fuel is wood Set QSet Qcc=0 when all fuel consumed at time=0 when all fuel consumed at time

cvvc HHAQ 092.0

vv HA

Mt

092.0

Evaluation of Terms - QEvaluation of Terms - QRR

Radiation through opening governed by Stefan-Radiation through opening governed by Stefan-Boltzmann equationBoltzmann equation

Epsilon value uncertain. Drysdale suggestsEpsilon value uncertain. Drysdale suggests

With K=1.1mWith K=1.1m-1-1 and x and xff the flame thickness the flame thickness

)( 40

4 TTAQ gvR

)(1 fKx

e

Evaluation of terms - QEvaluation of terms - QLL

The rate of energy loss due to exchange of The rate of energy loss due to exchange of gases isgases is

The mass flow rate is determined semi-The mass flow rate is determined semi-empirically by Prahl and Emmons using empirically by Prahl and Emmons using Bernoulli’s equationBernoulli’s equation

)( 0TTcmQ gpl

5.05.0 HAm v

Evaluation of terms - QEvaluation of terms - QWW

Convection into wallConvection into wall Conduction through wallConduction through wall Convection out of wallConvection out of wall Not steady stateNot steady state

Temperatures in a compartment Temperatures in a compartment boundaryboundary

Evaluation of terms - QEvaluation of terms - QWW

21

21

11

111

2221

kx

kx

TT

kx

TT

t

Txc

g

Heat transfer into first layer of wall

Rate of change in stored energy

Convectioninto layer

Conduction outof layer

Substitute in Heat Balance Substitute in Heat Balance EquationEquation

1

2/1

1

1

10

2/1

21

)(09.0

)(2

1)(09.0

kx

AAHAc

qTTkx

AATHAcq

T

ivtvp

rgwtvpc

g

IntrinsicNeeds to be solved numerically

Swedish CurvesSwedish Curves

Swedish CurvesSwedish Curves

Swedish CurvesSwedish Curves

NOTE: Fire load calculated based on NOTE: Fire load calculated based on TOTAL surface area of the compartmentTOTAL surface area of the compartment

Implicit nature awkwardImplicit nature awkward

Parametric T-t CurvesParametric T-t Curves

Used in EurocodesUsed in Eurocodes Avoid implicit nature of Swedish CurvesAvoid implicit nature of Swedish Curves

– Growth curve based on opening factorGrowth curve based on opening factor– Peak temperature (time) based on fuel loadPeak temperature (time) based on fuel load– Linear decay curveLinear decay curve

0

100

200

300

400

500

600

700

800

900

1000

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Time (hr)

Tem

pera

ture

(C

)

Eurocode parametric temperature-timeCurveq=400MJ/m2

A=400m2

Peak temp depends onfire load or ventilation

Linear decay phase

STEEL STRUCTURESSTEEL STRUCTURES

GeneralGeneral

Actions on structure in fire < Strength of structure in fireActions on structure in fire < Strength of structure in fire

Spray protection: Spray protection: £6/m£6/m22 1 hour, wet trade, poor 1 hour, wet trade, poor

application in winter conditionsapplication in winter conditions

Board protection: Board protection: £8/m£8/m2 2 1 hour, 1 hour, Higher labour – fixing etc. Higher labour – fixing etc. Not good for external, Slower than sprayNot good for external, Slower than spray

Blanket: Blanket: same price as boarding, poor same price as boarding, poor

appearance, appearance, dry tradedry trade

Intumescents: Intumescents: Most expensive material, off site Most expensive material, off site

optionoption

PaintsPaints– React to heat, React to heat,

swelling to form a swelling to form a protective coating protective coating

MasticsMastics Epoxy intumescentEpoxy intumescent

Off site intumescentOff site intumescent Plates and bolts need to be cleaned, primed and Plates and bolts need to be cleaned, primed and

painted on sitepainted on site Bolt caps recently introduced to the marketBolt caps recently introduced to the market Aiming for a completely offsite productAiming for a completely offsite product

Why contractor may propose Why contractor may propose off-site application:off-site application:

Faster construction Faster construction Cost savingsCost savings Reduction in site disruptionReduction in site disruption Improved safetyImproved safety Better QABetter QA EnvironmentalEnvironmental Where site access is limitedWhere site access is limited

Disadvantages of off site Disadvantages of off site applicationapplication

Careful handling requiredCareful handling required Mechanical damageMechanical damage Coat connections once erectedCoat connections once erected Damaged by through deck stud weldingDamaged by through deck stud welding Water-based systems are not Water-based systems are not

sufficiently durable for off-site sufficiently durable for off-site applicationapplication

Automated application process at Automated application process at ENOB LtdENOB Ltd

Elimination of topcoat?Elimination of topcoat? Top coat functionTop coat function

– improved durability, cleanability, appearanceimproved durability, cleanability, appearance– protects tfi from mechanical damage, uv degradationprotects tfi from mechanical damage, uv degradation

Why remove: Cost!Why remove: Cost! Do considerDo consider

– in internal, heated, air-conditioned environmentsin internal, heated, air-conditioned environments– where tfi is protected from damagewhere tfi is protected from damage

Don’t considerDon’t consider– where high RH, condensation are anticipatedwhere high RH, condensation are anticipated

NBNB– ponding more likely to cause water damageponding more likely to cause water damage– programme delays could lead to damageprogramme delays could lead to damage

Appearance on site (without top Appearance on site (without top coat)coat)

Elimination of primer?Elimination of primer? Primer function:Primer function:

– prevent corrosion of steelprevent corrosion of steel– provide good substrate to which tfi adheresprovide good substrate to which tfi adheres

Why remove: CostWhy remove: Cost Only consider in C1 environmentOnly consider in C1 environment NB:NB:

– mechanical damage to tfi will allow rustingmechanical damage to tfi will allow rusting– making good - abrading, spot priming, tfimaking good - abrading, spot priming, tfi– uncoated areas may be primed or left as black steeluncoated areas may be primed or left as black steel– delays - loss of tfi & rusted steeldelays - loss of tfi & rusted steel

Pros and Cons of Protection Pros and Cons of Protection materialsmaterials

SystemSystem CostCost Steel surface Steel surface preparationpreparation

DurabilityDurability Max FRMax FR(hrs)(hrs)

SpraySpray LowLow Not usuallyNot usually Internal and Internal and externalexternal

44

BoardBoard Mineral fibre-Low Mineral fibre-Low Plasterboard-med Plasterboard-med Calcium silicate-Calcium silicate-highhigh

NoNo Internal and Internal and externalexternal

224 for Calcium 4 for Calcium silicatesilicate

IntumescentIntumescent 1hr low1hr low2 hrs high2 hrs highEpoxy very highEpoxy very high

YesYesBlast cleaned + Blast cleaned + primerprimer

Internal and Internal and externalexternal

22

EncasementEncasement Very HighVery High NoNo Internal and Internal and externalexternal

Pros and Cons of Protection Pros and Cons of Protection materialsmaterials

SystemSystem Impact Abrasion Impact Abrasion resistanceresistance

AdvantagesAdvantages LimitationsLimitations

SpraySpray Depends on Depends on densitydensity

Easy/rapid to applyEasy/rapid to applyLow costLow costComplex details coveredComplex details coveredCementitious sprays inhibit Cementitious sprays inhibit corrosioncorrosionCan be applied directlyCan be applied directly

Wet tradeWet tradeAffects other tradesAffects other tradesPoor in winter conditionsPoor in winter conditionsPoor appearancePoor appearanceOven spray on siteOven spray on sitePrimer can reduce Primer can reduce adhesionadhesion

BoardBoard Med-goodMed-good Surface finish in final priceSurface finish in final priceClean try trade on siteClean try trade on siteFactory manufactured guaranteed Factory manufactured guaranteed thicknessthicknessBoxed appearance suitable for Boxed appearance suitable for visible membersvisible membersGood surface finish possibleGood surface finish possible

Higher labourHigher labourNot good for externalNot good for externalSlower than spraySlower than sprayFitting around detailsFitting around details

IntumescentIntumescent Low-medLow-med ThinThinAppearanceAppearanceDecorative finishes availableDecorative finishes availableComplex details coveredComplex details coveredOff siteOff sitePost protection fixing simplifiedPost protection fixing simplifiedRapid application on siteRapid application on site

Must specify for Must specify for appropriate durabilityappropriate durabilityCost higher than spray Cost higher than spray but comparable with but comparable with boardboardWet trade on siteWet trade on siteOver sprayOver sprayEnvironmental conditionsEnvironmental conditions

Market sharesMarket shares Approximate market shares by mApproximate market shares by m22::

Vermiculite sprayVermiculite spray 30%30%

BoardBoard 50%50%

Thin film intumescentsThin film intumescents– On site appliedOn site applied– Off site appliedOff site applied

20%20%90%90%10%10%

EpoxyEpoxy specific apps onlyspecific apps only

CostsCosts Approximate applied costs £/mApproximate applied costs £/m2 2 (1 (1 hour):hour): Vermiculite Vermiculite sprayspray

66

BoardBoard 8-158-15 Thin film Thin film intumescentsintumescents

– On site appliedOn site applied– Off site appliedOff site applied

10-1310-1313-1513-15

EpoxyEpoxy ~~1919

Partially protected steelPartially protected steel

Web in-filled columnsWeb in-filled columns– blockworkblockwork– concrete unreinforcedconcrete unreinforced– concrete reinforcedconcrete reinforced

Concrete filled hollow sectionsConcrete filled hollow sections

Typically 30-90 minutes FRTypically 30-90 minutes FR

Partially protected steel –Partially protected steel –Composite floor systemsComposite floor systems

Shelf Angle Floor beamsShelf Angle Floor beams Slim floor beamsSlim floor beams

– SLIMFLORSLIMFLOR– SLIMDEKSLIMDEK

Up to 60 minutes possible with Up to 60 minutes possible with bare steel flange.bare steel flange.

90 and 120mins fire resistance 90 and 120mins fire resistance possible with protected flangepossible with protected flange

Hidden costsHidden costs The quality of finish – decorative finishes are more The quality of finish – decorative finishes are more

expensiveexpensive Difficulty or ease of access, manpower, time on siteDifficulty or ease of access, manpower, time on site Size of projectSize of project Location of project e.g. tall congested city centreLocation of project e.g. tall congested city centre Type, size and weight of steel sectionType, size and weight of steel section

CONCRETE STRUCTURESCONCRETE STRUCTURES

Heat Heat penetration penetration in concrete in concrete

beamsbeams

Heat penetration in concrete Heat penetration in concrete slabsslabs

(mm)