欧洲建筑防火规范(Introduction_to_Eurocode_Structural_Fire_Engineering)

IntroductiontoEurocodeStructuralFireEngineeringStructuralSteelworkEurocodesSteelsoftensprogressivelyfrom100-200°Cup.Only23%ofambient-temperaturestrengthremainsat700°C.At800°Cstrengthreducedto11%andat900°Cto6%.Meltsatabout1500°C.Steelstress-straincurvesathightemperatures12341000°C800°C20°C200°C400°C600°CStrain(%)NormalisedstressConcretealsolosesstrengthandstiffnessfrom100°Cupwards.Doesnotregainstrengthoncooling.Hightemperaturepropertiesdependmainlyonaggregatetypeused.Concretestress-straincurvesathightemperaturesThefiretriangleFuel+Oxidant=CombustionproductsCH4+O2=CO2+2H20Stagesofanaturalfire-andthestandardfiretestcurveFlashoverTheEC1(ISO834)standardfirecurve30010020004005006007008009001000060012001800240030003600Time(sec)GasTemperature(°C)576675739781842945200400600800100012000120024003600Time(sec)GasTemperature(°C)Fireresistancetimesbasedonstandardfurnacetests-NOTonsurvivalinrealfires.EC1ParametricFiretemperature-timecurves.Basedonfireloadandcompartmentproperties(<500m2).Onlyallowedwithcalculationmodels.DifferentEC1time-temperaturecurvesTemperatureLoad-bearingresistanceTimeTimeUsedtoratefireseverityorelementperformancerelativetofurnacetest.MatchestimestogiventemperatureinanaturalfireandinStandardFire.Time-equivalenceFurnacetestsonstructuralelementsFireTestingLoadkeptconstant,firetemperatureincreasedusingStandardFirecurve.Maximumdeflectioncriterionforfireresistanceofbeams.Loadcapacitycriterionforfireresistanceofcolumns.ProblemsLimitedrangeofspansfeasible,simplysupportedbeamsonly.Effectsofcontinuityignored.Beamsfailby“run-away”.Restrainttothermalexpansionbysurroundingstructureignored.StandardfireresistancefurnacetestStandardfireresistancefurnacetestStandardFireStructuralfireprotectionPassiveProtectionInsulatingBoardGypsum,Mineralfibre,Vermiculite.Easytoapply,aestheticallyacceptable.Difficultieswithcomplexdetails.CementitiousSpraysMineralfibreorvermiculiteincementbinder.Cheaptoapply,butmessy;clean-upmaybeexpensive.Pooraesthetics;normallyusedbehindsuspendedceilings.IntumescentPaintsDecorativefinishundernormalconditions.Expandsonheatingtoproduceinsulatinglayer.Cannowbedoneoff-site.InherentfireprotectiontosteelbeamsStructuralfireprotectionCompositesectionsPassiveProtection–CompositesectionsTraditionaldownstandbeamtopflangeupperfacetotallyshieldedbytheslabStructuralfireprotectionCompositesectionsPassiveProtection–CompositesectionsBeamswithconcreteencasementHavehighfireresistance(upto180minutes).Involvecomplicatedconstructionofjoints.Requireformwork.StructuralfireprotectionCompositesectionsPassiveProtection–CompositesectionsSteelbeamswithpartialconcreteencasementConcretebetweenflangesreducestherateofheatingoftheprofile'swebandupperflange.Concretebetweenflangescontributestotheload-bearingresistance.Thebeamcanbefabricatedintheworkshopwithouttheuseofformwork.Simpleconstructionofjoints.LoadreductionfactorinfireEstablishingFireResistance:StrategiesEurocodesallowfireresistancetobeestablishedinanyof3“domains”:Time:tfi.d>tfi.requLoadresistance:Rfi.d.t>Efi.d.tTemperature:cr.d>dMaterialpropertiesSteelMechanical(effectiveyieldstrength,elasticmodulus,...)ConcreteThermal(thermalexpansion,thermalconductivity,specificheat)Mechanical(compressivestrength,secantmodulus,...)Thermal(thermalexpansion,thermalconductivity,specificheat)Strength/stiffnessreductionfactorsforelasticmodulusandyieldstrength(2%strain).Strain(%)0.51.01.52.0Stress(N/mm2)03002502001501005020°C200°C300°C400°C500°C600°C700°C800°CSteelstress-straincurvesathightemperaturesDegradationofsteelstrengthandstiffness0300600900120010080604020%ofnormalvalueTemperature(°C)StrengthandstiffnessreductionsverysimilarforS235,S275,S355structuralsteelsandhot-rolledreinforcingbars.(SS)Cold-workedreinforcingbarsS500deterioratemorerapidly.(Rft)10050020040060080010001200Temperature(°C)Strength(%ofnormal)DegradationofconcretestrengthandstiffnessConservativefornormaldensityconcretewithcalcareousaggregates,.StrengthreductionfactorsConcretestrengthinheatingandcoolingThermalexpansionofsteelandconcrete00,51,01,52,02,53,03,54,04,5100200300400500600700800900Temperature(°C)ExpansionCoeff/°C(x10-6)OthersteelthermalpropertiesOtherconcretethermalpropertiesThermalanalysisThermalanalysis:bothEC3Part1.2andEC4Part1.2unprotectedandprotectedsteelbeamsLowerandupperflangesConsiderablydifferenttemperaturespropercalculationoftemperatures!TemperatureincreaseofunprotectedsteelSectionfactorAm/V-unprotectedsteelmembers!TemperatureincreaseofprotectedsteeldpSomeheatstoredinprotectionlayer.SectionfactorAm/V-inherentlyprotectedsystemsSectionfactorAp/V-protectedsteelmembers!