歐洲建筑防火規(guī)范(Introduction-to-Eurocode-Structural-Fire-Engineering)共33張幻燈片

1、Introduction to Eurocode Structural Fire EngineeringStructural Steelwork Eurocodes1Strain (%)0.51.01.52.0Stress (N/mm2)03002502001501005020C200C300C400C500C600C700C800CSteel softens progressively from 100-200C up.Only 23% of ambient-temperature strength remains at 700C. At 800C strength reduced to 1

2、1% and at 900C to 6%. Melts at about 1500C. Steel stress-strain curves at high temperatures21.0012341000C800C20C200C400C600CStrain (%)Normalised stressConcrete also loses strength and stiffness from 100C upwards.Does not regain strength on cooling. High temperature propert

3、ies depend mainly on aggregate type used. Concrete stress-strain curves at high temperatures3The fire triangleFuel + Oxidant = Combustion productsCH4 + O2 = CO2 + 2H20Reaction occurs when Oxygen/fuel mixture hot enoughHeatOxygenFuel4Stages of a natural fire - and the standard fire test curveCooling

4、.ISO834 standard fire curveIgnition - SmoulderingPre-FlashoverHeatingPost-Flashover1000-1200CNatural fire curveTimeTemperatureFlashover5The EC1 (ISO834) standard fire curve30010020004005006007008009001000060012001800240030003600Time (sec)Gas Temperature (C)5766757397818429456200400600800100012000120

5、024003600Time (sec)Gas Temperature (C)Typical EC1 Parametric fire curveExternal FireStandard FireHydrocarbon FireFire resistance times based on standard furnace tests - NOT on survival in real fires.EC1 Parametric Fire temperature-time curves. Based on fire load and compartment properties (500m2). O

6、nly allowed with calculation models.Different EC1 time-temperature curves7CompartmentTemperatureLoad-bearing resistanceTimeTimeFire severity time equivalentUsed to rate fire severity or element performance relative to furnace test.Matches times to given temperature in a natural fire and in Standard

7、Fire.Fire resistance time equivalentStandard fireNatural fireElementTime-equivalence8Furnace tests on structural elementsFire Testing Load kept constant, fire temperature increased using Standard Fire curve. Maximum deflection criterion for fire resistance of beams. Load capacity criterion for fire

8、resistance of columns.ProblemsLimited range of spans feasible, simply supported beams only.Effects of continuity ignored. Beams fail by “run-away”.Restraint to thermal expansion by surrounding structure ignored. 9Standard fire resistance furnace test1002003000120024003600Time (sec)Deflection (mm)10S

9、tandard fire resistance furnace test1002003000120024003600Time (sec)Deflection (mm)Span2/400dIf rate tfi.requLoad resistance:Rfi.d.t Efi.d.tTemperature:cr.d dUsually only directly feasible using advanced calculation models.Feasible by hand calculation. Find reduced resistance at design temperature.M

10、ost usual simple EC3 method. Find critical temperature for loading, compare with design temperature.18Material propertiesSteel Mechanical (effective yield strength, elastic modulus, . )Concrete Thermal (thermal expansion, thermal conductivity, specific heat) Mechanical (compressive strength, secant

11、modulus, . ) Thermal (thermal expansion, thermal conductivity, specific heat)19Strength/stiffness reduction factors for elastic modulus and yield strength (2% strain).Strain (%)0.51.01.52.0Stress (N/mm2)03002502001501005020C200C300C400C500C600C700C800CElastic modulus at 600C reduced by about 70%.Yie

12、ld strength at 600C reduced by over 50%. Steel stress-strain curves at high temperatures20RftDegradation of steel strength and stiffness0300600900120010080604020% of normal valueTemperature (C)RftEffective yield strength(at 2% strain)SSElastic modulusSSStrength and stiffness reductions very similar

13、for S235, S275, S355 structural steels and hot-rolled reinforcing bars. (SS)Cold-worked reinforcing bars S500 deteriorate more rapidly. (Rft)2110050020040060080010001200Temperature (C)654321Strain (%)Strength (% of normal)Strain at maximumstrengthDegradation of concrete strength and stiffnessNormal-

14、weight ConcreteAccurate for normal density concrete with siliceous aggregates.Conservative for normal density concrete with calcareous aggregates,.Lightweight ConcreteConservative for light-weight concretes. All types treated the same.Strength reduction factors22Concrete strength in heating and cool

15、ing Stress-strain relationship in cooling from 700C (at 400C)Stress-strain relationship in heating phase (700C)515250,010,020,03Stress-strain relationship at ambient temperatureStress-strain relationship in heating phase (400C)Stress-strain relationship after cooling from 700C (at 20C)23Thermal expa

16、nsion of steel and concrete00,51,01,52,02,53,03,54,04,5100200300400500600700800900Temperature (C)Expansion Coeff /C (x 10-6)SteelSteel thermal expansion stops during crystal structrure change in the 700-800C range.Normal-weightconcreteConcrete unlikely to reach 700C in time of a building fire.Lightw

17、eight concreteLight-weight concrete treated as having uniform thermal expansion coefficient.24la=45W/mK (EC3 simple calculation model)Thermal conductivity (W/mK)102030405060020040060080010001200Temperature (C)Steelca=600J/kgK(EC3 simple calculation model)Other steel thermal propertiesSpecific Heat (

18、J/kgK)5000020040060080010001200Temperature (C)4000300020001000Steel25Other concrete thermal propertiesNCLCNCLCMay assume constant value for NC: 1,60 W/m.KMay assume constant value for NC: 1000 J/kg.Kcc*Specific heat cc (J/kg.K)400800100012002006001000 CThermal conductivity lc (W/m.K)2006001000 C1232

19、6Thermal analysis Thermal analysis: both EC3 Part 1.2 and EC4 Part 1.2 unprotected and protected steel beams Lower and upper flanges Considerably different temperatures proper calculation of temperatures!Temperature 27Temperature increase of unprotected steel Temperature increase in time step Dt:Heat flux hnet.d has 2 parts:Radiation:Convection:Steel temperatureSteelFire temperatur