欧洲建筑防火规范（Introduction to Eurocode Structural Fire Engineering） .ppt

1,Introduction to Eurocode Structural Fire Engineering,Structural Steelwork Eurocodes,2,Steel softens progressively from 100-200C up.Only 23%of ambient-temperature strength remains at 700C.At 800C strength reduced to 11%and at 900C to 6%.Melts at about 1500C.,Steel stress-strain curves at high temperatures,3,1,2,3,4,1000C,800C,20C,200C,400C,600C,Strain(%),Normalised stress,Concrete also loses strength and stiffness from 100C upwards.Does not regain strength on cooling.High temperature properties depend mainly on aggregate type used.,Concrete stress-strain curves at high temperatures,4,The fire triangle,Fuel+Oxidant=Combustion productsCH4+O2=CO2+2H20,5,Stages of a natural fire-and the standard fire test curve,Flashover,6,The EC1(ISO834)standard fire curve,300,100,200,0,400,500,600,700,800,900,1000,0,600,1200,1800,2400,3000,3600,Time(sec),Gas Temperature(C),576,675,739,781,842,945,7,200,400,600,800,1000,1200,0,1200,2400,3600,Time(sec),Gas Temperature(C),Fire 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).Only allowed with calculation models.,Different EC1 time-temperature curves,8,Temperature,Load-bearing resistance,Time,Time,Used to rate fire severity or element performance relative to furnace test.,Matches times to given temperature in a natural fire and in Standard Fire.,Time-equivalence,9,Furnace tests on structural elements,Fire Testing Load kept constant,fire temperature increased using Standard Fire curve.Maximum deflection criterion for fire resistance of beams.Load capacity criterion for fire 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.,10,Standard fire resistance furnace test,11,Standard fire resistance furnace test,Standard Fire,12,Structural fire protection,Passive ProtectionInsulating Board Gypsum,Mineral fibre,Vermiculite.Easy to apply,aesthetically acceptable.Difficulties with complex details.Cementitious Sprays Mineral fibre or vermiculite in cement binder.Cheap to apply,but messy;clean-up may be expensive.Poor aesthetics;normally used behind suspended ceilings.Intumescent Paints Decorative finish under normal conditions.Expands on heating to produce insulating layer.Can now be done off-site.,13,Inherent fire protection to steel beams,14,Structural fire protectionComposite sections,Passive Protection Composite sections,Traditional downstand beam top flange upper face totally shielded by the slab,15,Structural fire protectionComposite sections,Passive Protection Composite sections,Beams with concrete encasement Have high fire resistance(up to 180 minutes).Involve complicated construction of joints.Require formwork.,16,Structural fire protectionComposite sections,Passive Protection Composite sections,Steel beams with partial concrete encasement Concrete between flanges reduces the rate of heating of the profiles web and upper flange.Concrete between flanges contributes to the load-bearing resistance.The beam can be fabricated in the workshop without the use of formwork.Simple construction of joints.,17,Load reduction factor in fire,18,Establishing Fire Resistance:Strategies,Eurocodes allow fire resistance to be established in any of 3“domains”:,Time:tfi.d tfi.requ,Load resistance:Rfi.d.t Efi.d.t,Temperature:cr.d d,Usually only directly feasible using advanced calculation models.,Most usual simple EC3 method.Find critical temperature for loading,compare with design temperature.,19,Material properties,Steel,Mechanical(effective yield strength,elastic modulus,.),Concrete,Thermal(thermal expansion,thermal conductivity,specific heat),Mechanical(compressive strength,secant modulus,.),Thermal(thermal expansion,thermal conductivity,specific heat),20,Strength/stiffness reduction factors for elastic modulus and yield strength(2%strain).,Strain(%),0.5,1.0,1.5,2.0,Stress(N/mm2),0,300,250,200,150,100,50,20C,200C,300C,400C,500C,600C,700C,800C,Steel stress-strain curves at high temperatures,21,Degradation of steel strength and stiffness,0,300,600,900,1200,100,80,60,40,20,%of normal value,Temperature(C),Strength and stiffness reductions very similar for S235,S275,S355 structural steels and hot-rolled reinforcing bars.(SS),Cold-worked reinforcing bars S500 deteriorate more rapidly.(Rft),22,100,50,0,200,400,600,800,1000,1200,Temperature(C),Strength(%of normal),Degradation of concrete strength and stiffness,Conservative for normal density concrete with calcareous aggregates,.,Strength reduction factors,23,Concrete strength in heating and cooling,24,Thermal expansion of steel and concrete,0,0,5,1,0,1,5,2,0,2,5,3,0,3,5,4,0,4,5,100,200,300,400,500,600,700,800,900,Temperature(C),Expansion,Coeff/C(x 10-6),25,Other steel thermal properties,26,Other concrete thermal properties,27,Thermal 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,!,28,Temperature increase of unprotected steel,Temperature increase in time step Dt:,Heat flux hnet.d has 2 parts:Radiation:,Convection:,29,Section factor Am/V-unprotected steel members,!,30,Temperature increase of protected steel,dp,Some heat stored in protection layer.,Heat stored in protection layer relative to heat stored in steel,Temperature rise of steel in time increment Dt,31,Section factor Am/V-inherently protected systems,32,Section factor Ap/V-protected steel members,!,