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Click to edit Master title style,*,EC4,Introduction to Eurocode Structural Fire Engineering,Structural Steelwork Eurocodes,1,Strain (%),0.5,1.0,1.5,2.0,Stress (N/mm,2,),0,300,250,200,150,100,50,20C,200C,300C,400C,500C,600C,700C,800C,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,2,1.0,0.9,0.8,0.7,0.6,0.5,0.4,0.3,0.2,0.1,0,1,2,3,4,1000C,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,3,The fire triangle,Fuel + Oxidant = Combustion products,CH,4,+ O,2,= CO,2,+ 2H,2,0,Reaction occurs when Oxygen/fuel mixture hot enough,Heat,Oxygen,Fuel,4,Stages of a natural fire - and the standard fire test curve,Cooling .,ISO834 standard fire curve,Ignition -,Smouldering,Pre-Flashover,Heating,Post-Flashover,1000-1200C,Natural fire curve,Time,Temperature,Flashover,5,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),576,675,739,781,842,945,6,200,400,600,800,1000,1200,0,1200,2400,3600,Time (sec),Gas Temperature (C),Typical EC1 Parametric fire curve,External Fire,Standard Fire,Hydrocarbon Fire,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 (500m,2,). Only allowed with calculation models.,Different EC1,time-temperature curves,7,Compartment,Temperature,Load-bearing resistance,Time,Time,Fire severity time equivalent,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.,Fire resistance time equivalent,Standard fire,Natural fire,Element,Time-equivalence,8,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.,Problems,Limited 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.,9,Standard fire resistance furnace test,100,200,300,0,1200,2400,3600,Time (sec),Deflection (mm),10,Standard fire resistance furnace test,100,200,300,0,1200,2400,3600,Time (sec),Deflection (mm),Span,2,/400d,If rate ,t,fi,.,requ,Load resistance:,R,fi,.d.t,E,fi,.d.t,Temperature:,cr.d,d,Usually only,directly,feasible using advanced calculation models.,Feasible by hand calculation. Find reduced resistance at design temperature.,Most usual simple EC3 method. Find critical temperature for loading, compare with design temperature.,18,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,),19,Strength/stiffness reduction factors for elastic modulus and yield strength (2% strain).,Strain (%),0.5,1.0,1.5,2.0,Stress (N/mm,2,),0,300,250,200,150,100,50,20C,200C,300C,400C,500C,600C,700C,800C,Elastic modulus at 600C reduced by about 70%.,Yield strength at 600C reduced by over 50%.,Steel stress-strain curves at high temperatures,20,Rft,Degradation of steel strength and stiffness,0,300,600,900,1200,100,80,60,40,20,% of normal value,Temperature (C),Rft,Effective yield strength,(at 2% strain),SS,Elastic modulus,SS,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,),21,100,50,0,200,400,600,800,1000,1200,Temperature (C),6,5,4,3,2,1,Strain (%),Strength (% of normal),Strain at maximum,strength,Degradation of concrete strength and stiffness,Normal-weight Concrete,Accurate for normal density concrete with siliceous aggregates.,Conservative for normal density concrete with calcareous aggregates,.,Lightweight Concrete,Conservative for light-weight,concretes,. All types treated the same.,Strength reduction factors,22,C,oncrete,strength,in heating and cooling,Stress,-,strain relationship in cooling from 700C (at 400,C),Stress,-,strain relationship in heating phase (700,C),5,15,25,0,01,0,02,0,03,Stress,-,strain relationship at ambient temperature,Stress,-,strain relationship in heating phase (400,C),Stress,-,strain relationship after cooling from 700C (at 20,C),23,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,),Steel,Steel thermal expansion stops during crystal,structrure,change in the 700-800C range.,Normal-weight,concrete,Concrete unlikely to reach 700C in time of a building fire.,Lightweight concrete,Light-weight concrete treated as having uniform thermal expansion coefficient.,24,l,a,=45W/mK (EC3 simple calculation model),Thermal conductivity (W/mK),10,20,30,40,50,60,0,200,400,600,800,1000,1200,Temperature (C),Steel,c,a,=600J/kgK,(EC3 simple calculation model),Other steel thermal properties,Specific Heat (J/kgK),5000,0,200,400,600,800,1000,1200,Temperature (C),4000,3000,2000,1000,Steel,25,Other,concrete,thermal properties,NC,LC,NC,LC,May assume constant value for NC:,1,60 W/m.K,May assume constant value for NC:,1000 J/kg.K,c,c,*,Specific heat c,c,(J/kg.K),400,800,1000,1200,200,600,1000 C,Thermal conductivity,l,c,(W/m.K),200,600,1000 C,1,2,3,26,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,!,Temp,erature,27,Temperature increase of unprotected steel,Temperature increase in time step,D,t,:,Heat flux,h,net,.d,has 2 parts:,Radiation:,Convection:,Steel temperature,Steel,Fire temperature,28,Section factor A,m,/V - unprotected steel members,perimeter,c/s area,exposed perimeter,c/s area,h,b,2(b+h),c/s area,90%,!,29,Temperature increase of protected steel,Steel temperature,Steel,Protection,Fire temperature,d,p,Some heat stored in protection layer.,Heat stored in protection layer relative to heat stored in steel,Temperature rise of steel in time increment,D,t,30,exposed perimeter,Total c/s area,exposed plate,Total c/s area,exposed flange,Total c/s area,Section factor A,m,/V - inherently protected systems,31,Section factor,A,p,/V - protected steel members,Steel perimeter,steel c/s area,h,b,2(b+h,),c/s area,inner perimeter of board,steel c/s area,90%,!,32,
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