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Presentation for Dissertation - Eurocode 1

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Anuj Ramdas
Anuj Ramdas

This document provides information on calculating thermal actions for external members using simplified calculation methods from Eurocode 1 for general actions on structures exposed to fire. It describes the calculation of maximum compartment fire temperature, flame size emanating from openings, and other parameters. Methods are presented for scenarios with and without forced draught/through ventilation, and the effects of windows, wind, projections above openings, and other factors on flame height, width, temperature, and heat transfer coefficients are summarized.

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Department ofCivil and Structural EngineeringAnnex B[informative]THERMAL ACTIONS FOR EXTERNAL MEMBERSEurocode 1Actions on structures BS EN 1991 Part 1-2:2002 General actions Actions on structures exposed to fire
Thermal Calculation Thermal action for external members - Simplified calculation methodThe method is used to determine the maximum compartment fire temperature. It gives the temperature and size of flame emanating from the openings.For various parameters, the method considers steadystate condition. This method is adopted for fire loads greater than 200 MJ/m2.Thermal Calculation
Usage conditionsUsage conditionsIf there are more number of windows in a fire compartment, the weighted average height of openings heq, summation of width of windows (wt = wi) and vertical openings total area Av are used. The compartment dimensions limited to 70m, width to 18m and 5m height. All along the thickness and width of flame the flame temperature remains uniform.Usage conditions
Usage conditionsUsage conditionsIf windows are present only on one side of wall 1, then the D/W ratio D/W = W2/wtIf more number of windows are present on more than one wall of the fire compartment, then D/W ratio is given as D/W = (W2 Av,1) / (W1 Av)Where,W1 - wall width on side 1, generally side containing greatest area of windowAv,1 - summation of window area on side 1W2 - wall width perpendicular to side 1 Usage conditions
Wind effectMode of VentilationIf there are windows present on either side or when the fire is fed with additional external supply of air, then the forced draught method is used for calculations. Else, no forced draught conditions are used.Deflection of flame by windFlames coming out of fire compartment are assumed to be in a direction perpendicular to the facade; At an angle 45, due to deflection by wind effects.Wind effect45135windFlame deflection due to wind - Horizontal cross section
No forced draughtBurning RateFor most types of furniture found in buildings, F is about 1200sec so that for a free burning fire of furniture, the rate of burning is [MW]Vertical opening area of walls, AvHeight of window, heqTotal enclosure area (ceiling, floor, walls along with windows), AtRatio of compartment depth to width, D/WNo forced draught
No forced draughtFire compartment temperatureTf = 6000(1 e - 0.1/o) o1/2 (1- e -0.00286 ) + ToFlame heightThis equation may be simplified by taking g = 0.45 kg/m3 and g = 9.81 m/s2 as,No forced draught
No forced draughtFlame height2h /32h /3eqeqLLHHNo forced draughtLLLLw2h /32h /3teqLeqLh1h1eqeqFlame dimensions No through draught
No forced draughtFlame widthFlame width is taken as window width, wiFlame depthTaken as 2/3rd of the window height, i.e. 2/3 heqHorizontal projection of flameIf a wall is present above window, thenLH = heq/3 if heq1.25wtLH = 0.3 heq (heq / wt) 0.54 if heq>1.25wt and distance to any other window > 4wtLH = 0.454 heq (heq / 2wt) 0.54 in other casesIn case of a wall not existing above the window, LH = 0.6 heq (LL / heq) 1/3No forced draught
No forced draughtLength of flame along axisWhen LL > 0Lf = LL + heq/2 if wall exist above window or if heq1.25 wtLf = (LL2 + (LH - heq/3)2)1/2+heq/2 if wall exist above window or if heq>1.25 wtWhen LL = 0, then Lf = 0Flame temperature at windowTw = 520/(1-0.4725(Lf wt/Q))+To with Lf wt/Q < 1Emissivity of flame at windowThe flame emissivity at window is taken as 竜f = 1.0The temperature of flame along the axisTz = (Tw To)(1-0.4725(Lx wt/Q))+To with Lx wt/Q < 1No forced draught
No forced draughtThe emissivity of flames 竜f = 1 e-0.3 dfConvective heat transfer coefficient留c = 0.00467 (1/ deq)0.4 (Q/Av)0.6Effect of projection above windowThe flame height LL decreased by Wa(1+2)The horizontal projection of the flame LH increased by WaAs per EN1991-1-2, 留c= (1/ deq)0.4 (Q/Av)0.6But has error in units4.67No forced draught
No forced draughtEffect of projection above windowcedbcNo forced draughtbaa a-b-c = Lf a-b-c-d-e = Lf and wa = a bVertical cross section: Deflection of flame due to balcony
No forced draughtIf the wall does not exist on top of the window or heq>1.25wt- The flame height LL reduced by Wa- The projection of flame in horizontal direction LH with the above LL is increased by WaNo forced draught
Forced draughtForced DraughtBurning RateWith ample ventilation known as the free burning condition F is determined by the burning characteristics of fire load, generally taken as 1200 sec. The rate of burning is given byQ = (Afqf,d)/F = (Afqf,d)/1200Fire compartment temperature, TfTf = 1200((Afqf,d)/ 17.5 e -0.00228 + ToForced draught
Forced draughtFlame heightFor general conditions the equation is simplified with u = 6 m/s as,Forced draught
Forced draughtFlame height - Flame dimensions for through draught or forced draughtLHHLLheqForced draughtwwfhteqLf
Forced draughtHorizontal projection of flameComparing the previous equation, as the speed of wind increases, the horizontal projection increases as the height of flame decreases. It is independent of presence of wall above or not.LH = 0.605 (u2/heq) 0.22 (LL + heq)For simplified calculations, using u = 6 m/s,LH = 1.33 (LL + heq) / heq0.22Forced draught
Forced draughtFlame widthIn forced draught, the flames tend to widen outwards with hot gases away from the opening as shown in the figure above. The width of flame is given bywf = wt + 0.4 LHFlame length along axisThe length of flame along axis, Lf, from tip of flame to the window is found using simple Pythagoras formulaLf = (LL2 + LH2)1/2Temperature of flame at windowTw = 520 / (1- 0.3325 Lf (Av) 1/2 / Q) + To; with LfLf (Av)1/2 / Q < 1The flame emissivity at the window, 竜f = 1.0Forced draught
Forced draughtThe temperature of flame along axisLx is the length of axis at any point of calculation to the window.Flame emissivity 竜f = 1 eConvective heat transfer coefficient留c=0.0098 (1/ deq)0.4 (Q/(17.5Av) + u/1.6)0.6The simplified form of the above formula after the inclusion of wind speed, u = 6 m/s,留c = 0.0098 (1/ deq)0.4 (Q/(17.5Av) + 3.75)0.6Forced draughtAs per EN1991-1-2, 留c= (1/ deq)0.4 .............But has error in units9.80
Forced draughtEffect of projection above window - Deflection of flame due to balcony/awningbForced draughtcawningaabff
The End

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Presentation for Dissertation - Eurocode 1

  • 1. Department ofCivil and Structural EngineeringAnnex B[informative]THERMAL ACTIONS FOR EXTERNAL MEMBERSEurocode 1Actions on structures BS EN 1991 Part 1-2:2002 General actions Actions on structures exposed to fire
  • 2. Thermal Calculation Thermal action for external members - Simplified calculation methodThe method is used to determine the maximum compartment fire temperature. It gives the temperature and size of flame emanating from the openings.For various parameters, the method considers steadystate condition. This method is adopted for fire loads greater than 200 MJ/m2.Thermal Calculation
  • 3. Usage conditionsUsage conditionsIf there are more number of windows in a fire compartment, the weighted average height of openings heq, summation of width of windows (wt = wi) and vertical openings total area Av are used. The compartment dimensions limited to 70m, width to 18m and 5m height. All along the thickness and width of flame the flame temperature remains uniform.Usage conditions
  • 4. Usage conditionsUsage conditionsIf windows are present only on one side of wall 1, then the D/W ratio D/W = W2/wtIf more number of windows are present on more than one wall of the fire compartment, then D/W ratio is given as D/W = (W2 Av,1) / (W1 Av)Where,W1 - wall width on side 1, generally side containing greatest area of windowAv,1 - summation of window area on side 1W2 - wall width perpendicular to side 1 Usage conditions
  • 5. Wind effectMode of VentilationIf there are windows present on either side or when the fire is fed with additional external supply of air, then the forced draught method is used for calculations. Else, no forced draught conditions are used.Deflection of flame by windFlames coming out of fire compartment are assumed to be in a direction perpendicular to the facade; At an angle 45, due to deflection by wind effects.Wind effect45135windFlame deflection due to wind - Horizontal cross section
  • 6. No forced draughtBurning RateFor most types of furniture found in buildings, F is about 1200sec so that for a free burning fire of furniture, the rate of burning is [MW]Vertical opening area of walls, AvHeight of window, heqTotal enclosure area (ceiling, floor, walls along with windows), AtRatio of compartment depth to width, D/WNo forced draught
  • 7. No forced draughtFire compartment temperatureTf = 6000(1 e - 0.1/o) o1/2 (1- e -0.00286 ) + ToFlame heightThis equation may be simplified by taking g = 0.45 kg/m3 and g = 9.81 m/s2 as,No forced draught
  • 8. No forced draughtFlame height2h /32h /3eqeqLLHHNo forced draughtLLLLw2h /32h /3teqLeqLh1h1eqeqFlame dimensions No through draught
  • 9. No forced draughtFlame widthFlame width is taken as window width, wiFlame depthTaken as 2/3rd of the window height, i.e. 2/3 heqHorizontal projection of flameIf a wall is present above window, thenLH = heq/3 if heq1.25wtLH = 0.3 heq (heq / wt) 0.54 if heq>1.25wt and distance to any other window > 4wtLH = 0.454 heq (heq / 2wt) 0.54 in other casesIn case of a wall not existing above the window, LH = 0.6 heq (LL / heq) 1/3No forced draught
  • 10. No forced draughtLength of flame along axisWhen LL > 0Lf = LL + heq/2 if wall exist above window or if heq1.25 wtLf = (LL2 + (LH - heq/3)2)1/2+heq/2 if wall exist above window or if heq>1.25 wtWhen LL = 0, then Lf = 0Flame temperature at windowTw = 520/(1-0.4725(Lf wt/Q))+To with Lf wt/Q < 1Emissivity of flame at windowThe flame emissivity at window is taken as 竜f = 1.0The temperature of flame along the axisTz = (Tw To)(1-0.4725(Lx wt/Q))+To with Lx wt/Q < 1No forced draught
  • 11. No forced draughtThe emissivity of flames 竜f = 1 e-0.3 dfConvective heat transfer coefficient留c = 0.00467 (1/ deq)0.4 (Q/Av)0.6Effect of projection above windowThe flame height LL decreased by Wa(1+2)The horizontal projection of the flame LH increased by WaAs per EN1991-1-2, 留c= (1/ deq)0.4 (Q/Av)0.6But has error in units4.67No forced draught
  • 12. No forced draughtEffect of projection above windowcedbcNo forced draughtbaa a-b-c = Lf a-b-c-d-e = Lf and wa = a bVertical cross section: Deflection of flame due to balcony
  • 13. No forced draughtIf the wall does not exist on top of the window or heq>1.25wt- The flame height LL reduced by Wa- The projection of flame in horizontal direction LH with the above LL is increased by WaNo forced draught
  • 14. Forced draughtForced DraughtBurning RateWith ample ventilation known as the free burning condition F is determined by the burning characteristics of fire load, generally taken as 1200 sec. The rate of burning is given byQ = (Afqf,d)/F = (Afqf,d)/1200Fire compartment temperature, TfTf = 1200((Afqf,d)/ 17.5 e -0.00228 + ToForced draught
  • 15. Forced draughtFlame heightFor general conditions the equation is simplified with u = 6 m/s as,Forced draught
  • 16. Forced draughtFlame height - Flame dimensions for through draught or forced draughtLHHLLheqForced draughtwwfhteqLf
  • 17. Forced draughtHorizontal projection of flameComparing the previous equation, as the speed of wind increases, the horizontal projection increases as the height of flame decreases. It is independent of presence of wall above or not.LH = 0.605 (u2/heq) 0.22 (LL + heq)For simplified calculations, using u = 6 m/s,LH = 1.33 (LL + heq) / heq0.22Forced draught
  • 18. Forced draughtFlame widthIn forced draught, the flames tend to widen outwards with hot gases away from the opening as shown in the figure above. The width of flame is given bywf = wt + 0.4 LHFlame length along axisThe length of flame along axis, Lf, from tip of flame to the window is found using simple Pythagoras formulaLf = (LL2 + LH2)1/2Temperature of flame at windowTw = 520 / (1- 0.3325 Lf (Av) 1/2 / Q) + To; with LfLf (Av)1/2 / Q < 1The flame emissivity at the window, 竜f = 1.0Forced draught
  • 19. Forced draughtThe temperature of flame along axisLx is the length of axis at any point of calculation to the window.Flame emissivity 竜f = 1 eConvective heat transfer coefficient留c=0.0098 (1/ deq)0.4 (Q/(17.5Av) + u/1.6)0.6The simplified form of the above formula after the inclusion of wind speed, u = 6 m/s,留c = 0.0098 (1/ deq)0.4 (Q/(17.5Av) + 3.75)0.6Forced draughtAs per EN1991-1-2, 留c= (1/ deq)0.4 .............But has error in units9.80
  • 20. Forced draughtEffect of projection above window - Deflection of flame due to balcony/awningbForced draughtcawningaabff