FIRE DESIGN OF STEEL MEMBERS - Civil and Natural Resources ...

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Sp. Heat (J/kg K) 2000 1600 1200 800 400 To 5000 0 0 200 400 600 800 1000 1200 Temperature ( o C) Equation 1.4 Equation 1.3 Equation 1.5 Figure 1.1: Variation of the specific heat of steel with temperature. This discontinuity at around 750 °C corresponds to a phase change of steel when the steel changes from ferrite to austenite. The increase in specific heat reflects the latent heat of transformation (Gilvery and Dexter, 1997). Purkiss, (1996) also states that a constant value of 600 J/kg K can be used for the specific heat of steel, which is commonly used in spreadsheet analyses and simple hand calculations. The British Steel Code recommends a constant value of 520 J/kg K. Harmathy, (1996), suggests using known formulas for the specific heat of steel of the different components of steel, such as Ferrite, Austenite and Cementite. This is more complicated, however if the exact mixture of the steel is not known which is likely to be the case for designers. Thermal Conductivity: The thermal conductivity of steel varies slightly between different grades of steel, and with changes in the temperature of the steel. The difference between the grades of steel is not very significant, and ENV 1993-1-2 gives the following equation for the thermal conductivity of steel, k s , where T s is the temperature of the steel (°C). k = 54 − 0. 0333 for T s < 800°C 1.6a s T s k = 27.3 for T s > 800°C 1.6b s 13
The thermal conductivity is not important in this report as we are concerned with the average and maximum temperatures found in the steel beams, which will relate to the strength of the beam. In the SAFIR programme the thermal conductivity of the steel is present because conduction takes place between the elements of the cross section, however the average temperature is not influenced by the thermal conductivity and it is not present in any equations used in this report. The thermal conductivity of the insulation when applied is important as this gives information on the transfer of heat to the steel beam. 60 50 40 30 20 10 0 0 200 400 600 800 1000 1200 Temperature (C) Equation 1.6 Constant Value Figure 1.2:Variation of thermal conductivity of steel with temperature For approximate calculations, the thermal conductivity of steel may be taken to be k s = 45 W/mK, (Purkiss 1996), which is also recommended in Eurocode 3 and BS 5950:Part 8. Density: The density of steel is recommended by Purkiss, (1996) to remain at a value of 7850 kg/m 3 for all temperatures normally experienced during a fire, so this value has been used throughout this report. Thermal Expansion: When heated, steel expands linearly at a rate of: ∆ l l − = 1.4x10 5 T s 1.7 14
Page 1 and 2: Fire Design of Steel Members K R Le
Page 4: ABSTRACT: The New Zealand Steel Cod
Page 8 and 9: TABLE OF CONTENTS: ABSTRACT:.......
Page 10 and 11: 5.4 RESULTS FOR FOUR SIDED EXPOSURE
Page 12 and 13: LIST OF FIGURES: FIGURE 1.1: VARIAT
Page 14: FIGURE 5.11: TEMPERATURE CONTOUR LI
Page 17 and 18: designed with confidence. Full scal
Page 19 and 20: eams and struts when subjected to a
Page 21 and 22: Gilvery and Dexter, (1997), prepare
Page 23 and 24: with conditions specified to ensure
Page 25 and 26: 1.6 BACKGROUND INFORMATION: 1.6.1 F
Page 27: experienced in fire situations, but
Page 31 and 32: [ The heated perimeter of the steel
Page 33 and 34: The advantages of board systems are
Page 35 and 36: The values for the thermal properti
Page 37 and 38: insulation has on the rise of the s
Page 39 and 40: ( T − T ) k H p f s ∆t ∆T
Page 41 and 42: spreadsheet method very closely, wi
Page 43 and 44: protection, and for user defined fi
Page 45 and 46: This equation originates from the y
Page 47 and 48: 1400 1200 1000 800 600 400 200 0 0.
Page 49 and 50: time. The value of the wall lining
Page 51 and 52: The Eurocode does not define a meth
Page 53 and 54: f f y y ( T ) (20) = 1.0 0 < T < 21
Page 55 and 56: temperature is chosen because it is
Page 57 and 58: The variation of yield stress data
Page 59 and 60: 15 m -1 < H p /A < 275 m -1 in NZS
Page 61 and 62: = H p A (m -1 ) 7.85 The cons
Page 63 and 64: Connections: NZS 3404 requires that
Page 66 and 67: 4 CALCULATION OF STEEL TEMPERATURES
Page 68 and 69: 4.1.2 Analysis Between Methods of T
Page 70 and 71: Figure 4.2 shows the variation of t
Page 72 and 73: Minimum temperatures Maximum temper
Page 74 and 75: For all three sizes of beam, the sp
Page 76 and 77: Temperature ( o C) 1200 1000 800 60
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The ECCS equation has a time period
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4.3.1 Results from simulations with
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From Figure 4.5 a-c, the formula ra
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Temperature ( o C) 1000 800 600 400
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average temperature of the beam, be
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Temperature ( o C) 1400 1200 1000 8
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significantly decreased from a cool
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Since both programmes use the same
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Therefore, the ECCS equations provi
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5 CALCULATION OF STEEL TEMPERATURES
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calculations made by the spreadshee
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susceptible to heating, heat up mor
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Figure 5.3 a-c show the results fro
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7850*600*10500 > 2*775*1100*(1869*2
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As can be seen from Figure 5.4 a-c,
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310 UB 40.4 beam H p /A = 241 m -1
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The SAFIR results fit between the t
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constant specific heat being used i
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From Figure 5.7 a-c, it appears tha
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800 Temperature ( o C) 600 400 200
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To examine the limits of the thickn
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1000 Temperature ( o C) 800 600 400
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Thermal conductivity, k i = 0.19 W/
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1000 Temperature ( o C) 800 600 400
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the slab except to reduce the secti
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Figure 5.14 shows the correlation b
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5.8 CONCLUSIONS: The thermal behavi
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6 COMPARISON OF METHODS USING OTHER
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Temperature ( o C) 1200 1000 800 60
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6.2.4 Results for protected steel:
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Figures 6.2 b shows the comparison
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Figure 6.3 a shows that the average
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The fire that the test beams were e
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7 ADDITIONAL MATERIAL IN EUROCODE 3
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For thermal analysis in Eurocode 3,
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To determine the performance of a s
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The plastic neutral axis is located
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It is therefore recommended that th
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These methods may be used to provid
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Eurocode has a large annex with gui
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8.3 CHANGES TO NZS 3404: The follow
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H v height of the ventilation (m) I
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EC3, 1995. Eurocode 3: Design of St
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Temperature Conditions. National Re
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APPENDIX A - SPREADSHEET METHOD: Be
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APPENDIX B - SAFIR: In Figure B.2 i
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*.str file developed by the pre pro
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22 FISO 23 FISO FISO 24 FISO FISO 2
Page 176:
APPENDIX C - FIRECALC Below in Figu
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