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

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Figure 6.3 a shows that the average temperature of the unprotected steel member as tested by Wainman and Kirby, (1988), gives results very close to the average temperature predicted by SAFIR. The results from the spreadsheet method are significantly higher than the average temperature reached in SAFIR and the test data. The spreadsheet does not consider the cooling effects of the concrete slab on top of the beam however, and differs from four sided exposure by the reduced section factor only. Although the concrete slab cools the top flange significantly by absorbing heat from the flange and consequently cooling it, the bottom flange is not affected by the presence of the slab. Failure can still occur when the top flange is relatively cool if the bottom flange and web is too hot. Figure 6.4 b below shows the comparison between the maximum temperatures reached in SAFIR with the temperatures measured in the bottom flange in the experimental data from the same beam and test mentioned above. 1000 Temperature ( o C) 800 600 400 200 Max SAFIR Experimental 0 0 10 20 30 40 50 60 Time (min) Lower Flange Temp SAFIR Fire Temp ISO fire Figure 6.4: Comparison between the temperature results measured from an experimental fire test with the maximum temperatures found from a SAFIR simulation, and temperatures from the spreadsheet method. From Figure 6.4, the maximum temperature from the SAFIR simulation is slightly higher throughout the test than the temperature in the lower flange of the beam measured in the experimental data. The maximum temperatures of the steel beam with this construction are found in the web during the early stages of the test, but 125
the lower flange and web tend to the same temperatures as the fire progresses. The top of the web is slightly cooler than the rest of the cross section of the member due to the top flange being cooled by the concrete slab, and as a result slightly cooling the top of the web. Although in Figure 6.3, the results from the spreadsheet method were significantly higher than the temperatures from the experimental data and from SAFIR, in Figure 6.4 the temperatures from the spreadsheet method at the later stages of the fire correspond well with those from these other sources. After around 30 minutes the spreadsheet and the maximum temperatures from SAFIR and the experiment give temperatures with small error. This suggests that the spreadsheet method will give designers a good indication of the maximum temperatures of the steel because the time frame that designers are concerned with are generally at least 30 minutes and longer. For a limiting temperature of around 600 °C however, the time to reach this temperature is significantly faster with the spreadsheet method than found from the experimental data and SAFIR. These results from the spreadsheet method are therefore a bit too conservative and too low. 6.3.2 Protected Steel: The experimental data for a protected member comes from ‘Natural Fires in Large Scale Compartments’, (Kirby et al 1994). The beam is sized according to British Steel Products, and is of dimensions 254 x 146 mm, and mass of 43 kg/m. The protection applied to the beam is Vicuclad © board protection by Promat Fire Protection. The insulation is applied to three sides of the steel beam, with a 50mm thick paving slab on the top flange to simulate the thermal effects of a concrete slab. Vicuclad is a vermiculite based product mixed with inorganic binders. The properties of this board are not included in Kirby et al, (1994), so the following assumptions have been made: Density: 400 kg/m 3 (from Promat internet site) Specific heat: 1100 J/kg K Thermal conductivity: 0.15 W/m K (Buchanan, 1999) 126
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Fire Design of Steel Members K R Le
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ABSTRACT: The New Zealand Steel Cod
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TABLE OF CONTENTS: ABSTRACT:.......
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5.4 RESULTS FOR FOUR SIDED EXPOSURE
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LIST OF FIGURES: FIGURE 1.1: VARIAT
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FIGURE 5.11: TEMPERATURE CONTOUR LI
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designed with confidence. Full scal
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eams and struts when subjected to a
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Gilvery and Dexter, (1997), prepare
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with conditions specified to ensure
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1.6 BACKGROUND INFORMATION: 1.6.1 F
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experienced in fire situations, but
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The thermal conductivity is not imp
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[ The heated perimeter of the steel
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The advantages of board systems are
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The values for the thermal properti
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insulation has on the rise of the s
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( T − T ) k H p f s ∆t ∆T
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spreadsheet method very closely, wi
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protection, and for user defined fi
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This equation originates from the y
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1400 1200 1000 800 600 400 200 0 0.
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time. The value of the wall lining
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The Eurocode does not define a meth
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f f y y ( T ) (20) = 1.0 0 < T < 21
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temperature is chosen because it is
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The variation of yield stress data
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15 m -1 < H p /A < 275 m -1 in NZS
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= H p A (m -1 ) 7.85 The cons
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Connections: NZS 3404 requires that
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4 CALCULATION OF STEEL TEMPERATURES
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4.1.2 Analysis Between Methods of T
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Figure 4.2 shows the variation of t
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Minimum temperatures Maximum temper
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For all three sizes of beam, the sp
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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
Page 90 and 91: significantly decreased from a cool
Page 92 and 93: Since both programmes use the same
Page 94 and 95: Therefore, the ECCS equations provi
Page 96 and 97: 5 CALCULATION OF STEEL TEMPERATURES
Page 98 and 99: calculations made by the spreadshee
Page 100 and 101: susceptible to heating, heat up mor
Page 102 and 103: Figure 5.3 a-c show the results fro
Page 104 and 105: 7850*600*10500 > 2*775*1100*(1869*2
Page 106 and 107: As can be seen from Figure 5.4 a-c,
Page 108 and 109: 310 UB 40.4 beam H p /A = 241 m -1
Page 110 and 111: The SAFIR results fit between the t
Page 112 and 113: constant specific heat being used i
Page 114 and 115: From Figure 5.7 a-c, it appears tha
Page 116 and 117: 800 Temperature ( o C) 600 400 200
Page 118 and 119: To examine the limits of the thickn
Page 122 and 123: Thermal conductivity, k i = 0.19 W/
Page 126 and 127: the slab except to reduce the secti
Page 128 and 129: Figure 5.14 shows the correlation b
Page 130 and 131: 5.8 CONCLUSIONS: The thermal behavi
Page 132 and 133: 6 COMPARISON OF METHODS USING OTHER
Page 134 and 135: Temperature ( o C) 1200 1000 800 60
Page 136 and 137: 6.2.4 Results for protected steel:
Page 138 and 139: Figures 6.2 b shows the comparison
Page 142 and 143: The fire that the test beams were e
Page 144 and 145: 7 ADDITIONAL MATERIAL IN EUROCODE 3
Page 146 and 147: For thermal analysis in Eurocode 3,
Page 148 and 149: To determine the performance of a s
Page 150 and 151: The plastic neutral axis is located
Page 152 and 153: It is therefore recommended that th
Page 154 and 155: These methods may be used to provid
Page 156: Eurocode has a large annex with gui
Page 159 and 160: 8.3 CHANGES TO NZS 3404: The follow
Page 161 and 162: H v height of the ventilation (m) I
Page 163 and 164: EC3, 1995. Eurocode 3: Design of St
Page 165 and 166: Temperature Conditions. National Re
Page 168 and 169: APPENDIX A - SPREADSHEET METHOD: Be
Page 170 and 171: APPENDIX B - SAFIR: In Figure B.2 i
Page 172 and 173: *.str file developed by the pre pro
Page 174 and 175: 22 FISO 23 FISO FISO 24 FISO FISO 2
Page 176: APPENDIX C - FIRECALC Below in Figu
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