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

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Temperature ( o C) 1000 800 600 400 200 0 Spreadsheet SAFIR 1 SAFIR 2 0 10 20 30 40 50 60 70 time (min) SAFIR 1 SAFIR 2 Spreadsheet 1000 Temperature ( o C) 800 600 400 200 0 0 10 20 30 40 50 60 70 time (min) SAFIR 1 SAFIR 2 Spreadsheet Temperature ( o C) 1000 800 600 400 200 0 0 10 20 30 40 50 60 70 time (min) SAFIR 1 SAFIR 2 spreadsheet Figure 4.11a-c: Comparison of results from SAFIR and the spreadsheet method for an unprotected steel member subjected to three sided exposure of the ISO 834 fire from top to bottom a. 180 UB 16.1, b. 310 UB 40.4, c. 530 UB 82.0 69
From Figure 4.11 a-c, the spreadsheet curve is close to the SAFIR 1 curve without a concrete slab protecting and cooling the top flange of the steel beam. This is because the spreadsheet method as used in this report makes no allowance for the effect of a concrete slab absorbing heat. The spreadsheet assumes that all heat transferred to the steel section is absorbed by the section and all energy absorbed in turn contributes to the temperature rise of the member. Differences between the spreadsheet method and SAFIR 1 result from the spreadsheet assuming a constant thickness over the cross section of the beam, while SAFIR accounts for the true thickness and allows conduction across the beam. The effective thickness of the section as used in the spreadsheet method is increased with three sided exposure due to a decreased section factor as the heated perimeter decreases, see Section 1.6.3. The conduction feature in SAFIR means that although the beam is not heated on the top face of the top flange in the SAFIR 1 simulation, there are no outside influences to stop it rising in temperature. The SAFIR 2 simulation has concrete protection on the top flange so that although it does heat up, a significant amount of the energy transferred to the top flange is then conducted to the concrete slab. Using the spreadsheet results is a conservative method of predicting the temperature of three sided fire exposure, since the temperatures that this method predicts are higher than other methods. Since in most ‘real’ cases of three sided exposure to fire, a slab would be present, the spreadsheet method is possibly too conservative for the average temperature. A reduction in the formula of the heat transferred to the beam could be an alternative method of estimating the likely temperatures that would be reached in a fire. By considering the average temperature in the slab at each time step, an energy balance could be found to account for the heat and energy loss to the slab, resulting in a more accurate estimation of the likely temperatures reached in the steel section. The SAFIR 2 simulation with the concrete slab resting on the top flange is at a significantly lower temperature throughout the test run. The difference in temperature between the two SAFIR results is the effect of the addition of a concrete slab, which lowers the temperature of the top flange and therefore the 70
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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
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
Page 78 and 79: The ECCS equation has a time period
Page 80 and 81: 4.3.1 Results from simulations with
Page 82 and 83: From Figure 4.5 a-c, the formula ra
Page 86 and 87: average temperature of the beam, be
Page 88 and 89: 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
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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
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APPENDIX C - FIRECALC Below in Figu
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