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

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The ECCS equation has a time period limitation during which the equation is valid. This does not appear to be necessary as the lines resulting from this formula fit to the spreadsheet curve for a longer time period than that suggested. For the NZS 3404 equations, the limitations imposed on the equations currently are logical and fit well with the data. The ECCS equations give limitations that are too conservative and can be extended. The upper temperature limit should be extended to 750 °C instead of 600 °C and linear interpolation should be recommended for temperatures below 400 °C. The limitations on the section factor appear necessary as Figure 4.5 a shows, but the time limitations do not seem necessary at all. 4.3 RESULTS FOR THREE SIDED EXPOSURE: Three sided exposure usually occurs for unprotected steel beams when the beam is supporting a concrete floor slab on its top flange. It can also occur if there is another material protecting the top flange such as insulation between supported purlins, so two cases are considered in this chapter. SAFIR 1 results are results found from simulations in SAFIR without a concrete slab on the top flange, but with no fire exposure on the top face of the top flange, modelling an insulation effect. SAFIR 2 has a concrete slab resting on the top flange, providing the beam with protection against the fire and thus making three sided exposure. The concrete slab used in these simulations is a 150 mm thick slab of calcareous based concrete with properties from Eurocode 2, with aggregate material primarily of limestone. The thickened lines around the beam in Figure 4.6 indicate the contour that is exposed to the ISO 834 fire in the simulations. The layout for the SAFIR 2 simulation is shown in Figure 4.6: 63
Concrete slab Steel UB beam Figure 4.6: Layout of three sided exposure with a concrete slab The results for three sided exposure to an ISO 834 fire differ from those of four sided exposure. The SAFIR results have a greater temperature spread between the maximum and minimum values for different elements due to cooler steel temperatures at the unexposed face. The option of simulating three sided exposure with or without a slab present gives more variation to the results found. With three sided exposure to the fire, the steel section has a temperature gradient across the cross section. With a concrete slab in place, the variation is greater across the section during to the cooling effects of the slab. The average temperature is assumed to be the average of all elements from the SAFIR simulation, which is acceptable for a thermal analysis, and best for a comparison with the spreadsheet method. However, if a structural review of the member was being made, the temperatures at vital points of the section such as the temperature of the lower flange should be considered. 64
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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
Page 25 and 26:
1.6 BACKGROUND INFORMATION: 1.6.1 F
Page 27 and 28: experienced in fire situations, but
Page 29 and 30: The thermal conductivity is not imp
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
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 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
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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
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APPENDIX C - FIRECALC Below in Figu
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