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

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For thermal analysis in Eurocode 3, the thermal properties of steel are not modified by a safety factor as this is given a value of one, but the value of the particular property is modified for the effect of an increase of temperature of the steel. For strength and deformation properties for structural analysis, the safety factor is also unity, but the properties at ambient temperatures are modified by a ‘reduction factor’ which is dependent on the material temperature. The assessment methods available for use by Eurocode 3, and the rules that they must satisfy are listed. The document then gives the analysis methods available for structural analysis and recommended to use. These are: Global structural analysis Analysis of portions of the structure Member analysis It is also stated that design may be based on the results of tests, and that to verify standard fire resistance requirements, a member analysis is sufficient. Global Structure Analysis: When a global structure analysis is carried out, the relevant failure mode from fire exposure, the temperature dependent material properties and the member stiffnesses must be taken into account. It must then be verified that E fi d R fi, d , t , ≤ 7.1 Where E fi,d is the design effect of actions for the fire situation, including the effects of thermal expansions and deformations and R fi,d,t is the corresponding design resistance at elevated temperatures. Global structural analysis considers the structure as a whole. Analysis of portions of the structure: Instead of analysing the whole structure by the global structural analysis method, a portion, or subassembly comprising appropriate portions of the structure may be 131
carried out. Here the design actions at the boundaries of the subassembly may be obtained by a global structural analysis for normal temperature design by using: E , = η E 7.2 fi d fi d where E d is the design value of the corresponding action for normal temperature design and η fi is the reduction factor for the design load level for the fire situation given by: γ GAGk + ψ 1,1Qk ,1 η fi = 7.3 γ G + ψ Q G k Q,1 k ,1 where Q k,1 is the principal variable load, γ GA is the partial factor for permanent actions in accidental design situations and ψ 1,1 is the combination factor for frequent values. η fi from Eurocode 3, is equivalent to the load factor r f , from the New Zealand as this is the ratio of the loading on the structure or member with fire conditions to the loading on the structure for normal conditions. Equation 7.2, therefore, shows that the design resistance of a member when exposed to elevated temperatures from a fire, is a proportion of the resistance available in normal conditions based on the loading ratio between the two conditions. Member analysis Alternatively, individual members may be analysed for fire situations. For this analysis the restraint conditions at supports and ends of members; and the internal forces and moments at supports and ends are assumed to remain at the values calculated for normal temperatures throughout the fire test. 7.2.2 Structural fire Design: Eurocode 3 gives complete design guidelines to follow when designing structural members to fire standards. These methods involve determining the fire loads enforced on a structure and analysing the strength of each member at elevated temperatures. The layout in this section follows that of Eurocode 3, and has also been based on the work of Buchanan, (1999). 132
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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
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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
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 140 and 141: Figure 6.3 a shows that the average
Page 142 and 143: The fire that the test beams were e
Page 144 and 145: 7 ADDITIONAL MATERIAL 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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