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

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e) The conditions of support are the same as the prototype and the restraints are not less favourable than those of the prototype; and f) The ratio of the design load for fire to the design capacity of the member is less than or equal to that of the prototype. These conditions mean that the results from the tests can only be used when the prototype gives equal to or more severe results than those of the member being analysed, particularly in relation to the span of the beam; the load restraints; the support conditions; the section factor and the thickness of the insulation. To obtain results from experimental tests, the member is usually shorter than that of the member in service. This complies with e) above. No alteration to the results obtained from experimental tests may be made, however, to account for different insulation thickness or steel section factor. The Eurocode states only once in the document that experimental data may be used to confirm the fire resistance rating of a member. The British Standard, BS 5950:Part 8 gives options to use fire resistance test data to confirm the fire resistance applied to the steel members, giving limitations concerning the applicability of the tests similar to those stated above as listed in NZS 3404. NZS 3404 also has a clause to cater for circumstances where there is three sided exposure with concrete densities which differ by more than 25 %, or for slabs with a thickness that varies by more than 25 %. This clause makes an allowance for the resulting effect on the steel temperature that these variations make. The effect of different concrete densities and thicknesses are small so a considerably large difference must be present in the construction before the members must be treated as separate cases. 3.1.7 Special Considerations: A conservative approach is given for designing the fire resistance of connections and web penetrations. 47
Connections: NZS 3404 requires that the connections to protected members shall have protection applied with the same thickness as the maximum thickness of the members framing into the connection. This thickness should be maintained over the entire section of the connection including bolt heads, welds and splice plates. This is a conservative approach to the connection. Connections that transfer design actions from a member requiring a fire resistance rating, and achieve this by satisfying the equations in Section 3.1.4, must satisfy the following conditions: a) Connection components shall comply with ‘3.1.4’, using the limiting temperature calculated from ‘3.1.3’ and the Section Factor for the exposed cross section of the connection component b) Connectors shall achieve the same or lower value of (r f ) for the connectors as that for the member being supported, where r f is defined in ‘3.1.3’ This is to ensure that the connection meets the fire resistance requirements of the member that it is attached to, ensuring failure of the connection does not occur. The Eurocode does not give guidelines for the fire resistance rating of connections, but since it gives details on the design of the members, this theory can be transferred to the design of connections. Beam Web Penetrations NZS 3404 states Unless determined in accordance with a rational fire engineering design, the thickness of fire protection material at and adjacent to web penetrations shall be the greatest of: a) That required for the area of beam above the penetration considered as a three sided fire exposure condition; b) That required for the area of beam below the penetration considered as a four sided fire exposure condition; c) That required for the section as a whole considered as a three sided fire exposure condition The thickness shall be applied over the full beam depth and shall extend each side of the penetration for a distance at least equal to the beam depth, and not less than 300 mm. 48
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Fire Design of Steel Members K R Le
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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 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: = H p A (m -1 ) 7.85 The cons
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 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
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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
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APPENDIX C - FIRECALC Below in Figu
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