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

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average temperature of the beam, because heat is conducted from the beam and absorbed by the concrete. This causes a large variation between the maximum and minimum temperatures of the beam as can be seen in Section 4.3.1 and in Figure 4.7 and Figure 4.8. 4.3.3 Comparison with NZS 3404 and ECCS formulas for three sided exposure: The New Zealand Steel Code has a different equation for three sided exposure, from that for four sided exposure as stated in Section 4.2.3. This is in the form below: A t = −5 .2 + 0.0221T l + 3. 40Tl 4.3 H p The temperature range and limitations on the cross section of the member are the same as described in Section 4.2.3 for equation 4.1, as stated below: Equation 4.3 is valid in the temperature range of 500 °C to 850 °C by the New Zealand code, and up to 750 °C for the Australian code. Below 500 °C, linear interpolation is used between the time that the steel becomes 500 °C and a temperature of the steel of 20 °C at the start of the test. The beams size limitations are based on its Section Factor, with the H p /A value between 15 and 275 m -1 . The ECCS recommendations use the same formula as with four sided exposure, equation 4.2, but with an altered H p /A value to allow for three sided exposure to the fire. This formula is: t = 0.54( T − 50) A l H p 0.6 with temperature limitations of 400 °C to 600 °C, time of between 10 and 80 minutes, and is valid for beam sizes with a section factor, H p /A, value of between 10 and 300 m -1 . In Figure 4.12 a-c the curves that the two straight-line equations are compared with are both from SAFIR, namely SAFIR 1 and SAFIR 2 as used earlier in Section 4.3. 71
The SAFIR curves are the result of simulations with ISO 834 fire exposure to three sides of the cross section, with and without a 150 mm concrete slab resting on top. The addition of the slab lowers the of steel temperatures estimation because not only does it protect the top face of the beam from fire, but it also absorbs heat with its high thermal mass and subsequently cools the steel beam. The equations show consistency with the two curves in Figure 4.12 a-c. Equation 4.3, provided in NZS 3404 and AS 4100, fits closely to the SAFIR 2 timetemperature curve with the concrete slab. Comparing the line given by equation 4.3 with the curve from the SAFIR 1 simulation, however, gives predictions that are too low and unsafe, see Section 4.1.2. Since most three sided situations would occur with a slab present, using equation 4.3 to predict the average steel temperatures for three sided exposure appears to be more realistic. This formula is based on regression analyses based on British temperature data and a more substantial modification is made from the four sided exposure formulas than those that is recommended from ECCS (1985) committee. The ECCS line, which results from equation 4.2 with a lowered H p /A value, agrees well with the results from the SAFIR 2 simulation in the temperature range recommended. When using equation 4.2 to calculate the temperature of the beam at elevated temperatures for three sided exposure to fire the only change made to the calculation is the section factor, or effective width. As can be seen in Figures 4.4 and Figure 4.11, the SAFIR results are close to that calculated from the spreadsheet method, in which the variation between four and three sided exposure is also only a change in section factor. This all means that the ECCS equation fits best with the SAFIR 1 curve because it fits well with the SAFIR curve for four sided exposure and the same principles and assumptions are used with the SAFIR 1 curve but not the SAFIR 2 curve due to the concrete slab in the latter simulation. 72
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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
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 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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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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