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

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Figure 4.2 shows the variation of temperature between the different points on the cross section of the beam. The maximum and minimum temperatures shown in the graph are the maximum and minimum temperatures of an element at each time step over the time period examined here. The element in which the maximum or minimum temperature is found is not necessarily the same throughout the entire time period of the graph. During the later stages of the simulation, however, the same element in the cross section has the maximum and minimum temperatures. The average temperature on the curve is simply an average of all elements at each time step. No consideration due to the size or position of the element on the cross section has be made. In the later stages of the test this is especially acceptable because these temperatures of all the elements merge to within a small temperature range, and the later temperatures are more vital when considering the structural behaviour of the beam. In each of the SAFIR curves there is a small plateau region in the temperature of the steel, when the beam has been subjected to the fire for around 20 minutes. This reduction in the rate of temperature rise is due to the increase in specific heat of steel, which occurs when the temperature of steel is between 650 °C and 800 °C. The same behaviour and similarities are present in all three sizes of beams tested. The specific heat changing has an impact on the rate of temperature increase because it governs the amount of energy that is required to be absorbed by the steel for its temperature to be raised. The value of the specific heat of steel changes from being between 600 – 800 J/kg K at temperatures below 650 °C, to a maximum of 5000 J/kg K when the steel reaches a temperature of 735 °C as shown in Figure 1.1. This variation in magnitude of about 8 causes the significant flattening of the curves. The maximum, minimum and average temperatures of elements in the SAFIR tests are shown in Figure 4.2. The maximum difference between the maximum and minimum temperatures is 49 °C, which occurs 5 minutes after the start of the simulation when the temperature range is 353 to 402 °C, and the average 55
temperature is 360 °C. This results in the maximum temperature being 14 % higher than the minimum temperature and 12 % higher than the average. The maximum temperature at this time is located at the element in the middle of the length of the web and the minimum temperatures at this stage are located midway along overhang of the flange from the web-flange intersection as shown in Figure 4.3: The central element of the web is the hottest region due to the width of the web being only 4.5 mm compared with the width of the flange being 7.0 mm. Since the web is relatively long in comparison with the length of half the flange width, the neighbouring elements of the web are also hotter and heat is conducted through to the central element of the web from both sides giving it the highest temperature. The mid section of the flange is the coolest area by the same theory. It has a thicker width, and very little heat is conducted into the element because the whole of the flange is of similar temperature. The middle section is the coolest because the ends are subjected to fire on three sides and are therefore at a cooler temperature, and where the web meets the flange there is conduction from the hotter web sections increasing the temperature. The elements of the flange and web vary only slightly in temperature but the difference between the flange and the web can be quite significant during some stages of the fire test. 56
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Fire Design of Steel Members K R Le
Page 4:
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
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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 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 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
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 120 and 121:
1000 Temperature ( o C) 800 600 400
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Thermal conductivity, k i = 0.19 W/
Page 124 and 125:
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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