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

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esponse times of sprinklers or smoke detectors, plume filling rates and egress times from rooms, (CSIRO, 1993). The function applicable to this report is ‘Steel Beam Load Bearing Capacity’ which has output providing the temperature of the standard fire, the temperature of a chosen steel beam and the proportion of original or ambient strength the steel beam still has after 18 minute time intervals. The programme has the capacity to simulate unprotected steel beams with box or spray on protection. The user can also choose whether a ceiling slab is present. The inputs required are the weight per unit length and perimeter of the beam and the thermal properties of the insulation. This programme is designed specifically for three sided exposure to fire with a concrete slab and using the programme for other beam configurations is not recommended. An input option is included to specify the moisture content of the insulation, which provides a delay time at around 100 °C when the water is evaporated, as the insulation is able to absorb latent heat energy without increasing in temperature. Moisture also affects the flow of heat to the beam through the insulation, which is allowed for in this model. The background for calculations made in this programme comes from heat transfer theory, from an emitter to a receiver. Radiation and convection are both considered when calculating the energy transmitted to the insulation using fundamental heat transfer equations. The coefficient for convective heat transfer is 83.6 kJ/m 2 hr K, which is equivalent to 23.2 W/m K. Information not specified in the user manual is the emissivity constant for radiation; the equation to evaluate the delay due to the moisture content, properties of steel and whether these vary with temperature. The load bearing capacity of the steel beam is also calculated, which is given in a ratio form of a proportion of the initial load on the beam. The equation used to estimate the load bearing capacity of the beam at elevated temperatures is: L = 905 − T T 690 s > 215 °C 2.11a and L = 1. 0 T s < 215 °C 2.11b 29
This equation originates from the yield stress proportion formula, which can be found in NZS 3404. The programme therefore assumes that the load bearing capacity of a member is directly proportional to the ratio of yield stresses at elevated temperatures to normal temperatures as is used in NZS 3404. Using this method eliminates the need to consider the safety factors and different loadings that the beam may have been designed for, and considers only the variation of the yield stress with temperature. The moisture concept is not included in the SAFIR programme so for comparisons with the SAFIR results, this has been assumed to be zero for consistency, when using Firecalc. 2.4 FIRE CURVES: 2.4.1 Standard Fire – ISO 834: The standard fire is a fire that is used to perform tests on building materials and structural elements. The ISO 834 fire is the standard fire most commonly used in New Zealand. The formula for this fire is: T = 345log10 (8t + 1) + T 2.12 0 The time-temperature curve of the ISO 834 fire is shown below: 1000 Temperature ( o C) 800 600 400 200 0 0 10 20 30 40 50 60 70 Time (min) Figure 2.4: Time temperature curve of the ISO 834 Standard Fire Curve The standard fire is primarily used in experimental fire tests, as although it does not resemble a ‘real’ fire, it can be replicated in a controlled environment. By using a standard fire, manufacturers can test their product and find a fire resistance time that 30
Page 1 and 2: 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
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: protection, and for user defined fi
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 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
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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
Page 122 and 123:
Thermal conductivity, k i = 0.19 W/
Page 124 and 125:
1000 Temperature ( o C) 800 600 400
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 146 and 147:
For thermal analysis 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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