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

1000
Temperature ( o C)
800
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400
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0
0 20 40 60 80 100 120
Time (min)
min ave max
Figure 5.12: Variation of maximum and minimum temperatures from a simulation in SAFIR for a
180 UB 16.1 beam with heavy protection and a concrete slab.
The maximum and minimum temperatures vary greatly across the cross section as
shown in Figure 5.12. The maximum temperature difference between the
maximum and minimum temperatures is over 200 °C, and the difference appears to
have reached a constant value. The variation between the maximum and minimum
temperature is much more marked due to the concrete slab in place, which absorbs
heat energy from the steel and subsequently cools the top flange. The maximum
temperatures located in the web and the lower flange is not affected by the
presence of the concrete slab. When comparisons are made with four sided
exposure as stated in Section 4.3.1, the maximum and therefore the likely limiting
temperature of the concrete slab does not change with between four or three sided
exposure conditions.
5.6.2 Heavily Protected Beams with Three Sided Exposure:
Three sided exposure is modelled in SAFIR as explained in Section 5.6.1, and the
results from these simulations are compared with results from calculations made
by the spreadsheet method in this section. The ISO 834 fire is subjected to the
steel section on the three sides that are protected with insulation, while the fourth
side is left at ambient temperatures to represent the effect of having a concrete slab
with a top surface in a different compartment, not experiencing elevated
temperatures.
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