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

The spreadsheet results are from calculations using a reduced section factor as
used with unprotected steel, refer to Section 1.6.3 for more detail in the calculation
of the section factor. The results are shown in Figure 5.13 for the 180 UB 16.1,
which gives typical results for the three beam sizes analysed.
The spreadsheet method aims to give the average temperature of the steel, whether
protected or unprotected. From Figure 5.13, however, the results from calculation
made by the spreadsheet method give temperatures closer to the maximum
temperatures found in SAFIR. Although the temperatures found by the
spreadsheet method differ substantially from the average temperature found by the
SAFIR results, this is due to the variation in temperatures found from the SAFIR
simulations with three sided exposure from cooling effects of the concrete slab that
is not seen with four sided exposure as in Figure 5.1.
1000
Temperature ( o C)
800
600
400
200
0
0 20 40 60 80 100 120
Time (min)
ave max Spreadsheet
Figure 5.13: Comparison between maximum and average temperatures found from the SAFIR
programme with the results from the spreadsheet calculations for a 180UB16.1 beam exposed to an
ISO fire on three sides.
The maximum temperatures found from the SAFIR results with three sided
exposure as seen in Figure 5.13 are the same as the maximum temperatures found
for four sided exposure. This is because the lower flange and web are unaffected
by the concrete slab which cools the top flange and therefore lowers the average
temperature of the beam. The spreadsheet method does not model any effects of
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