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

The SAFIR results fit between the two spreadsheet results for most of the test and
as in all simulations made in this report, the rate of temperature rise decreases at
about 650 °C when the higher specific heat becomes a larger factor in the
temperature rise of the steel. The results from the Spreadsheet 2 analysis are very
similar to the results from the Spreadsheet 1 analysis, with a maximum difference
of around 50 °C. Since simplifying the formula used in the spreadsheet for light
protection gives higher temperatures, the simplified formula can be used with
confidence instead of the full equation provided the criteria from equation 2.4 is
met. The insulation will always affect the temperature of the steel to some amount
so the full spreadsheet analysis is acceptable to use in place of the simplified
version if preferred.
Assuming the SAFIR programme gives an accurate portrayal of the behaviour of
the steel beam when protected by the insulation described, the full equation gives
slightly lower temperatures and therefore non-conservative results at the beginning
of the test. The maximum temperature deficit of temperatures found from the
spreadsheet with the heat capacity included, compared with the average SAFIR
results is 20.3 °C, which occurs when the temperature is about 250 °C. Although a
difference of around 10 % is reasonably substantial, it is not of too much
importance here due to that the steel member would not have lost a significant
amount of strength at this temperature.
The spreadsheet temperatures are greater than the steel temperatures after 93
minutes of the test, when the temperature is about 550 °C, which is much closer to
the limiting temperature of steel. After 93 minutes the SAFIR curve drops below
the spreadsheet curves at a faster rate due to the thermal properties of the steel in
the SAFIR programme.
The curve from the simplified spreadsheet method is consistently higher than both
the full spreadsheet curve and the SAFIR curve. At the very start of the test the
SAFIR curve is slightly higher than the simplified spreadsheet curve, but this could
be due to the slow starting conditions found with the spreadsheet method. The
maximum difference is 3 °C and after 30 minutes the spreadsheet method curve is
95