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

As can be seen from Figure 5.4 a-c, the line resulting from this formula fits well
with the spreadsheet curve on each graph. The temperature range that this
equation is valid for is from 400 °C to 600 °C but the upper limit of this could be
extended to 800 °C from the evidence seen here. The lower limit could also be
extended beyond the range suggested, to around 300 °C, although linear
interpolation for temperatures below 400 °C from a starting temperature of 20 °C
as is recommended with the formulas from NZS 3404 would be a better option.
The ECCS formula for the light steel beam appears to have good correlation with
the spreadsheet curve even though the beam size has a section factor outside of the
recommended range. For unprotected steel this light beam gave results that did not
fit with the SAFIR curves for four sided exposure, see Section 0, although for three
sided exposure for unprotected beams the results fit well.
There appears to be little difference in the accuracy of the formula between the
three beam sizes used here, and the formula appears to give a very accurate
estimation of the temperature of the steel during the temperature range of 350 °C
to 800 °C. Again the SAFIR curves are used to compare the accuracy of the
formulas as this programme shows the thermal response of steel to great accuracy.
Using the modified ECCS equation gives excellent results when compared with the
results from the SAFIR programme. Purkiss’ simplified version of the modified
equation also gives good accuracy, but the assumption that the specific heat of the
insulation is twice that of steel is a bit non conservative, as the specific heat values
for heavy insulation can vary significantly.
5.3 RESULTS FOR FOUR SIDED EXPOSURE WITH LIGHT
PROTECTION:
The same comparisons that are made with heavy protection are applied in this
section to examine the effect of the simplifications and assumptions made with
light protection. The insulation used to model the effect of light protection is
Mandolite, by Firepro. The properties of this are as below:
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