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

constant specific heat being used in the spreadsheet method, but since the
difference is small in both cases; the simple method of keeping the specific heat
constant appears to be more reasonable.
Using a specific heat that varies with temperature in the spreadsheet method shows
how closely the spreadsheet method results match those that are given by the finite
element computer programmes. Because the spreadsheet method is much easier to
access and work compared with the computer programmes, for thermal
calculations of simply supported beams with four sided fire exposure. this method
is the best to use.
5.3.2 Comparison with the ECCS Formula:
Comparisons with the formulas recommended by ECCS have been plotted against
the results from the SAFIR simulations and the simplified spreadsheet results in
Figure 5.7 a-c. Equation 5.1, by ECCS used in Section 5.2.3, is used in its original
form without the modification for heavy insulation, since the properties of
Mandolite satisfy the conditions of equation 2.4, as shown in Section 0.
Figure 5.7 a-c shows the accuracy of the ECCS formula when applied to steel
sections with light protection. The ECCS formula is compared to results from the
spreadsheet method with the light insulation simplification, but with a constant
value for the specific heat of steel. Results from SAFIR are also included to
compare the formula with ‘real’ behaviour of steel under the conditions of the
analysis.
When light protection is used as in Figure 5.5 a-c, the unmodified spreadsheet
method has slightly lower temperatures than the simplified version. The SAFIR
results are lower than the results from both spreadsheet methods due to the
changing thermal properties installed in the programme. The ECCS equation has
the best correlation with the spreadsheet 2 curve, which neglects the heat capacity
of the insulation term. The section factor for the lightest beam, 180UB16.1, is out
of the recommended range of beam sizes for the ECCS equation, but the formula
predicts the temperatures equally well for this beam as with the other beam sizes.
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