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

5.8 CONCLUSIONS:
The thermal behaviour of protected steel members has been examined in this
section. In the New Zealand code at present there are no formulas available to aid
designers in the estimation of the temperature of protected steel members. The
equations recommended by ECCS relate closely to the results found from the
spreadsheet method and SAFIR.
The empirical equations used in this section from ECCS give good results when
compared with the time-temperature curves resulting from SAFIR simulations. As
in Section 4, the upper temperature limit can be increased to allow more use to be
made of these equations. The upper temperature value for protected steel can be
increased to 800 °C and remain within the same accuracy as the line within the
present temperature range criterion. The other limitations imposed on the steel
member regarding the time and beam sizes for which the equation is valid do not
seem to be a factor in the accuracy of the equations. The limitation regarding the
thickness and thermal conductivity of the insulation has not been discussed
because all tests examined in this report have complied with the range suggested
for the equations.
The original form of the equation is intended for use of steel beams protected with
‘light’ insulation, but for ‘heavy’ insulation there is a modified formula, which
accounts for the thermal capacity of the insulation. This formula only applies well
for four sided exposure with protected members, and although the equation
compares well with results from the spreadsheet method for three sided exposure,
this is rather conservative as the spreadsheet method assumes a smaller amount of
protection applied with its smaller section factor. When considered that most three
sided exposure results from conditions with a concrete slab overlaying a steel
beam, this equation gives a time-temperature relationship which is high for three
sided exposure.
The formula does works well for four sided exposure and is a useful tool and a
simple alternative to the present guide in the New Zealand code to use data from
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