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

Therefore, the ECCS equations provide a better indication of the time and
temperature that failure will occur.
The ECCS formula should have an extended temperature range to up to around
750 °C; with linear interpolation for temperatures less than 400 °C. The
temperature limitations of the ECCS equations should be examined closer and
adjusted so the equations can be put more to use than the limiting temperature
range that is presently imposed on them. The suggestion of a maximum
temperature at least 750 °C rather than the present value of 600 °C is based on the
results of the comparisons made in this report only. The ECCS equations would
give better and more useable results than the present formula in NZS 3404 for four
sided exposure with an extended temperature range.
A concrete slab is present for most three sided cases, so the NZS formula gives a
more accurate estimation of the average temperature of the steel beam for these
cases but not the maximum temperature. If the ECCS equation was adopted for
four sided exposure based on the evidence seen here, however, it would simplify
the code to use the ECCS equation for three sided exposure also as the difference
in temperature is only small, and differs conservatively from the present equations.
The spreadsheet method gives an accurate indication of the thermal response of
steel members when subjected to the ISO 834 fire when compared to the steel
temperatures assumed by the SAFIR programme. If the average temperature of
unprotected steel is required for a calculation in a temperature or time range where
the formulas are not valid, the spreadsheet method is the simplest method to use.
The time step method gives accurate results, especially for four sided exposure
where there is less variation across the cross section of the member. For three
sided exposure, the time step spreadsheet method gives conservative results if the
beam has a slab protecting the top flange, and only the average temperature of the
steel can be calculated. To analyse the maximum temperatures likely to be
reached in the section a finite element programme such as SAFIR needs to be used.
Although the spreadsheet offers only the average temperature of the steel, with
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