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

the test. This formula has a limit for the size of the steel beams, based on its
Section Factor, with the H p /A value between 15 and 275 m -1 .
ECCS, (1985) recommend using:
0.6
t = 0.54( T − 50)
A
l
4.2
H
p
ECCS limits this formula to the steel temperature range of 400 °C and 600 °C.
The time when these temperatures may occur are limited by the time period of
between 10 and 80 minutes, and the formula is valid for members with a section
factor, H p /A, value of between 10 and 300 m -1 .The lightest beam used in this
report, 180 UB 16.1 has a section factor, which is out of the recommended size
range for these equations.
Figure 4.5 a-c show the accuracy of the formulas provided in NZS 3404 and AS
4100; and recommended by the ECCS for four sided exposure to unprotected steel
beams. The range for both has been extended beyond that which is recommended
by the committees formulating the formulas, but as can be seen the lines generally
fit within the same accuracy of the recommended range for a much larger
temperature spread and longer time period than those suggested. The time
temperature curve to which these equations are being compared to is calculated
using the spreadsheet method, which is considered to be an accurate account of the
true behaviour of a steel member in a standard ISO 834 fire test.
From Figure 4.5 a-c, the formula range for the ECCS formula, Equation 4.2, can be
extended to at least 700 °C as an upper limit. This could even be extended to 800
°C as this temperature is within the same accuracy from the spreadsheet curve as
temperatures that are in the recommended range. Below 400 °C, linear
interpolation method could be recommended as this will gives conservative or
shorter values for the times that a temperature is reached. The temperature range
suggested by for the New Zealand code equations appears valid, with an upper
temperature limit of 850 °C, and linear interpolation for temperatures below 500
°C.
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