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

15 m -1 < H p /A < 275 m -1 in NZS 3404 and AS 4100
To obtain times for temperatures below 500 °C, linear interpolation can be used
with starting temperature of 20 °C.
These formulas were obtained from regression analyses of British temperature data
for unprotected steel. Design temperatures for different fire resistance times for
beams and columns are found in the British Steel Code, BS 5950: Part 8: 1990,
which were used as the basis of the regression analysis. The upper temperature
limit has been increased from its original value due to research performed in recent
years, such as by Clifton and Forrest, (1996). The Australian code has not revised
the upper temperature limit and this remains at 750 °C.
Eurocode 3 does not contain simple empirical formulas such as these, but rather
gives a heat transfer formula to calculate the temperatures in a spreadsheet form.
The formula is in a slightly different form than that stated in Section 2.1.2, but the
same heat transfer principles are applied:
where
H
p
∆ T
A
s t
= h
,
net,
c ρ
h
net , d
s
s
d
∆t
3.10
is the design value of the net heat flux per unit area (W/m 2 ). h
net , d
replaces the variables in the spreadsheet formula and can be calculated by
net,
d
t
( T − T )
h = h to give an equation of equivalent to the spreadsheet formula
given in Section 2.1.2.
f
s
This method of estimating temperatures of unprotected steel gives the designer
more freedom to evaluate the temperature time curve throughout the full ISO 834
fire exposure without any limitations to consider. The evaluation method is not
difficult and once set up in a spreadsheet form, the results can be found very easily.
3.1.5 Temperature rise of protected steel:
The temperature rise of protected steel as specified in the New Zealand and
Australian codes is to be based on results of tests on members with the appropriate
protection. To evaluate the performance of a protected member, temperature data
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