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

average temperature of the beam, because heat is conducted from the beam and
absorbed by the concrete. This causes a large variation between the maximum and
minimum temperatures of the beam as can be seen in Section 4.3.1 and in Figure
4.7 and Figure 4.8.
4.3.3 Comparison with NZS 3404 and ECCS formulas for three sided
exposure:
The New Zealand Steel Code has a different equation for three sided exposure,
from that for four sided exposure as stated in Section 4.2.3. This is in the form
below:
A
t = −5 .2 + 0.0221T
l
+ 3. 40Tl
4.3
H
p
The temperature range and limitations on the cross section of the member are the
same as described in Section 4.2.3 for equation 4.1, as stated below:
Equation 4.3 is valid in the temperature range of 500 °C to 850 °C by the New
Zealand code, and up to 750 °C for the Australian code. Below 500 °C, linear
interpolation is used between the time that the steel becomes 500 °C and a
temperature of the steel of 20 °C at the start of the test. The beams size limitations
are based on its Section Factor, with the H p /A value between 15 and 275 m -1 .
The ECCS recommendations use the same formula as with four sided exposure,
equation 4.2, but with an altered H p /A value to allow for three sided exposure to
the fire. This formula is:
t = 0.54( T − 50)
A
l
H
p
0.6
with temperature limitations of 400 °C to 600 °C, time of between 10 and 80
minutes, and is valid for beam sizes with a section factor, H p /A, value of between
10 and 300 m -1 .
In Figure 4.12 a-c the curves that the two straight-line equations are compared with
are both from SAFIR, namely SAFIR 1 and SAFIR 2 as used earlier in Section 4.3.
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