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

t
d
0.00013et
=
A
v
H
v
A
t
where e t is the fuel load in the compartment (MJ/m 2 total surface area)
2.14
After the period of heating, t d , has been completed the fire cools down linearly.
Buchanan (1999), modified the original Eurocode method of decay because there
appeared to be confusion between fictitious time and real time, and the Eurocode
method gave excessive cooling rates with larger openings. Wickstrom suggested that
the decay rates apply to real time, with cooling magnitudes of 625 °C for fires of
duration of less than half an hour, decreasing to 250 °C for fires of greater than two
hours duration, (Buchanan 1999)
For the purpose of this project the decay rate used will be as suggested by Buchanan:
dT F
kρc
v
= 625
p
dt 0.04
1160
This is also the form of the decay rate equation that is used in the pre-processor
developed by John Mason used in later sections of this report.
2.15
As seen in equations 2.7 a-b, the growth rate of the Eurocode parametric fire is
independent of the fuel load in the compartment, which intuitively appears incorrect
that the fuel load does not affect the temperature of the fire. Since the Eurocode
Parametric fires are ventilation controlled, however, the fuel load does not affect the
temperature rise, as the temperature is more dependent on the ventilation available to
the fire. In the early stages of the fire, however, when the fire is more likely to be fuel
controlled, the amount of fuel would affect the fire temperatures. Since for
establishing the fire resistance of structural members the fire has a significant duration,
this assumption of ventilation controlled fires is not inappropriate.
Since the Eurocode fire is a function of three variables, namely ventilation factor, fuel
load and wall lining properties, there are a large number of possible fires to be formed
when different values are used for each variable. To reduce the number of fires
studied here, a standard case has been chosen, from which one variable is changed at a
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