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

If the above equation is true then the insulation can be considered ‘light’ and the heavy
insulation term in brackets, {}, can be omitted to simplify the equation. To see the
effect of this omission, refer to Section 5.3.1.
2.2 ALTERNATIVE FORMULATIONS OF THE SPREADSHEET
METHOD:
There are alternatives to the spreadsheet method as primarily used in this report. The
method used in this report and described in Section 2.1, based on the principles of heat
transfer, was developed by the European Convention for Constructional Steelwork
(ECCS, 1983). The formula for protected steel, with heavy insulation is as below:
∆ T
s
H
=
p
A
( k d ρ c )
i
i
s
s
ρ
sc
s
ρ c
( T − T ) ∆t
f
s
s
s
1 H
2
d
A
ρic
p
+
i i
For light, dry, or relatively thin insulation, the middle term in {} brackets can be
negligible and therefore ignored.
Another method as recommended by ECCS in earlier work gave the following two
formulas for light and heavy insulation. The heat flow to insulated steelwork was
divided into these classes because the formulas used for heavy insulation gave unstable
results when the insulation was termed ‘light’ from equation 2.4. The method for
heavy insulation can not be justified on theoretical grounds, but the formulas have
been included here for completeness, (Purkiss, 1996). The light insulation equation is
the same as stated above with the heat capacity term neglected.
Light insulation:
∆T
s
k H
i
p
=
dic
s s
A
ρ
( T − T ) ∆t
f
s
2.5
and for heavy insulation:
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