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

than elsewhere, and more insulation protects the internal corner of the beam as
shown in Figure 5.2:
Minimum steel
temperatures
Maximum Steel
Temperatures
Figure 5.2: Location of the maximum and minimum temperatures on the cross section of a steel
beam with spray on protection
These minimum temperatures are in different locations to where the lowest
temperatures are found in unprotected steel, (See Section 4.2.1), as the lowest
temperatures in these cases are found midway between the flange tip and
intersection with the web, or at a quarter of the flange length from the flange tip.
The temperature at the intersection of the web and the flange in unprotected steel is
only slightly higher than the temperature of the quarter flange points, but with
protected steel there is a larger temperature gradient along the flange.
The difference between the maximum and minimum temperatures with protected
steel increases as the test progresses, as in Figure 5.1, which is the opposite of the
behaviour seen with unprotected steel. At the start of the test all parts of the beam
are immediately protected from the fire, so the initial heating of the steel is slow in
all areas of the beam. As the test continues the areas of the beam that are most
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