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

susceptible to heating, heat up more than those parts of the beam which are more
protected due to the geometry of the beam, ie. the thickness or length of the
segment, or the location of the point, ie. the centre of the web compared with the
corner of the flange-web intersection.
5.2.2 Heavily Protected Beam with Four Sided Exposure:
Four sided exposure is modelled in the SAFIR programme using insulation with
the properties stated earlier in Section 5.2. The steel section is protected on all
four sides, and an ISO 834 fire is subjected all sides of the protection. The
temperature variation across the cross section of the element is small, and of
similar proportions to that of four sided exposure for unprotected steel.
The results from SAFIR and from the spreadsheet method are compared, and these
are also graphed against the estimations from the ECCS equations in Section 5.2.3.
There are no formulas provided in NZS 3404 for protected steel members.
Figure 5.3 a-c show the results from four sided exposure to the standard ISO 834
fire, for 66 minutes. The graphs show a very close correlation between the
temperatures predicted by the spreadsheet and the average temperatures found
from the SAFIR simulation. The spreadsheet method gives higher temperatures
than SAFIR at lower temperatures of the test, but the difference between the
average SAFIR temperature and the spreadsheet temperature increases as the beam
gets hotter, with the spreadsheet temperatures exceeding those determined from
SAFIR.
This is again due to the thermal properties of steel remaining constant with the
spreadsheet method, but varying with SAFIR. The curves tend to separate more as
the temperature increases, and the spread increases greatly at around 650 °C to 700
°C as this is where the thermal properties of SAFIR deviate most from the constant
value of 600 J/kg K that is used in the spreadsheet.
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