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

Concrete slab
Steel UB beam
Figure 4.6: Layout of three sided exposure with a concrete slab
The results for three sided exposure to an ISO 834 fire differ from those of four
sided exposure. The SAFIR results have a greater temperature spread between the
maximum and minimum values for different elements due to cooler steel
temperatures at the unexposed face. The option of simulating three sided exposure
with or without a slab present gives more variation to the results found.
With three sided exposure to the fire, the steel section has a temperature gradient
across the cross section. With a concrete slab in place, the variation is greater
across the section during to the cooling effects of the slab. The average
temperature is assumed to be the average of all elements from the SAFIR
simulation, which is acceptable for a thermal analysis, and best for a comparison
with the spreadsheet method. However, if a structural review of the member was
being made, the temperatures at vital points of the section such as the temperature
of the lower flange should be considered.
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