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

e) The conditions of support are the same as the prototype and the
restraints are not less favourable than those of the prototype; and
f) The ratio of the design load for fire to the design capacity of the
member is less than or equal to that of the prototype.
These conditions mean that the results from the tests can only be used when the
prototype gives equal to or more severe results than those of the member being
analysed, particularly in relation to the span of the beam; the load restraints; the
support conditions; the section factor and the thickness of the insulation. To obtain
results from experimental tests, the member is usually shorter than that of the
member in service. This complies with e) above.
No alteration to the results obtained from experimental tests may be made,
however, to account for different insulation thickness or steel section factor.
The Eurocode states only once in the document that experimental data may be used
to confirm the fire resistance rating of a member. The British Standard, BS
5950:Part 8 gives options to use fire resistance test data to confirm the fire
resistance applied to the steel members, giving limitations concerning the
applicability of the tests similar to those stated above as listed in NZS 3404.
NZS 3404 also has a clause to cater for circumstances where there is three sided
exposure with concrete densities which differ by more than 25 %, or for slabs with
a thickness that varies by more than 25 %. This clause makes an allowance for the
resulting effect on the steel temperature that these variations make. The effect of
different concrete densities and thicknesses are small so a considerably large
difference must be present in the construction before the members must be treated
as separate cases.
3.1.7 Special Considerations:
A conservative approach is given for designing the fire resistance of connections
and web penetrations.
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