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

It is therefore recommended that the spreadsheet equation method be entered into
the New Zealand Steel Code as an alternative method for a more accurate time
temperature curve for design. The equations in the spreadsheet method can be
used with more realistic fires to provide designers with a likely response of the
steel member, and with the current use of computers, there is no need to use the
simple hand calculation methods that provide only an estimate of the time
temperature relationship.
The spreadsheet equations for the timestep method used in this report for protected
steel should also be included in the New Zealand Steel Code. Further research into
the alternative time step results commented on in Section 5.7 could be made if the
simple equation used in this report is not deemed satisfactory.
If engineers using NZS 3404 wish to use the results of standard fire furnace tests,
the regression analysis method should still be available to them, but with the
increased confidence in theoretical calculations for behaviour of steel in fire, these
are not necessary and the use of theoretical calculations can allow more freedom
when designing rather than being limited by the availability of data.
7.2.4 Mechanical Properties:
As stated in Section 3.1.2, the mechanical properties of steel differ from that of the
New Zealand Steel Code, but it is beyond the scope of this project to determine
which gives the most accurate variation of the yield stress and modulus of
elasticity of steel with temperature. The Eurocode formulas give data points of
these properties rather than a formula, and the limiting temperature where the
values of these properties tend to zero is consistent. A possible change to the New
Zealand Steel Code, which will give more technically correct information, is to
modify the formulas included in the code for the mechanical properties of steel to
tend to zero at the same temperature.
The limiting temperature is a direct rearrangement of the formula of proportion of
yield stress remaining at elevated temperatures.
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