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

adjust for this underestimate of strength, (Proe et al, 1986). This factor has not
been considered in this report.
The temperature at which the proportion of the yield stress at elevated temperature
is considered to have dropped to zero differs from that of the modulus of elasticity.
Inwood, (1999), found this discrepancy in the New Zealand Concrete Standard,
and suggested an adjustment to the curves so they tend to zero at the same
temperature. This gives more reasonable results, as a zero yield stress can not
occur when the modulus of elasticity has a value. The Eurocode 3 formulae,
which give the variation of mechanical properties with temperature, tend towards
zero at the same temperature of 1200 °C.
Comparing the Eurocode curves for the mechanical properties of steel with those
obtained from the New Zealand Steel Code show that for the yield stress, the
Eurocode gives generally less conservative or higher values, while for the modulus
of elasticity the Eurocode 3 curves are more conservative and lower than those
from NZS 3404.
1.2
Yield Stress or Modulus of
Elasticity Ratio
1
0.8
0.6
0.4
0.2
0
NZS Yield
NZS MOE
Eurocode
Modification
to Yield in
NZS 3404
0 200 400 600 800 1000 1200 1400
Temperature ( o C)
NZS Yield NZS MOE Eurocode Yield Mod Yield
Figure 3.3: Variation of Yield Stress and Modulus of Elasticity with temperature
Figure 3.3 above shows the variation with temperature of the yield stress of steel as
given by the New Zealand Steel Code and the Eurocode, and an adjusted line of
yield stress from NZS 3404 so that the limiting temperature is 1000 °C. This
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