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

The Eurocode does not define a method to calculate a time for structural adequacy
of an element. It is instead based on the structural performance of a steel member
at time t, which is an analysis in the strength domain. The corresponding design
resistance at this time must be greater than the design action imposed on the
element during the fire, i.e. U
*
f
≤ R
f
Where
*
U
f
is the design force applied on the structure during a fire at a given
temperature and
R
f
is the load bearing capacity at that temperature.
Slightly different methods are given for tension and compression members, for
bending and shear, and for different end conditions.
3.1.2 Variation of Mechanical Properties of Steel with Temperature:
Variation of Modulus of Elasticity with Temperature:
The mechanical properties of steel vary with temperature, generally decreasing as
the temperature of the steel increases. Steel has a limited strength, meaning that at
a certain temperature the strength of the member will decrease to virtually zero.
The equations for the variation of the modulus of elasticity adopted in the New
Zealand and Australian codes are those recommended by the French Technical
Centre for steel construction, CTICM, (Wong and Petterson, 1996). The
advantage of using these equations is that they cover a large range of temperatures
from 0 °C to 1000 °C.
The variation of the modulus of elasticity with temperature is given by:
E(
T )
T
= 1.0 +
0 < T < 600 °C 3.1a
E(20)
T
2000ln
1100
T
6901
−
1100
=
T − 53.5
600 < T < 1000 °C 3.1b
Eurocode 3 gives values for the proportion of Modulus of Elasticity in a table with
varying temperature. Figure 3.1 below shows the variation of the modulus of
36