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

where the temperature of the steel, T s is in °C, (Purkiss, 1996, BSI, 1990, EC3 1995).
This value can vary as Harmathy, (1993), uses a value of 1.14 rather than 1.4. ENV
1993-1-2 also adopts a more variable approach to the thermal elongation of steel, with
the following relationship between thermal elongation and temperature:
∆l
l
∆l
l
∆l
l
= 1.2x10
= 1.1x10
= 2x10
−5
−5
−2
T
T
−8
2
−4
s
+ 0.4x10
Ts
− 2.416x10
20 < T s < 750 ° 1.8a
750 < T s < 860 °C 1.8b
−3
s
− 6.2x10
860 < T s < 1200 °C 1.8c
The variation of these formulas with temperature are shown in Figure 1.3.
0.02
Thermal expansion of steel
0.016
0.012
0.008
0.004
0
0 200 400 600 800 1000 1200 1400
Temperature ( o C)
Equation 1.8 Equation 1.7
Figure 1.3: Variation of thermal expansion of steel with temperature
1.6.3 Section Factor, H p /A:
The ratio of the heated perimeter to the cross sectional area gives the inverse of the
effective width of the steel member. This term is called the Section Factor (SNZ,
1991). Throughout this report the notation used is H p for the heated perimeter and A
for the cross sectional area. Other notations include F for the heated perimeter, or the
same ratio can be achieved in a three dimensional sense with the heated area per unit
length to the volume per unit length used instead, A/V. Here A for heated surface area
should not be confused with A of cross sectional area used in this report.
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