Steel · Fire, corrosion & serviceability
Fire: limiting steel temperature calculator
Limiting temperature from the load ratio, yield stress and modulus reduction factors at a given temperature, and exposed surface area to mass ratio ksm.
Standard: AS 4100 Section 12 (Cl 12.4, 12.5)
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Load ratio r_f | 0.5 | |
| Steel temperature to evaluate | 550 | °C |
| Exposed perimeter | 1200 | mm |
| Mass per metre | 59.7 | kg/m |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Limiting temperature 905 − 690 r_f | 560.0 | °C |
| fy(T)/fy(20): 1 ≤ 215 °C else (905 − T)/690 | 0.514 | |
| E(T)/E(20) | 0.603 | |
| Exposed surface area / mass ksm | 20.10 | m²/t |
- ✓ Steel temperature below limiting temperature
Method, formulas and assumptions
- Limiting temperature 905 − 690 r_f = 905-690*0.5 = 560 °C
- fy(T)/fy(20): 1 ≤ 215 °C else (905 − T)/690 = IF(550<=215,1,MAX(0,(905-550)/690)) = 0.51449
- E(T)/E(20) = IF(550<=600,1+550/(2000*LN(550/1100)),690*(1-550/1000)/(550-53.5)) = 0.60326
- Exposed surface area / mass ksm = 1200/59.7 = 20.101 m²/t
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.