This document discusses three nominal temperature-time curves used to model thermal action on structures during fires: 1) The standard curve represents a fully developed fire and is used in fire resistance tests. It is defined by the equation T=345log(8t+1)+20. 2) The external curve models fires exposing external walls and is defined by T=660(1-0.687e^-0.313t)+20-3.8t^0.32. 3) The hydrocarbon curve models full hydrocarbon combustion and is defined by T=1080(1-0.325e^-0.675t)+20-2.5t^0.167. An example calculates the temperature

1. 1. THERMAL ACTION
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Thermal action on structure is defined as time -temperature
curve - time evolution of the gas temperature surrounding
the structure – this is the basis for heat flux calculation,
which is transmitted from surrounding to the structure.
Nominal temperature-time curve – as it does not represent
real fire, but insted the temperature measured at previous
fires.
EUROCODE 1 – three different nominal time-temperature curves
• Standard temperature-time curve
• External temperature-time curve
• Hydrocarbon temperature-time curve

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Standard temperature-time curve
It is still used today in standard fire tests for evaluation of fire
resistance of structural and separating elements. It represents fully
developed fire in fire compartment.
10T 20 345log (8t 1)  
External temperature-time curve
It is used for external walls exposed to fire – outer surface of
separating walls of fire compartment.
 0.32 3.8
T 20 660 1 0.687 0.313t t
e e 
   
Hydrocarbon temperature-time curve
It is used for full combustion of hydrocarbons( gasoline, oil, other fuels).
 0.167 2.5
T 20 1080 1 0.325 0.675t t
e e 
   

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External Curve Hydrocarbon Curve Standard Curve

4. Example 1.1
What will be the temperature of all three nominal curves after 30 minutes?
10T 20 345log (8 30 1) 841.8 Co
x   
 0.32 30 3.8 30
T 20 660 1 0.687 0.313 679.97 Cx x o
e e 
    
Standard curve
External curve
 0.167*30 2.5*30
T 20 1080 1 0.325 0.675 1097.66 Co
e e 
    
Hydrocarbon curve