Size Effect on Temperatures of Structural Steel in Fire

In current design practice for steel structures in fire, the temperature profile of a steel member will not change with its locations if it is subject to the same fire environment according to a certain standard or natural fire curves. This study shows that for the same steel member under the same fire curve, the temperature profile of the member will be different if it is erected in compartments of different sizes. The difference arises from the fact that the gases within the compartment transfer the heat energy to the steel member through radiation along different path lengths. While it is difficult to calculate the heat energy precisely for each gas molecule to travel along each path length, it is relatively easy to perform such calculations for the total volume of gases by means of an average path length, termed the mean beam length, in terms of the size of the compartment. The effect of the mean beam length is implicitly included in the formulation of the gas properties for heat transfer calculations.