what is steelwork fire resistance?

All hot rolled structural steel sections have some inherent fire resistance and this is a function of the size of the section, its degree of exposure to the fire and the load that it carries. Fire resistance is usually measured in relation to the ability of the structural section to survive in a standard fire test as outlined in BS 476 Parts 20, ISO 834 and BS EN1363-1. This test takes place in an approved furnace and follows a standard time-temperature curve which is the same for all materials and components.

The strength of hot rolled structural steel decreases with temperature. Following an extensive series of standard fire tests, that strength reduction has been quantified. Recent international research has also shown that the limiting (failure) temperature of a structural steel member is not fixed but varies according to two factors, the temperature profile and the load.

For small, fully loaded hot rolled sections, exposed on all four sides, the inherent fire resistance without added protection can be as little as 12 minutes. For very large, hot rolled sections, lightly loaded and with some partial protection from concrete floor slabs on the upper flange, this can be as high as 50 minutes. Where the heated perimeter is further reduced by the method of the construction (e.g. shallow floor systems), up to 60 minutes inherent fire resistance can be achieved.