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Fire resistance of steel frame

22 June 2019

The fire resistance of the steel frame is special. After all, any degree of fire resistance can be achieved with steel. This depends on the construction of the wall. Steel does not burn or create smoke or heat, it is a non-combustible material. However, at temperatures that occur in a building fire, steel can lose some of its stiffness. The resistance starts to drop at 400°.

Fire classification of structures: fire resistance of steel frame

Where materials are still classified according to their reaction to fire, building parts and structures are assessed for their fire resistance.  The fire classification of structures is formulated based on functional requirements.  The behaviour in fire situations is tested in a full-scale furnace, using a standard fire curve for the evolution of temperature over time.  The following properties are tested and evaluated.

  • I = insulation
    The time it takes for the temperature on the cold side of the structural element to rise by a certain number of degrees.  Often 140 °C is taken as the value for this; with a steel frame, we can assume 350 °C before the steel starts to deform.
  • E = integrity
    The time it takes for the structural element to maintain its integrity against flames or hot gases.
  • R = load capacity
    The time it takes for the relevant structural element to be able to absorb the loads occurring in a normal fire development phase.
  • M = mechanical effect
    The capacity of the structural element to deal with the mechanical impact of a normal fire.

These test results are converted into an assessment in the form of a measurement of time that shows how many minutes the structural element can withstand the fire before the threshold for each criterion is exceeded.

A wall with REI 60 therefore means the wall can withstand fire for one hour in terms of load-bearing capacity, integrity and insulation.