Fire protection of concrete-filled, hollow structural steel

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Filling closed profile or structural hollow sections with concrete is a well-known practice in the design of buildings. This method has been used in the construction industry for decades and both circular and square/rectangularprofiles can be treated this way.

Filling hollow sections with concrete offers several advantages over unfilled hollow sections, such as cost versus strength optimisation, durability and aesthetics, increased fire resistance and more.

Concrete core filling examples

On occasion, it is necessary to protect these types of sections from fire, in order to meet construction code fire resistance requirements that filling with concrete alone will not meet.

Reactive coatings that are commercially available must be fire tested and assessed to the appropriate test standard that is relevant to the local construction code.

Fire testing of reactive coatings normally encompasses the fire-testing of various sizes of structural steel sections at a number of different thicknesses of protection followed by a statistical analysis, producing interpolations within defined parameters. In Europe these fire tests and assessments for plain structural steel is currently carried out in accordance with EN13381-8:2013. However, there was no standard for testing and assessing concrete filled hollow sections has not been included in this until recently. Prior to having established such testing parameters, how to calculate the amount of intumescent coating for concret- filled hollows was unspecified. This can lead to interpretation and inconsistency in the market and the potential for an uneven competitive landscape. Several academic papers exist and have been used as the basis for guidance. However, suitability of the one size fits all approach is unproven, especially with the market advancing with multiple technologies.

The market position has changed with the publication of EN 13381-6:2012 - “Applied protection to concrete filled hollow steel columns”. This standard has been specifically introduced to allow the testing, and assessment of results, to be done in a consistent manner across all commercially available passive fire protection materials, including reactive coatings available on the fire protection of structural steel market.

Suitable testing and assessment in accordance with this standard is the only way to achieve classification of structural fire resistance in accordance with EN13501-2.

As EN13381-6:2012 is an active standard, it is our recommendation that this should be the sole method of testing and assessment used for concrete-filled hollow steel columns. The use of other mathematical models should be avoided.

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