Fire Walls Made from Concrete and Masonry - Barriers against a Fire Spreading

Abstract

Fire exposure of a construction represents an accidental load (temporary with a high intensity) and it´s appearance during service life of the construction is improbable. All structural eurocodes, which deal with the normal temperature (20°C) design of structures made from loadbearing materials (steel, steel and concrete composite, concrete, masonry and timber), include always Part 1-2: Structural fire design. Concrete, similar to the masonry, has (in comparison with other construction materials such as steel and timber), an excellent resistance against fire exposure. This is why both of these materials are used for construction of fire walls, which create barriers against the fire spreading. Fire walls separate two spaces and they are designed for fire resistance and structural stability, including resistance to mechanical impact. In the case of fire and failure of the structure on one side of the fire wall, fire spread beyond the wall is avoided. Properties of concrete and masonry walls, subject to fire exposure, are however negatively influenced. Concrete compressive strength is reduced depending on the aggregate choice. The strength of reinforcing bars is also reduced at elevated temperature, by an amount which strongly depends on the axis distance of the reinforcing bars from an edge of a cross section, too. The behaviour of a masonry wall depends on a masonry unit type and material, type of the mortar, the density of units, type of the wall construction, and applied surface finishes. In the present article we discuss basic principles of the design and assessment of various concrete and masonry fire walls and compare their effect - fire resistance period – depending on their thickness.