AUST – HENDRY building surveyors advise that the Building Code of Australia and various Australian Standards require that the design of buildings incorporate specific measures to mitigate the effects and risk of fire. Fire rated masonry is an integral part of providing safety for buildings.
Where elements of buildings are required to be fire rated under the Building Code of Australia, such as for load bearing walls, building boundary walls or walls to fire stairwells, the materials used in their construction also need to be fire rated. The Building Code of Australia requires these materials to be tested under laboratory conditions and from their test values the results are tabulated, and can be incorporated into Australian Standards.
What is Fire Rated Masonry Under the Building Code of Australia?
In the case of masonry, fire rated is an industry term used to describe the technical aspects of the performance of the masonry under live and dead load conditions under the Building Code of Australia, where dead load refers to the weight of the building structure itself, and live load refers to the weight of chattels and occupants.
How is Fire Rated Masonry determined under the Building Code of Australia?
The Standard AS 3700 ‘Masonry Structures’ is nominated by the Building Code of Australia as the starting point in determining fire rated masonry, and this Australian Standard is used to determine the fire rated suitability of the product for the purpose intended.
The Building Code of Australia nominates fire rated masonry to be made up of 3 components;
- Structural adequacy (minutes)
- Integrity (minutes)
- Insulation (minutes)
These three elements are expressed in the Building Code of Australia as “FRL” in minutes e.g. 90/60/30:
The Building Code of Australia and Standards nominates structural adequacy of fire rated masonry is affected by factors such as:
- Slenderness ratio (effective height)
- Super imposed axial loads
- Unequal loading of double leave brickwork (double brickwork)
- Location of control joints
- Nature of support at edges of the panel
- Adequacy of lateral restraints
Where fire rated test results are being used, a test to Australian Standard AS 1530.4 (Fire Resistance Tests on Elements of Construction), the “standard fire test”, must prove the adequacy of the fire rated masonry unit under the Building Code of Australia.
If reinforced masonry is being used, a lateral design load of 0.5kPa must be withstood unless the element is spanning vertically, where additional considerations apply. Masonry reinforcement must be provided with minimum cover by the masonry being used.
Building Code of Australia integrity values are usually met by satisfying minimum material thickness for achieving the required insulation levels, expressed in minutes for fire rated masonry.
Building Code of Australia insulation values of the fire rated masonry element are an important factor, which must be established in conjunction with structural adequacy.
Insulation properties limit the rate of heat rise (heat transfer) through the fire rated masonry from the fire side. Fire rated masonry unit density will affect its insulation properties, as does the type of core material used to produce the masonry unit (for example, clay, calcium silicate, or concrete block).
The Building Code of Australia allows service recesses and chases within the fire rated building element can usually be ignored, provided;
- The limit in depth of material removed is not exceeded.
- The total area is not exceeded.
- The length of chase allowed is not exceeded
- For walls spanning vertically and horizontally, the slenderness ratio may need to be re-evaluated for the given chase.
The Building Code of Australia allows fire rated masonry to be used to provide a fire rating to otherwise unprotected steel.
Material thickness to be provided is usually equivalent to that required to achieve structural adequacy.
Where fire rated masonry is providing a fire rating function according to the Australian Standard, the Building Code of Australia requires structural elements to be designed by a structural engineer, (since the effective height and thickness of the masonry is related to its perimeter support and other structural features). Where in doubt about the fire resistance compliance of your building, seek professional advice from a building surveyor.
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