Structural Floor Panels Design Guide - Hebel Supercrete AAC ...

1.4 Fire Performance
1.4.1 Fire
The New Zealand Building Code only requires a floor
assembly to resist fire if it is an inter-tenancy floor, such
as those in multi-residential apartments or commercial
offices, or certain industrial applications, etc. However, in any
building, whether it is a home or a work place, preventing
the spread of fire is a sensible aim for designers and building
owners.
Timber floor structures are flammable and often only
protected by thin plasterboard sheeting underneath. They
are not good resistors of fire between storeys.
Dense reinforced concrete and steel are not flammable, but
because they are poor insulators and good conductors of
heat, within a short period of being subjected to the intense
heat of a fire below, the steel (both the supporting beams
and the reinforcement rods within the concrete floor) will
soften and lose yield strength. The heat causes expansion
of the steel reinforcing rods and the stone aggregate
chips within dense concrete. The differential movement of
the steel, stones, sand and cement in the slabs can cause
cracking and flaking of the concrete. The reduced strength
of the steel, combined with these expansion cracks and the
heavy self weight of the floor, can lead to collapse. There
have been numerous structural failures of heavy concrete
floors under fire load in recent years.
Using Supercrete Structural Floor Panels reduces the
chances of failure in a fire situation. Supercrete possesses
many fire resisting properties;
• Supercrete Panels will not burn, smoulder or smokethey
are totally non flammable.
• Supercrete Panels have no stone chip aggregateonly
powdered ingredients - so there is no differential
thermal expansion rates within it to cause cracking and
flaking.
• Supercrete has a cellular structure which provides
great insulation, protecting the reinforcement from heat.
• Supercrete has a slow thermal lag time, or thermal
inertia, meaning heat takes a long time to pass through
it.
• Supercrete has a low self weight, so the forces acting
on a floor experiencing fire loads are less.
1.4.2 Fire Resistance Ratings
Fire Resistance Ratings (FFR) are given in minutes of fire
resistance for three categories:
• Structural Adequacy
• Integrity
• Insulation
The tested ratings in each category are rounded down to
the nearest to the following increments; 30, 60, 90, 120, 180,
& 240 minutes. Test furnaces are shut down at 241 minutes,
giving a maximum possible rating of four hours.
For instance, a floor may have a 180/120/90 FRR for
structural adequacy/integrity/insulation respectively. Non
load bearing items, such as screen partitions may have no
structural requirement and may have ratings expressed
without any number for structural adequacy (i.e. -/30/30).
In New Zealand, the building code requirements for
Fire Resistance Ratings depend upon the building type,
occupant load and the activities within the building. Typically,
inter-tenancy floors require at least a 30/30/30 rating, but
this may be much higher based on the fire calculations
contained within Section C of the New Zealand Building
Code.
1.4.3 Fire Resisting Supercrete
As the requirement to resist more minutes of fire increases,
the permissible span of Supercrete Structural Floor
Panels decreases.
All Supercrete Structural Floor Panels achieve at least a
90/90/90 FRR. Structural capacity then governs the panel
spans, but it results in a minimum 90 minute FRR for all
panel thicknesses.
By increasing the cover to the steel reinforcing, which in
turn slightly reduces the maximum span for the panel under
a given load, greater resistance to fire is achieved, up to a
three hour, 180/180/180 FRR.
The Span Chart for all these fire-rated panels is shown in
Tables 9 & 10, page 17.
Very few building products can achieve such high fire
resistance ratings. Supercrete is the ideal choice for
protecting building investments.
SFP 2012 14 Copyright © Supercrete Limited 2008