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

2.2.2.2 No Structural Topping
Poured concrete toppings are not used with Supercrete
Structural Floor Panels to provide diaphragm action.
Poured toppings are heavy and simply add mass, resulting
in thicker panels being required to take the gravitational
load, additional wall bracing below to accommodate the
higher bracing demand, along with the additional time
and construction problems associated with wet poured
suspended slabs. To pour a topping over the panels ignores
the tremendous advantages of the dry diaphragm method
of floor bracing offered by Supercrete Structural Floor
Panels.
2.2.2.3 Thin Screeds
Thin screeds for creating falls for bathroom tiled areas or
external decks are permissible, but their additional weight
should be included in the superimposed dead load when
determining the panel thickness.
Where a thin screed is used to encase under floor heating
pipes for hot water systems, (as in Detail SFP 4-1, page
49) this mass should also be included as a superimposed
dead load. The mass of these screeds should be kept as
low as possible by using lightweight replacements for the
aggregate such as vermiculite. It is also essential when
using a screed, that a slip layer such as polythene sheeting is
laid under the screed so that the differential shrinkage and
movement of the screed may occur.
Floor panels in individual bays (diaphragms).
2.2.2.4 Individual Diaphragms Between
Lines of Support
Each set of panels, surrounded by a perimeter ring anchor/
bond beam, are considered to act as a separate diaphragm
made up of a group of panels acting together.
Diaphragms laid end to end are not considered to work
as a continuous diaphragm, as it is unlikely that shear forces
and bending moments will be transferred across the ends
of the panels, and the supports for the panel ends where
the panels are fastened down, will transfer longitudinal as
well as gravity forces into the support structure.
When panel ends join on a steel support beam, this
beam will take the tension load instead of the ring anchor
reinforcement - which is not required in this case, as the
steel support beam is effectively a large reinforcing rod.
2.2.2.5 Pinning the Diaphragm to the
Supports
It is important to note that the Supercrete Structural
Floor Panels do not just rest on supporting Supercrete
Block walls or steel beams, but have a method of
transferring horizontal shear forces to the support
structure. In the case of Supercrete Block, this occurs via
the vertical rods in the block walls which act as dowels into
the perimeter ring anchor.
With steel support beams, the reinforcing in the panel
joins pass through holes in cleats welded to the top of the
steel I-beams, or, if the panels are set into the web of steel
I-beams, the reinforcing passes through holes cut through
the beam web. (See Section 2.1.6.4, page 25).
All of these methods will transfer horizontal diaphragm
forces into the foundations via the bracing walls.
2.2.3 Engineering Design
Analysis Overview
2.2.3.1 Design Methodology
There is no New Zealand Standard or Code of Practice for
autoclaved aerated concrete.
Design of reinforced concrete structures in NZ are usually
carried out in accordance with NZS 3101 (Concrete
Structures Standard). However, it is not possible to
directly apply this standard to Supercrete AAC Floor
Panels, due to the unique material characteristics of AAC,
which has a concrete strength that is approximately 1/6
of poured insitu 25 MPa concrete, with lighter reinforcing
to match. The different crystalline properties of AAC, due
to the autoclaving process, the absence of aggregates and
the cellular structure means that it is vastly different to
conventional concrete.
NZS 3101 Clause 1.1.4 does allow for alternative design
methods to be used where these have been the result of
special study or experimental verification. This describes
the methodology that follows, based on The International
Handbook, which details the primary design methods
for AAC developed in Germany, and confirmed by
experimental testing. The methods used will be familiar
to most New Zealand design engineers, but may not have
been used to analyse floors in this particular manner.
When designing a Supercrete Structural Floor Panel
diaphragm floor, New Zealand design engineers shall use
the following methods.
SFP 2012 34 Copyright © Supercrete Limited 2008