This article about Waffle Slab shows some examples of this special structural slab around the world.

1. I
n December 1971, The Concrete
Society published a working
party paper(1–3)
on the proposed
standardisation of waffle floors and
trough floors. This proposed a module of 600
and 900mm rib centres for waffle slabs and
600mm rib centres for trough slabs.
This recommended standardisation was
generally accepted in the UK construction
industry at that time.
In the early days of the use of these
Standards,the manufacturers of the moulds –
mostly scaffolding and formwork companies
– had the moulds produced with narrow
flanges on two opposing sides of the moulds,
to allow the moulds to be used on a quick-
strip,drop head system held on their support
systems.
As most of the moulds were produced by
injection moulded polypropylene,the life
of the moulds was much longer and reuses
could be counted in the hundreds,so hiring
a complete package of moulds and support
systems became very popular.
Over the years,this changed in many
countries and the demands of contractors
for moulds with wide flanges on all sides
increased. This allowed contractors to hire
the moulds only and use whatever support
system they had,be it timber hit-and-miss
planks or complete flat decking.
In 1992, The Concrete Society published
Technical Report 42(4)
. This report was an
update from the 1971 report and having had
20 years’experience is,in fact,a work manual
of the practical uses of trough and waffle
slabs.
The report also mentions the different
types of materials used then and now for the
manufacture of moulds and the different sizes
that can now be produced to meet special
needs.
With all the gathered knowledge,this
change,in certain countries,has led to the
manufacture of both waffle and trough
moulds with full flanges all round and an
increase in the number of units available.
Also,there have been changes in the ways
to vary the lengths of trough units to fill a
variety of span lengths. These variations have
included telescopic pieces,bridging pieces
and infill sleeves,as well as longer length
troughs of up to 1125mm. They have also led
to an increase in the number and type of units
available for hire to the contractor.
Since 1971,use in the UK of waffle and
troughs reached a peak and then slowly
declined,until now there are few buildings
using the systems.
This has happened for a combination of
reasons.In the early days,the scaffolding and
formwork companies had many salespeople
on the road introducing the systems to
consulting engineers and this had a positive
effect on the number of contracts using the
systems.However,as the scaffolding and
formwork companies were badly effected
by the depression,they let go of many of
these salespeople,so fewer consultants were
reminded of the advantages of the systems.
Trough and waffle floors
Above: Edge
gymnasium in
São Paulo, Brazil
(designer, Casimiro
Fernandes;
contractor,
Alves Barcelos
Construction).
(Photo: Marcelo Donadussi.)
A residential block in the Czech Republic (contractor: Uninox).
Duringthepast63years,AlanCokerofATEXhasspenthisworkinglifeinvolved
intheformingofholesorvoidsofdifferenttypesandsizesinconcrete.Firstwith
rubbertubesfrom20mmto2mindiameter,thensteelovalsectionsofdifferent
sizesandmovingontosteeltroughformsofdifferentdepths.Allthisexperience
wasinvaluableforwhatwastofollow.
18 www.concrete.org.ukconcrete

2. Also,an increase in the number of fast
precast concrete systems meant a speeding up
of the work and a corresponding reduction of
labour on-site.
However,an interesting development has
taken place recently. The author knows of
two contracts in London at present where
alterations and additions to buildings that
were originally designed on waffle moulds,
are now using the same size and type of
waffle moulds to carry out the extensions or
alterations.
Overseas
Moving from the market in the UK and
Europe,to other overseas markets – for
example,in South Africa and South America
– we find a very different situation.
For some years,many contracts were
completed using both waffles and troughs
in South Africa and these contracts
encouraged consultants to design projects
in other African countries such as Angola,
Mozambique,Nigeria,Namibia and
Kenya. There are scaffolding and formwork
companies hiring out waffles and troughs in
these countries.
In South America,there is again a very
different situation.In Brazil,one company
has seven depots throughout the country,
manufacturing its own injection moulded
units and hiring them out, as well as forming
partnerships in Argentina,Peru,Mexico,
Bolivia,Colombia and Paraguay and hiring
out moulds in those countries too.
This company also markets 120 different
sizes and types of moulds as well as a flat slab
formwork system and quick strip support
systems.
Certain technological developments in
the systems have helped in these markets,
together with companies offering to redesign
for consultants to find the most economical
design alternatives,so reducing the consulting
engineer’s time spent on details that are best
handled by a specialist.
The use also by these companies of
computer programs – such as CypeCAD,
SAP2000,Eberick,Anasy and TQS –
makes the work so much faster and easier
for the client,and more economical for the
developer.
However,it is worth noting that with all
the developments in the sizes and variation
of moulds available,the basic dimensions in
most countries are still 900mm rib centres
for waffles and 600mm for troughs – that is,
the original sizes that The Concrete Society
recommended for standardisation in 1971.
In the 46 years that ATEX has existed,
it has sold waffle and trough moulds to 47
different countries and has seen companies
hiring and selling ATEX moulds established
in Brazil,Greece,Lebanon,Portugal,
Singapore and South Africa.
Lookagain
It is surprising that the number of buildings
in Europe using waffle and trough slabs has
reduced so much over the years.Has the
construction industry become so much more
sophisticated or the economics changed so
dramatically that the systems are no longer
viable? Or is it due to the lack of advertising
and promotion by the suppliers of moulds?
If it is just the lack of publicity or
availability,then it would be very good
if consulting engineers in Europe would
look again at the structural advantages and
economics of using a waffle and trough
system. ■
References:
1. CONCRETE SOCIETY.Trough and waffle floors. Report
of the working party on standardisation. Concrete,
Vol.5, No.12, December 1971.
2. CONCRETE SOCIETY.Trough and waffle floors. Report
of the working party on standardisation. Appendix 1
–Trough floors. Concrete,Vol.6, No.1, January 1972.
3. CONCRETE SOCIETY.Trough and waffle floors. Report
of the working party on standardisation. Appendix 2
–Waffle floors. Concrete,Vol.6, No.2, February 1972.
4. CONCRETE SOCIETY. Troughandwafflefloors.
Technical Report 42,The Concrete Society,Camberley,
1992,36pp.
Center Minas Mall Belo Horizonte, Brazil (designer, Raul
Neuenschwander; contractor, Smart Architects).
Residential block in Porto Alegre, Brazil (designer, Paulo
Stumm; contractor, Smart Architects).
www.concrete.org.uk concrete 19