TITLE
Modular Composite Floor Units
DESCRIPTION
Field of the Invention
The invention relates to modular composite floor units, being components of
modular building systems or of steel frame building systems for the rapid
construction of buildings for use either as industrial or commercial premises or
as dwellings. The invention also relates to a method for the manufacture of
such modular composite floor units.
Background Art
Modular buildings can be constructed from prefabricated wall panels which
are bolted or welded together on site to create the framework of the building.
The prefabricated wall panels can include pre-installed window frames, door
frames, electrical connections and/or plumbing connections to reduce the
building and finishing time on-site, and in a typical modular construction
process are assembled on-site by being moved into position by a crane or
other lifting equipment before being connected together to create a rigid
structure. If the building is a steel-framed building then similarly the girders
are lifted into position on-site and connected together to create the rigid
framework of the building onto and into which are secured the desired
external and internal wall panels.
The floors of such buildings can be hollow or solid. By "hollow" floors there is
conventionally meant floors created from planks or panels, generally of timber
or timber-based composite materials such as plywood, chipboard and
oriented particle board, laid over a supporting structure such as timber joists
or metal beams. By "solid floors" there is conventionally meant concrete
floors.

Solid floors are often preferred for their better sound insulation properties, and
are often specified for multi-occupancy buildings such as apartments, hotels
and student accommodation and for industrial and commercial premises.
Generally solid floors are made principally from concrete or reinforced
concrete, which may be poured on-site. The edges of the solid floor created
by pouring wet concrete are defined by the brick work or block work defining
the periphery of the building or the room within the building into which the floor
is being laid, or by edge shuttering positioned on-site. That edge shuttering
may then be removed once the concrete has set, or may remain in position.
Solid floors may alternatively be created by laying pre-cast concrete flooring
panels. Those panels are pre-cast off-site in open moulds and generally
incorporate metal reinforcement bars. They are often cast with longitudinal
holes or channels to reduce the overall weight, and also are often cast with a
slight convex shape which assists stress distribution in the final building.
Ultimately however each array of pre-cast solid flooring panels is covered with
a cement screed to smooth out the surface imperfections and irregularities.
The screeded area must be kept clear of construction personnel while the
cement screed dries and sets, and this of necessity slows down the
construction process requiring work on-site to be stopped or diverted to other
areas until the screed is sufficiently hard and durable to accept foot traffic
without damage.
EP-A-881067 discloses a modular composite wall or floor; unit and a method
for its manufacture. In fact the strength requirements and in particular the fire
resistance performance specifications for wall and floor units are vastly
different, so the teaching of EP-A-881067 should not be misunderstood as
being that a single product can be laid vertically as a wall or horizontally as a
floor. The wall and floor units are substantially different products but
according to EP-A-881067 can share common design concepts. The

following summary of the relevant teachings of EP-A-881067 is therefore
restricted to its teachings of floor units only.
The floor unit of EP-A-881067 is a modular floor unit in the sense that t is cast
off-site and then transported to the site of the building under construction. It is
a composite floor unit in the sense that it is not a single cast slab of concrete
that would typify a solid floor unit. It is cast as two concrete slabs separated
by an air space or by a layer of insulation (thermal and/or acoustic insulation).
The two concrete slabs are cast one at a time in a metal form which has a
base and sides. The base gives a smooth finish to the underside of the first
slab to be cast, while the sides of the form create the side shuttering for the
wet concrete of that first slab. A corrugated plate or array of metal I-beams is
placed over the top of the first slab to be cast, and creates a support surface
for the base of the second slab to be cast. The sides of the second cast slab
are defined by the same shuttering as that used to define the sides of the first
cast slab, namely the sides of the metal form. If desired, an edge detail such
as a peripheral recess can be added to the second cast slab by positioning a
form liner around the periphery of the form before casting the second concrete
slab. After casting, and after the concrete has set, the cast composite floor
unit is lifted out of the form and any form liner removed, to obtain the final
composite floor unit in which the valleys of the corrugated sheet or the bottom
flanges of the I-beam are partially immersed in the set concrete of the first
(bottom) cast slab and the peaks of the corrugated sheet or the top flanges of
the I-beams are partially immersed in the set concrete of the underside of the
second (top) cast slab. The composite structure includes a void between the
two cast slabs, although that void may if desired be filled with a thermal or
acoustic insulation such as a foamed resin composition.
Both the thermal and the acoustic performance of the composite floor unit of
EP-A-881067 leaves much to be desired. Acoustically, the I-beams or spans
of the corrugated metal sheet connecting the top and bottom cast slabs
provide a direct sound path from one cast slab to the other, so the filling of the

void with an acoustic insulating material does very little to prevent the
transmission of sound from the floor defined by the top face or the top slab to
the ceiling defined by the bottom face of the bottom slab. Fire resistance is
also very poor. In a first test, the bottom slab would rapidly detach from the
corrugated metal sheet or I-beams, and the structural integrity of the
composite floor unit would soon be lost. The composite floor unit of EP-A-
881067 would therefore fall very far short of compliance with British Standard
476, Part 21 : 1987, clause 7. That fire resistance standard requires that the
structural integrity of the floor unit should be maintained within specified limits
even after exposure of one face of the floor unit to a furnace temperature
rising to over 1150°C over a period of 4 hours, and that the mean temperature
rise of the face remote from the furnace should be no more than 140cC, with a
peak temperature rise of no more than 180°C. Test results are normally
reported in terms of the time duration that elapses before one of the
monitored parameters indicates failure of the test specimen, either by some
loss of structural integrity or by an unacceptable temperature rise at the face
remote from the furnace.
It is an object of the invention to create a modular composite floor unit which
exhibits both good thermal and good acoustic insulation and is capable of
markedly better performance characteristics than that of EP-A-881067.
It is desirable that both the upper and lower surfaces of the composite floor
unit are smooth. Therefore without on-site screeding the floor unit will present
an acceptably smooth finish suitable for tiling or carpeting; whereas the
underside is preferably smooth enough or has a sufficiently accurate surface
finish to be visible as a decorative smooth or patterned ceiling finish to the
room below.
Most importantly, however, it is a further object of the invention to create a
modular composite floor unit which can meet the fire resistance performance
demands of British Standard 476, Part 21: 1987, clause 7.

The invention
The invention provides a modular composite floor unit as defined in claim 1.
The invention also provides a method for the manufacture of such a floor unit,
as defined in claim 26.
One feature of the floor unit of the invention that is not found in the floor unit
described in EP-A-881067 is that according to the invention the edge frame
forms a permanent part of the floor unit, whereas according to EP-A-881067 it
is a temporary form from which the floor unit is removed prior to use. The
edge frame of the floor unit of the invention is welded or brazed to the ends of
the lattice of reinforcing rods which ultimately will reinforce the material of the
ceiling slab. Also the spaced metal joists which take the weight of the two
cast slabs are, according to the invention, welded or brazed at their ends to
the metal of the edge frame. The result is a composite floor unit which
considerably outperforms that of EP-A-881067 in fire resistance tests, and
which can survive the test of BS 476, Part 21 : 1987, clause 7 for the full 4
hours of the test duration without failure. At first it appeared desirable to weld
or braze to the edge frame the lattice of reinforcing rods which ultimately will
reinforce the material of the flooring slab. Surprisingly however it has been
found that the above excellent fire resistance is obtained when only the
reinforcing rods of the cast ceiling slab are welded or brazed to the edge
frame, and the reinforcing rods of the cast flooring slab are free from the edge
frame. Freeing the ends of the reinforcing rods of the flooring slab in this way
makes it possible for the flooring slab to be constructed as a floating floor,
which gives the composite floor unit of the invention really outstanding
acoustic insulation properties. Although fire resistance could in theory be
improved further by connecting the ends of the flooring slab reinforcing rods to
the edge frame, this would be at the expense of increased sound transmission
through the composite floor unit, and it has been established that the

preferred composite floor unit according to the invention is one with only the
reinforcing mesh of the ceiling slab welded or brazed to the edge frame.
The supporting joists fulfil two different functions. Support for the second (top)
slab must be to building regulation standards for the strength and fire
resistance of a load-bearing floor. That may be provided by having the top
slab simply rest on the joists, but preferably the top slab is physically
anchored to the joists by having the longitudinal top edges of the supporting
joists embedded in the material of the top slab or by having anchorage
members secured to the longitudinal top edges of the supporting joists and
embedded in the material of the top slab. Support for the first (bottom) slab
may be to the lower building regulation standard for the strength and fire
resistance of a suspended ceiling, although according to the invention it is
possible to surpass that standard by a very considerable margin. The
required support may be provided by having the longitudinal bottom edges of
the supporting joists embedded in the material of the bottom slab or by having
suspension members supported by the relevant supporting joists and
embedded in the material of the bottom slab.
The sound insulating material may wholly or partially fill the space between
the two cast slabs, which may be of the same or different materials, and the
same thickness as each other or of different thicknesses. The top slab must
be of a cement based material, such as concrete. The bottom slab may be of
a cement based material such as concrete or a gypsum based material.
Typical dimensions are that the individual slabs may be from 50 to 100 mm
thick with a separation of from .150 to 300 mm. Preferably each slab has a
thickness of about 65 mm and preferably the separation is about 225 mm.
Other preferred or optional features of the invention will be apparent from the
following description of the drawings.
Drawings

Figure 1 is a perspective view of a modular composite floor unit according to
the invention, with a generally rectangular periphery;
Figure 2 is a section taken along the line A-A of Figure 1;
Figure 2A is an enlarged section of the right hand end portion only of Figure 2;
Figure 2B is a section through the cold-rolled sheet metal edge member of
Figure 2A illustrating its method of construction;
Figure 2C is a section through one of the joists of cold-rolled sheet metal
visible in Figure 2A, illustrating its method of construction;
Figure 3 is a section similar to that of Figure 2A, but taken along the line B-B
of Figure 1 through another of the cold-rolled sheet metal edge members;
Figure 3A is a section through the cold-rolled sheet metal edge member of
Figure 3, showing its method of construction;
Figure 4 is a perspective view similar that of Figure 1, but through the modular
composite floor unit before the top layer of concrete is poured;
Figure 4A is a section, greatly enlarged, through one of the reinforcing cross-
straps visible in Figure 4;
Figures 5 to 12 are enlarged sections, similar to that of Figure 2A, through
eight different embodiments of the invention, the sequence of Figures being
chosen to illustrate sound proofing considerations and the techniques that can
be used according to the invention to decrease the sound transmission in
various wavebands through a series of modular composite floor units
according to the invention;
Figure 13 is a perspective view of a connector cradle for connecting the
hollow beams of Figure 12 to the top lattice of reinforcing rods or wires;
Figure 13a is a plan view of a sheet metal blank which can be folded to form
an alternative connector cradle;
Figure 13b is a perspective view of the alternative connector cradle created by
folding the blank of Figure 13a;
Figure 14 is an enlarged section, similar to that of Figure 2A, through a ninth
embodiments of the invention to illustrate another sound proofing technique
that can be used according to the invention to decrease the sound

transmission in various wavebands through a modular composite floor unit
according to the invention;
Figure 15 is a perspective view of a connector hanger for connecting the
lower row of hollow beams of Figure 12 to the bottom lattice of reinforcing
rods or wires;
Figures 16 and 17 are enlarged sections through sheet metal edge members
of an edge frame of a modular composite floor unit according to the invention,
being the edge members of respectively a side and an end of the edge frame,
and showing an alternative cold-rolled sheet metal profile to those shown in
Figures 2B and 3A;
Figure 18 is a vertical section though the junction between two floor units
according to the invention as installed in a building and two wall panels of the
building, to illustrate the support of the floor units by their out-turned flanges;
Figure 19 is an enlarged section, similar to that of Figure 2A, through a
preferred embodiment of the invention;
Figure 20 is a perspective view of the linking strut XX as used in Figure 19;
and
Figure 21 is a detail illustrating the construction of the metal edge member of
Figure 19.
The modular composite floor unit of Figure 1 comprises an edge frame 10
made from cold-rolled sheet metal edge members brazed or welded together
to form an accurately sized and proportioned edge shuttering for the floor unit.
Into that edge frame 10 is built up a composite floor assembly comprising two.
spaced layers of poured reinforced concrete separated by filler materials, as
will be particularly described below.
The overall structure of the layered infill for the edge frame 10 is illustrated in
Figure 2. A bottom layer of poured concrete 12 and a top layer of poured
concrete 14 are separated by a space containing a layer of significantly less
dense material such as lightweight walling blocks 16. The walling blocks 16
are supported and separated by an array of mutually parallel spaced joists 18

of cold-rolled sheet metal, the precise shapes of which are better illustrated in
Figures 2A and 2C. The parallel spaced joists 18 are welded or brazed to the
edge frame 10 at their opposite ends, and L-section pieces of cold-rolled
sheet metal 20 and 22 are welded or brazed to the joists 18 and to the
respective edge frame members 24 which make up the edge frame 10, so as
to provide runners for supporting the walling blocks 16.
The bottom slab of poured concrete 12 is poured around a reinforcing lattice
of rods or wires 26 which are welded or brazed to the edge frame 10 all
around its periphery. A similar lattice of rods or wires 28 provides
reinforcement for the top layer of poured concrete 14. The fact that the rods
or wires 28 are secured at their ends to the edge frame 10 by welding or
brazing has proved to be of enormous importance in providing the fire
resistance of the composite floor unit according to the invention. The ceiling
and floor slabs with those rods or wires as internal reinforcement are joined
integrally to the edge frame 10 in a row of such welded or brazed connections
which preferably extend completely around the periphery of the composite
floor unit. Furthermore the anchorage of the cast slabs (ceiling and floor) to
the edge frame 10 can be considerably enhanced by allowing the unset
material of the cast slabs to flow into an around channel ends of C-shaped
cold rolled sections of the edge frame 10, and preferably through apertures
formed in the material of the C-shaped sections. For example the poured
concrete of both the bottom and top concrete slabs extends through apertures
25, 31 formed in the edge frame members 24 and 30 into the internal cavities
of the edge frame members 24 (Figure 2A) and 30 (Figure 3) so that the edge
frame becomes an integral part of the composite floor unit. The mutually
parallel spaced joists 18 which support the walling blocks 16 are also
embedded at their top and bottom edges in the concrete of the bottom and top
layers 12 and 14, which adds to the reinforcement of those concrete slabs
and to the strength of the finished floor unit.

The edge frame members 24 and 30 (Figures 2A and 3) could conceivably
have the same section as one another, although the corner joints of the edge
frame 10 would then have to be mitred. An alternative is illustrated in Figure
3, in which the edge frame member 30 sits inside the generally C-shaped
section of the edge frame member 24 of Figure 2A, with an end plate 32 being
welded or brazed to the edge frame member 30 to bring it to the full height of
the edge frame 10.
The method of construction of the modular composite floor unit of Figure 1 will
now be described. First of all the edge frame 10 is built up in factory
conditions. The edge frame members 24 and 30 can be laser-cut to a very
high degree of accuracy. The edge frame members are then preferably set
out on a factory floor or work bench and held in a jig while they are welded
together to the precise size and proportions of the intended final floor unit.
The joints 18 are welded or brazed to opposite edge frame members 30 while
the edge frame 10 is held in the jig, and in this way the tolerances to which
this work can be completed are vastly superior to those attainable on a
building site. The first lattice of rods or wires 26 is then welded or brazed into
position. Each of the lattices of rods or wires 26 and 28 may be a mesh of
reinforcing rods or wires welded together into a square or rectangular grid of
crossing rods or wires, such as the reinforcing mesh sold under the Trade
Mark WELDMESH. If desired the top lattice 28 may be of heavier duty than
the bottom lattice 26 because the bottom lattice 26 will in the final multi-storey
building become a part of the ceiling of the room below, and will therefore be
subject to less strict building regulations. The securing of the bottom lattice
26 takes place all around the periphery of the edge frame 10, and all of the
assembly up to and including this stage is carried out with the floor unit under
assembly being inverted, so that the lattice of rods or wires 26 is welded to
inturned flange portions 24A and to what will ultimately become the lower
surface 30a of the edge frame members 24 and 30 respectively. If desired,
instead of a pre-welded mesh of rods or wires the lattice 26 could be of pre-
tensioned wires 26 as described in GB 0515075.0, the individual wires being

drawn through apertures in the outer walls of the edge frame members 24 and
30, placed under tension, and then welded from the outside of the edge frame
10. This pre-tensioning of the reinforcing lattice 26 can be repeated for the
reinforcing lattice 28, and is possible because the edge frame 10 is securely
held in the jig on the work floor or work bench. The pre-tensioning of the
lattice is not, however, essential to the method of construction of the
composite floor unit according to the invention, and an alternative or additional
method of using pre-tension to create a very stable edge frame structure is to
incorporate diagonal cross-braces 32 as illustrated in Figure 4. Each cross-
brace 32 is formed by unrolling a strip of sheet metal from a roll. If a slight
crease 34 is formed in the strip metal of the cross-brace 32, by cold-forming
the strip into a slight apex along the line 34 as shown in Figure 4A along most
of its length, then the tendency of the cross-brace strip to re-form into a curl
can be largely or completely eliminated. Each cross-brace 32 is welded or
brazed at its ends to inturned flange portions of the edge frame 10, and
preferably the cross-braces 32 when cold are under a slight tension to ensure
complete stability of the edge frame 10. The cross-braces 32 may extend
generally from corner to corner of the edge frame 10, or may be arranged in
any other pattern of triangulation.
When the welding of the edge frame 10, the lattice 26 and the optional cross-
braces 32 is complete, the edge frame 10 is turned over onto a smooth flat
casting surface, ready for the casting of the bottom layer 12 of poured
concrete. The casting surface (not illustrated in the drawings) may be any
smooth flat surface coated with a concrete mould release agent. It may, for
example, be a flat metal surface such as the smooth flat surface of a steel
plate decking in the factory. Mirror steel may be used to provide an even
smoother cast finish to the concrete that is poured. Alternatively, the casting
surface may be textured, to give an attractive textured appearance to the
underside of the cast floor unit, which will become the ceiling of the room
below in the finished building. Clearly any texturing must be carefully
regulated so that it does not interfere with the mould release.

Alternatively, the casting surface may be covered with paper or fabric that is
preferably wetted, for example by spraying, with a bonding adhesive that
causes it to adhere to the concrete that is poured into the edge frame 10.
That provides a paper or textured fabric finish to the underside of the resulting
floor unit, which provides the best possible paintable surface for ultimate
ceiling decoration.
The concrete layer 12 may be poured as a single layer of liquid concrete, or it
may be built up in layers. For example a first layer, about 5 mm deep, of a
grano gel coat may be poured first, followed by 25 mm of C30 grade concrete.
Concrete with a lightweight or porous aggregate is preferred, and the depth of
the concrete is preferably marginally above the level of the runners 20 and 22,
as shown by a broken lead line 36 in Figure 2A and in Figure 3. It will be
noted that the concrete layer 12 flows through the apertures 25 into the edge
cavities 38 and 40 created by the shape of the edge frame members 24 and
30 respectively (see Figures 2A and 3). Care should be taken to fill those
cavities completely for maximum strength.
While the poured concrete is still unset, rows of walling blocks 16 are placed
on the runners 20 and 22 and between adjacent parallel spaced joists 18,
completely to fill the floor space as defined by the edge frame 10. The walling
blocks 16 are preferably wetted before installation using a water-based
bonding agent to ensure good adhesion to the concrete, and are preferably
pressed into the unset concrete until they rest on the runners 20 and 22, so
that the displaced concrete is pushed up between adjacent walling blocks, to
provide better bonding with the walling blocks 16. The top edges of the
walling blocks 16 create a generally planar surface, indicated in Figures 2A
and 3 by the broken lead line 42, for the pouring of the top layer of concrete
14.

Before the top layer of concrete 14 is poured, however, the second lattice 28
of rods or wires is placed over the protruding tops of the parallel spaced joists
18, and welded to an inturned flange 44 of the edge frame members 24 and to
an inturned flange 46 of the edge frame members 30. Over the top of the
lattice 28 there are then preferably welded diagonal cross-braces 32 as
illustrated in Figures 4 and 4A.
The top layer of poured concrete 14 is then poured over the tops of the
walling blocks 16. The concrete will settle down into any gaps between the
walling blocks, and will flow through apertures in the edge frame members 24
as indicated by the shaded portions 48 of the joist members 18 in Figures 2A
and 2C, further to enhance the stability and rigidity of the resulting floor unit.
Although the top layer of poured concrete 14 will flow down and around the
individual warning blocks 16, that concrete flow will not be sufficient to fill
every void between the top and bottom layers of concrete 14 and 12, and
simply for ease of representation, in Figures 2A and 3 the seepage of the top
layer of poured concrete 14 down below the level of the tops of the walling
blocks 16 is not shown. The top layer of concrete 14 may be the same
thickness as that of the bottom layer 12, or may be a different thickness. In
Figures 2A and 3 the top layer is shown as being of a lesser thickness.
Finally, the top surface of the top layer of poured concrete 14 is finished with a
power float, to create a final finished floor unit which has a surface finish at
least as smooth as the final screeded finish of conventional building
techniques. That finish is certainly smooth and flat enough to take carpet, or
tiles, or laminate flooring in the final building, without requiring a final top
screed.
To lift the finished floor unit from the casting surface, lifting apertures or hooks
or other handling formations (not shown) are formed around the edge frame
10, and the finished floor unit can be lifted, after the concrete has set, by
suitable handling equipment directly onto a lorry or other transport vehicle, to
the final site of the building under erection. The accuracy of the dimensions of

the floor unit, made under factory conditions, is such that it can be presented
up to pre-established mounting bolts or spigots on or in the building under
construction, with a virtual guarantee of accurate alignment
Many modifications are possible to the method of construction described
above. The function of the walling blocks16, being less dense than concrete,
is to reduce the overall weight of the floor unit. For this reason, the above
description refers by way of example to the use of lightweight walling blocks.
Walling blocks made from a cinder or porous aggregate are highly suitable,
such as those sold under the Trade Mark THERMALITE™. The blocks 16 are
provided for their sound insulation properties and to create additional
thickness to the floor unit without adding unduly to the overall weight, and a
number of alternative materials may therefore be used. For example, in place
of walling blocks there may be used blocks of expanded polystyrene, blocks
of balsa wood, sheets of rockwool, sheets of fibreglass matting, or hollow
moulded plastic boxes. The blocks 16 could even be replaced by hollow
boxes made from waxed cardboard. Plastic or cardboard boxes, when used,
are preferably filled with a sound absorbing material such as rockwool,
fibreglass matting, shredded newspaper, papier mache, compressed straw,
reclaimed particulate rubber or other lightweight products of the rubbish
recycling industry. Alternatively the longitudinal spaces between the bottom
and top layers 12 and 14 of poured concrete can be filled by a lightweight
particulate material such as chopped straw, pelleted newspaper waste, hollow
balls or polystyrene beads. Boards of wood or of a wood-based product such
as plywood or oriented particle board may then be placed over the fill material
to create the generally planar surface 42 onto which the top layer of concrete
14 is to be poured, and the remainder of the method of assembly is exactly as
described above. If the loose or particulate fill material is compressible, or if it
does not completely fill the space separating the two cast concrete slabs 12
and 14 of the finished floor unit, then it will be preferred to incorporate runners
(not illustrated) similar to the runners 20 and 22 of Figure 2A, to support the
boards.

The complete floor units may be transported quite easily and safely and with
very little added protection required during transport, because they are
protected from accidental edge damage by the edge frame 10 which becomes
an integral part of the construction.
It will be seen from Figures 1, 3, 3A and 4 that the edge frame members 30
are formed with out-turned flanges 33 on their end plates 32. Similar out-
turned flanges could if desired be formed on the edge frame members 24
although they are not illustrated. The function of the out-turned flanges is to
support the floor unit during transportation and in the final building, where the
floor unit can be laid in position to span an assembly of pre-assembled wall
panels suspended initially by the flanges before being screwed, bolted, riveted
or welded for final securement.
The top surface of the floor unit is as flat and smooth as the power float
operator can produce, which is a smoothness equal to that of conventional
floors screeded on-site. The under-surface is as smooth as the casting
surface on which the floor unit is made which, being in factory conditions, is a
very high standard of smoothness. Alternatively it may be paper-covered by
casing onto paper as described above. Alternatively it may be textured, by
casting onto a textured fabric which adheres to the underside of the floor unit
after casting and which thus establishes the texture of the resulting visible
ceiling; or by casting onto a textured casting surface.
The embodiment of Figures 1 to 4 utilises a sound insulating material shown
in Figures 2, 2A and 3 as walling blocks, which full the full height of the space
between the bottom and top cast concrete slabs 12 and 14. That creates a
floor unit which provides good acoustic insulation over a range of
wavelengths, but for better sound insulation and also, incidentally, for better
thermal insulation the sound insulating material should occupy less than the
total space between the first and second concrete slabs. Figures 5 to 11

show seven alternative embodiments of modular composite floor units
according to the invention in which the sound insulation material is provided in
a layer confined to the bottom portion of the space between the first and
second concrete slabs, with an air gap above that insulation. In Figures 5 to
11 the same reference numerals have been used wherever possible to those
used in Figures 1 to 4, and the following description is limited to the
differences between the different embodiments.
The sound insulating material illustrated in Figures 5 to 11 is represented as a
series of mats 50 of a sound insulating material such as rockwool. It will be
understood that any alternative particular sound insulating material could be
used, or any of the other materials discussed earlier in this specification. In
the embodiment of Figures 1 to 4 the joists 18 have a J configuration as
shown in Figure 2C, the upturned flange at the bottom of the J being, used as
a ledge on which to locate the walling blocks 16. A simpler shape of joist 18A
is shown in Figure 5, being of C section. Advantageously the level to which
the bottom layer of concrete 12 is to be poured may be marked on the joists
18A by means of a scribe mark (not shown) or an aperture (not shown)
punched through the vertical wall of the joists 18A before assembly, so that
the bottom layer of concrete 12 can be poured until it reaches the scribe
marks or the tops or bottoms of the punched apertures. As with the previous
embodiment, the first and second lattices of reinforcing rods or wires 26 and
28 are welded to the edge frame, as are the ends of the joists 18A.
After the bottom concrete slab has been cast to the required depth, the
insulation mats 50 are laid between the joists, and boards 52 are placed on
longitudinal supporting runners 54 which have been welded or brazed to the
supporting joists. A similar runner 56 is spot welded or brazed to the inside of
the edge frame member 24. The boards 52 provide a base for the pouring of
the second concrete slab 14 which is poured and float-finished as described
earlier.

The air gap above the mats 50 in Figure 5 reduces some of the sound
transmission between the top and bottom concrete slabs 14 and 12, and of
course enhances the thermal insulation of the composite floor unit of Figure 5.
The longitudinal division of that air gap into relatively narrow horizontal
channels, by virtue of the joists 18A does act to reduce the sound
transmission laterally along the floor unit, but the joists 18A themselves
provide a direct linkage and sound transmission path from one floor slab to
the other, and therefore provide a path for the transmission of sound of certain
frequencies. That sound transmission path can be broken by ensuring that
the joists are divided into two sub-groups of joists, namely joists 18B
anchored at their ends in the top concrete slab 14 as shown in Figure 6, and
joists 18C anchored at their lower ends in the bottom concrete slab 12. In
Figure 6 those joists 18B and 18C are shown as having a J section, the
additional inturned flange portion of the J section as opposed to the simple C
section of Figure 5 providing the joists with increased stability and strength
against buckling along their unsupported edges. Nevertheless the joists 18B
and 18C of Figure 6, which are shown arranged directly aligned one above
the other, necessarily have a wall portion depending from the top slab of
concrete 14 or a wall portion upstanding from the bottom concrete slab 12
spanning less than half of the base between the two concrete slabs. The
reinforcing effect of the joists 18B and 18C can be enhanced significantly by
using wider joists as shown in Figure 7, and staggering them so that the joists
18B are offset on one side of the joists 18C. By having a relatively small
spacing between pairs of adjacent joists as shown in Figure 7, the turning
moment transmitted from one joist to the other at the outside edge of the edge
frame is maximised, for maximum strength. The number of joists 18B and
18C used, and their mutual spacing, is dependent on the width of the floor unit
and the length which each joist has to span.
Figure 8 shows an alternative arrangement of joists, with a pair of joists 18C
bedded in the bottom concrete slab 12 alternating with a pair of joists 18B
embedded in the top concrete slab 14 across the width of the floor unit. The

advantage of this arrangement is that if desired reinforcing straps 80, one only
of which is shown in Figure 8, can be welded or brazed between the free
edges of the pairs of adjacent joists, to strengthen the joist assembly and
resist buckling.
It will be seen in each of Figures 6 to 8 that the runners 54 supporting the
boards 52 are welded or brazed to the joists 18B which are ultimately to be
embedded in the concrete of the top slab 14. One alternative, method of
supporting the boards 52 is shown in Figure 9. Blocks of expanded
polystyrene 90 are placed on the top edges of the joists 18C, and taller blocks
of expanded polystyrene 92 are placed on the inturned and upturned bottom
edges of the joists 18B. The boards 52 are simply balanced between
adjacent pairs of blocks 90 or 92 prior to pouring the concrete of the top layer
14. Expanded polystyrene is a very poor conductor of sound, so that there is
very little sound transmission from the top concrete slab 14 to the bottom
concrete slab 12 through the blocks 90 and 92, which do not play any
structural role in the final floor unit once the concrete layer 14 has set. It will
be understood of course that a combination of polystyrene blocks and runners
could be used. For example Figure 10 shows a combination of the
polystyrene blocks 90 placed on the tops of the joists 18C, and runners 54
welded to the joists 18B. Figure 10 also illustrates how service ducts can be
incorporated into the floor units of the invention. Figure 10 illustrates a
service duct 100, which may be for example a plastic conduit, extending
laterally of the joist 18B and 18C. The duct 100 is suitable for carrying
electrical wiring either completely across the floor unit or from an outside edge
to a mid position where it could be taken down through the ceiling, up through
the floor, or simply turned at 90° to run parallel with the joists. The conduit
100 passes through holes punched in the joists 18B and 18C, but those holes
are of different sizes so that the conduit contacts and is supported by the
joists 18B as illustrated in Figure 10, whereas it makes no contact at all with
the joists 18C. Equally, the relative sizes of the holes punched in the joists
could be reversed so that the conduit is supported by the joists 18C and

makes no contact with the joists 18B. By avoiding contact with the joists of
one set, it can be ensured that sound transmission through the floor unit does
not travel through the conduit 100.
Figure 11 shows an alternative location for the service conduit 100, beneath
the joists 18B and supported by holes punched in the joists 18C. The
acoustic insulation mats 50 in Figure 11 are shown as thicker than those in
Figures 5 to 10, but that is principally because in this embodiment the mats
have to be wrapped up and over the conduit 100, giving them increased
height along the section line of Figure 11. Of course, the acoustic insulation
mats 50 of Figures 5 to 11 can be of any thickness, even occupying the full
height between the bottom concrete slab 12 and the boards 52 on which the
top concrete slab 14 is laid.
In Figures 5 to 8 the top slab 14 is cast over an array of discrete boards 52.
These boards 52 are supported on runners 54 secured to the joists 18A or
18b which support the top slab across its width. Use of separate boards 52,
one between each pair of adjacent supporting joists 18A or 18B, requires an
additional step of cutting the individual boards 52 to size and assembling them
one by one between the joists and supported on the runners 54. A preferred
construction is to use a single board 52A as shown in Figure 12. That board
52A is placed directly over the top of joists 18D which support the top slab 14
across its width. Those joists 18D are shown in Figure 12 as being hollow
box section joists, although they are made from cold-rolled sheet metal, as
are the joists 18 of Figure 2C and the joists 18A of Figures 5 to 8. The very
fact that the rigid board 52A rests on the hollow section joists 18D means that
the joists 18D support the top slab 14 across its width, but that support is
advantageously considerably enhanced by a series of anchorage members
60 which are screwed to the hollow joists 18D by means of self-tapping
screws 62 which pass through the solid board 52A. The anchorage members
60 are cradle-shaped as shown in Figure 13, each comprising a pair of upright
sides 64 upstanding from a flat base 66. Slots 68 are cut in the top portions of

the upright sides 64 to straddle the rods or wires of the enforcing lattice 28.
When the anchorage member 60 is screwed to the hollow beams 18D through
the rigid board 52A, this provides the total support for the reinforcing lattice 28
both in the upward direction and the lateral directions, as well as the main
load bearing downward direction.
Each cradle 60 of Figure 13 supports the reinforcing rods or wires of the
lattice 28 running in one direction only, but different cradles 60 can be
oriented in mutually perpendicular directions so that together they support
both the longitudinal and the lateral reinforcing rods or wires of the lattice 28.
Alternatively cradles 60a as illustrated in Figures 13a and 13b can be used.
Figure 13a illustrates a sheet metal blank 60b from which the cradle 60a of
Figure 13b can be formed by bending. Rows of oval cut-outs in the blank 60b
are separated by relatively narrow metal webs 63 so as to define fold lines
enabling the sheet metal blank of Figure 13a to be easily bent by hand to the
shape of Figure 13b. A pre-formed hole 65 is provided in the flange which
becomes the base of the final cradle 60a to receive the screw 62 of Figure 12,
and slots 68a and 68b receive the longitudinal and lateral reinforcing rods
respectively of the reinforcing lattice 28. The slots 68a and 68b may be at the
same distance from the base as shown in Figure 13b, in which case the
cradfe 60a is easily twisted along one of the fold lines in use to bring the slots
to the mutually different levels of the longitudinal and lateral reinforcing rods;
or the slots 68a and 68b may be at mutually different heights to reflect rhe
different levels of the longitudinal and lateral reinforcing rods.
Figure 12 shows that the joists 18C supporting the bottom slab 12 are
constructed in the same way as those of Figure 8, and connected together at
intervals by lateral straps 80. The box section joists 18D are considerably
stronger than the separate J-section joists 18C even when those joists 18C
are joined together by straps 80, and an even stronger construction is
therefore that shown in Figure 14 in which the joists supporting the bottom
slap 12 are hollow box section joists 18E, similar to the hollow joists 18D

supporting the top slab. The support between the hollow joists 18E and the
bottom slab 12 is provided by a series of hangers 70 which are as shown in
Figure 15. Each hanger is a metal strap which passes over the joist from
which it is suspended, and hangs down on opposite sides of that joist.
Transverse slots in the lower ends of the hangers hook around and support
the reinforcing rods or wires of the first lattice 26 to provide the necessary
support across the width of the bottom slab 12.
It will be understood that instead of the metal of the strap hangers 70 as
shown in Figure 15, the reinforcing lattice 26 for the bottom slab could be
supported from the hollow joists 18E by wires. Depending on the length and
diameter of the supporting wires, this will provide very limited sound
transmission between the hollow beams 18E and the lower slab 12, which
gives the possibility of a further embodiment (not illustrated) in which each
transverse joist 18 can be formed as a hollow box section joist that both
supports the top slab as shown in Figure 12 and supports the bottom slab by
means of connecting wires.
Although not illustrated, the hollow box section joists 18D and 18E of Figures
12 and 14 can be wholly or partially filled by a sound-absorbing material.
Instead of the joists 18 of Figure 12 and the joists 18D and 18E of Figure 14
being formed as hollow box sections as illustrated, an improvement in
strength, as compared with the simple J-section joists 18B and 18C of Figures
6 to 11, can be obtained by forming each joist of Figure 12 or 14 from two
identical J-section joists placed back-to-back and secured together by spot-
welding.
Another modification (not illustrated) is to place a layer of acoustic rubber over
the tops of the box sections 18D or the single or back-to-back J-sections,
together possibly with an edge trim of acoustic rubber between the cast
concrete of the top slab 14 and the edge frame 10. This gives a floating floor

without detracting from the excellent rigidity and acoustic superiority of the
modular floor units as described and illustrated.
Figures 16 and 17 show an alternative section for the edge frame members
24 and 30 of the edge frame 10. Figure 16 shows that the out-turned flange
148 at the top of the edge frame member 30 is slightly lower than the top level
of the concrete slab 14. As with Figure 3A the edge frame member 30 is
made in two pieces, 30a and 30b, with an outer side plate 30A forming that
out-turned flange 148. Figure 17 shows the out-turned flanges being level
with the top of the top slab 14 of concrete. The way in which the lowered
flange 148 of Figure 16 is useful in the actual construction of buildings using
floor units according to the invention is illustrated in Figure 18. 140 shows the
top of a wall of the building, on which two floor units according to the invention
are supported. Figure 18 shows one floor unit 142 to the right of the wall top
140, and one floor unit 144 to the left. A rubber sheet 146 is placed over the
top cap of the wall top 140 to reduce sound transmission through the final
building, before the top floor units are placed in position, suspended on their
out-turned flanges 148. Self tapping screws or anchorage bolts 150 are
passed through downwardly extending anchorage plates 152 that are welded
or brazed to the side plates 32 of Figure 16 to render the assembly rigid. The
building is then ready to be increased in height by one further storey. If the
flanges were not recessed below the top of the top floor slabs, there would be
no positive line along which to locate the next higher wall panel 154. By virtue
of the recessed nature of the flanges 148, the next wall panel 154 can be
positively located in the shallow slot formed between adjacent floor units 142
and 144, and is preferably protected from direct metal to metal contact with
the flanges 148 by another strip of rubber 156. If desired, filler pieces of
rubber, plastic or metal can be placed between the top edges of the adjacent
floor units 142 and 144 and the wall panel 154 being assembled into position,
to shim the wall panel 154 into totally accurate alignment.

Figure 18 also shows a pair of flexible hangers 158 of the wall pane! 154, to
which plasterboard panels 160 are attached in conventional manner. An
intumescent strip 162 is placed along the bottom of each set of plasterboard
panels 160, to fill the gap between the plasterboard and. the floor of the
building being constructed.
It will be appreciated that the construction detail shown in Figure 18 reduces
the amount of sound transmission vertically through the building, so that the
sound insulation properties of the floor units of the invention are put to very
good effect.
The most remarkable advantage of all of the embodiments of composite floor
unit according to the invention as illustrated in Figures 1 to 18 is however their
fire resistance. There is very little distortion of the floor units in the event of a
fire, because of the anchorage of the rods or wires of the internal
reinforcement of the two cast slabs to the edge frame by welding or brazing,
and because of the anchorage of the joists 18, 18A, 18B, 18C, 18D and 18E
of the various embodiments to the edge frame by welding or brazing. The
joists 18 to 18E of the various illustrated embodiments described above have
been cold-rolled steel profiles. A further embodiment as illustrated in Figures
19 to 21 uses hot-rolled metal section joists 18F which are of parallel flanged
channel profile. Alternative hot-rolled profiles would be I-beam or hot-rolled
box section. A modular composite floor unit as described with reference to
Figure 19 was extensively tested in a fire resistance test and amazingly
survived the test for the full 240 minutes of the BS 476 Part 21 : 1987, Clause
7 test.
Referring to Figures 19 to 21, the sides of the edge frame 30 are constructed
in two pieces as in Figure 21. The parallel flanged channel joists 18F are
welded or brazed to the edge frame 30 at their ends. Hangers 70 shaped as
in Figure 15 straddle the joists 18F and support a welded mesh lattice 26 of
reinforcing rods which will provide the reinforcement for the bottom cast slab

12 (the ceiling slab). All ends of the welded mesh lattice 26 are welded or
brazed to an upturned and intumed flange portion of the edge frame 30. The
welded mesh reinforcing lattice 26 is therefore supported across its central
portion by the hangers 70 and secured firmly to the edge frame 80 all around
the periphery. At this stage the ceiling slab 12 is cast, with the cement-based
or gypsum-based casting material flowing into the edge channel of the edge
frame 30 all around the periphery of the floor unit and around the reinforcing
lattice 26 across the centre. A bottom portion of each hanger 70 is encased in
the cast slab 12 but the joists 18F are above the level of the cast slab 12.
Insulation 50 such as high density rockwool insulation matting (for example
that sold under the Trade Mark BEAMCLAD) is then packed into the voids
above the cast slab and between the joists 18F, and one or more solid boards
95 placed over the tops of the joists 18F. A very suitable material for those
boards 95 is a fibre board impregnated with bitumen, as sold under the Trade
Mark BITROC. If desired, additional support for the boards 95 can be
provided by first placing transverse beams 96 between pairs of adjacent joists
18F at intervals along the length of the joists 18F. Each transverse beam 96,
of which one is shown in perspective view in Figure 20, comprises a box
section support portion for the solid board 95 and a pair of mounting plates
97, one at each end. The mounting plates 97 overlie the joists 18F as shown
in Figure 19, and can if desired be secured in position by self-tapping screws
(not shown) or by spot welds.
The solid boards 95 provide a base support for the upper slab of concrete 14
that is to be cast over the top of the composite floor unit. Before that concrete
is poured, however, the lattice 28 of reinforcing rods is secured in position.
Mesh anchorage members 60 or 60a, as already illustrated in Figure 13 or in
Figures 13a and 13b, are secured at intervals over each joist 18F and are
secured to the joist 18F using self-tapping screws 62 which pass through the
solid board 95 and into the joist. The lattice 28 of welded reinforcing rods is
supported by the slots in the anchorage members 60 or 60a and held spaced

above the boards 95 across the width of the composite floor unit. The edge
frame 30 is itself made from two components 30a and 30b welded together as
illustrated in Figure 21.
Although not illustrated in Figure 19, a sheet of polythene is laid over the
boards 95. The edges of the polythene sheet are trapped in the C-section
component 30b of the edge frame 30 by strips 30c of expanded polystyrene
inserted into the C-section component 30b between its upper and lower
flanges. The cast floor slab 14 is therefore effectively a floating floor,
supported across its width by the parallel flanged channel joists 18F but
isolated from the edge frame 30 by the expanded polystyrene strips 30c. The
improvement in acoustic insulation of the resulting composite floor unit is
remarkable. There is very little sound transmission from the floor slab 14 to
the frqamework of the building (for example to the wall top 140 of Figure 18)
because of the provision of the expanded polystyrene strips 30c and the free
floating nature of the floor slab 14. Fire resistance could of course be
improved by welding or brazing the ends of the reinforcing rods of the lattice
28 of the floor slab 14 to the edge frame 30, just as the ends of the reinforcing
rods of the reinforcing lattice 26 of the ceiling slab are so welded or brazed.
That would however be at the expense of the sound insulation improvement
that si obtained by making the floor slab free-floating. Surprisingly, it has
been found that the fire resistance is so outstandingly good when only the
bottom reinforcing lattice is welded or brazed to the edge frame 30 that a
similar edge connection of the top reinforcing lattice is unnecessary.
The floor unit as illustrated in Figures 19 to 21 was tested for fire resistance in
accordance with British Standard 476: Part 21: 1987, clause 7. The unit was
tested for its ability to comply with the performance criteria for load-bearing
capacity, structural integrity and thermal insulation. During the test the
specimen floor unit being tested carried a surface load of 2 KN/m2 evenly
distributed over its top surface. Thermocouples were positioned over the top
surface of the unit being tested, and the unit was suspended over a furnace

which enabled it to be heated from below. The test was continued for four
hours as specified in BS476, and the specimen survived the full duration of
the test.
Even though the furnace temperature was raised to 1152°C during the test,
the maximum temperature of the top surface of the floor unit even after 4
hours was only 68°C, indicating excellent thermal insulation between the top
and bottom slabs of the floor unit. Structural integrity and load-bearing
capability were maintained for the full 4 hours of the test although there was a
slight (but acceptable) bowing or sagging of a part of the bottom slab towards
the end of the test. The specimen under test still satisfied the test criteria for
upper surface temperature, load-bearing capacity and structural integrity at
the end of the 4-hour test, which represents really astonishing performance
characteristics, way beyond expectations which were for at most a 90-minute
satisfaction of all of the test criteria.
In addition to the quite unpredictably high fire resistance of the specimen floor
being tested, that same floor unit had previously been subjected to a test for
acoustic insulation. It was found to be far superior to conventional solid floors
and to conventional hollow floors. The excellent acoustic properties are
thought to be a combination of the dense nature of the top and bottom slabs,
the fact that those slabs are anchored all round their periphery to the edge
frame by virtue of the welded or brazed connections between the reinforcing
lattice of rods or wires and the edge frame and between the joists and the
edge frame, and the less dense interior of the composite floor unit. The less
dense interior, provided by the rockwool 50 and the air gap over the rockwool,
provides good acoustic insulation. The direct acoustic paths through the
composite floor unit from the top surface to the bottom surface are largely
confined to the self-tapping screws 62 linking the top slab 14 to the joists 18F,
and the mesh hangers 70. By judicious spacing of those hangers 70 the
composite floor unit of the invention achieves, in a total thickness or depth of

less than 300 mm for the floor unit, a level of acoustic insulation that might be
expected of a conventional floor unit at least twice as thick.

CLAIMS
1. A modular composite floor unit for an above-ground-level floor of a
building, comprising:
an edge frame made from cold-rolled sheet metal edge members
welded or brazed together to form an accurately sized and proportioned edge
shuttering for the floor unit:
a cast cement-based or gypsum-based ceiling slab cast within the
edge frame and encasing a first lattice of reinforcing rods or wires; and
a cast cement-based flooring slab spaced from the ceiling slab and
cast within the edge frame, encasing a second lattice of reinforcing rods or
wires which are welded or brazed at their ends to opposite edge members of
the edge frame;
each of the ceiling and flooring slabs being supported across its width
by an array of mutually parallel spaced metal joists which extend across the
floor unit between the cast slabs and are welded or brazed at their opposite
ends to opposite edge members of the edge frame; and
the space between the ceiling and flooring slabs containing a sound
insulating material of lower density than that of the cast ceiling and floor slabs.
2. A floor unit according to claim 1, wherein the sound insulating material
completely or substantially completely fills the inter-joist space between the
cast ceiling and floor slabs.
3. A floor unit according to claim 2, wherein the sound insulating material
comprises an array of blocks of lower density than that of the material of the
cast ceiling and floor slabs.
4. A floor unit according to claim 3, wherein the blocks are blocks of a
cinder-based or porous aggregate-based cement walling block material,
expanded polystyrene, rockwool, compressed straw or balsa wood; or are
plastic or cardboard boxes filled with loose particulate material such as

rockwool, shredded newspaper, papier mache, chopped straw, glass fibre
matting or reclaimed particulate rubber.
5. A floor unit according to claim 3 or claim 4, wherein the cast floor slab
has been cast directly over the tops of the array of blocks and has been
allowed to flow around and between the blocks of the array.
6. A floor unit according to claim 2, wherein the sound-insulating material
comprises a layer of a lightweight sound absorbing material laid over the top
of the cast ceiling slab and between the joists, and a solid board or an array of
solid boards placed over the sound absorbing material, the board or boards
being supported by the sound absorbing material or by the joists.
7. A floor unit according to claim 5, wherein the cast floor slab has been
cast over the top of the solid board or boards.
8. A floor unit according to claim 1, wherein the sound insulating material
only partially fills the space between the cast ceiling and floor slabs.
9. A floor unit according to claim 8, wherein the sound insulating material
comprises a layer of lightweight sound absorbing material laid over the top of
the cast ceiling slab and between the joists, and a solid board or an array of
solid boards supported by the joists at a level spaced from the top of the layer
of sound-absorbing material.
10. A floor unit according to claim 9, wherein the cast floor slab has been
cast over the top of the solid board or boards.
11. A floor unit according to any preceding claim, wherein each joist has
one longitudinal edge embedded in the material of the cast ceiling slab and an
opposite longitudinal edge em+bedded in the material of the cast floor slab.

12. A floor unit according to claim 11, wherein the joists are made from
cold-rolled C-section steel.
13. A floor unit according to any of claims 1 to 10, wherein each joist has
one longitudinal edge embedded in the material of one of the cast slabs and
an opposite longitudinal edge in the space between the cast slabs, in an
alternating sequence of joists or pairs of joists across the floor unit.
14. A floor unit according to claim 13, wherein the joists are made from
cold-rolled J-section steel, the inturned longitudinal edge of each section
being that which is located in the space between the cast slabs.
15. A floor unit according to claim 13 or claim 14, wherein the joists having
a longitudinal edge embedded in the material of the cast ceiling slab are offset
laterally from those having a longitudinal edge embedded in the material of
the cast floor slab, the wall portions of the respective joists extending more
than half way across the space between the cast ceiling and floor slabs.
16. A floor unit according to claim 15, wherein pairs of adjacent joists, one
having an edge embedded in the material of the cast ceiling slab and the
other having an edge embedded in the material of the cast floor slab, are
closely adjacent one another and separated by a greater distance from
adjacent similar pairs of joists.
17. A floor unit according to claim 16, wherein free edges of adjacent joists
having edges embedded in the material of the same cast slab, those free
edges being the edges located in the space between the slabs, are joined
together at intervals along the length of the joists by straps which transfer
buckling loads between the joists.

18. A floor unit according to any of claims 1 to 4, 8, 9 and 10, wherein the
joists are hollow box section joists or hot rolled PFC (parallel flanged channel)
joists.
19. A floor unit according to claim 18, wherein the cast ceiling slab is
supported by the joists across its width by hangers suspended from the joists
or from some of the joists and supporting the first lattice of reinforcing rods or
wires across the width of the cast ceiling slab.
20. A floor unit according to claim 19, wherein the hangers are wire
hangers.
21. A floor unit according to claim 19, wherein the hangers are metal straps
which pass over the joists from which they are suspended and hang down on
opposite sides of those joists, having transverse slots in lower ends of the
hangers which hook around and support the reinforcing rods or wires of the
first lattice.
22. A floor unit according to any of claims 18 to 21, wherein the cast floor
slab is supported by the joists across its width by being cast on a solid board
resting directly on the top of those joists.
23. A floor unit according to claim 22, wherein the cast floor slab is
anchored to the joists which support it across its width by an array of
anchorage members which are connected to the second lattice of supporting
rods or wires and are screwed to the joists which support the cast floor slab
through the solid board.
24. A floor unit according to any of claims 18 to 23, wherein each of the
box section joists supports both the cast ceiling and floor slabs.

25. A-floor unit according to any of claims 18 to 23, wherein alternate ones
of the box section joists across the width of the floor unit support the cast
ceiling slab and intermediate ones of the box section joists support the cast
floor slab.
26. A floor unit according to any of claims 18 to 25, wherein the box section
joists contain a sound-absorbing material.
27. A floor unit according to any preceding claim, wherein embedded in the
cast ceiling slab and/or the cast floor slab are reinforcing diagonal cross-struts
welded at their ends to the edge frame.
28. A floor unit according to claim 18, wherein the reinforcing diagonal
cross-struts are made from ribbons of sheet metal that have been unrolled
from a roll and prevented from curling by imparting a longitudinal crease
thereto.
29. A floor unit according to any preceding claim, wherein each of the cast
ceiling and floor slabs has a thickness of from 50 to 100 mm, and the space
between the cast ceiling and floor slabs is from 150 to 300 mm.
30. A floor unit according to claim 29, wherein each of the cast ceiling and
floor slabs has a thickness of about 65 mm.
31. A floor unit according to claim 29 or claim 230, wherein the space
between the cast ceiling and floor slabs is about 225 mm.
32. A floor unit according to any preceding claim, wherein the surface finish
of the underside of the cast ceiling slab is a paper or fabric material that has
been laid over the casting surface on which the ceiling slab has been cast.

33. A floor unit according to any of claims 1 to 22, wherein the surface
finish of the underside of the cast ceiling slab is the surface finish of a board
or plate that has been covered with a mould release agent before casting the
ceiling slab.
34. A floor unit according to any preceding claim, wherein the surface finish
of the top surface of the cast ceiling slab is a power float finish.
35. A method for the manufacture of a floor unit according to any of claims
1 to 34, which comprises:
forming an edge frame by welding or brazing together cold-rolled sheet
metal edge members;
welding or brazing to the edge frame an array of mutually parallel
spaced metal joists;
welding or brazing to the edge frame the ends of the reinforcing rods or
wires of the first lattice;
casting the ceiling slab by pouring wet concrete or gypsum-based
plaster into the shuttering created by the edge frame, to a depth sufficient to
encase a first inturned lip of the edge frame, to encase the first lattice of
reinforcing rods or wires, and to embed lower longitudinal edges of some or
all of the parallel spaced joists of cold-rolled sheet metal or of hangers
suspended from those joists;
placing between the parallel spaced joists of cold-rolled sheet metal the
sound insulating material of lower density than the concrete of the cast slabs
and optionally the array of solid boards to form a base for the cast ceiling slab;
welding or brazing to the edge frame the ends of the reinforcing rods or
wires of the second lattice;
pouring wet concrete over the top layer of sound insulating material or
over the tops of the solid boards to a depth sufficient to encase a second
inturned lip of the edge frame, to encase the second lattice of reinforcing rods
or wires and optionally to embed upper longitudinal edges of some or all of
the parallel spaced joists of cold-rolled sheet metal; and
providing a smooth surface finish to the top of the cast floor slab using
a power float.

The invention provides a modular composite floor unit and a method for its manufacture. The floor unit is factory-
made. An edge frame (10) is provided from cold-rolled sheet metal members (24 and 32) welded or brazed together to create edge
shuttering. A cast concrete ceiling slab (12) is cast within the edge frame (10) over a smooth casting surface. The cast ceiling slab
(12) encases a first inturned lip of the edge frame (10), a first lattice (26) of reinforcing rods or wires anchored at their ends to
opposite sides and ends of the edge frame (10), and the bottom edges, or hangers (70) suspended below the bottom edges, of an array
of mutually parallel spaced metal joists (18) which are welded or brazed to the edge frame (10) at their opposite ends. An infill layer
is then created from blocks (16) or particulate material filling most of the height of the exposed portions of the array of mutually
parallel spaced joists (18). A concrete floor slab (14) is cast within the edge frame (10) over the top of the infill layer, encasing an
upper inturned lip of the edge frame (10), a second lattice (28) of reinforcing rods or wires anchored at their ends to opposite sides
and ends of the edge frame (10), and the top edges, or anchorage members (60) secured to the top edges, of the mutually parallel
spaced joists (18). The top surface of the cast floor slab (14) is float-finished to create a final floor unit that requires no screeding.
The bottom surface of the cast ceiling slab (12) has a finish defined by the surface on which it was cast, and is visible without further
treatment as the ceiling of the room below the floor unit when the unit is used in the construction of a multi-storey building.