Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Precast Building Construction System
Technical Field
[1] The present invention relates to building systems which use precast
concrete
elements. More specifically, the present invention relates to systems in which
the
structure is supported using only concrete columns and walls rather than being
steel
framed or using separate horizontal beams to support the structure.
[2] The invention is particularly applicable to building systems for
residential
applications for multiple occupancy such as hostels, blocks of flats or
hotels, which
due to the number of identical or similar residential units, lend themselves
to modular
construction. Such constructions are also divided into relatively small units
making
them an appropriate size to be created from a series of precast panels.
Technical problems
l3l The challenge with precast concrete buildings that do not have a frame
with
horizontal beams, is that the joints between precast elements need to transmit
vertical
loads, lateral diaphragm forces to a stability structure, typically cores
and/or shear
walls, and provide a degree of vertical and horizontal tying capacity for
robustness as
required by most building codes. A conventional solution would be to cast an
in situ
structural topping.
[4] A further challenge is that construction tolerances of any in situ
topping prevents
direct placement of finishes and, if floor joints are exposed, then the joints
open and
close as the floors are loaded, which damages finishes. A conventional
solution
would be to provide an additional in situ architectural screed upon the
structural
topping.
[5] A further challenge is that floors generally need to sit on beams,
which in turn sit on
columns and walls. The conventional solution to avoiding beams is using a
thick two-
way spanning flat slab. The building services distribution occurs below the
floor slab.
The thickness of the slab impacts the building height.
[6] There is therefore a technical problem to create a precast construction
system that
allows a variety of layouts to be created without independent supporting beams
2
together with a connection system requiring the minimum of site assembly
whilst
achieving the structural performance requirements as described above. Solving
this
problem reduces the installation time and overall cost of the construction.
[7] There is also a technical problem of minimising the thickness of the
floor in order to
minimise the overall building height and costs of the construction,
particularly that of
cladding, as well as vertical structures needed to support the floors, while
maximising
the number of units for a given height.
[S] Many precast components for various purposes have been disclosed in
the prior art.
For example DE19842742 23 March 2000 (DENNERT) discloses a prefabricated
modular base plate for a building which has separate depending feet at each
corner.
While it is taught that the slabs can be connected, said connections are non-
positive,
do not transmit vertical and/or horizontal loads, and, the feet are not
coupled. It is only
intended that these panels be used for the foundation layer.
[91 Solution of the Present Invention
[10] The solution of the invention is a building construction system that
uses large format
precast floor panels, that do not require independent, separate supporting
beams, site
placed in situ structural toppings, that are connected together to create a
complete
floor. The panels have downstands around the perimeter. The downstands come
together and are jointed. The panels can be supported only by vertical
concrete
column and wall elements that define the structure without the need for
independent
beams.
[11] The floor panels are typically sized to overlie a single residential
unit such as a hotel
or student accommodation room, or a bedroom or living room area, such that the
downstands around the perimeter match the periphery of the residential unit.
[12] Embodiments of the invention use precast concrete panels that are
sized to be lifted on
a single crane hook. The panels are provided with perimeter longitudinal and
transverse downstands. The longitudinal downstands are preferably along the
edges of
the panel and abut one another when the panels are assembled in an array in
order to
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allow the panels to be interconnected and to be connected to supporting
columns or
walls, without the need for direct support of each panel.
[13] The downstands provide support to the slab which allows it to be
considerably thinner
than normal flat slab construction. The floor services below the slab, can
penetrate
the downstands allowing the combined thickness of the floor slab and services
to be
reduced. This results in a lower floor to floor height.
[14] The connection system between the panels uses a combination of cast-in
steel
brackets and grouted connectors in preformed voids or sockets, and grouted
shear
keys formed into the side of adjacent downstands, designed to create a
continuous
floor across adjacent panels. Connectors can be designed for holding adjacent
panels
together both on the upper surface to prevent hogging and as tension
connectors at the
lower surface to prevent sagging, where the panels are not supported by a
column.
[15] The upper surface connectors also limit movements under loading,
preventing grouted
joints opening, and with the substantially flat surface allow for the direct
placement of
finishes with only a debonding membrane, removing the need for a cast in situ
architectural screed.
[16] The grouted shear key in combination with the connectors enable the
continuous floor
panels to transmit lateral diaphragm forces to stability elements and provide
sufficient
robustness tie capacity, without the need of any cast in situ structural
toppings.
Description of the Drawings
[17] In order that the invention can be well understood some embodiments
thereof will
now be described, by way of example only, with reference to the accompanying
diagrammatic drawings, in which:
[18] Figure 1 shows a perspective view of an array of four interconnected
panels of the
present invention showing the connection to supporting wall sections and
columns;
[19] Figure 2 is a view from below of the array of Figure 1;
[20] Figure 3 shows the connections between the panels for the array of Figure
1;
[21] Figure 4 shows how the array of Figure 1 forms part of a floor of a
building
construction;
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[22] Figure 5 shows how an array of panels can form part of a building
construction;
[23] Figure 6 is a view from below of an array similar to Figure 5;
[24] Figure 7 is a perspective view of a single panel of the present
invention;
[25] Figure 8 is a series of drawings showing the stages of construction of a
floor of a
structure using the system of the present invention;
[26] Figures 9 is a perspective view of connections joining adjacent panels;
[27] Figure 10 is a view from below of the adjacent panel connections of
Figure 9;
[28] Figure 11 is a sectional view of the connections joining adjacent panel
downstands of
Figure 9 and Figure 10;
[29] Figure 12 shows a perspective view of a further type of connector in situ
and isolated;
[30] Figure 13 shows an example of a panel connection to a column, which uses
embedded
reinforcing double-headed studs in a downstand;
[31] Figure 14 shows an example of a panel connection to a wall, which uses
embedded
reinforcing double-headed studs in a downstand supported by a wall section;
and
[32] Figure 15 is a perspective view of a detail of a corner connection
between four
adjoining panels, in a situation where there are no downstands within a
central access
corridor;
Description of an Embodiment
[33] The building construction system being described is primarily for
multiple occupancy
residential buildings, where the building is divided into residential units
that may
contain a bathroom pod and which are of sufficiently modest size, for example
3m x
7.2m and preferably no more than 4.5m wide or 10m long. The building element
which creates both floor and ceiling is a large format precast plank or panel
10. The
panels have substantially flat upper surfaces 12 at least in the central
portion of the
panels and can have rounded or bevelled upper edges 14. A floor plan of the
building
can be assembled from an array of interconnected panels which may be all of
the
same size or selected from a restricted set of panel sizes. Each panel
consists of a thin
concrete slab 16, for example 150mm deep, having downstands 18 of a depth of,
for
5
example, 300mm making a beam depth of 450mm, along the intended periphery of
the residential unit. The downstands 18 extend along each longitudinal edge in
this
embodiment and are joined by two transverse downstands 20 so that the
downstands
co-operate to create a continuous enclosure beneath the floor surface in the
manner of
an inverted "bathtub".
[341 The term downstand in the context of this specification is intended to
refer to
depending extension from the main plane of the panel which is of a depth to
transmit
required structural loads to adjacent panels and supports.
[35] The depth of the downstand 18 dictates the overall depth of the panel
and are typically
located within architectural wall zones. The depth of the thin concrete slab
16, kept to
a structural minimum is located within the usable plan area of an
architectural space
thereby minimising the overall building height. For a panel with dimensions of
3m x
7.2m as discussed above with 300mm downstands, the ratio of overall depth of
the
panel to floor-to-floor height is typically 1:9, and the ratio of slab depth
of panel to
floor-to-floor height is typically 1:18. These figures are given as examples
only to
illustrate that the depth of the downstand and slab is small relative to the
height of
supporting columns 90 or walls 30 (typically 2.5m) within the structure. The
present
invention does not encompass proposals for precast elements which provide
large and
cumbersome LT shaped structures combining wall and floor elements.
[36] If there is a central corridor, then one of the transverse downstands
20 can be offset
from the end of the panel as best shown in Figure 2 and Figure 15. This
results in the
downstand enclosure terminating short of the end of the slab 28. This allows
the
downstands 18 to surround the residential unit and provide for a corridor
needed for
access. The adjacent downstands of abutting floor panels together create an
integrated
beam which supports the panels. Openings 22 of appropriate sizes are provided
in the
slab 16. The openings in the slab should be designed so as not to interfere
with the
downstands. Openings 23 in the downstands are detailed to allow services to
pass
through. The openings in the downstand are designed as slots to allow services
distribution to be integrated within the depths of the downstands.
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[37] Notches 24 are pre-formed at various positions along the side edges of
the panel to
facilitate the alignment with rebar 26 projecting from supporting wall
sections 30 or
columns 90.
[38] Proprietary channel connections 27 are cast into the building perimeter
side edge of
the panel to facilitate the installation of the building facade.
[39] The panels 10 may include radiant heating and cooling pipes in the
precast
component.
[40] A panel of size 3m x 7.2m as described above would weigh about 10 tonnes
and be
capable of being lifted into position on a single crane hook. For larger units
a
maximum weight of, for example, 20 tonnes would still allow single hook
lifting.
Connections
[41] Connections join adjacent panels, creating a continuous floor capable of
transmitting
vertical loads to supporting columns 90 or walls 30, and a lateral diaphragm
structure.
The general principle of the connectors to be described herein is that they
have
connector plates, usually fitted within preformed recesses 43 in the panel.
The plates
are bolted into the panel and to another adjacent panel, so that adjacent
downstands
are connected together to create integral beams which, when grouted, enable
the
panels to transmit vertical loads, supporting the floor on walls or columns
only.
Several types of connector will now be described.
[42] Where adjacent panels are not supported, the connectors enable the
panels'
down stands to form an integral continuous beam between supports. Connector
recesses 43 may also be formed in a lower surface of the downstands, at
locations
where sagging may be an issue. Figures 9 to 11 show an example of a connector
for
use in this situation. With this connector, plates 54, 56 are fitted both on
the upper
surface of the panels and the lower surface of two adjoining downstands. The
location
of this type of connector is shown in Figure 9. Voids 58 with internal
grooves, extend
from the upper surface of each panel to the lower surface of the downstand.
Each
plate, 54, 56 has two pairs of projecting bolts 57 which fit into the voids.
The plates
and bolts fitted from both sides are grouted into position.
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[43] Another design of connector is shown in Figure 12. A base 60 of this
connector
supports four projecting rods 62 each with a socket 64 as an upper end. The
connector
with rods fit into the voids 58 within adjacent panels. An upper part 66 of
this
connector is a plate with four projecting bolts 65 which fit into the sockets
in the rods.
The plates and rods are grouted into position.
[44] Additional jointing recesses 42 with grooved voids 44 are also formed
along the sides
of the panel 10, at hogging supports where the top of the panels are in
tension, to
receive connectors of the type described in GB1721561.7 Laing O'Rourke Plc
filed
2321 December 2017. These connectors use plates 50 that fit across adjoining
recesses 42. The plates are fixed into the panels by bolts 52 which pass
through holes
in the plates into the voids 44 beneath. The connectors can then be grouted in
position. Similar connectors can also be used where there is no recess and it
is not
necessary to have a flat upper surface at that point. An example of such a
connector
location is shown in Figure 3.
[45] Recesses 32 are formed at the corners of the panels at an inner end so
that rectangular
connector plates 34 can be bolted into position where four panels join
together where
there is no downstand. The corner connector plate 34 is shown sectioned in
Figure 15
in order to illustrate how headed bolts 36 fixed to the connector plate are
received into
grooved voids 40 preformed within the base of the recess 32. The connector
plate
together with its headed bolts is grouted in position over the junction of the
four
panels to make a permanent connection between the panels. The bolts 36 can be
permanently welded to the plates 34 or be screwed in position so that the
connection
can be demountable.
[46] Although a limited number of connector types may be needed for different
positions
within the structure depending on the type of forces arising at the various
junctions,
all of the connectors can be devised using similar principles of plates and
bolts so that
in many cases the parts are common and interchangeable.
[47] Reinforcing double-headed studs 68 can be positioned both in horizontal
and vertical
orientations within the body of a downstand as shown in Figures 13 and 14. The
studs
are positioned during the factory casting process. These studs will cooperate
with the
rebar 26 to reinforce the structure at that point above the columns and wall
sections.
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[48] Upon installation and grouting of connectors 54, 56, 57 or 60, 62, 66,
and 50, 52,
adjacent panels are structurally connected together and can span between
supporting
columns or walls without the need for independent beams as the downstands
together
with the connectors create integral beams that provide the necessary
structural support
that would, in the prior art be supplied by separate beams that would require
a
separate construction step.
[49] Upon installation and grouting of all connectors, a floor slab is formed
that has
sufficient horizontal tying capacity for robustness.
[50] Between adjacent panel downstands 18,20, the vertical face of the
downstand is
longitudinally recessed 19, forming a shear key void 59 between connected
panels.
This shear key void is grouted when panels are installed.
[51] Upon installation and grouting of connectors and grouting of shear keys
59, a
continuous floor slab diaphragm is formed, capable of transmitting lateral
forces to
the building stability structure.
Construction process
[52] Figures 4 to 6 and Figure 8 show how the system is used to create a floor
or storey of
a building. Panels 10 are laid out in accordance with the plan and connected
to
concrete columns 90 and wall sections 30 constructed as required. It will be
noted that
the downstands define the periphery of a residential space. For the larger
spaces
shown in the design of Figures 5 and 6, two or more panels combine to provide
the
floor/ceiling of that residential space. Then the next floor is constructed by
lifting on
the next layer of panels 10 in the same configuration as the floor below. The
soffit or
underside of a panel can form an exposed ceiling of the residential unit and
also the
floor of the unit above.
[53] As shown in Figure 8, which illustrates an example sequence of events in
the
construction process, minimal propping is required. Shoring props 80 are only
needed
at the positions where adjacent panels join at positions where there is no
permanent
column or wall section needed by the structure. Column and wall elements can
be
structurally joined by rebars 26 which pass between the adjoining downstands.
The
notches 24 provide space for rebar and surrounding concrete. The rebar 26 can
be
grouted or concreted in position.
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[54] A variety of connectors as described above are used at different positons
depending
on the forces arising.
[55] Where sagging is possible connectors as described with reference to
Figures 9 to 12
are used. Where these connectors are installed at positions where temporary
props are
provided the connector plate 56 or 60 with its bolts in position and
projecting
upwardly can be placed on the tops of the props so that as the panel is
lowered into
position it can be manoeuvred so that the projecting bolt enters the preformed
void 58.
[56] Where columns or wall sections are constructed with projecting rebar, it
may be
possible to lower panels into position so that the rebar is sandwiched between
the
adjoining downstands.
[57] For certain types of connection it may be necessary to notch or thicken
the downstand
in certain limited areas, for instance it may be possible to notch the panel
so that they
can be supported on the edges of a column. These features can be preformed
into the
panel when it is cast. The downstands 18 may terminate short of the free end
as
shown in Figure 2 and Figure 15 to allow room for passage of services such as
air
ducts in a central portion of a corridor region. Notching may also be required
adjacent
wall panels.
[58] The panels or panels are bolted together by connector plates and grouted
joints to
create a flat surface that is ready for use. The solution has no concrete
structural
topping or architectural screed and because services are integrated within the
depths
of the beam this generally results in a reduction of floor depth and building
height.
[59] By using panels as described the construction time can be considerably
reduced
relative to pre-existing techniques resulting in cost savings. The overall
weight of the
construction is also reduced leading to saving in foundations, piles and other
construction elements.
[60] By using panels it is possible to include radiant heating and cooling
within the slab,
which is a low-energy cooling or heating system.
[61] Matching the downstands to the periphery of the residential unit will
frequently allow
the soffit of the panel to form a ceiling for the unit.
