Note: Descriptions are shown in the official language in which they were submitted.
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Demountable Floor Construction
Technical Field
[1] The present invention relates to precast concrete floors suitable for
use in concrete
buildings, for schools, hotels, office, retail and other premises.
[2] The invention is also applicable to precast concrete floors that
connect to conventional
steel framed buildings. It is an alternative to building floors that consist
of concrete on
metal deck spanning onto steel beams, and it can be integrated with this
solution or
used as a direct replacement.
[3] The invention is particularly applicable to floors which are required
to be
demountable in order to change the configuration and/or to have deck openings.
Prior Art
[4] The challenge with precast concrete buildings is the joints between
precast elements.
If the joints are exposed, then the joints open and close as the floors are
loaded, which
damages finishes. A conventional solution would be to either cast an in situ
topping
or an in situ joint.
[5] A steel framed building will typically have an array of vertical
columns arranged in a
grid structure joined at each floor level by horizontal beams. Various types
of floor
system for creating a floor or deck supported by the beams have been proposed.
Existing steel and metal deck solutions create composite floors with a layer
of
concrete over a profiled metal deck. These solutions are low-profile and
relatively
lightweight and set a standard that must be matched by alternative
constructions
[6] A joint between concrete elements has been described in EP2882905 Laing
O'Rourke
Plc published on 17 June 2015. That joint is formed by overlapping headed bars
extending from adjacent faces of the concrete elements with vertical
transverse studs
between the bars. Such a joint technology has been used successfully to create
floors
without proppings or toppings from concrete elements in the form of solid
precast flat
slabs. However, such a strategy requires significant site construction in
order to create
the joints between adjacent concrete elements. The joints, so made, are also
permanent.
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Technical problems
[7] There is therefore a technical problem to create a flooring system from
precast and
prefabricated elements that does not require a topping or in situ joints, that
can be
assembled easily on site, and that will perform in a way similar to normal
steel framed
buildings and remain competitive in terms of weight and profile depth with
prior art
solutions.
[8] The jointing problems that a solution needs to address include the
transfer of
diaphragm forces across a floor, as well as making sure that joints do not
open up, or
suffer excessive cracking when the floor is subject to vertical loads and in-
plane
loads.
[9] There is also a technical problem to create a demountable flooring
system from
precast and prefabricated elements that can be assembled easily on site and
remain
competitive in terms of weight and profile depth with prior art solutions.
Solution of the Present Invention
[10] Embodiments of the present invention utilise primary precast floor
components made
from reinforced concrete or prestressed concrete elements. The secondary
components are an inverted U-shaped planks with a depending rib running along
each
longitudinal edge. These secondary components abut (with a narrow grouted gap)
other secondary components along the longitudinal edge to create a ribbed
floor. The
secondary planks are connected together at regular centres by intermediate
connector
plates that transfer tensile forces across the grouted joint so that the floor
can act as a
complete diaphragm.
[11] The ends of the secondary components are supported on primary beam
elements that
typically span between columns. The secondary components have a corner
connector
plate that extends across the grouted joint at the primary beam, to reduce
cracking
over the primary beam and to provide continuity across that joint, so that the
floor can
act as a complete diaphragm.
[12] The primary beams can be an inverted T-shaped profile which enables the
secondary
components to sit on a support nib. Alternatively, or in addition, primary
support
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beams can also be rectangular beams below the planks, or steel beams. The
secondary
planks are continuous over such support beams.
[13] The primary beams support the secondary planks and sit on columns. A
connector
plate at the column, connects the secondary planks to the primary beam and to
the
column above. The column connector plates transfer diaphragm action across the
joints and are designed to reduce cracking in the floors and to create a
performance
similar to a concrete floor on metal deck on steel beams.
[14] All the connector plates are designed to transfer tensile forces
across joints. The plates
can be recessed into the floor. Tolerance is achieved by inserting the
connector plates
into grouted or concreted joints.
[15] The connector plates are designed to be unbolted and thus the system can
be
demounted, with concrete/stone splitters used to split the grout joint once
the
connector plates have been removed.
[16] The planks are precast with sleeves for bolt holes and recesses so that
the various
elements of the flooring system can be interconnected with metal plates bolted
into
the concrete elements. These plates work in combination with grouted joints to
create
a complete diaphragm. Bolted joints are normally not possible because of the
need to
allow tolerances.
[17] The floors are connected together by a series of connector plates and
grouted joints
that provide a complete diaphragm action and loadable surface.
[18] The solution of the present invention avoids the use of large in situ
joints, or welded
connections and makes the connections from bolts that can easily be undone.
Therefore, the system can be disassembled in order to remove or re-configure
the
floor allowing at least some components to be reused.
[19] The elements are stable in their own right and the infill joints are
simple.
[20] Because the floors do not have any propping, nor do they rely on any
topping, they
can be loaded immediately after erection.
[21] Because the floors are connected by plates that can be unbolted, the
floors can be
completely demountable.
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[22] The invention is defined in the appended claims.
Description of the Drawings
[23] 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:
[24] Figurel shows a perspective view from below of a floor section within a
single bay or
grid rectangle;
[25] Figure 2 is a perspective view of a primary beam;
[26] Figure 3 is a perspective view of a plank showing how it would be
supported for
craning into position together with a transparent view showing its internal
reinforcement;
[27] Figure 4 is a view of a floor bay from above;
[28] Figure 5 shows a perspective view of two floors;
[29] Figure 6 is a detail showing a primary beam to column connection;
[30] Figure 7 shows an exploded view of a typical column connection;
[31] Figure 8 shows a slab connector plate for use in connecting the edges of
two adjoining
planks;
[32] Figure 9 shows an exploded perspective view showing a beam connector
plate for use
in connecting planks on either side of a beam in position;
[33] Figure 10 shows the beam connector plate figure 9;
[34] Figure 11 shows an exploded view of a beam connector plate showing the
elements of
the bolts;
[35] Figure 12 shows an exploded view of a typical column, beam, and plank
connection.
Description of an Embodiment
[36] The modular flooring system described is intended to be installed in a
multi-storey
building such as a low rise office, retail premises, hotel or school. The
building is
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defined by means of an array of vertical columns made up of individual floor
height
column sections 2 arranged in a grid structure, for example a 9m x 9m or 7.5m
x
7.5m, or 9m xl2m grid as shown in figure 5. A single bay of the grid is
illustrated in
the drawings for simplicity. In each bay four vertical column sections 4 are
interconnected by a pair of parallel horizontal primary beams 6. The floor
between
the beams is created by means of a series of adjoining precast concrete planks
10
which serve as the secondary components of the floor.
[37] Each concrete plank 10 is an elongate inverted U-shaped precast concrete
element
having ends 12 and ribs 14 depending on the longitudinal side edges. The plank
has a
substantially flat upper surface that defines the level of the floor. The
upper surface
has recesses as described later for the purpose of interconnecting the planks.
The
underside of the plank is the soffit. The concrete planks are precast with
internal
rebar reinforcement 20 as shown in figure 3. The planks have deeper side edges
or
ribs where the planks adjoin each other side by side creating a ribbed effect
in the
underside of the floor and providing sufficient depth of concrete to support
connecting
bolts. The outer, lower portion of each rib 14 has a slight projection 16 to
control the
spacing of the planks as they abut each other to form a grout joint zone that
when in-
filled provides a shear key between adjacent planks. The ribs act as beams
supporting
the flat plank surface.
[38] A typical inverted U channel plank has a width of 1500 to 3000mm between
its side
edges and a rib depth of 250 to 550mm at those edges and 120- 150mm in its
middle
region. The planks may span 6 to 12m between primary beams such that three
planks
can create a grid bay as illustrated in figures 1 and 4.
[39] The ends 12 of the longitudinal beams may be square or have an undercut
rebate 24
which is sized to cooperate with the adjacent beam and allows the plank to be
self-
supporting on the beams 6 during construction. The ends of the planks sit on
neoprene
pads 64 on the beams. The joints between the planks are filled with a grout or
concrete mix. Connector plates 54 link the planks across the beams 6 and
therefore
create a moment connection across the beams in the final condition.
[40] The longitudinal ribs 14 of the planks may be provided with apertures 44
for services
to pass through if required.
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[41] Lifting points 26 are provided on the plank so that it can be hoisted
into position as
shown in figure 3. Alternative lifting methods are possible such as by lifting
it
through service penetrations 44 in the ribs.
[42] Recesses 30 for the connector plates surrounding bolt sleeves 32 are pre-
cast in the
upper surface of the plank along the longitudinal edges. The bolt sleeves
extend from
the upper surface into the ribs 14. Recesses 40 surrounding bolt sleeves 42
are also
formed at each corner of the end of the plank. These recesses 30, 40 are deep
enough,
for example 20mm, to accommodate the various connector plates 52, 54, 56, and
58
which are used to join the components of the flooring system together. The use
of
connector plates 52, 54, 56, 58 and bolts 50 rather than welded or in situ
joints which
require construction work during assembly, allows this flooring system to be
demountable.
[43] The beams 6 are preferably of an inverted T-shaped section as shown in
figure 2 with
a lower flange 34 and web 36. The lower projecting flange 34 provides support
for a
base of a rib 14 during assembly, and neoprene pads 64 may be provided on this
support surface. The beam 6 can be provided with penetrations or apertures 38
for the
passage of services, as required.
[44] Connector plates 52, 54, 56, 58 are provided in various configurations as
shown in
figures 7 to 12. The plates are provided with bolts 50 that connect to the
plates and are
cast into and cooperate with the bolt sleeves 32, 42 precast into the planks.
As
illustrated in figure 11, each bolt 50 is assembled from a counter sunk head
53 and a
threaded stud 55. The head 53 is received in a hole in a connector plate and
is
connected to the stud 55 by means of a threaded sleeve coupler 51.
[45] Once the plates and bolts have been assembled, they can be fixed in
position by
grouting 62 to give moment continuity. The countersunk bolt head 53, can
simply be
unscrewed to facilitate removal of the connector plates 52, 54, 56, 58. Once
the
connector plates are removed the panels have no tensile capacity between the
precast
units, and can be separated by a concrete splitter for later reuse.
[46] The primary beams 6, are bolted to a column 4 through threaded bars 74
that sleeve
through the beam, as shown in figure 12. Where the column is narrower than the
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width of the beam, these threaded bars will sleeve through the web 36 of the
primary
beam 6. The column connector plate 56 connects the primary beam to adjacent
planks
through bolts 50 cast into sleeves. The column connector plate can be detailed
so that
it has threaded bars 70 to connect to standard column shoes 72, or can be
detailed to
connect to steel or concrete columns. Connector plates 52 connect adjacent
planks.
Connector plates 54 bridge across a primary supporting beam and connector
plates 58
can be used to connect other support beams below the planks.
[47] The flooring system made up of the components as described can be
assembled on
site without significant construction steps. There is no need for any propping
during
construction as the planks are self-supporting on the beams.
