Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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STRUCTURAL ELEMENT AND METHODS OF USE THEREOF
BACKGROUND
The present invention relates to structural engineering and more specifically
to a
structural member capable of use in the construction of structures such as
concrete slabs
and elements. The invention further relates to methods of use of the
structural member
including its application in preparatory formwork and as an element in a
composite
structure including in layered concrete. The invention also relates to
structures which
employ the structural member. The invention further relates to lightweight
structural
members used in a variety of concrete structures.
PRIOR ART
Slab beam concrete constructions is widely used in civil and structural
engineering. The typical structure will comprise columns of a size dictated by
applied
such as dead loads and self weight and live loads and of a spacing dictated by
loadings
and slab spans. Reinforced and pre stressed concrete floors for buildings are
generally
made in one of two methods. The floors are either cast in situ using
supporting temporary
formwork, or are formed from pre-cast concrete planks supported on beams or
walls
which are then typically covered in a relatively thin in situ layer of
concrete. Most major
construction work of concrete buildings typically relies on the first cast in
situ method in
which formwork is constructed as a temporary support for structural
reinforcing steel
over which is poured structural concrete. Cast in situ reinforced concrete
floors, require
extensive formwork, are relatively time consuming and labour intensive
particularly with
respect to the assembly and dismantling of formwork and the time required for
the in situ
concrete to achieve the required strength. Existing construction systems using
pre-cast
elements have significant cost and other disadvantages including poor
underside surface
finish , ribbed profiles on the underside necessitating separate ceilings in
many
applications, difficulty of running services through and lack of flexibility
of the type of
structures which can be built. These disadvantages render in situ casting
construction the
preferred method of slab and floor construction.
There are currently three different types of pre-cast floor systems which are
in
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common use in the building industry.
The first system often known as "Hollow Core" relies on the use of extruded,
pre-
tensioned, concrete generally rectangular planks which include a series of
cylindrical
holes or voids extending longitudinally along the plank. The planks are laid
on the top of
beams or walls and concrete is laid in situ over the top of the planks. This
construction
system can span relatively long distances, but has the disadvantage that it
typically has a
very poor surface finish on the underside necessitating in many applications a
false
ceiling or cladding over the concrete finish. The structural planks are
typically produced
in quite narrow strips requiring many joints and it is difficult to put
services through the
floor, as it is very difficult to access the voids. Also the planks are
relatively thick and
the services typically have to be either hung on the underside, also
necessitating false
ceilings in some applications or the services may be hidden in thick topping
concrete.
A second type of system commonly known as "Ultrafloor employs pre-cast ribs in
the shape of an inverted T and which are supported on walls or beams, and
these ribs
support a thin fibre cement panel such as a "Hardie panel" or the like
extending between
the ribs. A reinforced concrete floor is then laid over the ribs and panel.
This floor system
produces a ribbed soffit which necessitates the provision of a cover ceiling
in most
applications, but it does have the advantage that it is relatively easy to run
services
through, prior to casting the in situ layer. A further disadvantage of
Ultrafloor is that it
has a limited span both during concrete pouring and as a finished floor.
Ultrafloor is
limited in the types of floor structure which can be made from the basic panel
and from
the panel used in conjunction with the shell beam.
Another prior art system of floor construction is known as "Transfloor" in
which
a relatively thin 50mm thick plank of concrete includes longitudinally
extending steel
reinforcing bars in triangular arrangements of groups of three, with one bar
forming an
`apex' of the triangle spaced above the upper surface of the, concrete plank
and joined to
the other two bars with steel rods. The planks are placed on top of walls or
beams and
void/void formers are placed on the concrete plank between the reinforcing and
a
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concrete layer floor laid in situ on top of the plank. In the structural
engineering industry
the term void typically means an absence of concrete rather than an absence of
material.
Void formers are most commonly formed by polystyrene blocks although other non
cementitious materials such as pipe clay or the like can be used to form voids
in concrete
members. This system has the disadvantage that it is limited to relatively
short spans of
about 7m or so. Also there is a requirement to support the floor with props
and bearers at
relatively close spacings of between 2 and 4m while insitu concrete is being
poured and
is gaining strength. Any discussion of documents, acts, materials, devices,
articles or the
like which has been included in the present specification is solely for the
purpose of
providing a context for the present invention. It is not to be taken as an
admission that
any or all of these matters form part of the prior art base or were common
general
knowledge in the field relevant to the present invention as it existed before
the priority
date of each claim of this application.
INVENTION
The present invention seeks to provide an improved plank for use in forming
concrete flooring which addresses and at least partially alleviates some of
the problems of
the prior art assemblies as discussed above.
The present invention provides a structural member capable of use in the
construction of
structures such as floor assemblies, concrete slabs and structural elements.
The invention
further provides methods of uses for the structural member including its
application in
preparatory formwork and as an element in a composite structure including in
situ layered
concrete. The invention also provides structures which employ lightweight
structural
concrete members.
In a first aspect of the present invention, there is provided;
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a pre-formed structural element for use in forming a concrete floor of a
building or the
like, the plank comprising: a generally planar base portion; and a series of
formations
extending from the base portion, defining voids there between and wherein the
upper
portion of the formation is generally thicker than the lower portion of the
formations at
the junction with the base. .
Preferably the element is manufactured from concrete cast in a mould and the
formations
are generally parallel spaced apart ribs. The formations have sides which are
inclined
relative to the planar base.
In its broadest form the present invention comprises:
a generally elongated pre cast structural element for use in the construction
of a
composite floor and beam slab construction, the structural element comprising;
a base and an upper surface,
at least one formation extending from the upper surface and including a
plateau and side
walls each defining, with an opposing side wall of an adjacent formation, a
recess; the
side walls disposed for at least part of their length at an angle other than
normal to the to
the upper surface.
In another broad form the present invention comprises:
a generally elongated pre cast structural element for use in the construction
of a
composite floor and beam slab construction, the structural element comprising;
a base and an opposing upper surface,
at least two spaced apart formations extending from the upper surface and
including a
plateau and side walls each defining, with an opposing side wall of an
adjacent
formation, a tapered recess.
According to a preferred embodiment the tapered recess has a wide portion at
the upper
surface of the base of the structural element and a narrow portion at or near
the plateau
of the formations.
Preferably the formations form longitudinal ribs along the length of the
element.
Preferably each longitudinal rib is parallel to each other rib with even
spacing
therebetween. In an alternative embodiment, the element may be tapered along
its
longitudinal axis such that the ribbed formations converge in the direction of
one end
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and diverge in the direction of an opposite end. This embodiment might be used
in a case
where the elements are placed in a horizontal curve. Preferably, each rib
includes an
outward taper such that the plateau of the formation is wider than a junction
between the
formation and the upper surface of the element. In one embodiment, the taper
extends
from the plateau of each formation at least part way towards the junction
between the
formation and the upper surface of the element. In another embodiment, the
taper
extends the full distance from the plateau to the upper surface of the base of
element. In
another embodiment the taper is terminated short of the plateau. In a further
embodiment
there is provided a shoulder associated with the plateau which receives a
cover over the
recess thereby maintaining a void space in the element.
Preferably each formation has a generally dovetail geometry with a narrow
portion at the
junction between the upper surface of the element and the formation tapering
out to a
wide portion at the plateau.
In another broad form the invention comprises: a construction system using a
generally
elongated pre cast structural element comprising;
a base having a lower underside surface and an opposing upper surface, at
least two
spaced apart formations extending from the upper surface and including a
plateau and
side walls each defining, with an opposing side wall of an adjacent formation,
a tapered
recess; wherein the system employs at least one said elements as part of a
composite
concrete slab, wherein the slab is formed by said at least one element and an
overlay
layer which abuts said plateau of each said formations.
In another broad form the present invention comprises:
a composite structural floor comprising ;
at least one pre cast structural element having
a base having an underside surface and an opposing upper surface,
at least two spaced apart formations extending from the upper surface and each
including
a plateau and side walls each defining, with an opposing side wall of an
adjacent
formation, a recess, the side walls disposed at an angle other than normal to
the upper
surface of the base of the element;
an overlay layer which engages the at least one element via the formations.
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In another broad form the present invention comprises:
a composite structural floor comprising ;
at least one pre cast structural element having
a base having an underside surface and an opposing upper surface,
at least one spaced apart formation extending from the upper surface and each
including
a plateau and side walls each defining, a recess, the side walls disposed at
an angle other
than normal to the upper surface of the base of the element;
an overlay layer which engages the at least one element via the at least one
formation.
According to one embodiment when two elements having one formation are abutted
the
upper surfaces and adjacent walls of each element combine to define a void
recess
which receives either a void former or overlay concrete.
According to one embodiment, the overlay layer spans between the plateaus of
each said
formations closing said recess thereby forming voids in said slab. The system
is
preferably used in the construction of a composite suspended beam and floor
slab
assembly. The voids improve the structural performance of the element both
during
construction carrying wet concrete and in the permanent composite structure.
They also
provide through passages for services. Preferably, the structural elements are
formed in
a mould which includes a steel base which imparts a smooth high quality
surface finish
to the element soffit. The voids reduce the weight of the element. The
structural
geometry of the formations allow more efficient use of concrete in that the so
formed
composite has a large compression flange at the top of the formations
iinparting to the
composite a high strength to weight ratio for a given span. The elements may
therefore
be much thinner for a given span than a prior art conventional slab. In one
embodiment
the side walls of the formations are generally planar and are inclined at an
angle less
than 90 degrees and around 40 to 70 to the upper surface of the element. The
structural
element has a versatility allowing the voids to be filled with polystyrene,
cement or
concrete Alternatively the voids may be retained with empty spaces.
The base portion is preferably reinforced with fabric or steel rods and/or
reinforcing fibres and may be pre -stressed respectively by pre tensioning or
post-
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tensioning. Alternatively, the element may be non stressed. In one embodiment
the top of
the formations receive and support a sheet of material. In use, the building
slab elements
may be supported on walls or transverse beams arranged to define a floor. Gaps
between
adjacent like elements are sealed with part of a composite layer. The void
spaces in each
element are sealed and an in situ layer is poured over the plateaus of each
formation.
BRIEF DESCRIPTION OF DRAWINGS
The present invention will now be described according to a preferred but non
limiting
embodiments and with reference to the accompanying illustrations in which:
Figure 1 shows an end view of a pre-cast concrete element incorporating an
intermediate
formation and adjacent voids filled with a polystyrene filler.
Figure 2 shows an end view of a pre-cast concrete element of figure 1
incorporating an
intermediate formation and adjacent empty voids typically used as a spine
beam.
Figure 3 shows an isometric view of the spine beain of Figure 2;
Figure 4 shows a cross sectional view of a composite beam including the
element of
figure 1 and including an overlay layer.
Figure 5 shows a cross section of a composite beam comprising an abbreviated
element
supporting associated elements and an overlay layer disposed over formation
plateaus
and associated elements.
Figure 6 shows a perspective view of a banded beam flooring system having two
columns with drop panels and two columns without drop panels and including
elements
arranged for co operation with support columns. An arrangement of temporary
propping
for this floor system is also shown.
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Figure 7 shows an enlarged abbreviated end view of a portion of a pre-cast
concrete
element with alternative formation geometry including shoulders.
Figure 7a shows an enlarged abbreviated end view of a portion of a pre cast
concrete
element with alternative formation geometry including radiused walls.
Figure 8 shows an enlarged cross sectional view of a portion of a pre-cast
concrete
element with alternative formation geometry including an abbreviated taper.
Figure 9 shows an enlarged cross sectional view of a portion of a pre-cast
concrete
element with alternative formation geometry including an abbreviation in the
taper near
its plateau.
Figure 10 shows an enlarged cross sectional view of a portion of a pre-cast
concrete
element with alternative formation geometry including an abbreviation in the
taper near
its plateau and radiused junction.
Figure 11 shows an enlarged cross sectional view of a portion of a pre-cast
concrete
element with alternative formation geometry including a radiused junction.
Figure 12 shows an enlarged cross sectional view of a portion of a pre-cast
concrete
element with alternative formation geometry including abutment shoulders and a
radiused junction.
Figure 13 shows a cross sectional elevation of a composite slab including a
structural
element and a reinforced overlay layer and including an edge profile on a
formation
which transmits shear to an adjacent member at right angles to it.
Figure 14 shows a sectional view through the end of the perpendicular member
of figure
13 showing the method of transmission of shear at an undercut to the ribs of
this
member.
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Figure 15 shows a perspective view of a flooring assembly which allows
production of a
flat plate structure or a flat slab with drop panels including an array of
structural
elements supported by columns according to one embodiment. In this arrangement
the
soffits of all the precast elements are in the same plane.
Figure 16 shows a sectional elevation view of a composite slab flooring
assembly of the
type shown in figure 15 including structural elements and composite slab
finish regime
about support columns. -
Figure 17 shows an enlarged sectional elevation view of the composite slab
flooring
assembly including structural elements and composite slab finish regime of
figure 16.
Figure 18 shows according to an alternative embodiment a perspective view of a
composite slab flooring assembly including precast structural elements and
composite
slab finish regime with cast in situ band beams about support columns.
Figure 19 shows a sectional elevation view of the composite slab flooring
assembly
including structural elements and composite slab finish regime of figure 18.
Figure 20 shows an enlarged sectional elevation view of part of the assembly
of figure
19 including structural elements and composite slab finish regime about a
support
column.
Figure 21 shows an enlarged sectional elevation view of the composite slab
flooring
assembly including structural elements and composite slab finish according to
the regime
of figure 6.
Figure 22 shows an enlarged view of a part of the assembly of figure 21.
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Figure 23 shows a cross sectional view of a shear junction between the side of
a
composite slab and support column or precast concrete wall..
Figure 24 shows a sectional view of a shear junction 0 between a composite
slab
assembly and a support wall/ column with alternative orientation of structural
element.
DETAILED DESCRIPTION
Figure 1 shows an end view of a pre-cast concrete element 1 comprising a base
2 having
an underside surface 3 and upper surface 4. Element 1 further comprises
formations 5, 6
and 7 which define void spaces 8 and 9. Void 8 is defined by upper surface 4
and side
walls 10 and 11. Void 9 is defined by upper surface 4 and side walls 12 and
13. In the
embodiment of figure 1 voids 8 and 9 are filled with polystyrene or similar
lightweight
material which maintains a lighter weight than an equivalent element with
voids filled
with concrete or cement. Element 1 typically includes reinforcing ( not shown)
in base 2,
typically reinforced with steel bars or prestressed reinforcement above which
two or
more polystyrene void formers 14 and 15 preferably in the shape of an
isosceles
trapezium are located.
Formations 5, 6 and 7 comprise ribs with longitudinal extent and whose width
increases
as the distance from surface 4 increases so that there is more material at the
top of the
formations 5, 6 and 7. The embodiment of figure 1 shows a symmetrical
intermediate
formation 6 which is dove tail ( or inverted trapezoidal) creating voids which
are
trapezoidal. Increase in material at the top of the rib plateaus 16, 17 and 18
improves the
performance of the element in bending in that it creates a compressive flange
of higher
capacity and which is more eccentric to the tensile reinforcement. This
increase in
bending capacity is in comparison to a prior art element having a rectangular
formation
were employed. Ideally walls 11 and 12 of formation 6 for instance will be
disposed at
an angle to surface 4 of base 2 of otller than 90 degrees. In the example of
Figure 1 the
side walls of the ribs extend at an angle of about 50 although the angle
could ideally fall
within the range of about 45 to 70 .
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Figure 2 shows an end view of the pre-cast concrete element 1 of figure 1 with
corresponding numbering and incorporating an intermediate formation 6 and
adjacent
empty voids 8 to 9 with no void formers. The arrangement of figure 2 would
typically be
used as a spine beam. Figure 3 shows an isometric view of the spine beam of
Figure 2
with corresponding numbering.
Figure 4 shows a cross sectional view of a composite beam assembly 20
including an
element 21 which is similar to element 1 of figure 1. Element 21 comprises
formations
22, 23, 24 and 25 which define void spaces 26, 27 and 28. Void 26 is defined
by upper
surface 29 and side walls 30 and 31. Voids 27 and 28 are similarly defined. In
the
embodiment of figure 4 voids 26, 27 and 28 are filled with polystyrene which
maintains
a lighter weight than an equivalent element with voids filled with concrete or
cement.
Element 21 includes tensile reinforcing comprising a series of longitudinally
extending
reinforcing steel rods 32 which may, as required, be pre-tensioned, post-
tensioned or
unstressed depending on the application and the requirements for element 21 .
Element
21 includes three polystyrene void formers in respective voids 26, 27 and 28.
Formations 22, 23, 24 and 25 comprise ribs of longitudinal extent and whose
width
increases as the distance from surface 29 to respective plateaus 33, 34, 35
and 36 so there
is more material at the top of the formations 22, 23, 24 and 25 . The
embodiment of
figure 4 shows symmetrical intermediate formations 23 and 24 which are dove
tail ( or
inverted trapezoidal) creating voids which are trapezoidal. Also in base 37 of
element 21
is a sheet of mesh, loose reinforcement or fibre reinforced concrete 39 to
provide
resilience to handling of the element 21 and help resist cracking and breaking
of the
element. Typically element 21 would be manufactured in a mould or extruded.
Where
the element is moulded, it is preferred that a mould having a steel floor is
used so that
the underside or soffit 40 of base 37 remains smooth. Typically, steel bars 32
will be
pre-stressed along with an untensioned fabric 39. An approximately 20mm to
80mm
layer of concrete is poured into the base of the mould so as to cover the
reinforcing steel
bars 32. Void formers are then put into position on the top of the base in
voids 26, 27
and 28 and the remaining concrete is poured to bring the height of the rib
formations ribs
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up to the top of the void formers. The concrete is then allowed to set before
the
composite is removed from the mould. Should reinforcement 20 be pre stressed ,
then it
is either pre tensioned before the casting of elements 37 and 22, 23, 24 and
25 or post
tensioned after the concrete achieves sufficient strength. Once element 21 is
erected in its
final position in the structure, a relatively thin overlayer 42 is poured over
element 21
evenly supporting the overlayer which adheres to plateaus 33, 34, 35 and 36.
As an
alternative embodiment overlay layer 42 may be factory cast prior to site
installation of
the composite.
Alternatively, element 21 may be extruded through a die using a relatively
stiff
concrete mix. Extrusion is the preferred method where polystyrene void formers
are
not used, although either method may be used. In use, with reference to Figure
4, a
plurality of concrete elements 21 are placed on top of beams or walls (not
shown) and a
layer of reinforcement 43 is placed on top of the elements 21 as required. The
element
21 is then covered with a relatively thin in situ layer of concrete 42.
Because of the
design of the elements 21 and in particular, the thickening of the ribs distal
from the
base 37, element 21 performs well in bending and can be much lighter than
other
known pre-formed elements. Thus, the system uses less concrete which reduces
materials cost. Also, for a building of given height, the building will weigh
less and this
allows the columns and footings to be less extensive and consequently cheaper.
Also as
the floors are thinner, the space saved may be equivalent to one or more extra
floors in a
building.
Figure 5 shows a cross section of a composite beam assembly 50 including
element 51
and an overlay layer 66 disposed over formation plateaus 53, 54 and 55 of
formations
56, 57 and 58 which define voids 59 and 60. Located and bearing on plateau 53
is a
beam element 63 . Located and bearing on plateau 55 is a second element beam
64.
Because the base 49 of the element 51 is relatively thin, it is possible to
place
reinforcing 67 inside the voids close to the base 49 of the resultant spine
beam ( element
51) to resist bending of the beam. It is also possible, to place reinforcement
65 at the top
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of the beam when concrete overlay layer 66 is poured in situ into the spine
beam 51 and
over adjacent elements 63 and 64.
In a variant of the element cross-section shown in Figures 1 to 5, the
rib/formation
shape of the elements may be varied. Also, the representations shown in
figures 1-5 are
of indefinite width and it will be appreciated that the elements may include
more or less
than the numbers of formations/ribs illustrated.
Figure 6 shows an abbreviated section of a flooring assembly including
elements
employed as formwork prior to pouring of an overlay layer ( not shown) but
analogous
to overlay layer 66 of figure 5. Shown a perspective view of a banded beam
flooring
system 70 having two columns with drop panels and two columns without drop
panels.
The system shown includes elements arranged for co operation with support
columns.
An arrangement of temporary propping 99 for this floor is also shown. Banded
beam
flooring system 70 includes elements arranged for co operation with support
columns 71,
72, 73 and 74. The arrangement of figure 6 provides formwork of elements which
will
provide a base for a composite slab and band beam system similar to the
arrangement of
figure 4 in the slab spanning direction and figure 5 in the band spanning
direction.
System 70 comprises transverse elements 75 of a first span length determined
according
to structural design requirements. Elements 76 on the outside of columns 71
and 72 and
columns 73 and 74 are abbreviated. Transverse elements 75 are supported at
their
ends on longitudinal spine beam elements 77 and 78. Elements 78 on the outside
of
columns have been abbreviated for clarity. Figure 6 shows the assembly of
panels prior
to the placement of reinforcement along the spine beam elements 77 and 78 and
over the
entire assembly including elements 75 and 76 and the placement of a concrete
layer over
the entire assembly. In this arrangement, conventional formwork is used to
form the drop
panel 79.
It should be noted that Elements 77 and 78 may or may not incorporate void
formers.
There are two different junctions shown between elements 77 and 78 and the
columns
71, 72, 73 and 74. Columns 71 and 72 are either cast with the floor or are
precast and
are provided with shear keys and the spine beams 77 and 78 abut the columns.
In the
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second form there is a drop panel 79 formed by conventional formwork which
connects
the spine beams and adjacent slab beams to the column.
The in situ panel 79 produced with conventional formwork may be terminated at
the
underside plane of the precast panels 77 and 78 or may project below the
general floor
soffit. Throughout the specification the term soffit will betaken to mean an
underside
surface of a structural member. Temporary supports 99 may be required as shown
to
support the whole floor assembly while concrete is being poured and until it
acquires
sufficient strength.
Figure 7 shows an enlarged abbreviated end view of a portion of a pre-cast
concrete
element 80 comprising a base 81 having an underside surface 82 and an upper
surface
83. Extending from upper surface 83 are dove tail formations 84 and 85 which
define
void space 86. Wall 87 of formation 84 terminates at upper plateau 88 in
shoulder 89.
Likewise wal190 of formation 85 terminates at upper plateau 91 in shoulder 92.
A sheet
93 of fibre cement or the like can be rested on shoulders 89 and 92 spanning
void space
86. This obviates the need to include a void former in void space 86.
Formations 84 and
85 are generally in the shape of an inverted trapezium.
Figure 7a shows an enlarged abbreviated end view of a portion of a pre cast
concrete
element with alternative formation geometry including radiused walls. In this
embodiment, element 94 comprises a base 95 having an underside surface 96 and
an
upper surface 97. Extending from upper surface 97 is formation 98 including
walls 98a
aild 98b which are substantially S shaped each with opposing radii of
curvature.
Figure 8 shows an enlarged abbreviated end view of a portion of a pre-cast
concrete
element 100 with alternative formation geometry. In this embodiment, element
100
comprises a base 101 having an underside surface 102 and an upper surface 103.
Extending from upper surface 103 is formation 104 including walls 105 and 106.
Walls
105 and 106 each have a first portion 108 disposed at an angle normal to the
plane of
surface 103 and a portion 107 at an angle to surface 103 other than normal.
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Figure 9 shows an enlarged abbreviated end view of a portion of a pre-cast
concrete
element 110 with alternative formation geometry. In this embodiment, element
110
comprises a base lll having an underside surface 112 and an upper surface 113.
Extending from upper surface 113 is formation 114 terminating in plateau 115
and
including walls 116 and 117. Walls 116 and 117 are disposed at an angle less
than
normal to surface 113 and terminate in a perpendicular abbreviation 118.
Figure 10 shows the embodiment of figure 9 with a radiused junction 119
between
surface 113 and formation 114.
Figure 11 shows an enlarged end view of a portion of a pre-cast concrete
element 120
with alternative formation 121 geometry including a radiused junction 122
between base
123 and formation 121.
Figure 12 shows an enlarged end view of a portion of a pre-cast concrete
element with
alternative formation geometry including abutment shoulders and a radiused
junction.
Element 130 comprises a base 131 having an underside surface 132 and an upper
surface
133. Extending from upper surface 133 are dove tail formations 134 and 135
wllich
define void space 136. Wall 137 of formation 134 terminates at upper plateau
138 in
shoulder 139. Likewise wall 140 of formation 135 terminates at upper plateau
141 in
shoulder 142. A sheet 143 of fibre cement or the like can be rested on
shoulders 139 and
142 spanning void space 136. This obviates the need to include a void former
in void
space 136. Wall 137 terminates in a radiused portion at the junction of
formation 134
and base 131. Likewise wall 140 of formation 135 terminates in a radiused
portion 144 at
the junction of formation 135 and base 131.
An advantage of the above elements is that where a floor is required to resist
bending in a lateral as well as a longitudinal direction, and/or to locally
enhance the
elements shear capacity, it is possible to remove portions 143 of fibre
reinforced cement
formwork where present and simply fill the voids with concrete in those areas
where
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such lateral resistance to bending and/or shear capacity, is required.
Similarly it is
possible, though not as convenient to remove the void formers of Figure 4 in
order to
allow the abovementioned local improvements of transverse bending and /or
shear
capacity to be implemented.
Figure 13 shows a cross sectional elevation of a composite slab assembly 150
including
a structural element 151 and a reinforced overlay layer 152 and including an
edge profile
153 on a formation 154 which transmits shear to an adjacent abutment member
155. The
arrangement of figure 13 is an example of one form of engagement between
element 151
and an abutting support. Element 151 includes dovetail formations 156 as
described
earlier defining voids 157. Edge profile 153 of formation 154 opposes abutment
155 and
is arranged to transmit shear forces between element 151 and abutment element
155.
Overlay layer 158 is laid over plateaus 159 of formations 154 and is
preferably
reinforced with a reinforcing steel 160. Element 155 has its void formers
terminated a
short distance from its end to allow overlay in turn a shear connection with
the edge
profile 153 of Element 151. In this way a concrete layer 158 to be poured
around the
dovetail ribs 144 of element 155 and to thus create a shear connection between
the
overlay concrete 158 and the dovetail ribs 144 and in turn a shear connection
is made
between elements 155 and 151 as indicated by arrows 161 and 162.
Figure 14 shows element 155 rotated 90 degrees from its orientation in figure
13.
Element 155 is incorporated with overlay layer 158 which forms a composite
beam
structure. Layer 158 co operates with element 155 via dove tail formations 144
which
define trapezoidal voids 147. Void 147 includes walls 145 and 146 which
receive shear
forces transmitted by undercasting via overly layer 158 as shown by arrows 148
and
149. This structural effect is repeated in each void between formations 144.
Figure 15 shows a perspective view of a flooring assembly including an array
of
structural elements supported by columns according to one embodiment. Shown is
a
flooring system 170 including elements arranged for co operation with support
columns
171, 172 , 173 and 174. The arrangement of figure 15 provides a formwork of
elements
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which will provide a base for a composite slab similar to the arrangement of
figures 4
and 5. System 170 comprises transverse elements 175 of a first span length
determined
according to structural design requirements. Elements 176 on the outside of
columns 171
and 172 and columns 173 and 174 are abbreviated for clarity. Elements 178 on
the
outside of columns have been abbreviated for clarity Transverse elements 175
are
supported at their ends next to and with their soffits ( underside surface) in
the same
plane as the soffits of the longitudinal spine beam elements 177 and 178.
Elements 175
may be temporarily supported independently of the spine elements 177 and 178
or may
be supported by temporarily connecting them to spine elements 177 and 178.
Figure 15
shows the assembly of panels prior to the placement of reinforcement along the
spine
beam elements 177 and 178 and over the entire assembly including elements 175
and
176 and the placement of a concrete layer over the entire assembly. In this
arrangement,
conventional formwork is used to form the drop panel 179. It should be noted
that
Elements 177 and 178 may or may not incorporate void formers. The structure
produced
by this assembly of panels has a flat and planar soffit over the entire
underside of the
floor. The in situ panel 179 produced with conventional formwork may be
terminated at
the underside plane of the precast panels 175, 176, 177 and 178 or may project
below the
general floor soffit.
Figure 16 shows a sectional elevation view of a column and composite slab
flooring
assembly of the type shown in perspective view Fig 15 taken perpendicular to
the spine
beams177 and 178. Assembly includes support columns 190 and 191 each
supporting
respective spine elements 192 and 193. Spanning therebetween are elements 194.
On
opposite side of column 190 and extending from spine beam element 192 is
element 195
abbreviated for clarity. On opposite side of column 191 and extending from
spine
beam element 193 is element 196 abbreviated for clarity. This arrangement
shows
the versatility and inter engagement of structural elements which on one hand
may be
used as a spine beam and on the other hand as transverse span beams. This also
demonstrates how the elements can be arranged as formwork in advance of
preparation
of a composite structural slab. This also demonstrates how all the precast
element may
be arranged with their soffits co-planar to produce a flat soffit. Elements
195, 192, 194,
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193 and 196 are overlaid with overlay layer 197 which completes the slab
composite and
floor assembly. Reinforcement has been omitted for clarity but it will be
appreciated by
persons skilled in the art that each representation of floor assembly shown
herein would
normally include design reinforcement in tensile regions of the composite and
to control
shrinkage cracking and to enhance the structure's shear capacity.
Figure 17 shows with corresponding numbering for corresponding parts an
enlarged
sectional elevation view of the composite slab flooring assembly including
structural
elements and composite slab finish regime of figure 16. This view also shows
overlay
layer 197. Void formers 187 have been terminated a short distance from the
respective
ends 185 and 186 of the panels 194 and 195 to allow the overlay concrete to
flow around
the dovetail ribs 188 and thus form a shear connection with the overlay
concrete 197
Spine beam element 192 includes an end formation 198 having an outer profile
199
which co operates with element 194 to establish a shear connection
therebetween.
Overlay layer 1971ocks element 192 to element 194 and assists in transmission
of loads.
Overlay layer 197 is in one embodiment supported by spine element 192 and
covers the
void formers or penetrates the voids ( not shown) when the void former is
absent in
elements 194 and 195 thereby completing the layered composite floor structure.
Voids 189 of spine element 192 will receive concrete from overlay layer 197
but in a
case where void formers are used, overlay layer will sit over ( bridge) voids
189.
Figure 18 shows a perspective view of a flooring assembly 180 including an
array of
structural elements supported by columns. Flooring assembly 180 includes
transverse
elements 240 arranged for co operation with support columns 181, 182 , 183 and
184.
The arrangement of figure 18 provides formwork for concrete to be supplied and
a base
for a composite slab similar to the arrangement of figure 15. Assembly 180
comprises
transverse elements 240 of a first span length determined according to
structural design
requirements. Elements 241 on the outside of columns 181 and 183 and elements
242 on
the outside of columns 182 and 184 are abbreviated for clarity. Elements 240
are
supported at their ends by longitudinal elements 243 and 244 which are cast in
situ on
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conventional formwork. Longitudinal beams 244 and 243 provide an abutment to
receive
elements 240, 241 and 242.
Figure 19 shows a sectional elevation view of a composite column slab flooring
assembly of the type shown in perspective view Fig 18. Figure 19 shows
according to an
alternative embodiment, a sectional elevation view of a composite slab
flooring
assembly 200 including structural elements and composite slab finish regime
about
support columns. Shown are support columns 201 and 202 each supporting
respective
cast in situ spine beams 203 and 204 which are formed with conventional
formwork.
Spanning between columns 201 and 202 the supply are elements 205. On opposite
side
of column 201 and extending from spine beam element 203 is element 206
abbreviated
for clarity. On opposite sides of column 202 and extending from spine beam
element
204 is element 207 abbreviated for clarity.
Figure 20 shows with corresponding numbering an enlarged sectional elevation
view of
the composite slab flooring assembly 200 of Fig 19 including structural
elements 205
206 and 203 and composite slab finish regime of figure 19.
Figure 21 shows a sectional elevation view of a completed composite column
slab
flooring assembly 210 of the type shown in the perspective view of Figure 6,
when a
section is taken through spine beams 77 and 78. Composite slab flooring
assembly 210
includes structural elements and composite slab retained about support
columns. Banded
beam flooring system 210 shows two columns 211 and 212 with drop panels
arranged
for co operation with the support columns. Flooring system 210 includes
transverse
elements 215 of a first span length determined according to structural design
requirements. Elements 216 on the outside of columns 211 and elements 217
outside
column 212 are abbreviated for clarity. Transverse elements 215 are supported
at their
ends on longitudinal beam elements 213 and 214. Overlay layer 218 is placed
over
element 215 and beam elements 213 and 214 to complete the floor slab
composite.
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Figure 22 shows an enlarged sectional elevation view of the composite slab
flooring
assembly 210 of figure 21 with corresponding numbering.
Figure 23 shows a cross sectional view of a shear junction 220 between a
composite
slab assembly 221 and support wall/ column 222. Column includes a recess 223
which
provides a key in lock for shear transmission at the junction 220. Composite
assembly
221 includes structural element 224 having a base 225 and extending therefrom
formations 226 defining voids 227. A reinforcing ferrule 235 is embedded in
column/wall 222 and engages reinforcing steel 228 which is embedded in overlay
layer
229 which lies over plateaus 230. Overlay layer 229 also fills recess 223 and
gap 232
between recess 223 and outer profile 233 of formation 234. The co operation
between
profile 233 and recess 223 when gap 232 is filled in with concrete from
overlay layer
229 results in transmission of shear between precast members 224 and column
222 as
indicated by arrows 235 and 236.
Figure 24 shows a sectional view of a shear junction 250 between a composite
slab
assembly 251 and support wall/ column 252. Column includes a recess 253 which
provides a key in lock for shear transmission at the junction 250. The void
formers of
composite assembly 251 are terminated a short distance from the end to
facilitate the
undercasting of concrete around the ribs 256 of assembly 251 to facilitate the
transmission of shear in a manner alike to that demonstrated in figures 13 and
14.
Composite assembly 251 includes structural element 254 having a base 255 and
extending therefrom formations 256 defining voids 257. A reinforcing ferrule
258 is
embedded in column/wall 252 and engages reinforcing steel 259 which is
embedded in
overlay layer 260 which lies over plateaus 261. Overlay layer 260 also fills
recess 253
and gap 262 between recess 253 and the void around the outer profile 254 at
the end of
element 251 and outer profile of formation 263. The co operation between
recess 253
and profile formation 263 when gap 262 is filled in with concrete from overlay
layer 260
results in transmission of shear between pre cast members 254 and column 252
as
indicated by arrows 264 and 265.
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The versatile use of the structural elements described above provides distinct
advantages over existing pre- formed concrete elements . The first advantage
is that it is
relatively easy to put services through the floor in voids between the
formations / ribs of
the elements. Secondly, the elements can be formed in a mould having a steel
base
which allows a high quality finish to the soffit of the element.
Thirdly, the provision of the voids reduces the weight of the element and the
shape of the formations/ ribs provides more concrete at the upper reaches of
the
composite thereby providing a large compression flange at the top of the ribs
where it is
required which allows the elements to be much thinner for a given span.
Fourthly, the void formers may be removed to allow overlay concrete to flow
around ( undercast) the dovetailed formations and engage them for shear
connection.
This allows these units to be readily joined to adjacent structural elements
with in situ
concrete producing both neat appearance and a joint which is readily fire
rated as
opposed to the external steel connections often employed which need to be
separately
fire protected.
The structural elements which form the composite floor slab have the capacity
for long
span without intermediate support both during construction when supporting wet
concrete and when integral with the completed composite structure. Element
dimensions
including depth, rib shape, rib spacing, panel width, and the plan shape of
the panel may
be varied according to design requirements. For instance, wide panels are not
restricted
by fixed extrusion equipment allowing quick erection of floors with fewer
joints.
The elements may be tapered relative to their longitudinal axis, for instance
in a case
where the elements form a horizontal radiused corner. Reinforcement in both
the tensile
and compression regions may be varied according to design requirements. No
extrusion
tools are needed to fabricate panels and the formation/ rib shape and height
is largely
determined by the void former shape and size which may be readily changed. The
elemer-ts may be fabricated as plain reinforced, pre tensioned reinforced or
post
tensioned reinforced members allowing for flexibility of manufacture dictated
by design
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requirements. Since the elements are lightweight pre cast elements, this
allows
economic transport and efficient lift by crane.
The use of lightweight elements allows for more lightly loaded columns and
consequently smaller footings. Shallow structural depth allows more efficient
buildings
saving on the lengths of services, facades, and allows for more useable
building space in
areas where there is a height restriction.
Each element has a smooth flat soffit over whole panel width which can be
treated as a
final finish with no mandatory need for separate suspended ceilings are
claddings. The
flat soffit combined with shallow structural depth and lack of ceiling space
realizes
economic operation of air conditioning with no wasted "dead air" between ribs
or in
ceiling spaces. A further advantage of the element is the access to voids
during
construction allowing the installation of services in the void areas and
through the
relatively thin base slab of the composite. The dovetail formations with void
blockouts removed provide shear connections to adjacent elements which are
both neat,
easily made and fire resistant as opposed to the conventional methods of other
pre cast
systems which either require bulky expensive and unsightly corbels or exposed
steelwork which requires fire protection. Very little tooling required for the
manufacture
of the elements which means a low cost set up, manufacture. Also mobile
manufacturing plants are economically feasible. The elements may also be
manufactured
on the construction site. Finally, irrespective of whether the elements are
manufactured
with air voids or voids filled with an insulating polystyrene, a floor is
created which has
optimal sound, heat and fire separation properties.
It will be appreciated by persons skilled in the art that numerous variations
and/or
modifications may be made to the invention as shown in the specific
embodiments
without departing from the spirit or scope of the invention as broadly
described. The
present embodiments are, therefore, to be considered in all respects as
illustrative and not
restrictive.
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