Throughout this specification, unless the context requires otherwise, the word “comprise” and variations such as “comprises”, “comprising” and “comprised” are to be understood to imply the presence of a stated integer or group of integers but not the exclusion of any other integer or group of integers
Throughout the specification unless the context requires otherwise, the word “include” or variations such as “includes” or “including”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
The present invention relates to a truss, a permanent formwork element incorporating a plurality of such trusses, and a slab incorporating such a permanent formwork element. The present invention also relates to a method of making such a permanent formwork element and to a method of making such a slab. The slab may be used in horizontal permanent formwork, such as flooring.
Any discussion of background art, any reference to a document and any reference to information that is known, which is contained in this specification, is provided only for the purpose of facilitating an understanding of the background art to the present invention, and is not an acknowledgement or admission that any of that material forms part of the common general knowledge in Australia or any other country as at the priority date of the application in relation to which this specification has been filed.
Various types of reinforcing bar trusses have been used for constructing concrete slabs for floors. For example, reinforcing bar trusses are typically made from metal, e.g. reinforcing steel, so as to provide reinforcing strength in precast concrete permanent formwork in floor construction. However, these precast concrete permanent formwork elements are cast into bespoke moulds depending on the shape required. These moulds are labour intensive and time consuming to set up. This results in high manufacturing costs.
In accordance with one aspect of the present invention, there is provided a truss comprising
an elongate metal strip having a first longitudinally extending edge and a second longitudinally extending edge, the first longitudinally extending edge being a substantially serrated edge such that apexes are formed along the first longitudinally extending edge, and
an elongate bar connected to the elongate metal strip at the apexes of the elongate metal strip,
such that openings are formed between the elongate bar and the serrated edge of the elongate metal strip.
Preferably, the elongate bar is connected to the metal strip by connecting the apexes to the elongate bar.
Preferably, the elongate bar is connected along its length to the metal strip such that the elongate bar is located substantially central to the first longitudinally extending edge of the elongate metal strip.
Preferably, the elongate bar is connected to the metal strip by welding the apexes to the elongate bar.
Preferably, the openings are substantially triangular in shape.
Preferably, the second longitudinally extending edge is rounded.
In accordance with another aspect of the present invention, there is provided a permanent formwork element comprising
a plurality of trusses, as herein before described, arranged in a substantially parallel arrangement, and
at least one sheet of material having trenches formed therein, the trenches being in a substantially parallel arrangement,
wherein the elongate metal strips are partly fixedly positioned in respective trenches such that second longitudinally extending edges of the elongate bars are positioned in the trenches.
Preferably, the elongate metal strips of the plurality of trusses are partly fixedly positioned in respective trenches such that the openings are substantially exposed above the surface of the sheet.
Preferably, the elongate metal strips of the plurality of trusses are partly fixedly positioned in respective trenches by adhesive.
Preferably, the edges of the trenches adjacent to the surface of the sheet are chamfered.
Preferably, the sheet is made of cementitious based material.
In accordance with another aspect of the present invention, there is provided a method of making a permanent formwork element incorporating a plurality of trusses as herein before described, comprising
providing at least one sheet of material having trenches formed therein, the trenches being in a substantially parallel arrangement,
inserting the second longitudinally extending edges of the elongate metal strips into respective trenches to position them in the trenches,
fixing the elongate metal strips in the trenches.
Preferably, fixing the elongate metal strips in the trenches comprises using adhesive to fix the elongate metal strips.
In accordance with another aspect of the present invention, there is provided a method of making a slab comprising calculating the expected deflections in a slab to comprise a permanent formwork element, as herein before described, and cementitious filler material to cover the permanent formwork element,
machining timber strips to have profiles that are mirror images of the profiles of the calculated expected deflections,
fixing the timber strips to supports,
positioning the permanent formwork element on the supports,
pouring cementitious material over the permanent formwork element and allowing the cementitious material to set, and
removing the supports.
The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
In
The elongate metal strip 10 has a first longitudinally extending edge 14 and a second longitudinally extending edge 16. The first longitudinally extending edge 14 and the second longitudinally extending edge 16 are transversely opposed to one another.
The first longitudinally extending edge 14 is in the form of a substantially serrated edge (i.e. a sawtooth-like edge) such that apexes 18 are formed along the first longitudinally extending edge 14.
The serrated edge at the first longitudinally extending edge 14 of the elongate metal strip 10 is formed by cut-out sections at the first longitudinally extending edge 14.
The elongate bar 12 is connected, along its length (i.e. longitudinally), to the elongate metal strip 10 at the apexes 18 of the metal strip 10. This may be done by welding. For example, using spot, resistance, mig, tig or arc welding methods. Typically, the elongate bar 12 is substantially central to the first longitudinally extending edge 14, as best seen in
Openings 20 are formed between the elongate bar 12 and the serrated edge of the metal strip 10.
The elongate bar 12 may be connected to the elongate metal strip 10 by welding the apexes 18 to the elongate bar 12.
The openings 20 between the elongate bar 12 and the serrated edge of the metal strip 10 may substantially triangular in shape.
The second longitudinally extending edge 16 of the elongate metal strip 10 may be rounded. This is best seen in
The elongate bar 12 may be a concrete reinforcing bar, circular in profile. Concrete reinforcing bars are typically used for reinforcing concrete.
The elongate bar 12 may be made of steel.
To protect against corrosion, the truss 1 may be galvanized and coated in a solid two-part structural polymer. This dual treatment (galvanizing and polymer coating) provides two layers of protection against corrosion.
The truss 1 may be used to make a permanent formwork element.
In
The sheet 52 may be cementitious board material. Typically, a plurality of such sheets 52 are used to make a permanent formwork element 50 because cementitious sheets are generally made in sizes smaller than is required to make a permanent formwork element 50, as such sizes permit easier manufacture and handling of the cementitious sheets.
Trenches, or channels, 54 are formed in the sheets 52. The trenches 54 are best seen in
As previously described herein, typically, a plurality of such sheets 52 are used to make the permanent formwork element 50. For example, the two (longitudinally extending) permanent formwork elements 50 shown in
Elongate metal strips 10, of the trusses 1, are partly positioned in respective trenches 54. Elongate metal strips 10 extend in respective elongated trenches 54 that are formed by end abutting sheets 52. Thus, for example, in the permanent formwork elements 50 shown in
The trenches 54 are formed to have a depth such that the metal strips 10 are positioned in the trenches 54 up to substantially the openings 20. That is, the maximum depth to which the metal strips 10 are positioned in the trenches 54 is such that the opening 20 are substantially exposed above the surfaces of the sheets 52. Referring to
The part of each elongate metal strip 10 that is positioned in trenches 54 may be fixedly positioned therein by adhesive 56, as best seen in
The rounded second longitudinally extending edge 16 facilitates insertion of the elongate metal strips 10 into the trenches 54. In addition, the edges of the trenches 54, adjacent to the surface of the sheet 52, are formed with chamfered edges 58 that taper inwardly from the surface of the sheet 52 such that the openings of the trenches 54 are wider than the lower part of the trenches 54. This arrangement may be seen, for example, in
The combined sheets 52 may be of any suitable dimensions. Typically, the maximum size is 2.5 metres by 12 metres. Similarly, the elongate bars 12 may be of any suitable dimensions, as required by the structural requirements of the project. Typically, this is in the range of between 8 mm diameter and 20 mm diameter.
Permanent formwork elements 50 may be transported onsite, where construction of the building is being undertaken. The permanent formwork elements 50 are installed in position, with the trusses 1 uppermost, to construct a floor of the building.
The longitudinally extending side edges 22 of the sheets 52 are provided respectively with a tongue 60 and groove 62, which are shown in
After permanent formwork elements 50 are installed, the concrete (or other cementitious filler) is poured over the permanent formwork elements 50 to cover the trusses 1 by the required depth, with the concrete (or other cementitious filler) passing through the openings 20 such that the trusses 1 are embedded in the concrete (or other cementitious filler). Once the concrete (or other cementitious filler) sets, a composite slab is formed. This forms the floor section in the building 110.
The permanent formwork element 50, according to the present invention, may span relatively large spans with deflections in the permanent formwork elements 50 within safe ranges. The sheets 52 and the portions of the elongate metal strips 10 that are fixed in the trenches 54 act together as one flange-like element of the composite slab permanent formwork element slab, whilst the serrated sections of the elongate metal strips 10 acts as a web-like element in the composite slab permanent formwork element, and the elongate bars 12 act as the other flange-like element.
The slab in accordance with the present invention may span relatively larger distances with a relatively thinner sheet 52. The arrangement of the bottom tensile sections of the elongate metal strips 10, such that they are surrounded by a solid two-part structural polymer adhesive on both sides, and the second longitudinally extending edge 16 along the entire lengths of the elongate metal strips 10 within the trenches 54 of the sheets 52, greatly enhances their ability to resist corrosion in situations where corrosive contaminants such as water, salt, carbon dioxide, oxygen and other corrosive contaminants might ingress the suspended slab and cause corrosion particularly in coastal areas and where the elements are exposed such as external balconies, stairs and carparks. The cementitious material of the concrete (or other cementitious filler material) also greatly resists the corrosion of the elongate bar 12 by offering typically 20 mm of cover (which can be varied, as required) in concrete (or other cementitious filler material) to the tensile concrete reinforcing bar 12.
During temporary construction loading and concrete placement in mid-span between primary supports 100, the respective portions of the web-like elements of the trusses 1 that are submerged in the trenches 54, as shown by distance D in
After the concrete sets and the falsework (e.g. temporary beams 100 and upright members 102) is taken away, the elongate member 12 of the truss 1 goes into tension in the long term and functions as a tensile reinforcing bar in reinforced concrete. Generally, cementitious materials have relatively poor performance in tension. Therefore, bringing galvanized and polymer coated & protected steel (namely, the trusses 1) into the tensile zone will increase span capacities (
Due to the superiority of the spanning distance and the structure of the permanent formwork elements 50, the thickness of the sheets 52 may be reduced, for example, sheets 52 that have a thickness of 18 mm (instead of 24 mm) may be used, which is a 33% reduction, and yet it may still be possible to increase the primary spacing of the falsework supports from 1200 mm to 1675 mm which is a 39.5% increase in spacing of the primary members for say a typical 200 mm thick concrete slab.
The bottom of reinforcing bar 12 of truss 1 may be used to easily change the concrete cover distance from typically 20 mm to 60 mm between the surface of the permanent formwork sheet 52 and the bottom of the elongate bar 12 by adjusting the height of the apexes 18. This may be automatically done during the manufacturing process such that the desired height of the apexes 18 is achieved.
The truss 1 may be made with any required sized reinforcing bar (as the elongate bar 12) off a coil typically from N8 to N20 (8 mm diameter to 20 mm diameter) which may result in typically no extra main directional reinforcing bar being required in the direction of the main span for a one-way spanning slab as the reinforcing bar in the composite truss 1 is the main elongate bar 12.
Since the truss 1 is spaced correctly during the manufacturing process, sometimes no distribution reinforcing steel in the opposite direction is required. Similarly, tensile steel is required only over supports under the slab. Steel fibres are used to control cracking in the concrete. This results in a much less labour intensive installation or less reinforcing steel and reduces costs significantly.
The trusses 1 be placed at any desired spacing in the sheets 52 to suit the permanent formwork element slab spans because of the way the trenches 54 are milled into sheets 52. Typically, this ranges from 150 mm to 300 mm spacing but may be smaller or greater depending upon the specific engineering requirements for the installation.
Another feature of the present invention described herein is the ability of the individual sheets 52 to be tongue and grooved, or ship lap joint and adhered together using adhesive and or mechanical fasteners to form one large permanent formwork element 50. This allows the whole permanent formwork element 50 to expand and contract as one which allows expansion joints to be placed where required in obscure locations that do not affect the architectural aesthetics of the building. This also allows the soffit of the element to be flushed (taped and jointed) at the joint instead of a glass reinforced skim coat being applied to the whole ceiling soffit. Further, as shown in
Another feature of the present invention described herein is the ability of the composite permanent formwork elements 50 to be arranged in a pre-calculated negative camber along the direction of the main span for a one way spanning slab. This is achieved by arranging the upright members 102 at different pre-calculated heights (
The wet concrete (or other cementitious filler material) to be laid on the permanent formwork elements 50 may have local falls to suit the expected deflection profile and to keep the concrete thickness reasonably constant. It also ensures that the top surface of the concrete does not overtly sag. Alternatively, the concrete can be laid flat as traditionally. After the propping and back propping is taken away and the suspended slab is loaded, the concrete surface on top will sag a little. Floor levelling compound can then be used to fill the valleys resulting in a concrete slab that is flat on top and flat on the bottom with fully tensioned elongate bars 12. Typically, around 85% of a slab's deflection is from the self-imposed weight. By cambering the soffit of the slab negatively we can arrest around 85% of deflection.
The simple one-way spanning slab deflection profile can be approximated using a simple slab deflection profile. However, when a designer wishes to design a 2-way spanning slab a Finite Element Analysis software is typically employed to economize concrete thickness and reinforcing bar rates. The reinforcing bar rate refers to the total cross-sectional area of the reinforcing bars in a slab relative to the total cross-sectional area of the slab. Depending on other elements around the slab, the actual expected deflections of the slab may vary greatly. These various deflections can be predicted using Finite Element Analysis computer programs. These are complex mathematical calculations of the slab element broken into thousands of smaller parts. An example of the output is shown in
As can be seen in
However, according to the present invention, the manner in which excessive deflections are dealt with is to profile the actual expected deflections of the slab where the primary formwork support will be located. By taking a cross section through the slab model, which shows the expected deflections at the planned locations of the primary supports, it is possible to identify the amount by which the slab will deflect. That calculated cross-section data is then used in a computer program (for example, a CAD/CAM program) to machine timber strips such that they have profiles that are symmetrically opposite, or mirrored, to the calculated deflection profile. In this way, the profiles of the timber strips are mirror images of the calculated deflection profile of the slab, such that low regions in the calculated deflection profile of the slab are correspondingly raised regions in the profile of the timber strips; and, conversely, raised regions in the calculated deflection profile of the slab are correspondingly low regions in the profile of the timber strips.
The timber strips are then fixed (e.g. by nailing) onto the top of the primary supports in a pre-planned sequence. The primary support tops are kept at a constant level. The net result is a topography of supports that is exactly opposite to the calculated expected deflections of the slab. The permanent formwork elements 50 are then craned onto this support topography. The connecting reinforcing bar is fixed in position. The fibre reinforced concrete (or other cementitious filler material) is poured onto the suspended deck. It is allowed to set, i.e. harden and strengthen. The falsework, i.e. the supports, below is removed. The slab begins to deflect downwards. As the reinforcing bar begins to come under tension, the deflection is stopped as the reinforcing bar strain hardens. Because the predicted deflection has been countered using opposite topography, the slab is expected to complete its initial deflection to a substantially flat position. This should also reduce the amount of cracking in the tensile zone of the concrete. Since there is an arch profile in the overall slab, the concrete at the bottom of the slab goes into compression instead of tension as the self-weight of the slab element takes effect. This provides a more advanced application of the negative camber application.
Whilst one or more preferred embodiments of the present invention have been herein before described, the scope of the present invention is not limited to those specific embodiments, and may be embodied in other ways, as will be apparent to a skilled addressee.
Modifications and variations such as would be apparent to a person skilled in the art are deemed to be within the scope of the present invention.
Number | Date | Country | Kind |
---|---|---|---|
2016905180 | Dec 2016 | AU | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/AU2017/051393 | 12/14/2017 | WO | 00 |