The present application claims priority from Australian Provisional Patent Application No. 2011901350 entitled “METHOD AND SYSTEM FOR FORMING A SUPPORT STRUCTURE” and filed on 11 Apr. 2011 whose contents are hereby incorporated by reference in their entirety.
The present invention relates to forming a hollow support structure. In a particular form, the present invention relates to forming a hollow support structure made from concrete for use as a pole in applications such as traffic and street lights, road signage and power transmission.
Circular hollow concrete poles are well known in applications ranging up to 30 metres in length. A process for constructing these hollow poles involves a spinning process where centrifugal force is used to spread a wet concrete mixture over the inner surface of a horizontally arranged mould. Concrete is fed into the slowly revolving mould which is then spun, squeezing out surplus water and evenly spreading compacted concrete over the inner surface.
While this method of forming hollow concrete poles has the benefit that the concrete wall of the pole is both dense and strong as a result of the centrifugal spinning action there are a number of serious drawbacks to this process. The first disadvantage is the lack of uniformity of wall thickness of the pole which can vary from one pole to another. The spinning process first involves the concrete being placed in the mould before it has been fully assembled. It is then left to an operator to decide precisely how much concrete is placed in any particular part of the mould which can lead to a degree of variability.
Where the pole is tapered, which is required in many standard applications such as a telecommunications or power transmission pole, when the mould is spun the concrete will not always relocate around and along the mould uniformly. In these circumstances, the concrete will as a result of the centrifugal force be distributed along the tapered profile to the place of least resistance at the thicker end of the mould. This results in a pole that will not have a uniform bending capacity because of the variation in wall thickness. Where the spinning process is used in combination with a prestressing process, the variation in thickness is likely to also cause the pre-stressed pole to distort immediately once it is removed from the mould.
A further and significant problem with a spun pole is the advent of a thick layer of laitance on the inner surface of the finished product. This layer is highly absorbent and can cause ground water to move up the inside surface of the pole and into the concrete. If this water contains any salt, the pH of the concrete will be reduced, thereby causing corrosion of any reinforcement of the pole.
In a first aspect, the present invention accordingly provides a method for forming an elongate support structure, the support structure having a central hollow portion, the method including:
In another form, attaching the external mould assembly includes first increasing the distance between first and second tensioning members with respect to each other by applying a separating force to provide a space between the first and second tensioning members to attach the external mould assembly.
In another form, the applying of a separating force also straightens the tensioning elements between the first and second tensioning members.
In another form, the concrete is injected from the bottom of the combined mould and core assembly.
In another form, the tensioning of the plurality of tensioning elements involves tensioning with respect to the first tensioning member acting as a dead end with respect to a live end corresponding to the location of the second tensioning member.
In another form, the external mould assembly bears the compressive load caused by tensioning the plurality of tensioning elements.
In another form, the step of forming a core assembly includes threading a reinforcing cage structure onto the elongate core member located between the first and second tensioning members.
In another form, the tensioning elements extend along the elongate core member external to the reinforcing cage structure.
In another form, the reinforcing cage structure includes one or more fittings to provide attachment points on the formed elongate support structure.
In another form, the method further includes arranging a reinforcing member along the elongate core member.
In another form, the reinforcing member is a helical wire that is extended along the elongate core member.
In another form, the helical wire is extended external to the tensioning elements.
In another form, the elongate support structure is a cylindrical pole and the central hollow portion is cylindrical.
In another form, the elongate support structure is tapered.
In another form, the method includes the step of after injecting concrete into the cavity the elongate core member is partially removed from the combined mould and core assembly.
In a second aspect, the present invention accordingly provides an elongate support structure formed by the method in accordance with the first aspect of the present invention.
In a third aspect, the present invention accordingly provides a combined mould and core assembly for forming an elongate support structure, the support structure having a central hollow portion, the mould and core assembly including:
In another form, the external mould assembly bears the compressive load resulting from tensioning the tensioned elements.
In another form, the combined mould and core assembly further includes a reinforcing cage extending along the elongate core member.
In another form, the combined mould and core assembly further includes a reinforcing member in the form of a helical wire extending along the elongate core member.
In a fourth aspect, the present invention accordingly provides a method for producing a hollow concrete pole having reduced laitance, the method including:
In another form, the combined mould and core assembly are oriented in a vertical configuration.
Illustrative embodiments of the present invention will be discussed with reference to the accompanying drawings wherein:
a is a part cross-section view of a spigoted jack housing attached to the spigoted arbor housing;
In the following description, like reference characters designate like or corresponding parts throughout the figures.
Referring now to
Referring now also to
As would be appreciated those of ordinary skill in the art, other core member configurations may be employed depending on the desired geometry and configuration of the resulting support structure. While in this illustrative embodiment both the core and pole geometry are both generally cylindrical, equally the external configuration of the structure may be different to the configuration of the hollow portion. As one non limiting example, the internal hollow portion may have a generally elliptical cross section while the external cross section of the pole may have a generally octagonal cross section.
Referring now to
In order to provide further reinforcing to the formed concrete pole 2000, in this illustrative embodiment an annular shaped cage structure 500 formed of steel and stainless steel is positioned over the core member 200 (see also
These fixtures include earthing ferules located on the pole for the grounding Many equipment located on the pole and furthermore step inserts for screw in steps to allow access up the pole. Cage structure 500 also aids in holding core member 200 centrally during the casting process. As best seen in
In order to fit the second tensioning member 400, first arbor member 420 is fitted to the tip or mounting spigot 240 of core member 200, thereby extending the length of the core member 200. Arbor member 420 functions to hold centrally a second tensioning member in the form of spigoted arbor housing 400 with respect to the core member 200 during the assembly process. Arbor housing 400 consists of an inner abutment flange 421 that on assembly will abut against the outer mould assembly 600 and an outer flange 422 that functions as a mounting plate for locking sleeves 430 that receive the tensioning elements 450. The arbor member 420 is later able to be removed and the remaining void is then used as an inlet port to inject concrete.
A further arbor extension member (not drawn) is also initially fitted to the end of arbor member 420 and provides a temporary extension to the core member 200 to aid assembly. One end of the arbor extension member threadably engages with the arbor member 420 and has an end shaped to support the spigoted arbor housing 400, In this illustrative embodiment, a further ligature coil 451 formed of continuous 5 mm diameter wire is positioned over the arbor member 420 prior to placement of the spigoted arbor housing 400. The ligature coil 451 is a pre-formed tapered helical wire coil that, once in position, functions as a further reinforcement member to the concrete by providing resistance to bursting during compression on bending of pole 2000.
The spigoted arbor housing 400 is then fitted onto the arbor extension member, thereby forming the “live end” 20 of the tensioning arrangement which in this illustrative embodiment will be tensioned with respect to the “dead end” 10 consisting of the barrel collar 300. Each of the tensioning elements or strands 450 is then threaded through the appropriate locking sleeve 430 located on the outer flange 422, and then through a corresponding aperture 423 in the inner abutment flange 421 of the spigoted arbor housing 400 and then further through the ligature coil 451 so that the ligature coil 451 is external to the tensioning strands 450.
The tensioning strands 450 are further extended along core member 200 external to cage structure 500 and then fed through the opposed corresponding apertures 343, 344 in the inner abutment flange 341 and intermediate flange 342 respectively of barrel collar 300 located at the opposite end of elongate core 200 (as best seen in
Referring now to
With the relative positions of barrel collar 300 and spigoted arbor housing 400 fixed by hydraulic jack 425 the six pre-stressing barrels & wedges 430 may be fitted with respect to tensioning elements 450. A light load of approximately 1 ton is then applied to the tensioning elements 450 by the use of the hydraulic jack 425. This light load ensures that the tensioning elements 450 are kept reasonably straight with respect to core member 200. Before removing the hydraulic line to jack 425, the input valve of the jack 425 is closed to ensure pressure is retained to maintain the separation force and hence extension distance between the spigoted arbor housing 400 and the barrel collar 300 i.e. between the first and second tensioning members.
The ligature wire 451 can now be drawn over the tensioning elements 450 from the spigoted arbor housing 400 to the barrel collar 300 forming an equally spaced spiral over the length of core member 200 (as best seen in
The ligature wire 451 is secured at each end to the cage structure 500. Nibs (not shown in the drawings) are welded to the cage structure 500 at intervals along its length and spaced around its circumference and function to hold the core assembly 1000 centrally within the external mould assembly 600. In this illustrative embodiment, each nib comprises a short rod which projects radially outwardly by an amount such to hold the core assembly 1000 concentrically within the mould assembly 600.
Referring now to
In this illustrative embodiment, core assembly 1000 is first placed in lower or subvert mould portion 620 where it is supported by the nibs to ensure correct spacing between the core member 200 and the lower mould portion 620. The upper or obvert mould portion 610 (as best shown in
In one illustrative embodiment, mould portions 610, 620 may include fittings that are to be incorporated into the formed concrete pole 2000 that initially are fixed through apertures in the mould and which following casting can be detached from the mould portion to remain in the concrete pole 2000.
In order to facilitate the manufacturing process, the various casting components of the combined mould and core assembly 1500, such as the elongate core 200 and the external mould assembly 600, are sprayed with an industry standard release agent to facilitate release of the concrete pole and also to improve the surface finish of product.
The jack 425 which to this point is operating to maintain the extension between the arbor member 420 and barrel collar 300 may now be released. This allows the spigoted arbor housing 400 and barrel collar 300 to move towards and abut against the ends of the external mould assembly 600.
Once the external mould assembly has been attached to the core assembly to form combined mould and core assembly 1500, the jack 425, shoulder ring housing 428, shoulder ring 426 and arbor member 420 may be removed from the spigoted arbor housing 400, thereby providing an inlet port for injection of concrete. At this stage, an alignment check is conducted to ensure that the spigoted arbor housing 400 and barrel collar 300 are in alignment with the top and bottom mould portions 610, 620. This is achieved by a series of location spigots on the mould portions 610, 620 to ensure alignment of the dead and live ends either side of the external mould assembly 600.
At step 140, the plurality of tensioning elements are tensioned between the first and second tensioning members by the use of a hydraulic jack that applies load to each tensioning element 450 progressively moving around the combined mould and core assembly 1500. In this illustrative embodiment, the first application of force should bring each tensioning element 450 up to half final load and a second load is then applied in the same progressive manner to raise the tension up to final pre-stressing load. In this illustrative embodiment, the final pre-stressing load applied to the tensioning elements 450 is 21 tonnes. Again, as would be appreciated by those of ordinary skill in the art the manner of application and extent of the pre-stressing load will vary according to the design and load requirements of the concrete pole being formed. Once the tensioning elements 450 are at the final pre-stressing load, the locking sleeves 340 and 430 may be locked off and any excess length of the tensioning element 450 then trimmed.
The resulting tension applied by the tensioning elements 450 to the spigoted arbor housing 400 and barrel collar 300 causes these components to abut and be compressed against either end of the top and bottom mould portions 610 and 620 resulting in the top and bottom mould portions 610 and 620 of external mould assembly 600 bearing the compressive load applied due to tensioning of the tensioning elements 450.
Alternatively, the spigoted arbor housing 400 and barrel collar 300 may be supported independently of the top and bottom moulds 610 and 620 of external mould assembly so that the load is not applied to them when tension is applied to the tensioning members 450.
At step 150, and as shown in
At step 160, concrete is injected into the cavity 630 formed between the elongate core member 200 and the external mould assembly 600 to form the concrete pole. In this illustrative embodiment, a victaulic coupling, pump slide gate and elbow 700 is fitted to the bottom or live end 20 of the combined mould and core assembly 1500. While the concrete could be satisfactorily injected at any location along the combined mould and core assembly 1500, the applicant has found that there are a number of significant additional advantages to injecting concrete into the bottom of the assembly when it is an upright configuration.
The vertical configuration allows rising air to be dispersed to atmosphere at the to of the concrete rather than rising to the obvert mould surface where it can create voids in the concrete surface. The head generated also helps to further compress the concrete to reduce the amount of trapped air around the joints of the reinforcement cage 500.
The concrete mix employed in this illustrative embodiment is comprised of aggregate (stone), sand, general purpose cement, water and additives to promote anti-corrosive qualities, workability and early strength through accelerated curing. The combinations of the materials will vary from time to time based on the availability and quality.
Referring now to
A breather hole is drilled into the end of the concrete pole 2000 through the spigoted arbor housing 400. The concrete is relatively soft at this stage so the hole can easily be drilled by hand. The breather hole relieves any vacuum that would otherwise form as the core 200 is withdrawn. After a further time period of approximately 5 to 20 minutes which varies in accordance with the factors such as the ambient temperature and temperature of materials, the elongate core 200 is fully removed to he subsequently cleaned with high pressure water. Combined mould and core assembly 1500 now minus the elongate core member 200 is then placed in a steaming chamber for approximately two to three hours for final curing.
Following final curing, the tensioning elements 450 may then be severed using suitable equipment such as a grinding disc, thereby transferring the tensile stress of tensioning elements 450 to the formed concrete pole 2000 from the first and second tensioning members. The barrel collar 300 and spigoted arbor housing 400 may then be removed from the external mould assembly 600 and any excess tensioning element material removed. As shown in
A concrete support structure formed in accordance with the present invention provides a number of substantial advantages over other prior art methods.
The mould assembly and associated method of use described herein have relatively low capital costs for medium levels of production. The mould also does not require a high skill level for the manufacturer of poles and there is a relatively low labour component required. The mould arrangement is very portable and can therefore be set up very close to locations where the poles would be used so as to minimise transportation costs.
There are also improved safety benefits as there are no moving components as would be the case with rotation moulding as described above.
Further, the processes described herein eliminate the concrete laitance that is normally found on the internal surface of poles produced using the rotation moulding process.
Poles manufactured using the process described herein also have uniform inner and outer compression which means that the concrete matrix is homogeneous and not susceptible to cracking due to differential shrinkage. Bi-directional compression promotes superior bonds between reinforcing steel and concrete. The homogeneous concrete also promotes a constant water cement ratio so that the pole is not prone to differential shrinking and cracking. Further, the use of an inner core provides controlled concrete cover to the reinforcement used within the pole through being able to provide uniform wall thickness. The manufacturing process also enables uniform poles to be produced which perform well under test conditions.
It will be understood that the term “comprise” and any of its derivatives (eg. comprises, comprising) as used in this specification are to be taken to be inclusive of features to which it refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.
Although illustrative embodiments of the present invention have been described in the foregoing detailed description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.
Number | Date | Country | Kind |
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2011901350 | Apr 2011 | AU | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/AU12/00371 | 4/11/2012 | WO | 00 | 11/11/2013 |