GB2353552A - Cage former for a concrete pile - Google Patents

Abstract

A cage former (Fig.10, 110) for use in assembling and maintaining a pile cage for a reinforced concrete pile has a single frame 12 (Fig.10, 112) and at least two guide members 14 (Fig 10, 114). The guide members comprise a metal loop, with overlapping ends secured together or a stiffener bar (Fig. 10, 102) and a spacer bar (Fig. 10, 104) secured together.

Description

2353552 CAGE FORMER

FIELD OF THE INVENTION

This invention relates to a cage former, and in particular to a cage former for use in assembling and maintaining a pile cage for a reinforced concrete pile.

BACKGROUND TO THE INVENTION

Reinforced concrete piles are known for use in the foundations of roadway bridges and the like. The piles are sunk deep into the ground and can for example provide a link between the bridge supports and the underlying rocks. The cage comprises a number of bars which in use are arranged to lie substantially along the longitudinal axis of the pile. The bars are interconnected so as to maintain their separation and alignment. The bars can be interconnected by a helical wire, or by one or more hoops arranged at intervals along the length of the bars.

In one known method of providing a reinforced concrete pile, a hole is drilled into the ground and a hollow metal tube known as a pile casing is inserted into the hole. The cage is lowered into the casing and then concrete is poured into the casing and around the cage. The casing is withdrawn so that it can subsequently be re-used.

In another method of providing piles, particularly smaller dimension piles, a hole is drilled into the ground by a hollow auger. When the hole has been drilled to the required depth the auger is removed. In this method, however, concrete is pumped down the central hollow shaft of the auger as it is removed. The introduction of concrete in this way avoids the requirement for a casing, and so provides a considerable saving in terms of cost. However, in the second-described method it is necessary to lower or push the cage into the concrete before it has set. This is not too onerous for smaller piles, but with larger dimension piles the risk of some of the concrete losing its workability before the cage has been inserted is significant, so that the first-described method is still used in such piles.

The cage former of the invention, and the prior art cage formers described below, are primarily intended for use with the latter method.

The cage acts both as a reinforcement for the concrete and also as a means to tie the bridge support of the like to the pile.

In order to maintain the integrity of the pile it is necessary to ensure that the metal cage bars (and also the metal of the frames or interconnecting wire) do not encroach too near the surface of the concrete, and it is recognised that a "cover zone" is required within which either no metal, or only metal which is protected against corrosion, should be present. The cover zone will typically comprise a layer several centimeters thick adjacent the surface of the concrete.

Should unprotected metal encroach into the cover zone there is a risk that over time water and other agents will contact the metal and cause it to corrode, eventually breaking down parts of the pile. It is usually uneconomic to manufacture the whole pile cage from protected metal such as stainless steel or otherwise corrosion resistant metal, and so the manufacturers of piles and pile cages therefore seek to ensure that any metal which is present in the cover zone is protected, usually by a plastic coating or sheathing.

- 3 DESCRIPTION OF THE PRIOR ART

It is known to provide a rigid structure comprising a pair of f rames to which the cage bars can be secured, the rigid 5 structure being referred to herein as a cage former.

One cage former is shown in GB patent application 2,235,223. In that cage former, two frames are interconnected by four rods. The frames are of dissimilar size, one frame being adapted to lie inside the cage bars in use, the other being adapted to lie outside the cage bars in use. The provision of dis-similar sized frames enables the cage formers to be "nested" during transportation, i.e. the smaller frame and part of the rods of one cage former lie within the larger frame of another cage former. In this way, the volume required to transport each cage former is reduced. However, the requirement to feed the cage bars inside one frame and outside the other presents considerable on-site difficulties, particularly if the cage requires several cage formers spaced along its length, as is often the case.

In an ef fort to ensure that no part of the cage bars or cage former encroaches into the cover zone it is known to fit spacers to the f rames of such a cage former. A widely used spacer for this purpose is a plastic wheel which has an opening so that it can be clipped onto the frame after the cage has been assembled. Such spacers suffer a number of disadvantages. Firstly, because the spacers are designed to be clipped into place on site they are relatively insecure; during subsequent on-site handling the spacers can readily become dislodged. Also, when the cage is being lowered or pushed down into the concrete the spacers can relatively easily become detached from the cage former so that part of one or more of the cage bars and/or the cage former(s) can encroach into the cover zone; because the spacer has become detached within the.concrete there is no way of knowing that this has occurred until the pile subsequently is either site-inspected or shows signs of corrosion damage.

Secondly, the spacers can migrate around the f rame so that two spacers may lie close to each other. The ability of the spacers to keep the cage bars out of the cover zone relies upon the spacers being substantially equally spaced, so that the grouping of two or more spacers severely impairs their effectiveness. Once again, there is no way to detect this until after the pile has been completed and the concrete has set.

European patent application 0 608 068 discloses a cage former having integral spacer means, which cannot easily become detached. The spacer means are provided by a number of plastic-sleeved guide members, the guide members comprising outwardly flared portions of the rods interconnecting the two frames. This cage former therefore avoids the problems associated with the use of the abovementioned clip-on wheel spacers.

However, the cage former of EP 0 608 068 has its own disadvantages. Firstly, the two frames of the cage former are of similar size and the cage former cannot therefore be "nested"; there is thus considerable wastage of space during transportation. Secondly, the plastic sleeves provide relatively small area contact between the cage and the surrounding earth as the cage is being lowered or pushed into the concrete. In soft earth and/or with a heavy cage it is known that the sleeve can cut into the earth, so that the cage is no longer maintained centrally within the hole and metal of the cage bars and/or of the cage former which is not protected by a plastic sleeve can encroach into the cover zone.

Thirdly, there is in practice a relatively large spacing between the frames, perhaps 25 - 30 cm. on the smaller cage formers, with a larger spacing on larger cage formers. This spacing is to some extent determined by the requirement to weld the rod to the frames after fitment of the plastic sleeve; a certain distance must be maintained between the ends of the sleeve and the respective f rame so that the plastic is not melted or otherwise damaged during the welding process. The rods are thus relatively long. Since the guide member portions of the rods extend outside the cage, these portions are particularly susceptible to damage if the assembled cage is mishandled on site. Thus, it is not uncommon that the cage will be dropped or lowered rapidly onto the ground, one or more of the guide member portions receiving a load substantially perpendicular to the longitudinal axis of the cage. Since the rods are supported at their ends, which as above indicated are some distance away from the guide member portion along the longitudinal axis of the cage, the load. acts some distance away from the joint between the rod and the frame. It is known in such circumstances f or the rod or rods to be bent, so that the ability of the cage former subsequently to space the cage from the surface of the pile is prejudiced; alternatively or additionally, the considerable torque experienced at the joint between the rod and the frame can deform the weld therebetween. In such eventualities, it is necessary for the cage former to be corrected on site, and this often involves an attempt to force the rod back into its original shape and/or position. If the rod has itself been bent then it may be susceptible to forced correction, but if the weld of the joint between a rod and a frame has been distorted, then seeking to correct this will typically cause the weld to break or become f ree of the rod or f rame. If a rod becomes free in this way, then either the cage former will have to be fully removed and replaced (which may be very difficult and time consuming if it is a central cage former located between several others), or else a prior art wheel spacer has to be added thereto to replace the missing guide member. Clearly, adding a wheel spacer introduces the disadvantages outlined above.

Fourthly, in EP 0 608 068 the rods serve three functions, namely the interconnection of the frames, the carrying of the guide members, and also the siting of the ties to the cage bars. Thus, in an assembled cage the cage bars typically lie adjacent the rods and are tied thereto. In larger cages, perhaps having twelve or more cage bars, the cage former will have twelve or more rods, each carrying a guide member with its plastic sleeve. Clearly, in such cases several of the guide members are redundant, and represent an unnecessary cost to the pile cage manufacturer.

DISCLOSURE OF THE INVENTION

The object of the invention is to seek to avoid the problems associated with the known cage formers described above.

According to the invention, there is provided a cage former having a frame and integral spacer means. the spacer means being provided by at least two guide members connected to the frame, characterised in that the cage former has only a single frame.

The provision of a single frame considerably reduces the volume of the cage former as compared to the prior art cage formers, and in particular EP 0 608 068, so that a considerable saving in transportation costs can be achieved.

Whilst it might be expected that a cage former having just a single frame would not provide the necessary resistance to "shearing" or "racking" of the cage, we have found that in the vast majority of cases it can do so, and in particular if care is taken in the siting and adequate securement of the ties by which the cage bars are fixed to the cage former.

In addition, the cage former of the present invention requires less material and so can be of lighter weight than an equivalent prior art cage former, so that the costs of manufacture and transportation can be reduced.

As an additional benefit, because the guide members are mounted to the single frame, it can be arranged that impact or other loads applied to the guide members in a direction substantially perpendicular to the longitudinal axis of the cage (as may occur if the cage is dropped on site) act through or close to the joint between the guide member and the frame, so that little or no torque is applied to the joint and it is far more likely to withstand the impact without bending of the rod or deformation of the joint.

It will be understood that for a single cage former to space the cage from the surface of the pile there must be a minimum of three guide members subtantially equi-spaced around the frame. However, since the cage former of the present invention is Of relatively low cost, it is believed to be practicable for a cage former to have only two guide members located approximately 1800 apart around the frame, it being intended that two such cage formers will be fitted to the cage, close to one another, with the guide members of the respective cage formers oriented approximately 900 apart. Alternatively, there will typically be four guide members on each cage former, located approximately 900 apart around the frame.

Preferably, the joint between the guide members and the frame is formed by a resistance weld; alternatively this can be formed by a mig weld.

Usefully, the guide member has an elongated substantially linear part adapted in use to lie within the cover zone and support the plastic sleeve. Thus, the plastic sleeve will have an elongated substantially planar surface which will be in contact with the surface of the pile, i.e. the surrounding earth. Such a spacer reduces the local pressure exerted on the earth and so reduces the risk of the spacer digging into the earth. In this regard, it is noted that the prior art cage f ormer EP 0 608 068 presents a substantially smaller surface to the surrounding earth and

8 - so is far more likely to dig into that earth than the present cage former; the length of the elongated part of the guide member of the present invention can be chosen to suit the conditions without having an effect on the spacing between the frames as in EP 0 608 068. Thus, it is understood that the guide members of EP 0 608 068 cannot be altered to provide a larger surface in contact with the surrounding earth without introducing disadvantages; in particular an increase in the surface area would likely require an elongation of the guide portions and so the rods, increasing the likelihood of the rods becoming bent if the cage was mishandled, as discussed above.

The guide members may comprise a loop of one piece of metal 15 having overlapping ends, the overlapping ends being welded together and the guide member subsequently being welded to the frame.

Alternatively, the guide member comprises a stiffener bar 20 and a spacer bar which are initially separate but which are secured together as part of the assembly of the cage former.

This permits the stiffener bar and/or spacer bar to extend beyond their intersection so as to provide an extension upon which the tie can be located. The tie can be f itted to the extension without the need to feed it through the loop of the guide member, i.e. without the need to feed it between the stiffener bar and the spacer bar.

Thus, it may sometimes be difficult and time-consuming for 30 personnel on-site to feed and secure the wire ties through the loop of the guide member, and the provision of an extension outside the region enclosed by the loop of the guide member enables the tying of the cage bar to the cage former without such feeding being required.

Preferably, the stiffener bar and the spacer bar are of different thickness materials. Thus, whilst the stiffener bar is required to be of large section and/or strong material to withstand the shear loading in use, it is not necessary for the spacer bar to be of the same material, and a thinner section and/or weaker material can be used for the spacer bar. This enables a saving on materials to be made, and avoids the possible compromise between strength and cost of material which might otherwise have been made.

Usefully, the stiffener bar can be linear. Accordingly, this bar, which may be of large sectional material, can be cut to length f rom a longer bar or rod, and does not require any bending operations.

Preferably, the spacer bar extends beyond its intersection with the stiffener bar; preferably also the ends of the spacer bar form a cup or other recess which can serve to locate the tie.

The welded joint between the guide member (and in particular between the stiffener bar thereof) and the frame desirably comprises two separate sections of weld to either side of the frame.

Usefully, the frame comprises a substantially circular metal ring, though other shapes could be provided as desired.

Usefully also the ends of the ring overlap to permit a welded joint to be made therebetween. The overlap can be in excess of forty times the diameter of the frame material, to match the requirements for concrete tying of the frame. Alternatively, the frame can be a helically wound strip comprising two or more turns, successive turns lying in contact with each other; such an embodiment would enable the spacing between the welds for each guide member to be increased, thus increasing the resistance to shearing or racking.

Preferably, there are locator bars intermediate the guide members. In common with the prior art the guide members also serve as locations for the tying of a cage bar to the cage former. With the present invention, for larger cages the number of cage bars can be greater than the number of guide members, locator bars being provided in addition to the guide members to which to tie certain of the cage bars.

Thus, it is a particularly desirable feature of the invention that the number of guide members does not need to equal the number of cage bars, so that the cost of the cage former can be reduced (the cost of a locator bar being far less than the cost of a guide member and sleeve).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with 15 reference to the accompanying drawings, in which:- Fig.1 is a side view of a cage former according to the present invention, with three of the cage bars shown in dotted outline; 20 Fig.2 is a side view of a guide member and part of the frame of the cage for-mer of Fig.1; Fig.3 shows an alternative joint between the guide 25 member and frame, Fig.4 is a view of the joint between the frame and guide member of the cage former of Figs. I and 2; Fig. 5 is an end view of the sleeve prior to fitment to the guide member; Fig. 6 is a plan view of part of the sleeve extrusion; Fig. 7 is an end view of part of a guide member carrying a sleeve according to Fig.6; Fig. 8 shows several alternative designs of locator bar for fitment to larger cage formers; Fig. 9 shows a plan view of an alternative guide member; 5 and Fig. 10 shows a side view, partly in section, of part of a cage former according to this improvement, with two cage bars shown in dotted outline.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The cage former 10 comprises a frame 12 and a number of (in this embodiment four) guide members 14 (only three of which can be seen), each of which guide members 14 carries a plastics sleeve 16.

As will be understood by those skilled in this art, in use the cage former 10 is connected to the bars 18 of the cage (three of the f our bars of the cage being shown in dotted outline in Fig. 1) by way of metal ties (not shown in Fig. 1, but numbered 120 in Fig.10).

As above described, in order for a single cage former effectively to space the cage bars 18 from the surface of the pile, a minimum of three guide members 14 are required, equi-spaced around the frame 12. However, it is possible to provide a cage former with only two guide members, if desired. Desirably, however, the cage former has at least three guide members, and in order to alleviate problems with manufacturing tolerances in ensuring that the frame is substantially circular, and that the guide members are substantially equi-spaced therearound, it is preferred that four guide members 14 be used, substantially equi-spaced around the frame 12.

12 - The cage former 10 is suited to a cage having f our cage bars 18, each cage bar 18 being tied to parts of a respective guide member 14. Each cage bar 18 will preferably be tied to a guide member 14 in two locations, adjacent the corners 20 of the guide member 14. Tying the bars 18 to the guide members 14 at two locations, spaced as f ar apart as possible, will reduce the likelihood of the assembled cage shearing or racking under an applied shearing load.

In the embodiment shown in Fig.1, the guide members 14 are made of a single metal bar of circular cross section, bent substantially into the shape of an isosceles trapezium. Typically, the cage bars 18 will be of "Type 2 Ribbed Material" having surface ribs which can assist in keying the bars into the concrete. In addition, however, the ribs ensure that the ties fixing the bars 18 to the guide members 14 (if properly fitted) cannot slide therealong. In an alternative embodiment the guide members can be made of Type 2 Ribbed Material also.

It will also be noted from Figs. 1 and 2 that if the cage is dropped on site, the load typically experienced by the guide member (represented by the arrow L in Fig.2) acts through or close to the joint 22 between the guide member 14 and the frame 12, so that little or no torque is imparted to the welds 24a and 24b securing the guide member 14 and frame 12 together. In addition, the length of the guide member 14 which is susceptible to bending under such loads can be minimised in this design.

As shown in Fig. 2, there are two welds 24a and 24b between the guide member 14 and the f rame 12. The provision of two welds is deliberate and believed to be necessary for a cage former 10 having only one frame 12, since otherwise shear forces on the cage former 10 could weaken or perhaps break the joint 22. Thus, shearing forces tending to rotate the guide member 14 clockwise (as drawn in Fig.2) relative to the frame 12 will seek to compress weld 24a but to extend weld 24b; in the absence of weld 24a the weld 24b might become separated from the frame 12, in known fashion. Similarly, the weld 24b acts to help prevent the separation of weld 24a from the frame 12 in the presence of torque tending to rotate the guide member 14 anti-clockwise as drawn in Fig.2.

As an alternative to the mig welds of the embodiment of Figs. 1 and 2, Fig. 3 shows a resistance weld in which a large electrical current has been passed through the joint 30, effectively melting the the frame 12 and guide member 14 together.

During the manufacture of the cage former 10, a plastic sleeve 16 is fed onto a substantially straight length of bar, the bar subsequently being bent into the shape of the guide member 14. The free ends 32a and 32b (Fig.4) of the bar are overlapped and welded together at 34 to provide a single guide member 14. The chosen number of formed guide members 14 are then fed onto the frame (before the frame is formed into a closed loop), the overlapping ends 32a,b subsequently being welded to the frame by way of mig welds 24a and 24b, or by a resistance weld. The f rame is then formed into a loop and is ends are joined together, suitably by an overlapping joint or by a butt joint (the joint is not shown in Fig. 1).

In the embodiments of Figs. 1-4, the material of the frame 12 is shown as of larger cross-section than the material of the guide members 14. It will be understood by those skilled in this art that this is not necessarily the case, i.e. the materials may be of similar or identical crosssection, or else the material of the guide members may be of thicker cross section than the material of the frame, as desired. In one specific embodiment having a frame 12 of diameter approximately 25 cm and carrying four guide members 14, the frame and guide members are both formed from steel of circular cross section approximately 8 mm in diameter.

As shown in Fig.5, the plastic sleeve 16 comprises an extrusion having an enlarged plate-like surface 40 joined to a bar-receiving section 42 of annular cross-section. As is common with the forming of plastic sleeves such as this, the sleeve is made as an extrusion which is cut or cropped to the length desired. The sleeve 16 in this embodiment is of polyethylene, though other suitable plastics materials could alternatively be used. The provision of the plate-like surface 40 is to increase the surface area of the sleeve which will be in contact with the earth surrounding the pile in use, so as to reduce the likelihood of the guide member digging into the earth and so causing the pile to be offcentre. It will also be noted from Figs. I and 2 that with this design the sleeve can be subtantially planar for a significant distance parallel to the longitudinal axis A-A of the cage, so that the effective area of the plate-like surface 40 which will contact the earth in use is large, and far greater than was achieved with the prior art designs.

Fig.6 shows a part of the extrusion of a further embodiment of sleeve, prior to cropping. In this embodiment, the extrusion is not only cropped to divide it into separate lengths, but is also punched to remove some of the material from the surface 40 - the dotted lines show the cropping and punching positions, i.e. the positions at which the extrusion will be severed to provide the finished sleeve. It is noted that the cropping and punching c: an be carried out by the same tool. The resulting sleeve 46 is therefore not of constant cross-section throughout its length, but is narrowed towards its ends. The purpose of removing the sections 44 will be apparent from Fig.7, which shows an end view of part of a guide member 50 carrying such a sleeve 46. It will be understood by those skilled in this art that since the assembled cage must be pressed into wet concrete, any reduction in the projected surface area of the cage will reduce the force required to push the cage into the concrete. The removal of the sections 44 allows the cage to - have a reduced projected area so that the force required to push it into the concrete is minimised. However, since only the ends of the sleeve 46 are punched to remove the sections 44, the area or the surface 40 in contact with the 5 surrounding earth is not reduced.

Fig.8 shows several designs of locator bar which may be secured (as by welding) to the frame 12 intermediate the guide members 14. As described above, the locator bars are provided for the location of cage bars in cages which have a greater number of bars than the cage former has guide members. Accordingly, in a cage having twelve bars the cage fomer can have four guide members 14,50 and eight locator bars, it being understood that the locator bars are of lower cost to manufacture than the guide members and fitted sleeves.

The locator bars are in the form of a plate 52, a wire formed into a "paper-clip" form 54, and a substantially linear wire with bent ends 56. The plate 52 has recesses 58 to receive and locate the ties (not shown); the location of the ties is accommodated by the closed ends of the "paperclip" 54, and by the bent ends 60 of the wire 56 in those designs.

In this embodiment the ends 60 of the wire 56 are bent substantially at right angles, but in other embodiments may be bent to other angles, as desired. The form of the bent wire 56, and in particular the form of its ends 60, can of course be chosen to suit the requirements, but it is desirable that the wire have end formations which can provide a positive location for the ties whilst providing the minimum increase in the projected area of the cage, so that the force to push the cage into the concrete is minimised.

Other forms or locator bar could alternatively be provided as desired. In a firast alternative the locato r bar comprises a wire having a substantially linear portion (similar to the linear central portion of the wire 56), the ends of the wire being bent around a curve through approximately 2700 so as to cross the linear portion, the crossing point being fixed by a spot weld or the like. In a second alternative the ends are formed into a "Shepherd's Crook", the free end of which engages and is welded to the linear portion. In a third alternative the ends are bent at approximately 900 (i.e. similar to the ends 60), and part of the ends bent by a further 1350 or thereabouts to meet the linear portion and be secured thereto. In a fourth alternative the wire is of three linear sections, one section comprising a linear portion as in the wire 56, the other two sections comprising cross-pieces so that the wire is in the form of a capital "I" in which the ends of the linear portion project slightly beyond the cross-pieces. it will be understood that the first three alternatives provide an "eye" at either end of the wire which will provide a positive location for a tie; the fourth alternative provides two spaced crosses which can also provide a positive tie location. Such alternatives, of which the above four are only a small selection, will provide more positive tie locations than the simple bent ends 60 of the wire 56, and so may be preferred to the wire 56. Whilst with the embodiments described above the frame comprises a single

loop of circular cross-section wire, it may be desirable in certain circumstances to increase the "width" of the frame, i.e. to increase the dimension in the direction of the longitudinal axis A-A of the cage former 10 and assembled cage (Fig.1). This may be achieved by using a band material to form the frame, i.e. a material of substantially rectangular cross- section, the dimension along the axis A-A of the cage being greater than the dimension perpendicular to this axis. Alternatively, the frame may comprise a number of loops with adjacent loops lying adjacent one another and being secured together, perhaps by a number of welds; it will be understood by those skilled in the art that such a multiple-loop frame will act subtantially as a band, increasing the separation of the welds between the frame and guide member (corresponding to welds 24a,b), so increasing the torque which can be resisted 5 by those welds.

A further design modification is shown in Fig.9. In this design the ends 64a, 64b of the guide member 62 are not overlapped and joined together, but rather are separately joined to the frame 12 at spaced locations around the frame. The spacing between the welded joints which connect the respective ends 64a,b to the frame 12 increases the ability of the guide member to withstand forces acting perpendicular to the longitudinal axis A-A of the cage former, i.e. in the directions shown by the double-headed arrow 66 in Fig.9.

Fig. 10 shows a part of a cage former 110. The cage f ormer 110 is generally similar to the cage former 10 of Fig.1, in that it comprises a frame 112 (only part of which is shown) and a number of guide members 114 (only one of which can be seen).

In this embodiment, however, each guide member 114 comprises a stiffener bar 102 and a spacer bar 104 rigidly secured together as by welds 106 or the like. The spacer bar 104 carries a plastics sleeve 16. In this embodiment the stiffener bar 102 is of a different material to the spacer bar 104, the stiffener bar material being of larger section than that of the spacer bar. In other embodiments the spacer bar can be of the same material as the stiffener bar, or can be of thicker section material, if desired. In addition, since in use the spacer bar is the only part of the cage former to lie within the cover zone, it may be practicable to produce the spacer bar from corrosion- resistant material such as stainless steel, so that a separate protective sleeve is not required. It may additionally be practicable to provide a corrosion-resistant spacer bar of similar form to that shown in Fig.7, i. e. to make part of the spacer bar "plate-like" so as to reduce the pressure upon the surrounding earth, without requiring a separate protective sleeve for this purpose.

The ends of the spacer bar 104 extend beyond the joint with the stiffener bar 102, and are "overbent" to form cups 108. The cups 108 serve to locate the wire ties 120 by which the guide member 114 may be secured to the cage bar 18 in known f ashion. The cups 108 provide a positive location for each respective tie, reducing or preventing the likelihood of the tie 120 sliding relative to the guide member 114.

It will be understood from Fig.10 that access between the stiffener bar 102 and spacer bar 104 to feed and secure the tie 120 is not required, so that the fitment of the ties 120 is likely to be easier in the embodiment of Fig.10 than in the embodiment of Fig.1 for example. In addition, it is well recognised that the resistance to shear forces will be improved by placing the wire ties 120 as far apart as possible, and the embodiment of Fig.10 allows a greater tie spacing than the embodiment of Fig.1 for a guide member enclosing a similar area. In other embodiments, the stiffener bar and/or the spacer bar can be extended further, to further increase the spacing between the ties, if desired.

It will be recognised that it is not necessary for both the stiffener bar and the spacer bar to extend beyond their intersections 100, only one of these bars need be extended to provide a site for location of the tie 120 outside the enclosed area between the spacer bar and the stiffener bar.

The embodiment of Fig.10 is for use with a large pile cage having eight cage bars 18. As above indicated, in the prior art systems in which the guide members serve the two functions of guiding the cage and locating the cage bars relative to the f rame 12, 112, in such a cage it would be necessary to employ eight guide members. The inventor has, however, realised that in such cages some of the guide members are redundant in performing their guiding function, i.e. the cage may be adequately spaced by three (though preferably four) guide members, and the provision of the additional guide members merely to locate the additional cage bars is expensive and an unnecessary waste of material.

Fig.10 also shows a separate locator bar 128, which is of similar form to the locator bar 52 of Fig.8, having spaced recesses 130 to receive respective wire ties 120 for securement of a cage bar 18a. In the complete cage former 110 there are four guide members 114 and four locator bars 128, each locator bar being located between two adjacent guide members (and vice versa). Accordingly, four cage bars 18 are located by guide members 114 and four cage bars 18a by the (much cheaper) locator bars 128.

Clearly, with larger cages having a greater number of cage bars the potential savings are increased. For example a cage having twelve cage bars might employ four guide members 114 and eight locator bars 128 (or 52,54,56 etc.). Even if the user specified six guide members and six locator bars for such a cage, the saving in material, weight and cost of the cage formers, and so the resulting cage, would be considerable.

Whilst locator bars 128 are described in relation to the embodiment of Fig.10, it is of course possible to use such bars, or any of the other described locator bars, with the earlier embodiments also.

Claims (21)

1. A cage former (10,110) having a frame (12,112) and integral spacer means (14,114), the spacer means being provided by at least two guide members connected to the frame, in which the cage former has only a single frame.

2. A cage former according to claim 1 having at least three guide members (14,114) substantially equi-spaced around the frame (12,112).

3. A cage former according to claim I or claim 2 in which a guide member provides spaced locations (20,108) for the securement of ties (120) by which cage bars of an assembled pile cage may be secured to the cage former.

4. A cage former according to any of claims 1-3 in which a guide member (14,114) has an elongated substantially linear part adapted in use to lie within the cover zone.

5. A cage former according to an of claims 1-4 in which a guide member (14) comprises a loop of one piece of metal having overlapping ends (32a, 32b), the overlapping ends being secured together.

6. A cage former according to any of claims 1-4 in which a guide member comprises a stiffener bar (102) and a spacer bar (104) which are initially separate but which are secured together as part of the assembly of the cage former.

7. A cage former according to claim 6 in which the stiffener bar (102) and/or spacer bar (104) extend beyond their intersection (100) so as to provide an extension upon which a tie (120) can be located.

8. A cage former according to claim 6 or claim 7 in which the stiffener bar (102) and the spacer bar (104) are of different thickness materials.

9. A cage former according to any of claims 6-8 in which the stiffener bar (102) is substantially linear.

10. A cage former according to any of claims 6-9 in which the spacer bar (104) extends beyond its intersections (100) with the stiffener bar (102), and the ends of the spacer bar (102) form respective cups (108) which can serve to locate a tie (120).

11. A cage former according to any of claims 1-10 in which the welded joint between the guide member (14,114) and the frame (12,112) comprises two separate sections of weld (24a,24b) to either side of the frame.

12. A cage former according to any of claims 1-11 in which the frame (12, 112) is a helically wound strip comprising two or more turns, successive turns lying in contact with each other.

13. A cage former according to any of claims 1-12 in which there are locator bars (52,54,56,128) intermediate the guide members.

14. A cage former according to claim 15 in which the locator bars have end formations (58,60,130) providing a positive location for the respective ties (120).

15. A cage former according to claim 14 in which the end formations are provided by closed loops.

16. A cage former according to any of claims 1-15 in which the guide member (14,114) is substantially in the form of an isosceles trapezium.

17. A cage former according to any of claims 116 in which the guide member carries a protective sleeve (46) having tapered side edges.

18. A cage former according to claim 1 in which the guide member (62) is not a closed loop, and in which the ends (64a,64b) of the guide member are joined to the frame at spaced locations around the frame.

19. A cage former according to any of claims 1-18 in which the joint (30) between a guide member (14,114) and the frame (14,114) is formed by a resistance weld.

20. A cage former constructed and arranged substantially as described in relation to Fig.1 or Fig.10 of the accompanying drawings.

21. A cage former having at least two guide members constructed and arranged substantially as described in relation to Fig.2 or Fig.9 of the accompanying drawings.