GB2363813A

GB2363813A - Bar end boot for a cage bar

Info

Publication number: GB2363813A
Application number: GB0112050A
Authority: GB
Inventors: Stephen Render
Original assignee: Rom Group Ltd
Current assignee: Rom Group Ltd
Priority date: 2000-05-18
Filing date: 2001-05-18
Publication date: 2002-01-09
Also published as: GB0011837D0; GB0112050D0

Abstract

A bar end boot (10) for spacing the end of a cage bar on a reinforced concrete pile is formed from a sleeve (12) made of plastic and is partially filled with a plug of concrete (24). When the concrete (24) is poured into the sleeve (12) it fills a first set of apertures (14) which retain the concrete plug (24) in the sleeve (12) once the concrete (24) has set. The sleeve (12) has a second set of apertures (20) through which a flexible self locking strip (30) is passed, which acts to hole the sleeve (12) on the cage bar.

Description

2363813 BAR END BOOT AND METHOD OF MANUFACTURE

FIELD OF THE INVENTION

This invention relates to a bar end boot and method of manufacture, and in particular to a boot for fitment to the end of a cage bar in 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 and/or by one or more frames arranged at intervals along the length of the bars.

The cage acts both as a reinforcement for the concrete and also as a means to tie the bridge support or 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 and/or interconnecting helical 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 in the pile.

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 non-protected metal does not enter the cover zone.

Several means of maintaining the (cylindrical) surface of the cage a predetermined distance away from the (cylindrical) surface of the earth surrounding the pile are known U S Patent 4,627,211 for example discloses a number of spacers (or "sleds") manufactured of plastics material and which can be secured to respective junctions between a pile cage and the helical wire to keep the metal of the pile cage out of the cover zone Preformed cage formers are also known which can serve to support and guide the cage In European patent application 0 608 068, for example, there is disclosed a cage former having integral spacers.

Unprotected metal adjacent the lower end (in use) of the pile cage must also be kept out of the cover zone, i e it is not only necessary to space the metal of the cage from the (cylindrical) sides of the pile but also to space it from the bottom of the pile, so that a layer of concrete of a thickness equal to or greater than the cover zone lies at the bottom of the pile, without any unprotected metal therein.

DESCRIPTION OF THE PRIOR ART

Means to space the cage away from the bottom of the pile hole when the cage is inserted into the pile hole are known, and are commonly referred to as "bar end boots", since they generally comprise a set of boots which can each be fitted over the end of a respective cage bar It is not always necessary to fit a bar end boot to every cage bar, but to a sufficient proportion of the cage bars to ensure that all of the cage bars will be kept out of the cover zone The cage bars which are not fitted with a bar end boot are therefore required to be suspended away from the bottom of the pile hole by their connections to the helical wire or other connecting means by which they are connected to the remainder of the cage.

The known design of bar end boot comprises a two-part construction of nylon The first part of the boot comprises a sleeve having inwardly-directed circumferential ribs, which sleeve is sized to fit over the end of a cage bar, the ribs cooperating with the deformations which are typically provided on the surface of a cage bar so as to prevent the boot from inadvertently becoming separated from the bar.

The second part of the bar end boot, and which part is intended to keep the cage out of the cover zone, comprises an extruded length of nylon bar, the length corresponding to the desired thickness of the cover zone The first and second parts of the boot are secured together so that in use the boot is retained upon a cage bar by its first part, with the second part being aligned with, and projecting beyond, the end of the bar.

The second part of the known bar end boot is not solid, but comprises a cylinder within which is located a series of substantially radial webs.

One disadvantage of this design of bar end boot is that air is present between the webs, and so in use air pockets are provided in the cover zone at the bottom of the pile This is not desirable since piling engineers generally wish that the pile hole is filled entirely with either concrete or metal, and that the cover zone is filled with either concrete or protected metal The presence of air (and to some extent also nylon) within the cover zone goes against this wish, and it is believed can reduce the strength of the resulting pile Notwithstanding that the proportion of air (and nylon) in the finished pile might be small, this is nevertheless a recognised concern for piling engineers.

In addition, it is necessary that the bar end boots be maintained free of water prior to installation, since if the spaces between the webs contain water or moisture, then the bar end boot will act to introduce water into the cover zone, closer to the metal of the cage than was intended.

DISCLOSURE OF THE INVENTION

The object of the invention is to seek to avoid the problems associated with the known design of bar end boot described above.

According to the invention therefore, there is provided a bar end boot comprising connecting means cooperable with an end part of a cage bar and adapted to retain the boot upon the cage bar, and supporting means adapted to project beyond the end of the cage bar, characterised in that the supporting means comprises a plug of concrete.

Since the supporting means is of concrete, the bar end boot of the invention can provide that the cover zone at the bottom of the pile hole is substantially filled with concrete The invention therefore satisfies the piling engineers requirement that the pile hole be completely (or more completely) filled with either concrete or metal.

Preferably, the connecting means includes a sleeve adapted to surround an end part of a cage bar Preferably also the connecting means includes a retaining means which is cooperable with the sleeve to retain the sleeve upon the cage bar.

Desirably, the sleeve is extended also to surround the concrete plug The sleeve could be of protected metal such as stainless steel, though a sleeve of a plastics material is expected to be suitable Thus, despite the fact that the part of the sleeve which surrounds the concrete plug will lie within the cover zone in use, it is expected that piling engineers will accept the use of a sleeve of plastics material, notwithstanding that this introduces material other than concrete (or protected metal) into the cover zone Thus, even in embodiments in which the sleeve is of a plastics material, it is believed that the absence of air in the cover zone will make the bar end boot of the invention far more acceptable to piling engineers than the prior design described above.

Preferably, the sleeve extends the full length of the plug of concrete; preferably also the sleeve is apertured, at least some of the apertures being filled with concrete In such embodiments, the sleeve may be used as a mould into which concrete may be poured so as to set within a part of the sleeve The apertures which are filled with concrete enable the concrete to be securely retained within the sleeve.

Preferably, the retaining means is a flexible tie member, a part of the tie member passing through an aperture in (the connecting part of) the sleeve Desirably, the tie member comprises a self-locking strip such as a cable tie or the like Ideally, the strip passes through one aperture in the sleeve and out of another aperture of the sleeve, the locking member for the strip being located outside of the sleeve where it is readily accessible to the fitter Inside the sleeve the strip will be formed into a loop which can receive the cage bar therewithin, the strip subsequently being able to be tightened around the cage bar.

The engagement between the strip and the cage bar, and therefore the ability of the strip to retain the bar end boot upon the cage bar, is enhanced by the surface deformations which are characteristic of the cage bars used in reinforced concrete piles.

Preferably, the concrete plug is around 75 mm long, this distance corresponding to the thickness of the cover zone in many piles Preferably also, the sleeve has an overall length around 75 mm greater than the length of the concrete plug, so as to provide a length of around 75 mm for securement to a cage bar.

Desirably the sleeve is manufactured from PVC, usefully having a wall thickness of around 4 mm The inner diameter of the sleeve should be 2-3 mm greater than the diameter of the cage bar (including the deformations), so that the sleeve can be slid easily over the end of the cage bar and can accommodate the tie member between the cage bar and the inside of the sleeve.

There is also provided a method of manufacturing a bar end boot as herein defined comprising the steps of {i} determining the length of plug required to maintain unprotected metal out of the cover zone, fiij providing a sleeve of corrosion-resistant material of a length greater than the length of plug required and of an internal dimension greater than the dimension of a cage bar to which the boot will be fitted, {iii} forming a first set of apertures in the wall of the sleeve, the first set of apertures being spaced from one end wall of the sleeve by a distance less than the length of the plug required, {iv} forming a second set of apertures in the wall of the sleeve, the second set of apertures being spaced from said end wall by a distance greater than the length of the plug required, fv} locating the sleeve in an outer shell, the outer shell being a close fit around the sleeve, {vi} pouring wet concrete into the sleeve to a depth substantially equal to the length of plug required, {vii} allowing the concrete to set, (viii} removing the sleeve from the shell, and {ix} locating retaining means in at least one of the second set of apertures.

Preferably, for a bar end boot for which the length of the concrete plug is round 75 mm, the overall length of the sleeve is around 150 mm In such a boot, the first set of apertures is desirably formed around 40 mm from one end of the sleeve, and the second set of apertures is desirably formed around 40 mm from the other end of the sleeve.

Usefully, there are three apertures in each set, the apertures being spaced apart approximately 1200 around the circumference of the sleeve Preferably, the diameter of each aperture is around 12 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Fig 1 is a perspective view of a bar end boot according to the invention; and Fig 2 is a sectional view along the lines II-II of Fig l.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The bar end boot 10 comprises a sleeve 12, which in this embodiment is a tube of PVC having a length of around 150 mm and a wall thickness of around 4 mm.

The sleeve 12 has a first set of apertures 14 formed therein, approximately 40 mm from the first end 16 (which end will be the lower end of the boot in use) The sleeve 12 has a second set of apertures 20 formed therein, approximately 40 mm from the second end 22.

Wet concrete has been poured into the sleeve 12, and has set therein to form a plug 24 The concrete has filled the first set of apertures 14, as also shown in Fig 2; it will be understood that the purpose of the first set of apertures 14 is therefore to receive respective parts of the concrete by means of which the plug 24 can be retained within the sleeve.

The set of apertures 14 comprises three apertures, separated by approximately 1200 around the circumference of the sleeve 12.

In alternative embodiments there are more than three apertures in the first set, and in other alternative embodiments there are fewer than three apertures If there is more than one aperture the apertures may be separated around the sleeve by any suitable separation, or by varying separations In further alternative embodiments there are other means of securing the concrete plug within the sleeve; for example surface deformities may be provided on the inside of the sleeve, or a cross-bar (such as a nail) may be located within the sleeve and engage separate parts of the side wall, which cross-bar becomes surrounded by and embedded within the concrete plug.

In use, when the second end 22 of the sleeve 12 is placed over the (lower) end of a cage bar, the cage bar will rest upon the plug at the bottom of the pile hole, the plug 24 spacing the metal of the cage bar from the earth underneath the pile hole.

To maintain the sleeve 12 upon the cage bar whilst the cage is moved around the site and/or whilst the cage is being lowered into the pile hole, a flexible strip 30 (in this embodiment a plastics cable tie) is used The strip is passed through two of the apertures which provide the second set of apertures 20 One end of the strip carries a locking member 32, and the free end 34 of the strip is passed therethrough As will be appreciated by those skilled in the art, the free end 34 of a cable tie such as this can be pulled manually (or by a suitable tool) through the locking member so as to tighten the tie upon a cage bar located within the sleeve 12, but the locking member and strip carry cooperating formations which resist the loosening of the tie.

It will be understood that alternative retaining means can be used, for example a wire tie which requires twisting by hand or tool so as to tighten the loop around the cage bar, or another of the many available suitable forms of flexible plastics strips.

In other embodiments the length of the sleeve can be increased (whether or not the length of the concrete plug changes), and can include two second sets of apertures 20, longitudinally spaced apart, to receive two retaining means.

The increased length of the sleeve which will overlie the end of the cage bar, and the possibility to locate two retaining means, will increase the securement of the boot upon the cage bar.

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Claims

1 A bar end boot comprising connecting means cooperable with an end part of a cage bar and adapted to retain the boot upon the cage bar, and supporting means adapted to project beyond the end of the cage bar, the supporting means comprising a plug of concrete.

2 A bar end boot according to claim 1 in which the connecting means includes a sleeve adapted to surround an end part of a cage bar.

3 A bar end boot according to claim 2 in which sleeve is of a plastics material.

4 A bar end boot according to claim 2 or claim 3 in which the sleeve is extended also to surround the plug of concrete.

A bar end boot according to claim 4 in which the sleeve extends the full length of the plug of concrete 6 A bar end boot according to claim 4 or claim 5 in which the sleeve is apertured, at least some of the apertures being filled with concrete.

7 A bar end boot according to any one of claims 2-6 in which the connecting means includes a retaining means which is cooperable with the sleeve to retain the sleeve upon the cage bar.

8 A bar end boot according to claim 7 in which the retaining means is a flexible tie member, a part of the tie member passing through an aperture in the sleeve.

9 A bar end boot according to claim 8 in which the tie member comprises a self-locking strip.

A bar end boot according to claim 9 in which the strip passes into one aperture in the sleeve and out of another aperture in the sleeve and forms a loop within the sleeve which can receive the cage bar therewithin, and in which the locking member for the strip is located outside of the sleeve.

11 A bar end boot according to any preceding claim in which the concrete plug is approximately 75 mm long.

12 A bar end boot according to any preceding claim in which the connecting means is adapted to span at least approximately 75 mm of the end part of the cage bar.

13 A method of manufacturing a bar end boot according to claim 1 comprising the steps of {i} determining the length of plug required to maintain unprotected metal out of the cover zone, {ii} providing a sleeve of corrosion-resistant material of a length greater than the length of plug required and of an internal dimension greater than the dimension of a cage bar to which the boot will be fitted, {iii} forming a first set of apertures in the wall of the sleeve, the first set of apertures being spaced from one end of the sleeve by a distance less than the length of the plug required, {iv} forming at least one second set of apertures in the wall of the sleeve, the second set(s) of apertures being spaced from said end by a distance greater than the length of the plug required, {v} locating the sleeve in an outer shell, the outer shell being a close fit around the sleeve, {vi} pouring wet concrete into the sleeve to a depth substantially equal to the length of plug required, {vii} allowing the concrete to set, and {viii} removing the sleeve from the shell.

12 - 14 The method according to claim 13 including the additional step of locating retaining means in at least one of the second set of apertures.

A method according to claim 13 or claim 14 in which for a bar end boot for which the length of the concrete plug is round 75 mm, the overall length of the sleeve is around 150 mm.

16 A bar end boot constructed and arranged substantially as described in relation to Figs 1 and 2 of the accompanying drawings.