GB2399126A

GB2399126A - Shackle for pile reinforcement

Info

Publication number: GB2399126A
Application number: GB0402178A
Authority: GB
Inventors: Stephen Render
Original assignee: Rom Group Ltd
Current assignee: Rom Group Ltd
Priority date: 2003-02-03
Filing date: 2004-02-02
Publication date: 2004-09-08
Anticipated expiration: 2024-02-02
Also published as: GB0402178D0; GB0302321D0; GB2399126B

Abstract

A shackle (30) for holding a reinforcing bar (14) used in pile forming includes a cam (50) which acts to grip the bar (14). The shackle (30) design is such that the weight of the reinforcing bar (14) acts to maintain the grip of the shackle (30). The shackle (30) is automatically released when the reinforcing bar (14) rests upon the bottom of the pile hole. The shackle (30) can include locking means (to secure the bar to the shackle and the cam) and may have a roughened surface to increase the frictional engagement with the bar.

Description

2399 1 26 - 1 -

SHACKLE

FIELD OF THE INVENTION

This invention relates to a shackle, and in particular to a shackle suitable for use in lifting a reinforcing bar of a concrete pile.

The shackle has been designed for use in lifting a reinforcing bar, and so the following description refers to such use; however, use of the shackle in other applications is not thereby excluded.

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.

A particular type of pile for which the invention is suitable is referred to as "driven cast in-situ", or "DCIS".

In the construction of such a pile, a tubular casing is driven into the ground with a shoe covering the leading end to prevent earth entering the casing. A reinforcing bar is subsequently lowered into the casing, and concrete is poured into the casing and around the reinforcing bar. Before the concrete has set the casing is withdrawn to be used again in the construction of another pile.

The reinforcing bar acts both as a reinforcement for the concrete and also as a means to tie an above-ground structure (such as a bridge support for example) to the pile.

In DCIS piles the reinforcement can be in the form of a single reinforcing bar fitted with lantern spacers or the - 2 - like at periodic intervals so as to keep the reinforcing bar substantially centred within the casing (and hence centred within the pile). In some arrangements a bundle of reinforcing bars are used in place of a single bar. The shackle of the present invention can be used with the latter arrangements but the following description refers to the former arrangements since these are more commonplace.

Because the casing is designed to be driven into the earth it is necessarily a robust structure, with a wall of steel perhaps 20 mm thick for example. The casing is a very expensive component, but the expense is justified by the ability to re-use the casing in a large number of DCIS piles.

Usually, the casing will not be made for a particular pile, but will be made of standard dimensions, for example 20m, 25m and 30m long. If the pile designer requires the pile to be 22m deep, a 25m casing is used, driven in to a depth of 22m.

A typical situation is that shown in Fig.1 of the accompanying drawings, which shows a casing 10 which has been driven into the earth 12 to the desired depth for the pile. A reinforcing bar 14 has been lowered into the casing on a cable 16 by way of a crane (not shown), the reinforcing bar being centred within the casing by four lantern spacers 20, in known fashion. An access platform 22 is erected adjacent the top of the casing, and upon which an operator can stand during installation of the reinforcing bar and subsequent pouring of the concrete.

It will be understood that the reinforcing bar 14 acts to add tensile strength to the pile. The reinforcing bar 14 also acts to allow the connection of further concrete structures at or above ground level, i.e the reinforcing bar 14 of the pile is connected to the reinforcing bar or bars of the above- ground structures. In order to allow the 3 reinforcing bar to perform this latter task it must project above ground level, as shown in Fig.1.

When it has set, it is desired that the concrete be at or close to ground level; this requires the concrete to be poured into the casing to above the ground level since the concrete level will fall as the casing is removed.

Accordingly, the casing must extend above ground level by a distance sufficient to contain the extra volume of concrete required. In addition, the casing may extend above ground level further still because the casing will be one of the standard lengths.

Accordingly, when the reinforcing bar 14 has been lowered into the casing 10 to rest upon the shoe 24 its top end will typically be below the top of the casing by a distance D. The reinforcing bar 14 is temporarily connected to the cable 16 by a clamp 26, and the operator standing upon the piling platform must release the cable from the reinforcing bar.

It is not uncommon that the clamp is too far down inside the casing to be reached by the operator. In such cases, the reinforcing bar 14 must be suspended out of engagement with the shoe 26 whilst the clamp is removed, the reinforcing bar being allowed to drop onto the shoe when released.

There is a danger that dropping the reinforcing bar will cause a part or parts of it to become distorted laterally away from the centre of the casing. This has the first disadvantage that unprotected metal may encroach too near to the surface of the pile, leading to a deterioration of the pile over time. It has the second disadvantage that distortion of the reinforcing bar will reduce the length of the bar which projects above ground level. It is for example known that the reinforcing bar lies fully within the concrete when the casing is removed, resulting in a pile that cannot be used to connect to above-ground structures. - 4 -

The above-described method of disconnecting the cable from the reinforcing bar and allowing it to drop to the bottom of the casing also represents a considerable safety concern, since the operator must release the clamp whilst it is supporting the weight of the reinforcing bar. In practice, the clamp may comprise one or more U-bolts or be of similar design to a scaffold clamp, requiring the operator to unscrew at least one nut from a bolt by use of a spanner.

There is little advanced warning of when the clamping force remaining will no longer support the weight of the reinforcing bar, and the operator necessarily has his hands near to the clamp as the reinforcing bar falls therefrom.

STATEMENT OF THE INVENTION

It is an object of the present invention to provide a shackle which can replace the known clamps for connecting the cable to the reinforcing bar, so reducing the problems associated with the above-described method.

According to the invention, therefore, there is provided a shackle for a member, the shackle having clamping means, the clamping means being movable between a first position in which the member is clamped by the shackle and a second position in which the member can be removed from the shackle, movement of the member relative to the shackle in a chosen direction acting to move the clamping means from its first position to its second position.

Accordingly, movement of the member (e.g. the reinforcing bar) in the chosen direction can be used to release the shackle from the member, and it is not necessary for the operator to release the shackle. This has the advantages that the operator is not required to perform a potentially dangerous operation, and also that the member can be positioned out of reach of the operator whilst the shackle is released.

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When the weight of the member is supported by the shackle it is arranged that the weights acts in a direction opposed to said chosen direction; reversing the direction of the force applied by the member upon the shackle can release the holding means from the member, allowing the member to be released from the shackle. When the shackle is used to support a reinforcing bar in a DCIS piling application, the direction of force applied by the reinforcing bar upon the shackle can be reversed by lowering the reinforcing bar until it engages the shoe, i e. the weight of the reinforcing bar no longer acts upon the shackle but instead the reinforcing bar is supported by the shoe and the weight of the shackle and cable provides the opposed relative force.

Preferably, the shackle has releasable locking or tensioning means for the holding means, the tensioning means acting to urge the holding means towards its first position. The provision of tensioning means is preferred so as to prevent the automatic release of the shackle when the automatic release is not required. Thus, it is often desired that the shackle will retain the reinforcing bar in positions in which the relative direction of the force between the member and the shackle varies or cannot be known, for example when the shackle is used to lift a horizontal reinforcing bar off the ground. The tensioning means will ensure that the shackle is not released regardless of the relative direction of the force applied to the shackle by the member.

Desirably, the holding means comprises a cam.

Desirably also, the tensioning means comprises a rod connected to the cam. Preferably, the rod is threaded and carries a compression spring and a nut, the rod being tensioned by tightening of the nut to compress the spring. 6 -

Preferably, the shackle has a body which includes a channel within which a part of the member can be located.

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 shows a prior art arrangement used in constructing a DCIS pile; Fig.2 shows a part-sectional view of the shackle according to the invention in its secured condition; and Fig. 3 shows a part-sectional view of the shackle of Fig.2 in its released condition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description of the prior art method of constructing a pile according to the DCIS method is described above with reference to Fig.1. As described, the prior art method utilises a clamp 26 to secure the reinforcing bar 14 to the lifting cable 16.

The present invention on the other hand replaces the clamp 26 with a shackle 30 as shown in Figs. 2 and 3, so that the reinforcing bar 14 (carrying the lantern spacers 20) is lowered into the casing 10 by way of the shackle 30.

Fig.2 shows the secured condition of the shackle, in which condition the shackle can be used to lift the reinforcing bar 14. The lifting operation will typically comprise raising the reinforcing bar 14 from a horizontal orientation lying upon the ground to a vertical orientation, and subsequently lifting the reinforcing bar from the ground, moving it over the casing 10, and lowering it into the casing.

The shackle 30 has a body 32 which in this embodiment is a steel fabrication. The body 32 has a sleeve portion 34 at I one end, into which the end part of the reinforcing bar 14 can fit (see Fig.3). The sleeve portion 34 mounts a pair of flanges 36 (one of which is seen in Fig.2, the other of which is seen in Fig.3). Tensioning rod 40 passes between the flanges 36, as will be further described later on.

The body 32 has two upstanding arms 42 at its other end, I only one of which arms 42 can be seen in these sectional views. The arms 42, and the part 44 of the body 32 upon which they are mounted, together form a "U"shaped channel within which can lie a part of the reinforcing bar 14.

In this embodiment the body 32 has a flat plate 46 between the channel 42, 44 and the sleeve portion 34, the plate comprising a continuation of the part 44. In other embodiments, all or part of the arms 42 can continue alongside the reinforcing bar 14 towards or all the way to! the sleeve portion 34, so that the "U"-shaped channel in which the reinforcing bar 14 lies runs for a large part of, or all of, the length of the body 32.

Between the arms 42 is mounted a pivot 48, and a cam member is mounted upon the pivot 48. The cam member 50 is arranged to be pivotable between a clamping position as shown in Fig.2 in which its cammed surface 51 engages a part of the reinforcing bar 14 and clamps the reinforcing bar 14 against the part 44, and a non-clamping position as shown in Fig.3 in which the surface 51 is spaced some distance away from the reinforcing bar 14 so that reinforcing bar is movable relative to the shackle 30 in a direction parallel I to its longitudinal axis. v 8 -

Connected to the cam member 50 is a tensioning rod 40, all or part of which is threaded, and which as above described passes between the flanges 36. A compression spring 52 is mounted upon the rod, and is retained thereon by a nut 54, the threads of the nut 54 cooperating with those of the rod 40.

Fig.2 shows the "lifting" condition of the shackle in which the cam 50 is in its clamping position, and is retained there by the tension in the rod 40 (the tension being provided by the spring 52 which is tightly clamped against the flanges 36 by the nut 54. In this lifting condition, the cam member 50 is held in engagement with the reinforcing I bar 14 by the tensioning rod 40.

A second "holding" condition of the shackle is available, and is not shown in the drawings. In the holding position, the tension of the rod 40 is removed and the shackle retains the reinforcing bar by virtue only of the weight of the reinforcing bar 14 and the action of the cam member 50.

This holding position is only applicable when the weight of the reinforcing bar 14 acts upon the shackle 30 in the direction W shown in Fig.2. The surface 51 of the cam member 50 can be roughened, or cut to form teeth, to increase the grip upon the reinforcing bar 14, if desired.

Alternatively, as shown the reinforcing bar has surface deformations 56 which can cooperate with the cam member 50 to increase the grip of the shackle 30 upon the reinforcing bar 14.

As above described, when the shackle 30 is to be used to lift the reinforcing bar initially, it will normally be located onto the end of the reinforcing bar 14 with the end of the reinforcing bar just outside the sleeve 34. The cam member 50 is moved to engage the reinforcing bar 14 and the nut 54 is tightened upon the rod 40 until the reinforcing bar 14 is clamped sufficently tightly to allow it to be lifted. In this regard it can be arranged, for example, - 9 - that: {i} the clamping is sufficient when the nut 54 has been tightened until adjacent coils of the compression spring 52 engage each other, or {ii} an indicator line marked on the rod 40 is passed by the nut 54, or {iii} a torque wrench is used to apply a determined torque to the nut 54.

As the reinforcing bar 14 is lifted (e.g. from substantially horizontal position on the ground), the direction in which its weight acts relative to the shackle gradually moves until the reinforcing bar is vertical and its weight acts in the direction W shown in Fig.2. During this movement, the cam member 50 is gradually (further) tightened upon the reinforcing bar as the weight of the reinforcing bar acts to increase the engagement between the surface 51 and the reinforcing bar 14, in addition to the force provided by the tensioning rod 40.

The reinforcing bar 14 can be lifted from the ground by way of the shackle 30, and lowered into the casing 10. When the reinforcing bar 14 has been lowered until the shackle 30 is l adjacent to the piling platform 22, the operator can loosen the nut 54, removing the tension in the rod 40. The reinforcing bar 14 remains suspended from the shackle 30, however, since it is arranged that in this "holding" condition the cam member 50 and the weight of the reinforcing bar 14 maintain the engagement between the surface 51 and the reinforcing bar 14. The operator loosens the nut 54 to a position adjacent the end of the rod 40 as shown in Fig.3, which will allow subsequent automatic release of the shackle as described below.

It will be understood that even if the shackle is faulty and the reinforcing bar 14 falls from the shackle when the nut! 54 is loosened, the situation will be no worse than with the, prior art arrangements in which the reinforcing bar drops t onto the shoe. This is not desired, however, and it is expected that the designer will ensure that the shackle is - 10 well able to support the weight of the reinforcing bar in the holding condition.

When the nut 54 has been loosened, the reinforcing bar 14 may be further lowered into the casing 10, until the reinforcing bar 14 rests upon the shoe 24. When the reinforcing bar 14 rests upon the shoe 24 its weight no longer acts upon the shackle 30. The weight of the shackle and the cable 16, however, cause the direction of the relative force between the reinforcing bar 14 and shackle 30 to reverse, i.e. the shackle 30 continues to move downwardly when the reinforcing bar 14 is supported upon the shoe 24.

This causes the shackle 30 to move downwardly as drawn relative to the reinforcing bar, towards the position shown in Fig.3. This movement drives the cam member 50 counter- clockwise as drawn, so that the surface 51 is moved out of contact with the reinforcing bar 14.

The weight of the cam member 50 maintains it in its release position as shown in Fig.3, i.e. there is no tendency for the cam member to return into engagement with the reinforcing bar. If desired, it can also be arranged that a small release spring is fitted to urge the cam member 50 towards its release position, the force of the release spring being small in relation to the force applied by the tensioning means in the lifting position, and also the force applied by the weight of the reinforcing bar in the holding position.

It will be understood that movement of the reinforcing bar 14 relative to the shackle 30 is a significant factor in driving the cam to rotate to its released position, and this is the reason why in the embodiment shown the reinforcing bar 14 is initially secured to the shackle with its end out of the sleeve portion 34, allowing the reinforcing bar 14 to move into the sleeve portion when it engages the shoe. The actual distance through which the reinforcing bar 14 must move can be determined in practice, and might be very small.

However, substantial relative movement is desired to ensure that the presence (or absence) of a rib 56 does not preclude release of the shackle.

When the shackle 30 has moved to its released position as shown in Fig.3, the cable 16 can thereafter be lifted to remove the shackle from the casing, leaving the reinforcing bar 14 in its desired position. The operator may need to manipulate the cable during this lifting operation to ensure that the reinforcing bar does not engage the surface 51 and move the cam member 50 back towards its secured position.

It is expected that such manipulation would be easy to achieve in practice, the operator readily being able to observe the shackle to ensure that the cam does not re engage; the operator may even choose to lift the cable by hand the small distance necessary to remove the shackle 30 from the reinforcing bar 14.

In the embodiment shown it is the relative movement between the shackle 30 and the bar 14 in the chosen direction (i.e. between the position shown in Fig.2 towards the position shown in Fig.3) which drives the cam member 50 to its release position, but it is the reversal of the direction of the relative force acting between the shackle 30 and the bar 14 which permits that relative movement to occur. Thus, only when the weight of the bar 14 is being supported other than by the shackle 30 (e.g. upon the shoe 24), can the required release movement occur. There is no need for the relative movement to be large, and in embodiments utilising a release spring the relative movement could be minimal.

It is also possible for the release mechanism to be configured to work upon force alone rather than relative movement, so that the shackle is released when the weight of the bar 14 is no longer supported by the shackle, and the relative (lifting) force between the shackle and bar becomes zero or reverses in direction, whether or not relative movement between the shackle and the bar also occurs. Such - 12 embodiments are, however, likely to be more complex than the embodiments described, and so as not preferred.

Claims

A shackle for holding a member, the shackle having holding means engageable with the member, the holding means being movable between a first position in which the member is held by the shackle and a second position in which the member can be removed from the shackle, the holding means being movable from its first position to its second position by movement of the shackle relative to the member in a chosen direction.
2. A shackle according to claim 1 in which the holding means comprises a pivoting cam.
3. A shackle according to claim 2 in which the cam has a curved surface which is engageable with the member, and in which the curved surface is roughened or cut into the form of teeth so as to increase the frictional engagement with the member.
4. A shackle according to any one of claims 1-3 having releasable locking means for the holding means, the locking means acting to retain the holding means in its first position.
5. A shackle according to claim 4 in which the locking means comprises a threaded rod connected to the cam and a nut by which the rod may be secured.
6. A shackle according to claim 5 in which the rod also carries a compression spring, the rod being tensioned by tightening of the nut to compress the spring.
7. A shackle according to any one of claims 1-7 in which the shackle has a body which includes a channel within which a part of the member can be located. - 14
8. A shackle according to any one of claims 1-7 for use in holding a reinforcing bar as the reinforcing bar is lowered into a pile casing during DCIS concrete piling.
9. A method of using a shackle according to any one of claims 1-8 in which the shackle is used to hold the member as the member is lifted, and in which the weight of the member, by way of its engagement with the holding means, urges the holding means into, and acts to maintain the holding means in, its first position.
10. A method according to claim 9 in which the shackle is released by supporting the weight of the member other than by the shackle, the weight of the shackle urging movement of the shackle relative to the member in the chosen direction so as to move the holding means from its first position to its second position.
11. A shackle constructed and arranged substantially as described in relation to Figs. 2 and 3 of the accompanying drawings.