GB2266905A - Concrete reinforcement cages - Google Patents

Abstract

A support structure 10 is described for use in producing a concrete reinforcement cage having a plurality of longitudinally extending bars 20 or 120 evenly distributed about a longitudinal central axis. The support structure 10 comprises a pair of frames connected to one another by two or more rods 12c or 112c extending along the length of the cage, the frames lying in planes transverse to the longitudinal axis of the cage. Each frame is in the form of polygon have sides formed by rods e.g. 18 which project beyond the corners of the polygon sufficiently to provide locating surfaces for the longitudinal bars of the cage without projecting beyond the permitted outside diameter of the cage. <IMAGE>

Description

Title Steel Reinforcement Cages Field of the invention The present invention relates to the manufacture of steel cages for the reinforcement of concrete piles.

Background of the invention One method of forming a concrete pile, known as the ATLAS system, involves first ramming a hollow tube or mandrel into the ground. The lower end of the mandrel is closed off by a specially designed pointed cap which can displace the ground ahead of the mandrel which is forced into the ground by downward pressure and rotation. The lower end of the mandrel is flared and only rests on the cap so that it can be withdrawn from the ground leaving the cap behind. Once the mandrel has been driven into the ground, a cage having longitudinally extending iron bars evenly distributed about its perimeter is lowered down the mandrel and concrete is poured down the mandrel to fill the mandrel at least partially. The mandrel is then withdrawn from the ground and the volume it occupied is taken up by the concrete which on setting forms the desired reinforced doncrete pile.

The reinforcement cages required for this application must meet exacting tolerances. If a cage is too large, it risks being jammed in the mandrel and being pulled out of the ground as the mandrel is withdrawn. If the cage is too small, it does not provide the degree of reinforcement required.

The conventional method of forming a cage for this application is to attach longitudinally extending bars to the outside of a helical coil of the outside desired diameter. The helical coil is intended only for locating the longitudinal bars in the correct positions rather than for reinforcement and is made of a bar of narrower gauge.

The helix is not therefore a rigid structure in itself and prior to assembly into a cage can be extended by pulling its coils apart. In practice, the outer diameter of the cage will vary with the pitch of the coils and the resulting cages do not always comply with the required tolerances.

Summary of the invention With a view to mitigating the foregoing disadvantages encountered in the prior art, the present invention provides a support structure for use in producing a steel reinforcement cage having a plurality of longitudinally extending bars evenly distributed about a longitudinal central axis, the support structure comprising a pair of frames of equal dimensions which, in use, lie in planes generally transverse to the axis of the cage and which are connected to one another by two or more rods which in use extend generally along the length of the cage, wherein each frame is in the form of polygon having sides formed by rods which project beyond the corners of the polygon sufficiently to provide locating surfaces for the longitudinal bars of the cage without projecting beyond the permitted outside diameter of the cage.

Preferably, the frames are formed as regular polygons having four to six sides.

The rods may conveniently be formed integrally with the sides of the frames. Thus, a structure may be manufactured by first bending both ends of two long rods through a right angle then welding the remaining sides of the frames to the bent ends.

It is possible to bend both ends of the rod in the same direction so as to form a U-shape. The frames in this case both extend to the same side of the plane defined by the two rods interconnecting the frames. The problem with such a construction is that the support structures cannot be compactly stacked for transportation.

In an advantageous development of the invention, the frames are connected to one another by two rods and are arranged to extend to opposite sides of the plane defined by the two rods. With such a support structure, the rods do not extend between corresponding corners of the two frames and do not therefore lie perfectly parallel to the cage axis. Instead, the interconnecting rods extend diagonally between opposite corners of the two frames and lie at slight angle to the axis. The angle is only small because the rods interconnecting the frames are significantly longer than the sides of the frames and the rods do still extend generally along the length of the cage. This is advantageous not only because of the ease of stacking but because the interconnecting rods can now act as braces giving further rigidity to the cage.

If the frames are formed to lie exactly at right angles to the interconnecting rods, then they too will lie at an angle which only approximates to 90" to the cage axis. This would not detract from the strength of the cage. It is however possible to form the frames at an angle of less that 90" to the plane of the interconnecting rods so that the support structures are slightly z-shaped when viewed from one side.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a support structure of the invention, shown alongside a reinforcement bar, Figure 2 is a section through a cage formed using the support structure of Figure 1, Figure 3 is a section similar to that of Figure 2 through a cage having five reinforcement bars, and Figure 4 is a section similar to that of Figures 2 and 3 through a cage having six reinforcement bars.

Figure 5 is a side perspective view of a support structure in accordance with a second embodiment of the invention, Figure 6 is a plan view from above of the support structure shown in Figure 5, Figure 7 is a side view showing a cage with bars secured to the support structure of Figure 5, and Figure 8 is a view similar to that of Figure of a further embodiment of the invention Detailed description of the preferred embodiments In Figure 1, a support structure of the invention, generally designated 10 is shown in perspective along side one of four reinforcement bars 20 which are to be secured to it to form a cage. The structure is itself formed of two U-shaped rods 12 and 14 connected to one another at one end by a pair of rods 16 and at the other end by a pair rods 18 which are welded in position.Each U-shaped rod, for example the rod 12, is formed of a long central section 12c, typically 80 cm in length, and two shorter end sections 12a and 12b, typically 10 cm in length, extending at right angles to the central section 12c. The bends connecting the end sections 12a and 12b to the central section 12c are sharp, that is to say they have a small radius of curvature, for reason that will become apparent from the following description.

As can be seen from Figure 2, the end sections of the Ushaped rods 12 and 14 form in conjunction with the rods 16 at one end of the support structure and the rods 18 at the other end of the structure a pair of square frames, the frames being connected to one another by the central sections of the rods 12 and 14. Each side of the frame is formed by a rod which projects beyond the corner of the frame to form locating surfaces for the longitudinal bars 20 of the cage. The bars are in this way located by the support structure and tie wires at the corners of the frames and along the length of the central sections of the rods 12 and 14 are used to secure the bars 20 of the cage to the support structure 10.The rods 12, 14, 16 and 18 must all project at each corner by an amount exceeding the radius of a cage bar 20 to provide an adequate locating surface, but must not project beyond the permitted outer surface of the cage to avoid the risk of jamming in the mandrel. The bends in the U-shaped rods need to be sharp in order to avoid having to weld the rods 16 and 18 onto the bends of the U-shaped rods 12 and 14, this being difficult to achieve with accuracy.

In a typical structure, the sides of the frame may be 10 cms long while the separation between the frames may be 80 cms, in other words the frame has an aspect ratio of 8:1. If the separation between the frames is excessive, the cage is weakened and it is undesirable for the separation to exceed ten times the size of the frames. At the other end of the scale, the separation of the frames may be as little as twice the size of the frame but in practice an aspect ratio of between 6:1 and 10:1 is to be preferred.

In a completed cage, two or more support structure may be provided along the length of the cage depending on its length and in this way the cage bars 20 are accurately maintained at their correct distances from the axis of the cage. Furthermore, unlike the case where a helix serves as the support structure, the rods are not only held at the correct distance radially but also tangentially so that rods cannot gather around one side of the cage or follow a skew path long the length of the cage.

The U-shaped rods 12 and 14 are mounted in Figure 1 in such a manner that the sections of rods 12 and 14 connecting the frames to one another lie on the same side of the cage.

This is not however necessary and it is alternatively possible for one of the U-shaped rods to be reversed if desired so that the rod sections connecting the end frames lie at opposite corners of the cage.

The embodiments of Figure 3 and 4 show that the same principle may be applied to cages having five or six cage bars 20. In the case of Figure 3, the frames are regular pentagons and are formed of five rods. Two of the rods 12' and 14' are formed by the end sections of the U-shaped rods similar to rods 12 and 14 in Figures 1 and 2, while the remaining three rods 18' are analogous to the rods 18 and are welded to the end sections of the U-shaped rods 12' and 14'.

In the embodiment of Figure 4, there are three U-shaped rods 30, 23 and 34 and the end frames have three additional rods 36 welded to the end sections of the U-shaped rods to form hexagonal frames.

In all the cases so far described, the support structures have rotational symmetry and when using two structures in the same cage it is convenient to arrange each structure at a different angle from the other so that the rod sections connecting the end frames lie adjacent different ones of the cage bars at the opposite ends of the cage.

When forming a support structure with only two rods interconnecting the end frames, it is preferred to use rods which are Z-shaped rather than U-shaped when viewed from the side to allow the support structures to be stacked during transit. One embodiment constructed in this manner is shown in Figures 5 and 6, while Figure 7 shows the attitude of the support structure within an assembled cage. A further embodiment constructed in this manner is shown in Figure 8.

To avoid unnecessary repetition, the parts of the support structure serving the same function as those in the embodiment of Figure 1 have been given the same reference numerals but preceded by a "1" in the case of the embodiment in Figures 5 to 7 and a "2" in Figure 8, so that, for example, the rod 212c in Figure 8, the rod 112c in Figure 5 and the 12c in Figure 1 are all equivalent.

In Figure 5, the end 112a is at right angles to the central section 112c and when the support structure 110 is assembled into a cage it lies tilted in the manner shown in Figure 7 relative to the cage bars 120. The central section 112c now extends diagonally between opposite corners of the two frames and acts a brace to strengthen the cage. The end frames are however also tilted, as shown in Figure 7 and are no longer normal to the cage bars 120.

Though this does not cause a serious problem, it can if desired be avoided by constructing the support structures in the manner shown in Figure 8 which differs from Figure 5 only in that the rods angles between the end sections 212a, 212b and the central section 212c are not right angles and the rod 212 is instead Z-shaped so that when they are vertically aligned, the end frames are still horizontal.

The structures of Figures 5 and 8 can readily be stacked for transportation and offer improved rigidity on account of the diagonal bracing. When using several such structures in a cage, it is desirable to rotate them with respect to one another so that the cage is strengthened in all planes.

The structures may first be formed by bending rods into a Ushape or a Z-shape, as the case may be, then welding the remaining rods 16, 18 or 116, 118 to complete the frames at the ends of each structure. It is however preferred to perform all the welding while the rods 12, 14 or 112 are all still straight to form a "flat-pack" which can subsequently be bent into the desired shape of the structure.

Claims (12)

1. A support structure for use in producing a doncrete reinforcement cage having a plurality of longitudinally extending bars evenly distributed about a longitudinal central axis, the support structure comprising a pair of frames of equal dimensions which, in use, lie in planes generally transverse to the axis of the cage and which are connected to one another by two or more rods which in use extend generally along the length of the cage, wherein each frame is in the form of polygon have sides formed by rods which project beyond the corners of the polygon sufficiently to provide locating surfaces for the longitudinal bars of the cage without projecting beyond the permitted outside diameter of the cage.

2. A support structure as claimed in claim 1, wherein the frames are formed as regular polygons having four sides.

3. A support structure as claimed in claim 1, wherein the frames are formed as regular polygons have five or six sides.

4. A support structure as claimed in any preceding claim, wherein the rods interconnecting the frames are formed integrally with sides of the frames.

5. A support structure as claimed in claim 4, wherein the structure is made by first bending both ends of two long rods through substantially a right angle then welding the remaining sides of the frames to the bent ends of the rods.

6. A support structure as claimed in claim 4, in which the frame rods are welded long rods to form a "flat-pack" which is subsequently bent to form a structure of the desired shape.

7. A support structure as claimed in claim 4, 5 or 6, wherein both ends of the rods are bent in the same direction such the frames lie to the same side of the plane defined by the rods interconnecting the frames.

8. A support structure as claimed in claim 4, 5 or 6, wherein the ends of the rods are bent in opposite directions such that the frames lie one to each side of the plane defined by the rods interconnecting the frames.

9. A support structure as claimed in claim 8, wherein the angle between plane of each frame and the plane of the interconnecting rods is less than a right angle, the structure being Z-shaped in side view.

10. A support structure as claimed in any preceding claim, wherein the rods interconnecting the frames are from 2 to 10 times as long as the sides of the frames.

11. A support structure constructed substantially as herein described with reference to and as illustrated in Figures 1 and 2, Figure 3, Figure 4, Figures 5, 6 and 7 or Figure 8 of the accompanying drawings.

12. A reinforcement cage comprising a plurality of longitudinally extending bars located at the corners of a polygon by being secured to a plurality of support structures as claimed in any preceding claim.