AU5170190A

AU5170190A - Anchors

Info

Publication number: AU5170190A
Application number: AU51701/90A
Authority: AU
Inventors: Michael Finlay; Ian Paterson
Original assignee: ITW Construction Systems Australia Pty Ltd
Current assignee: ITW Construction Systems Australia Pty Ltd
Priority date: 1989-03-07
Filing date: 1990-02-23
Publication date: 1990-10-09
Anticipated expiration: 2010-02-23
Also published as: AU642641B2

Description

"ANCHORS"

The present invention relates to anchors and more particularly to lifting anchors for incorporation into formwork for concrete beams or slabs prior to pouring the concrete in order to define lifting points by which the cast beam or slab can be lifted on site.

Prior lifting anchors for incorporation into pre¬ cast slabs or beams generally fall into two categories. One category consists of a so-called "face-lift" anchor which is incorporated into the thickness of a slab so as to provide a lifting point on the large face of the slab. The second category is a so-called "edge-lift" or

"erection" anchor which is incorporated into an edge of a slab, a beam or other component. In each case, a head of the anchor, usually incorporating a lifting eye for engagement with a lifting shackle, is located with a recess formed in the surface of the component.

One previously proposed form of face-lift anchor comprises a flat bar which is anchored within the slab by means of a circular-section pin which is embedded with the bar within the thickness of the slab and extends transversely through an aperture in the bar. When a lifting load is applied to the anchor, the transverse anchoring pin applies a tensile and shear load to the surrounding concrete of the slab. The anchorage is mainly dependent on the size of pin and the depth of embedment. As concrete is relatively weak in tension, the tensile forces applied by the pin to the concrete reduce the allowable loads which can be applied to the anchorage and this effect is particularly prevalent with thin panels where there is a reduced depth of embedment. Edge-lift or erection anchors conventionally comprise a flat bar having at its inner end splayed feet which diverge from opposite sides of the bar. The anchorage provided is satisfactory only if the anchor is surrounded by a sufficient thickness of concrete. If the anchor is used with relatively thin slabs or beams, either the allowable load falls considerably or additional reinforcing steel must be provided for co- operation with the anchor. The splayed feet also tend to deflect towards the axis of the anchor when subjected to the lifting loads, and this can lend to a decrease in the anchoring effect.

An object of the invention is to provide lifting anchors which provide a more secure anchorage within the concrete so as to permit an increased allowable load even under adverse anchoring conditions.

According to the present invention there is provided a lifting anchor for incorporation within a concrete component during casting of the component to provide a lifting point for the component, said anchor comprising a head portion adapted to remain at least partly exposed for engagement by lifting means and a body portion for embedment within the concrete, at least part of the body portion having one or more truncated forms with opposed sides which diverge in an axial direction away from the head portion, said one or more truncated forms being of such an extent as to provide substantial anchorage within the concrete, and said one or more truncated forms being such that collapse of the form by deformation of the sides of the form during lifting is prevented.

Further according to the invention, there is provided a lifting anchor for incorporation within a concrete component during casting of the component to provide a lifting point for the component, said anchor comprising a head portion adapted to remain at least partly exposed for engagement by lifting means and a body portion for embedment within the concrete, said body portion being shaped to cause secure anchorage of the anchor within the concrete under the lifting loads, said shape comprising at least one or more solid truncated forms having opposed sides which diverge in an axial direction away from the head portion, said one or more truncated forms extending along at least a majority of the length of the body portion and having such a lateral extent that the or each truncated form constitutes the primary means for securing anchorage within the concrete.

Still further according to the invention, there is provided a lifting anchor for incorporation within a concrete component during casting of the component to provide a lifting point for the component, said anchor comprising a head portion having an eye which remains exposed for engagement by lifting means extending through the eye, and a body portion for embedment within the concrete, said body portion being shaped to cause secure anchorage of the anchor within the concrete under the lifting loads wherein said head portion is of plate-like form with the eye being formed by an aperture extending through the plate-like head portion at right angles to the major surfaces of the head portion, and the body portion being shaped to define one or more truncated forms having upwardly facing opposed sides which diverge in an axial direction towards the base of the anchor, said divergent sides extending at least in the planes containing the major surfaces of the head portion, and the size and extent of the truncated forms being such that the forms provide substantial anchorage of the body portion within the concrete, and said one or more truncated forms being such that collapse of the form by deformation of the sides of the form during lifting is prevented.

The body portion may be defined by a single truncated form or by a series of axially-spaced truncated forms with divergent sides.

Preferably, the opposed sides of the or each truncated form are inclined to the longitudinal axis of the anchor«by an angle of between 5 and 50°, an angle of between 10 and 40° being especially preferred, and an angle of about 30° being the optimum.

In a preferred embodiment, the or each truncated portion of the body may be of a pyramid shape or a conical shape.

An embodiment of the anchor for use as a face-lift anchor wherein the head portion is incorporated in a face of a slab, may comprise an integral stand projecting from the base of the anchor to support the anchor from the base of a mould for the slab, with the base of the anchor being spaced above the base of the mould.

An embodiment of the invention for use as an edge- lift anchor for incorporation into the edge of a slab or beam is of bifurcated form comprising two substantially parallel legs depending from the head portion. Each of the legs has opposed sides profiled to define a series of axially spaced truncated forms with opposing sides which diverge away from the head portion.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 is a perspective view of a first embodiment of a lifting anchor in accordance with the invention;

Figure 2 is a front view of the anchor shown in Figure 1;

Figure 3 is a side view of the anchor shown in Figure 1;

Figure 4 is a front perspective view of a modified form of the lifting anchor shown in Figure 1;

Figure 5 is a front view of a second embodiment of a lifting anchor;

Figure 6 is a side view of the anchor shown in Figure 5;

Figure 7 is a front view of a third embodiment of a lifting anchor.

Figure 8 is a side view of the anchor shown in Figure 7;

Figure 9 is a plan view of an anchor with an integral stand for use as a face-lift anchor.

Figure 10 is a front view of the face-lift anchor shown in Figure 9;

Figure 11 is a fragmentary side view of an edge-lift anchor;

Figure 12 is an enlarged view showing in detail the profile formed on the legs of the anchor shown in Figure 11; and Figure 13 is an elevation of another embodiment of an edge-lift anchor.

As shown in Figures 1 to 3, a first embodiment of a lifting anchor in accordance with the invention comprises a head portion 2 of flat plate like form of rectangular cross-section with an aperture 4 extending at right angles through the plane of the head portion to define a lifting eye. Axially inwardly of the head portion 2, the body 6 of the anchor expands progressively in cross- section to define a truncated configuration with sides which diverge towards the base of the anchor. In Figures 1 to 3 the truncated body 6 is of pyramid shape whereby the truncation may be considered to be in a plane cjrvtaining the. plane of the head portion 2 and in a plane at right angles to that plane, or alternatively the anchor may be of uniform thickness in one direction, with the opposed larger faces of the body being truncated in opposed parallel planes containing the plane of the head portion as shown in Figure 4. In another alternative, the body may be of conical form. When embedded in concrete, the truncated body 6 with sides which diverge towards the base of the body apply, when a lifting force is acting on the anchor, a compressive and shear load to the surrounding concrete. The loading in compression and shear provides a significantly greater anchoring force than the loading in tension and shear as provided by the anchoring pin of the face-lift anchor discussed at the outset.

We have determined that to provide effective anchoring, the angle of inclination (alpha) of the inclined sides to the longitudinal axis of the body should be between 5 and 50° with a range of between 10 to 40° providing good results. We have determined that an inclination of about 30° provides optimum results. As will be appreciated the anchor shown in Figures 1 to 3 with a body 6 of pyramid configuration or a body of conical configuration will provide a greater anchorage than that shown in Figure 4 which is of constant thickness as viewed from the side, but this latter configuration can be used to advantage as an edge-lift anchor for thin panels or as an anchor for relatively thin beams where there is insufficient thickness to effectively utilise an anchor with the pyramid shaped body of Figures 1 to 3.

Figures 5 and 6 relate to a modification of the anchor shown in Figures 1 to 3 or Figure 4, in which the body 6 of the anchor comprises a series of axially-spaced truncated forms 10 interconnected by relatively short inwardly-directed wall-portions-12 preferably at right angles to the outwardly divergent sides 14. In the particular form shown, the body comprises a series of three truncated forms, although there may only be two. It may sometimes be desirable to provide more than three truncated forms (for example up to about six), although two or three will usually suffice. The use of a series of truncated forms provides a similar anchoring effect to that provided by the single truncated form of Figures 1 to 3 or Figure 4, but for a given length of anchor, requires less material in manufacture. Advantageously each of the truncated forms has sides which are inclined to the longitudinal axis of the body within the ranges specified above.

The anchors of Figures 1 to 6 may be fully moulded from a suitable plastics such as nylon or may comprise a composite of a plastics moulding 16 around a bar-like steel core 18 as shown in Figures 7 and 8 and which is apertured at the head end to provide the lifting eye. The anchors shown in Figures 1 to 8 can be used as edge-lift anchors for incorporation into an edge of a slab or for incorporation into a beam.

In the anchors shown in Figures 1 to 8, the body portion is directly connected to the head portion. For some applications it may be necessary for the body portion to lie at a substantial depth within the concrete with a relative long shaft extending between the body portion and the head portion at the surface of the component.

The anchors of Figures 1 to 8 can also be used as face-lift anchors. For this purpose, the anchors are used in conjunction with a stand having downwardly projecting - feet by which the anchor is supported from the base of the mould for the slab whereby the bottom of the anchor body will be spaced at a suitable distance above the bottom face of the slab or panel after casting. Although it is possible to utilise a separate stand to which the anchor can be clipped or otherwise secured, it is possible to provide the anchor with an integral stand, which is produced with the anchor preferably in a single moulding operation. Such an anchor is shown in Figures 9 and 10 with the integral base plate being designated 20. The base plate comprises outwardly-projecting legs 22 having, at their outer ends, depending feet 24 which rest on the mould base to support the anchor therefrom.

There is shown in Figures 11 and 12 an edge-lift anchor which is of bifurcated form to provide two parallel legs 30 depending from a head portion 32 having a lifting eye 34. The head portion also includes a recess 36 at each side for receiving part of the reinforcement. The anchor is of constant thickness as viewed from the side and is preferably formed by cutting from metal plate, for example by means of a plasma arc process.

Each of the two legs 30 of the anchor is formed with a multiplicity of truncated formations which extend only in the width dimension of the legs whereby the legs are of constant thickness. These formations, although extending in one plane only, are similar to those considered in relation to Figures 5 and 6 and the previous discussion concerning suitable angles of inclination are appropriate also to this anchor. Again, the optimum angle of inclination is 30 degrees. Whereas in the anchor of Figures 5 and 6 each truncated form is defined by opposed profiles which are symmetrical about the longitudinal axis of the body, in the anchor of Figures 11 and 12, the wave-like profiles on the opposite sides of each leg 30, although of mirror image, are axially displaced one relative to the other so that the crests 38 and troughs 40 of the two profiles are not in axial alignment as is clearly shown in Figure 12. This axial misalignment between the two profiles has two effects. Firstly, it prevents the formation of relatively narrow- lands which would otherwise exist at the points of coincidence of two opposed troughs 40 and which might therefore create zones of weakness along the length of the leg. Secondly, it permits a series of anchors to be cut simultaneously from the same plate, with the stock between the inner surfaces of the two legs of one another forming the opposed surfaces of the leg of a second anchor which is cut from the plate in inverted relation to the first anchor. Preferably, the axial misalignment of the two profiles is approximately one-half of the distance between adjacent crests of the profiles.

The bifurcated form of this edge-lift anchor enables the legs 30 to lie on opposite sides of reinforcing rods and reinforcing mesh without having to cut any of the reinforcement. In contrast, edge-lift anchors of solid construction across their width may sometimes require the reinforcement to be cut in order to permit the anchor to be placed within the mould at the required position.

The edge-lift anchor shown in Figure 13 is of bifurcated form similar to that of Figures 11 and 12 to provide two legs 42 depending from a head portion 44 having a lifting eye 46. The head portion 44 includes a recess 48 at each side for receiving part of the reinforcement. The anchor is of constant thickness as viewed from the side and is preferably formed by cutting from metal plate, for example by means of a plasma-arc process. Each of the two legs 42 of the anchor is formed with a multiplicity of truncated (that is, divergent) formations, the flanks of which are inclined to the longitudinal axis of the leg at a range of angles (alpha) as discussed above an optimum angle of inclination (alpha) being 30°. The outer profile 50 of each leg 42 is defined by a wave-like formation having alternating peaks and troughs of arcuate section symmetrical about an axis at right angles to the longitudinal axis of the formation, whereas the inner profile 12 is defined by a wave-like formation of which one flank 12a is of rectilinear shape.

The symmetrical outer profiles 50 facilitates manufacture of anchors simultaneously from a single plate whereby the stock between the two legs of one anchor forms two legs each associated with a different one of two anchors in inverted relation to the first anchor, and this manufacturing configuration requires the outer profile of each leg to be symmetrical in either orientation. In the configuration shown in Figures 11 and 12, the axes of the inner and outer wave-like profiles of each leg are parallel so that the two legs of the anchor are effectively parallel. Expressed differently, the crests of the wave-like formations on the inner and outer surfaces of each leg lie on a respective one of two parallel planes. In contrast, in the anchor of Figure 13, a line passing through the crests of the wave-like formation on the inner surface of the leg is inclined relative to that of a line passing through the crests of the outer wave-like formation so that the leg progressively tapers in width from the head end to the foot end of the anchor. We have determined that the legs carry a decreasing proportion of the load with increasing distance from the surface of the component in which the anchor is embedded. As the load carried by the leg decreases with increasing distance from the head end of the anchor, the width of the leg can therefore be progressively reduced away from the head end without impairing the load-carrying capabilities of the anchor. Generally speaking, the angle of taper (beta) will be up to 15 degrees, the higher end of the range being used for anchors where the legs are relatively short (about 150mm) and the wave-like formations have large amplitude. For most situations, for an anchor with a 5 tonne swl and a leg length of between about 300 and 400mm, taper angles of up to about 5° would be adequate. What is important is that the length of the portion of the legs with the wave- like formations is sufficient to transfer the load from the anchor to the concrete. The taper which provides the progressive reduction in width permits, for an anchor with a given load-bearing capacity, a reduction in cost of the anchor due to savings in material. The inclination which provides the taper is provided preferably only on the inner surface of each leg. Although it is preferred that the anchors of Figures 11 to 13 have wave like profiles at the opposite sides of each leg to provide the truncated forms, one side of each leg, preferably the inner side, could be rectilinear and parallel to the longitudinal axis of the leg. This would still provide a series of truncated forms with divergent sides, although the anchoring effect will be diminished to an extent; however, manufacture would be simplified.

The anchors described herein are embedded into a beam or slab, with the head of the anchor lying in a recess formed in the surface of the beam or slab so that the eye can be engaged with a lifting shackle of a lifting cable. The recess is produced during casting of the beam or slab by means of a removable recess former placed over the anchor head, as is well known.

In the embodiments described the truncated form or forms on the body portion are sucj as to provide at least a significant part, and sometimes the whole, of the anchorage for the anchor within the concrete, the size, and in particular the lateral extent of the form or forms being sufficient for this purpose. It is then not essential to add further reinforcement within the concrete to co-operate with the anchor to provide the required load-carrying characteristics. It will be noted that each truncated form is solid in order to prevent collapse of the truncation by deformation or bending of the sides of the truncation towards the longitudinal axis of the anchor under the forces applied during lifting. Although the solid structure is the simplest means of reinforcing truncated structure against collapse, other forms of reinforcing structure would be possible.

The embodiments have been described by way of example only and modifications are possible within the scope of the invention.

Claims

1. A lifting anchor for incorporation within a concrete component during casting of the component to provide a lifting point for the component, said anchor comprising a head portion adapted to remain at least partly exposed for engagement by lifting means and a body portion for embedment within the concrete, at least part of the body portion having one or more truncated forms with opposed sides which diverge in an axial direction away from the head portion, said one or more truncated forms being of such an extent as to provide substantial anchorage within the concrete, and said one or more truncated forms being such that collapse of the form by deformation of the sides of the form during lifting is prevented.

2. An anchor according to Claim 1, wherein the body portion is substantially defined by a single truncated form with divergent sides.

3. An anchor according to Claim 1, wherein the body portion is substantially defined by several truncated forms with divergent sides, each truncated form being spaced axially from an adjacent truncated form.

4. An anchor according to any one of Claims 1 to 3, wherein the or each truncated form has divergent sides in at least two mutually inclined axial planes.

5. An anchor according to Claim 4, wherein the or each truncated form is of generally pyramid shape or generally conical shape.

6. An anchor according to any one of Claims 1 to 3, wherein the body portion of the anchor is of substantially constant axial thickness in one axial plane and the or each truncated form is defined within a second axial plane at right angles, to the said one plane.

7. An anchor according to any one of Claims 1 to 6, wherein the or each truncated form is formed by moulding around a core element within the body portion, said core element extending into the head portion of the anchor and being apertured to provide a lifting eye in the head portion.

8. An anchor according to any one of Claims 1 to 7, wherein the anchor has, at a lower end of the body portion remote from the head portion, an integral stand of larger lateral extent that the body portion and operative to support the anchor from the base of a mould for the concrete component with the lower end of the body portion spaced above the base of the mould.

9. An anchor according to Claim 1 for incorporation into an edge of a concrete slab or beam, said anchor being of bifurcated form with two generally parallel legs depending from a head portion, each of said legs being profiled to define a series of axially spaced truncated forms with opposing sides which diverge away from the head portion.

10. An anchor according to Claim 9, wherein each leg extends over a substantial part of the length of the anchor.

11. An anchor according to Claim 9 or Claim 10, wherein the truncated forms of each leg are defined by a wave¬ like profile at each of two opposite sides of the leg, with the profile on one of said sides being axially offset relative to the profile on the other of said sides whereby to provide an out of phase relation between the profiles to define the truncated forms.

12. An anchor according to Claim 11, wherein the anchor is cut from sheet material of constant thickness and the wave-like profiles on each leg are formed in the thickness dimension of the leg whereby each leg is of constant thickness and varying widths defined by the opposing wave-like profiles.

13. An anchor according to Claim 12, wherein for each leg, the axes of the two wave-like profiles are relatively inclined whereby the leg is of reducing width in a direction away from the head portion.

14. An anchor according to Claim 13, wherein for each leg, the axis of the profile at an outer side of the leg is parallel to the longitudinal axis of the anchor, and the axis of the opposing profile at an inner side of the leg is inclined to the longitudinal axis to provide the reducing width.

15. An anchor according to any one of Claims 11 to 14, wherein the wave-like profile at an outer side of the leg has crests and troughs each of which symmetrical about an axis at right angles to the longitudinal axis of the profile.

16. An anchor according to any one of Claims 1 to 15, wherein each of the opposed sides of the or each truncated form are inclined to the longitudinal axis of the anchor at an angle of inclination of between 5 and 50°.

17. An anchor according to Claim 16, wherein said angle of inclination is between 10 and 40".

18. An anchor according to Claim 16, wherein said angle of inclination is substantially 30°.

19. An anchor according to any one of Claims 1 to 15, wherein at least one of the opposed sides of the or each truncated form is inclined to the longitudinal axis of the anchor at an angle of substantially 30°.

20. An anchor according to any one of Claims 1 to 19, wherein the or each truncated form is solid in order to prevent collapse of the form.

21. A lifting anchor for incorporation within a concrete component during casting of the component to provide a lifting point for the component, said anchor comprising a head portion adapted to remain at least partly exposed for engagement by lifting means and a body portion for embedment within the concrete, said body portion being shaped to cause secure anchorage of the anchor within the concrete under the lifting loads, said shape comprising at least one or more solid truncated forms having opposed sides which diverge in an axial direction away from the head portion, said one or more truncated forms extending along at least a majority of the length of the body portion and having such a lateral extent that the or each truncated form constitutes the primary means for securing anchorage within the concrete.

22. A lifting anchor for incorporation within, a concrete component during casting of the component to provide a lifting point for the component, said anchor comprising a head portion having an eye which remains exposed for engagement by lifting means extending through the eye, and a body portion for embedment within the concrete, said body portion being shaped to cause secure anchorage of the anchor within the concrete under the lifting loads wherein said head portion is of plate-like form with the eye being formed by an aperture extending through the plate-like head portion at right angles to the major surfaces of the head portion, and the body portion being shaped to define one or more truncated forms having upwardly facing opposed sides which diverge in an axial direction towards the base of the anchor, said divergent sides extending at least in the planes containing the major surfaces of the head portion, and the size and extent of the truncated forms being such that the forms provide substantial anchorage of the body portion within the concrete, and said one or more truncated forms being such that collapse of the form by deformation of the sides of the form during lifting is prevented.