NZ554672A - An improved edge lifting anchor - Google Patents

Abstract

An edge lifting anchor for casting into concrete elements is disclosed. The edge lifting anchor includes: a lifting portion that receives edge lifting forces; two or more substantially elongate and separated force transfer portions that extend from the lifting portion; one or more concrete engaging projections extending from the one or more force transfer portions; and one or more shear resisting portions projecting transversely to a direction defined by shear forces imparted to the edge lifting anchor in use.

Description

554672 *10055477930* PATENTS FORM NO. 5 Fee No. 4: $250.00 PATENTS ACT 1953 COMPLETE SPECIFICATION After Provisional No: 554672 Dated: 20 April 2007 AN IMPROVED EDGE LIFTING ANCHOR WE ITW NEW ZEALAND LIMITED, a New Zealand company of 23-29 Poland Road, Glenfield, Auckland, New Zealand. hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: 554672 James & Wells Ref: 232479/61 LR AN IMPROVED EDGE LIFTING ANCHOR TECHNICAL FIELD The present invention relates to anchors for concrete building elements. In particular it relates to anchors for edge lifted concrete building elements.

Background Art Some methods of constructing buildings use prefabricated concrete building elements. Typically these elements are used as wall sections in buildings which are added to the construction by tilting or lifting them upwards into position from a casting bed or transporter.

Edge lift anchors are used in the building industry to provide connection points for a tool which is used to lift the wall element at an edge. An edge lifting operation is characterised by an initial force perpendicular to the wall element. This force may be referred to as a shear force. An edge lifting operation is also characterised by an upwards force parallel to the wall element as the wall element reaches a 15 relatively vertical orientation and is thus suspended by the edge lift anchor. This force may be referred to as a tensile force.

Edge lift anchors generally include an aperture or device of some form at one end. in use, the aperture or device accommodates a tool which is used to pull upwards on the anchor to lift the edge of the wall element.

Concrete wall elements are intrinsically heavy so considerable shear and tensile forces can be exerted on the anchor during an edge lifting operation.

Also, concrete is a material which does not have intrinsic tensile strength. 2 554672 James & Wells Ref: 232479/61 LR Given the relative weight of concrete wall elements and their poor tensile strength, there is a tendency for edge lift anchors to fail by being torn from the concrete of the wall elements during the lifting process.

The tensile strength of cement is typically characterised by a cone of concrete 5 which will be torn from the wall element if an anchor is to fail under a tensile force. This cone typically has a radius at the edge of the wall element which is three times the depth of the cone into the wall element. The depth of the cone is closely related to the depth at which the tensile force is acting. This means that the effective strength of an anchor will depend on the depth at which the force to pull 10 the anchor from the concrete is effectively located by the anchor. For this reason, edge lifting anchors typically have portions which extend into a wall element.

Edge lift anchors also have a portion which extends to be engaged by a lifting tool. This is typically an aperture for engagement by the lifting tool. This may also be referred to as a lifting eye.

One type of conventional edge lifting anchor has additional apertures at an opposite end to allow lengths of reinforcing bar or strand to be hung from it before being cast into the wall element. These are known in the art as "hangers". These hangers extend into the concrete wall element to engage the concrete and transfer a tensile force from the anchor to the concrete at a depth from the edge of the wall 20 element.

Another type of anchor has two legs which extend from the portion that contains the aperture for the lifting tool. These legs are formed to have an undulating (or wave) profile in the plane of the portion which contains the aperture for the lifting device (Lifting Eye). The wave profile has regions which are transverse to the 3 554672 James & Wells Ref: 232479/61 LR direction of tensile force to engage the concrete of the wall element. This type of anchor is typically plasma cut from a plate of metal.

A limitation of this type of anchor is that it relies on the surface area provided by the plate to engage the concrete and resist shear forces. The anchor may need to be 5 cut from an excessively thick plate to provide strong resistance to any shear force exerted while a wall element is titled upwards.

Another limitation of this type of anchor is that, by the nature of the undulating profile, some of the transverse surfaces are situated relatively close to the edge of a wall element. This means the effective depth at which the tensile force will be 10 situated is made up in part by some of the undulations close to the edge surface of the concrete element. This in turn means that the effective depth of the force, and height of the cone characteristic are low. Therefore, the effective strength of the anchor of a given length is limited.

Another type of known anchor includes elements which project upwards out of the 15 plane defined by the portion that provides an aperture for a lifting tool. These projections provide a greater surface area than is provided by the depth of any plate forming the rest of the anchor. Therefore this means that they provide relatively good resistance to shear forces occurring when a wall element is lifted upwards. This type of anchor also has apertures from which to hang hangers 20 which transfer tensile forces into the concrete of the wall element. Although this type of anchor includes improved resistance to shear forces, it suffers the same limitations as other conventional anchors in regards to tensile forces. Additionally, forces exerted at the lifting eye which is at an end of the anchor can cause the anchor to rotate. This means that the projections provide less area to resist shear 25 forces. This can limit the effectiveness of the anchor to resist shear forces. In 4 554672 James & Wells Ref: 232479/61 LR some cases rotation of the anchor may act to shatter concrete in the proximity of the anchor and lead to failure.

Another type of anchor includes two legs with barbs extending in towards each opposite leg in a saw tooth configuration. These barbs transfer forces through the 5 concrete to reinforcing steel laid within the wall element. Tension forces are transferred from the portion that includes an aperture for a clip through the legs, through the barbs and onto the reinforcing steel. As the reinforcing steel extends a significant way into the wall element, this type of anchor provides effective resistance to tension forces. However, this type of anchor relies on reinforcing 10 steel being present in wall elements and relies on reinforcing steel extending to positions close to the edge of the wall element. Also, some co-ordination of the positions of the anchor and the reinforcing steel may be required, which may add to labour costs involved with the construction.

The applicant has observed that it would be advantageous to have a concrete 15 anchor which acts to locate the force caused from tension on the anchor relatively deeply into a wall element. The applicant has observed that this would relatively maximise the size of the cone that would need to be torn from the concrete to dislocate the anchor from the wall element and therefore relatively maximise the tensile force need to cause an anchor to fail.

Accordingly, it is an object of the present invention to provide a concrete edge-lifting anchor which provides improved resistance to being pulled from a wall element under a tensile force, or at least provides the public with a useful choice in concrete anchors.

The applicant has also observed that it would be advantageous to have a concrete 25 anchor which resists rotation under shear forces exerted on an eye, or at least to 554672 James & Wells Ref: 232479/61 LR provide the public with a useful choice in concrete anchors.

Accordingly, it is a further object of the present invention to provide a concrete edge-lifting anchor which resists rotation under shear forces or at least to provide the public with a useful choice in edge lifting anchors.

The applicant has also observed that it would be advantageous for an edge lifting anchor to combine means for resisting both tensile forces and shear forces to resist both types of failure of anchors.

Accordingly, it is a further object of the present invention to provide an edge lifting anchor that provides a combination of both tensile force resisting means and shear 10 force resisting means, or at least to provide the public with a useful choice in concrete anchors.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors 15 assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications or products may be referred to herein, this reference does not constitute an admission that any of these documents/products form part of the common general knowledge in the art, in New Zealand or in any 20 other country.

It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the 6 554672 James & Wells Ref: 232479/61 LR listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process.

Further aspects and advantages of the present invention will become apparent 5 from the ensuing description which is given by way of example only.

Disclosure of Invention In one aspect the present invention provides an edge lifting anchor for casting into concrete elements, the edge lifting anchor including: a lifting portion configured to receive edge lifting forces; two or more force transfer portions extending from the lifting portion, said force transfer portions separated by a distance to define a gap there between; one or more concrete engaging projections extending from said one or more force transfer portions; and one or more shear resisting portions projecting transversely to a direction defined 15 by shear forces imparted to the edge lifting anchor in use.

Preferably, the concrete engaging projections project transversely to a direction defined by tensile forces imparted on the edge lifting anchor in use.

Preferably, one or more concrete engaging projections are formed substantially at an end of the respective force transfer portion, said end being distal from the lifting 20 portion.

Preferably, said two or more force transfer portions have a substantially constant cross-section in a region between the lifting portion and the one or more concrete 7 554672 James & Wells Ref: 232479/61 LR engaging portions.

This invention provides the advantage that forces will be transferred between the lifting portion and only the end of the force transfer portion. This means that for a given length of force transfer portion, and therefore edge lifting anchor, the tension 5 forces received by the lifting portion will be transferred as deep as possible within a concrete flooring element without the need to use hangers or for the element to bind with reinforcing mesh in the concrete element. This will maximise the effective tensile strength of the concrete in which the edge lifting anchor is set.

Preferably the edge lifting anchor is substantially planar and the one or more 10 concrete engaging projections extend transversely to a plane substantially defined by said edge lifting anchor.

Preferably, the concrete engaging portions do not extend outwards from a periphery substantially defined by the edge lifting anchor within said plane. This allows an edge lifting anchor of given width to have relatively large tension resisting 15 projections and therefore it may be set into a relatively thin concrete wall element. This advantage is achieved because the tension resisting projections extend out of the plane of the anchor rather than out of the vertical side profile of the edge lifting anchor.

Preferably, the one or more shear resisting portions extend for a length 20 perpendicular to a shear force exerted on the edge lifting anchor in use.

This shear force predominates during early stages of an edge lifting operation.

Preferably, the edge lifting anchor includes two shear resisting portions each located at opposite sides of the edge lifting portion. 8 554672 James & Wells Ref: 232479/61 LR Preferably, the force transfer portions extend parallel to a tensile force exerted on the lifting anchor in use.

Preferably, the two or more force transfer portions are separated by a distance to provide a gap between adjacent force transfer portions.

A gap between the force transfer portions allows the anchor to straddle reinforcing steel which might be set into a wall member.

The force transfer portions are preferably rigid and adapted to transfer tension and compression forces.

This allows an upper tension transfer portion to act as a compression transfer 10 portion at an early stage in an edge lifting operation. During this stage a lower tension transfer portion 'pulls' on the concrete while an upper tension transfer member pushes on the concrete. These complementary actions prevent the edge lifting anchor tilting in the direction of the edge lifting force. If the anchor does not tilt, the maximum cross-section of shear resisting portions will be presented to the 15 concrete. This will minimise the potential for the anchor to fail.

Preferably, the edge lifting anchor includes two or more force transfer portions.

Preferably, the edge lifting anchor includes at least one concrete engaging projection extending from each force transfer portion.

Preferably, the edge lifting anchor includes at least two concrete engaging 20 projections for each force transfer portion, said concrete engaging projections extending in opposite directions out from the force transfer portion.

Preferably, each force transfer portion extends for a length perpendicular to tensile 9 554672 James & Wells Ref: 232479/61 LR forces imparted on the anchor in use.

Preferably, the force transfer portions are relatively elongate.

Brief Description of Drawings Further aspects of the present invention will become apparent from the following 5 description which is given by way of example only and with reference to the accompanying drawings in which: Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 shows a wall element which includes an edge lifting anchor; depicts an edge lifting anchor set into an edge of a wall element, the wall element is shown in a horizontal orientation such as in the initial stages of an edge lifting operation; shows an edge lifting anchor set into a wall element, the wall element is shown in a relatively vertical orientation such as in the later stages of an edge lifting operation; depicts a cone of concrete which characterises concrete failing under a tensile force such as transmitted through an anchor; shows a perspective view of an edge lifting anchor according to the preferred embodiment of the present invention; shows a side elevation of an edge lifting anchor according to the preferred embodiment as it would be set in a relatively thin wall element; shows an end elevation of an edge lifting anchor according to the preferred embodiment, and 554672 James & Wells Ref: 232479/61 LR Figure 8 shows a perspective view of an edge lifting anchor according to an alternative embodiment of the present invention.

Best Modes for Carrying out the Invention Figure 1 shows a wall element (1) laying horizontally and resting on a Casting Bed 5 (3) as it may do prior to being lifted into place. The wall element (1) has an edge lifting anchor (4) set into the concrete of the wall element (1). The wall element (1) has a recess (5) to permit access to the edge lifting anchor (4) during a lifting operation. The arrow A depicts the direction in which the edge lifting anchor (4) would be lifted during an edge lifting operation.

Figure 2 shows the edge lifting anchor (4) in a close up view with the wall element (1) in a relatively horizontal position corresponding to Figure 1. The arrow B depicts a shear force component which characterises a lifting force during the initial stages of a lifting operation when the wall element is horizontal.

Figure 3 shows an edge lifting anchor (4) in close up view with the wall element (1) 15 in a relatively vertical position, as it would be during the latter stages of an edge lifting operation. The arrow C depicts a tensile force which characterises a lifting force during the latter stages of an edge lifting operation, when the wall element is relatively vertical. It will be appreciated by those skilled in the art that as the wall element moves between the horizontal (Figure 2) and vertical (Figure 3) positions 20 during the edge lifting process, the force applied to the edge lifting anchor (4) changes from predominantly a shear force (B) to predominantly a tensile force (C). Those skilled in the art will be aware that any forces exerted on the edge lifting anchor during an edge lifting operation will in practice be a vector combination of tensile forces, as depicted by the arrow C, and shear forces, as depicted by the 11 554672 James & Wells Ref: 232479/61 LR arrow B.

If the edge lifting anchor (4) was to fail during the initial stages of an edge lifting operation it would be torn out of the upper surface of the wall element (1) in the direction depicted by arrow B in Figure 2.

If the edge lifting anchor (4) was to fail during the latter stages of an edge lifting operation it would be torn from the edge of the wall element (1) in the direction depicted by the arrow C in Figure 3.

Figure 4 depicts a cross-section of a cone which may be used to characterise a concrete wall element (1) and anchor (4) failing under a tensile force. The cone (7) is typically characterised by its radius (8) which is typically three times the height (9) of the cone (7). The height (9) is typically defined by the effective depth of the anchor and any hangers or metal reinforcing associated with the anchor. Those skilled in the art will be aware of variations to the ratio of radius (8) to height (9) for given types, compositions or examples of concrete.

As will be known to those skilled in the art Figure 4 illustrates that increasing the height (9) of the cone considerably adds to the amount of material defined by the cone (7) which must be removed. Therefore, those skilled in the art will also be aware that increasing the height of the cone corresponds to increasing the depth into the wall element (1) upon which a tensile force, depicted by C, acts.

An edge lifting anchor (10) according to a preferred embodiment of the present invention is now described with reference to figures 5, 6 and 7. These figures show a lifting portion (11) in which are formed apertures (12) and (13). Aperture (12) allows the lifting portion (11) to be engaged by a lifting tool (not shown) which imparts forces as required during a lifting operation. The aperture (13) allows an 12 554672 James & Wells Ref: 232479/61 LR extra anchor hanger to be engaged to complement the anchoring properties of the anchor (10). Suitable sizes, shapes and orientations of the apertures (12) and (13), for use with given lifting tools, will be apparent to those skilled in the art.

The arrow B depicts the shear component of lifting forces, which predominate 5 during initial stages of a lifting operation. Arrow C depicts tensile forces, which predominate during the latter stages of a lifting operation. Figures 5 to 7 also show concrete engaging projections (14). In the preferred embodiment these comprise a pair of tapered projections (15) and (16) extending in opposite directions. In the preferred embodiment these projections (15) and (16) arranged 10 to create a flat surface (17) substantially perpendicular to the direction of tensile force indicated by arrow C.

As shown in Figure 7, the projections (15) and (16) are formed as tapers which tend to compress the concrete outwards and therefore may better resist the whole edge lifting anchor tearing a plug from the wall element.

Alternative embodiments of a lifting anchor according to the present invention may have alternative shapes to features such as the lifting portion (11) and these projections (15) and (16). Suitable alternative shapes will be apparent to those skilled in the art. As an example, Figure 8 shows a perspective view of an alternative embodiment of the lifting anchor with variation to the shape of the lifting 20 portion (11).

Also, alternative embodiments may have only one or other of the projections (15) and (16). However, all of the embodiments of the present invention will have a concrete engaging portion (14) which has one or more projections that are substantially transverse to the direction represented by C. This is necessary for the 25 concrete engaging portions (14) to engage the concrete into which the edge lifting 13 554672 James & Wells Ref: 232479/61 LR anchor (10) is set and thereby resist tension which would otherwise pull the edge lifting anchor (10) from the wall element (1).

The concrete engaging portions (14) are connected to the lifting portion (11) by force transfer portions (18) which, in the preferred embodiment, are formed by a 5 pair of elongate, leg-like projections that are spaced apart. The force transfer portions (18) of the preferred embodiment have a constant cross-section, as shown by comparison of Figures 5, 6 and 7. This provides the advantage that they do not engage the concrete (not shown) of a wall element (1). This means force transfer portions (18) simply transfer all of the tensile force, as depicted by the arrow C, 10 between the lifting portion (11) and the concrete engaging portions (14). Therefore, any tensile lifting forces imparted to the lifting portion (11) will be transferred as deep as possible into the wall element (1) for any given length of edge lifting anchor (10). This, maximises the size of the cone (7) which characterises the failure of an anchor under tensile forces.

Also shown in Figures 5 to 7 are a pair of shear resisting portions (19). These shear resisting portions (19) extend transverse to the direction of a shear force imparted to the edge lifting anchor (10) predominantly under the initial stages of an edge lifting operation. These shear forces are depicted by the arrow B. As is apparent from Figure 7 in particular, the preferred embodiment is planar in shape 20 and the projections (15), (16) and (19), which form the concrete engaging projections (14) and the shear resisting portions (19), project out of the plane formed by the rest of the edge lifting anchor (10). These projections (15), (16)and (19) also extend for a length perpendicular to the direction of predominant shear and tensile forces imparted to the anchor during an edge lifting operation.

Preferably, the two or more force transfer portions (18) are separated by a distance 14 554672 James & Wells Ref: 232479/61 LR to provide a gap between them. The distance allows the anchor (10) to straddle boxing steel which might be set into a concrete wall member. The force transfer portions (18) are preferably rigid and adapted to also transfer compression. This allows a force transfer portion (18) to act as a compression transfer portion at an 5 early stage in an edge lifting operation. During this stage a lower force transfer portion (18) 'pulls' on the concrete while an upper force transfer portion (18) pushes on the concrete. These complementary actions prevent the edge lifting anchor tilting in the direction of the edge lifting force. If the anchor does not tilt, the maximum cross-section of the shear resisting portions (19) will be presented to the 10 concrete and the shear force will not be concentrated at any point along the shear resisting portions (19). Forces concentrated at any point may cause the concrete to fail prematurely.

The use of an edge lifting anchor (10) according to the preferred embodiment of the present invention will now be described with reference to Figures 1 and 5 to 7.

To lift a wall element (1) from a horizontal position as shown in Figure 1 to a vertical position as shown in Figure 3, a lifting tool (not shown) would typically be inserted into the aperture (12) as shown in Figure 6. The lifting tool (not shown) would then be pulled upwards in the direction depicted by the arrow A in Figure 1. As the wall element is horizontal initially, the lifting force will predominantly be in 20 the direction depicted by the arrow B in Figure 7. At this point, the shear force resisting portions (19) engage the concrete in which the edge lifting anchor (10) is set to resist the shear forces depicted by the arrow B from tearing the edge lifting anchor through and out of the wall element (1). The shear resisting portions (19) represent a relatively large surface area transverse to the relatively plate-like, 25 relatively planar edge lifting anchor (10) and thereby provide a significant improvement of the resistance of the edge lifting anchor (10) to a shear force 554672 James & Wells Ref: 232479/61 LR represented by the arrow B.

During the latter stages of an edge lifting operation the lifting forces are predominantly represented by tensile forces as depicted by the arrow C. At this point, the concrete engaging portions (14) engage the concrete of the wall element 5 (1) at a point that is relatively distil from the lifting portion (11) and edge of the wall element (1).

Similarly to the shear force resisting portions (19) the concrete engaging portions (14) resist the edge lifting anchor (10) being torn from the wall element (1) due to the projections (15) or (16) being transverse to the rest of the edge lifting tool (10) 10 which is relatively planar.

The combination of shear force resisting portions (19) and concrete engaging portions (14) provides effective resistance to both predominant components of any forces imparted to the edge lifting anchor (10) during an edge lifting operation.

As is apparent from Figure 6, the edge lifting anchor (10) approximately forms a 15 peripheral profile and the projections (15) and (16) (best seen in Figure 5) do not project outwards from this profile. This configuration allows the edge lifting anchor (10) to be set into relatively thin wall elements which may only very slightly exceed the height of the lifting anchor (10) as depicted in Figure 2.

Aspects of the present invention have been described byway of example only and 20 it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims. 16 554672 Received at IPONZ on 23 December 2009

Claims (2)

1. WHAT WE CLAIM IS: An edge lifting anchor for casting into concrete elements, the edge lifting anchor including: a lifting portion configured to receive edge lifting forces; two or more substantially elongate and separated force transfer portions extending from the lifting portion; one or more concrete engaging projections extending from said one or more force transfer portions; and one or more shear resisting portions projecting transversely to a direction defined by shear forces imparted to the edge lifting anchor in use. An edge lifting anchor for casting into concrete elements, the edge lifting anchor including: a lifting portion configured to receive edge lifting forces; two or more force transfer portions extending from the lifting portion said force transfer portions separated by a distance to define a gap there between; one or more concrete engaging projections extending from said one or more force transfer portions; and one or more shear resisting portions projecting transversely to a direction defined by shear forces imparted to the edge lifting anchor in use. 17 554672 An edge lifting anchor as claimed in claim 1 or claim 2, wherein the concrete engaging projections project transversely to a direction defined by tensile forces imparted on the edge lifting anchor in use. An edge lifting anchor as claimed in any one of claims 1 to 3, wherein the one or more concrete engaging projections are formed substantially at an end of the each said force transfer portion, said end being distal from the lifting portion. An edge lifting anchor as claimed in claim 4, wherein the one or more concrete engaging projections extend transversely to a plane substantially defined by said edge lifting anchor. An edge lifting anchor as claimed in any one of claims 1 to 5, wherein the two or more force transfer portions have a substantially constant cross-section in a region between the lifting portion and the one or more concrete engaging portions. An edge lifting anchor as claimed in any one of claims 1 to 6, wherein the one or more shear resisting portions extend for a length perpendicular to a shear force exerted on the edge lifting anchor in use. An edge lifting anchor as claimed in claim 7, wherein the edge lifting anchor includes two shear resisting portions each said shear resisting portion located at opposite sides of the edge lifting portion. An edge lifting anchor as claimed in any one of claims 1 to 8, wherein the force transfer portions extend parallel to a tensile force exerted on the lifting anchor in use. An edge lifting anchor as claimed in any one of claims 1 to 9, wherein the force transfer portions are adapted to transfer tension and compressive forces. An edge lifting anchor substantially as herein described with reference to and as illustrated by the accompanying drawings. 18 554672 A method of lifting a concrete building element substantially as herein described with reference to and as illustrated by the accompanying drawings. ITW NEW ZEALAND LIMITED by their authorised agents JAMES & WELLS Intellectual Office Property of M.
2. 2, APR 2008 RECEIVED 19