Concrete Lifting Anchor
An elongate substantially planar lifting anchor (61, 161, 261, 361) to be embedded in concrete panels (2) and the like is disclosed. The anchor (61, 161, 261, 361) has a through aperture (63) adjacent one end (65) and the other end (34) is adapted to form a mechanical interlocking anchor with the concrete of the panel (2) in which the other end (34) is embedded, wherein the through aperture (63) is shaped to simultaneously receive both a lifting shackle (28) and a reinforcing member (263). The concrete panel incorporates at least one of the abovementioned elongate substantially planar lifting anchors (61, 161, 261, 361) and a method of lifting a concrete panel (2) in which a lifting anchor has been embedded comprises the steps of: (i) passing the lifting anchor (61, 161, 261, 361) through the aperture (63), and (ii) lifting the shackle (28) to transfer load directly to the reinforcing member (263) and thereby raise the panel (2).
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The present invention relates to concrete lifting anchors. Lifting anchors to be embedded in a concrete element are known to enable the concrete element to be safely lifted and manoeuvred without damage. In order for concrete elements to be safely lifted using anchors located therein the tensile and shearing forces generated in the anchors by the application of the lifting force need to be transferred to the surrounding concrete without either failure of the anchor or of the concrete element.
BACKGROUND OF THE INVENTIONIf the magnitude of the forces transferred to the concrete exceeds the strength of the concrete at the location of the anchor then the concrete may crack or even fail completely.
There are three basic techniques for transferring the loads to the concrete. Firstly, the anchor is provided with features which result in a mechanical interlock between the anchor and the surrounding concrete. The interlock may be achieved by a substantial enlargement of the anchor body at the end embedded in the concrete or by deformations along the length of the anchor body. This is the simplest and cheapest method.
Secondly, the anchor is mechanically connected to a deeply embedded reinforcing element, eg a “hanger bar” which distributes the load over a large volume of concrete.
Thirdly, the anchor is mechanically attached to the reinforcing steel of the concrete element, e.g. by welding to the reinforcing. Welding is often not desirable because reinforcing steels may not be suitable for welding and may also be substantially weakened at the site of the weld or attempted weld.
In most cases, lifting anchors are designed to be used without additional reinforcement, relying on mechanical interlock to transfer the loads into the concrete. The maximum load which these anchors may transfer to the concrete is determined by the geometry of the anchor and the concrete element, the location of the anchor within the element, and the tensile strength of the concrete and the depth of embedment.
OBJECT OF THE INVENTIONThe genesis of the present invention is a desire to provide an improved lifting anchor, and concrete element containing same.
SUMMARY OF THE INVENTIONIn accordance with a first aspect of the present invention there is disclosed an elongate substantially planar lifting anchor to be embedded in concrete panels and the like, said anchor having a through aperture adjacent one end and the other end being adapted to form a mechanical interlocking anchor with the concrete of said panel in which said other end is embedded, wherein said through aperture is of non-circular cross-section, shaped to mate with a recess former with which the anchor is set into place in the concrete.
Preferably the through aperture is shaped to simultaneously receive both a lifting shackle and a reinforcing member.
In accordance with a second aspect of the present invention there is disclosed a concrete element such as a building panel incorporating at least one of the abovementioned elongate substantially planar lifting anchors.
In accordance with another aspect of the present invention there is disclosed a method of lifting a concrete panel in which a lifting anchor has been embedded, said anchor having a single aperture shaped to simultaneously receive both a lifting anchor and a reinforcing member, said method comprising the steps of:
(i) passing a lifting anchor through said aperture, and
(ii) lifting said shackle to transfer load directly to said reinforcing member and thereby raise said panel.
In accordance with a further aspect of the present invention there is disclosed a method of lifting a concrete panel in which a lifting anchor has been embedded in concrete panels and the like, said anchor having a through aperture adjacent one end and the other end being adapted to form a mechanical interlocking anchor with the concrete of said panel in which said other end is embedded, wherein said through aperture is of non-circular cross-section, shaped to mate with a recess former with which the anchor is set into place in the concrete.
Preferred embodiments of the present invention will now be described with reference to the drawings in which:
Turning now to
Provided that the anchor is not able to slip out of the concrete and is able to fully transfer the loads to the concrete, the failure of the anchor occurs when the concrete surrounding the anchor fails. This type of failure results in a cone of concrete surrounding the anchor being pulled out of the concrete component. The cone is known as a “concrete shear cone” and the failure is known as “concrete cone failure”. If the anchor is located within the concrete element, well away from any edges then the cone will be fully developed and substantially symmetrical. The diameter of the cone at the concrete surface is typically approximately six times the depth of embedment of the anchor which is the lowest point along the anchor body at which interlock has been achieved with the surrounding concrete.
The load at which the cone pulls from the concrete is related to the conical surface area of the cone and this is proportional to the square of the embedment depth “d”, the centre spacing “c” and the distance to any edge “a” as shown in
If the anchor is located close to an edge as illustrated in
Generally anchors 1 are placed as far away from the edges of a panel 2 as is possible to achieve the development of the full concrete shear cone. Anchors are designed for their maximum load capacity by choosing an embedment length and expected concrete tensile strength to develop the full concrete shear cone at the mechanical strength of the anchor itself
A significant problem arises in particular in the maneuvering of thin concrete panels 2 as illustrated in
If the anchor 1 is loaded perpendicular to its body, toward one of the faces of the concrete panel 2 as seen in
It is desirable to locate anchors in the edges of thin concrete panels 2 to enable them to be lifted into place with simple lifting equipment. This is particularly so when the panels 2 are to be used as walling panels or external cladding for buildings.
Most commonly, such thin concrete panels are cast on flat casting moulds rather than on their edges. Problems arise when these panels are to be tilted as illustrated in
Both shear and tensile forces and combinations of both types are transferred through the anchors 1 into the concrete panels 2 during normal lifting operations.
Anchors and lifting devices used to connect them to the hoisting system have been used for many years in Australia. For example U.S. Pat. No. 3,499,676 (Haeussler) and Australian Patent Specification 50739/85 disclose the anchor embedded below the concrete surface within a recess 4 formed around the exposed head 6 of the anchor 5 as illustrated in
Prior to this prior art innovation, lifting was achieved with threaded inserts (which were susceptible to fouling and damage) or loops of steel or other materials (which protruded from the surface). These loops were also susceptible to damage and made stacking and transport of the concrete panels difficult and required removal and expensive patching of the concrete component. The Haeussler anchors 5 provided a safe, simple multi-use connection point which overcame the limitations of conventional loops and threaded devices.
The Haeussler anchors 5 took the form of an anchor body 7 of a round transverse cross section, an enlarged “head” 6 to which was connected a “lifting-eye” 8 (a special pickup device), and an enlarged “foot” 10 at the distal end embedded in the concrete to provide efficient mechanical interlock with the concrete. These anchors 5 were manufactured cheaply by simple “upset” forging methods on machines used for mass production of bolts. The size and shape of the “foot” 10 was designed to maximise the transfer of tensile forces in the anchor 5 to the concrete to develop the maximum possible shear cone.
In a further development as disclosed in U.S. Pat. No. 5,469,675 (Arteon) and Australian Patent Specification No. 95391/94 (Mackay-Sim) the pullout strength of such anchors 5 in thin panels was improved by providing a transverse opening 9 in the distal end through which was passed a hanger reinforcement for deep embedment into the concrete.
When subject to shear forces, as indicated in
In thin panels 2 this compression led to concrete failure toward the edge which allowed the anchor to bend and in some cases pullout of the anchor by prising from the panel.
Methods for reinforcing against this behaviour are disclosed in Australian Patent Specification No. 64207/94.
Another form of anchor 11 illustrated in
The anchor body 12 and/or its distal end embedded in the concrete is provided with a means of transferring the loads into the concrete in the embedded section by either spreading the body shape by cutting, punching or forming and the provision of further transverse holes 19 through which additional reinforcing elements may be passed to improve transfer of the forces into the concrete.
A further development of these anchors by Fricker as disclosed in U.S. Pat. No. 4,173,856 and illustrated in
A further development of this anchor by Francies & Lancelot as disclosed in International Patent Specification No. WO 03/012214 included transverse apertures 19 for the fitment of additional reinforcement and an enlarged aperture to provide additional anchorage to the concrete. Another embodiment of this anchor (not illustrated) took the form of a substantially round bodied anchor of the Haeussler type but with a planar shaped head.
An alternate method of transferring the shear forces was developed by Ramset, was disclosed in Australian Patent Specification No. 51692/90 and is illustrated in
All of the foregoing anchors 5, 11 have a significant disadvantage in that being single bodied anchors designed for central location within the concrete panel 2 they may interfere with the placement of the reinforcing steel in the concrete panel and can be difficult to design and place.
Another prior art anchor 21 is illustrated in
A disadvantage of this anchor 21 is that the anchor is produced by welding processes which are inappropriate for reinforcing materials and lifting devices.
Turning now to
As seen in
The anchor 31 of
In a further development illustrated in
When thin concrete panels are cast on horizontal moulds or “casting beds” and rotated into the vertical position with anchors located in the edges “edge-lift anchors”, the lifting forces perpendicular to the centreline of the anchor generate bending and shear forces in the anchor and shearing forces in the surrounding concrete toward the (upper) free surface of the panel in the lifting direction.
Edge-lift anchors are desirably made with a substantially rectangular cross-section with the long side of the rectangle aligned with the direction of the bending force and of a section modulus and strength sufficient to resist bending and distortion within the anchor itself. The transfer of the lifting force through the anchor body by compression of the surrounding concrete adjacent to the (upper) surface of the anchor in the direction of lift may be of sufficient magnitude to exceed the strength of the concrete itself, resulting in cracking or complete failure of the concrete by cone failure immediately above the anchor body. Various failure mechanisms are illustrated in
A disadvantage of the shear bars disclosed in Australian Patent Specification No. 41735/85 (Fricker) and illustrated in
This problem is addressed in a modified form of anchor 5 as disclosed in Australian Patent Specification No. 60513/90 (Arteon) and illustrated in
Turning now to the first embodiment of the present invention illustrated in
A limitation of this type of anchor is determined by the geometry of the anchor with respect to the surface of the concrete. The minimum distance “concrete cover” between the surface of the outside lateral edge of the leg of the anchor and the concrete surface is fixed by serviceability requirements of construction standards.
The width of the hairpin leg is also determined by the requirement that its cross-sectional area be capable of withstanding a proportion of the tensile strength of the anchor to be transferred to the concrete. In the case of the most common arrangement which has two legs, each leg is designed to transfer half of the tensile load when the anchor is loaded axially.
In
In the second embodiment illustrated in
It will be apparent to those skilled in the art that the general arrangement of the anchor 61 of
(a) a means of providing a centre of lift which is aligned with the centre of mass of the panel,
(b) the distance between the upper surface of the anchor body and the upper free surface of the panel being a maximum to minimise cracking above the anchor toward the concrete surface,
(c) the embedment depth from the inside (upper) surface of its lower leg to the concrete surface being a maximum,
(d) respect for the requirements for concrete cover, and
(e) simplicity and cost of manufacture.
The anchor 61 avoids the limitations of prior art edge lift anchors and provides a universal anchor for lifting in tension and shear from anchors placed in the edges of thin concrete panels. The anchor 61 may be economically manufactured by mass production flame cutting or similar processes, interdigitizing the legs of the anchors to minimise waste.
The lifting and reinforcing elements are both located in one transverse aperture which gives an efficiency of manufacture.
A further development of this anchor provides an offset shear reinforcing surface of the hairpin legs from the centre of lift of the anchor body to increase the edge lifting capacity.
The shape and size of the transverse aperture 63 may be varied so as to provide a means of location for each separate element (i.e. the reinforcement 62 and shackle 28) in such a way that they do not interfere with each other whilst enabling each to function individually according to the various requirements.
Furthermore,
Numerous embodiments of the basic anchor 61 can be fabricated and these are schematically illustrated in perspective views
Furthermore, in plan views
In four additional edge elevations, as seen in
The above embodiments are summarised as follows:
The anchor 61 of the preferred embodiment is illustrated in
The recess former also has side flaps 82 extending along the longitudinal sides of the two halves 73 and 72 such that the attachment end 74 of the anchor 61 is enclosed by the recess former 70. This arrangement means that a gap 91 is formed between the attachment end 74 of the anchor 61 and the surface 92 of the recess 93 formed in the concrete slab 90. Thus when the recess former 70 is removed from the slab 90 ready to be lifted, the attachment end 74 is free from the surface of the concrete and therefore does not transfer the lifting load to the concrete at this location. The attachment end 74 is free to deflect without cracking the concrete within the vicinity of the recess. This is a preferred arrangement and the side flaps can be dispensed with resulting in no gap 91 being formed if so desired.
Also seen in
The recess former 70 is removed from the hardened concrete by rotating each half 71 and 72 of the recess former 70 about the central hinge section, thereby releasing the recess former 70 from the plug 76 and anchor 61. After the removal of the plug 76 from the attachment end 74 of the anchor 61, the transverse aperture 63 in the exposed anchor 61 is exposed with a clean surface through which the attachment device or lifting shackle may be easily connected.
In the variation of this embodiment illustrated in
The foregoing describes only some embodiment of the present invention and modifications, obvious to those skilled in the concrete arts, can be made thereto without departing from the scope of the present invention.
The term “comprising” (and its grammatical variations) as used herein is used in the inclusive sense of “including” or “having” and not in the exclusive sense of “consisting only of”.
Claims
1. An elongate substantially planar lifting anchor to be embedded in concrete panels and the like, said anchor having a through aperture adjacent one end and the other end being adapted to form a mechanical interlocking anchor with the concrete of said panel in which said other end is embedded, wherein said through aperture is of non-circular cross-section, shaped to mate with a recess former with which the anchor is set into place in the concrete.
2. The anchor as claimed in claim 1 wherein the through aperture is shaped to simultaneously receive both a lifting shackle and a reinforcing member.
3. The anchor as claimed in claim 2 wherein the through aperture is shaped to minimise the distance between the lifting shackle and the reinforcing member.
4. The anchor as claimed in claim 3 wherein the through aperture is shaped to mate with a lifting shackle having a non-circular transverse cross-section.
5. The anchor as claimed in claim 2 wherein said anchor has at least one additional through aperture for receiving a reinforcing element.
6. The anchor as claimed in claim 1 and having a longitudinal axis, the centre of lift of said lifting shackle applied to said through aperture being substantially aligned with said longitudinal axis, and said through aperture being shaped to locate said reinforcing member at a position which is substantially displaced from said longitudinal axis.
7. The anchor as claimed in claim 1 wherein said one end of said anchor has at least two protruding portions extending from the one end away in the direction away from the other end.
8. The anchor as claimed claim 1 wherein at least one notch is provided on each side of the one end of said anchor, said notches adapted to receive reinforcing members in addition to the reinforcing member received in said aperture.
9. The anchor as claimed in claim 1 wherein said other end embedded in the concrete has a pair of spaced apart legs.
10. The anchor as claimed in claim 9 wherein the spaced apart legs have wavelike, sawtooth or like deformations along their lateral edges.
11. The anchor as claimed in claim 9 wherein the legs are substantially parallel.
12. The anchor as claimed in claim 1 wherein the other end of the anchor is bent outwardly in a direction perpendicular to the plane of the anchor.
13. The anchor as claimed in claim 9 wherein the spaced apart legs have wavelike, sawtooth or like deformations in a direction perpendicular to the plane of the anchor.
14. The anchor as claimed in claim 1 wherein said other end has a single leg with an additional aperture for receiving reinforcing members.
15. The anchor as claimed in claim 14 wherein said other end is substantially wave shaped.
16. The anchor as claimed in claim 14 wherein said other end is substantially frustum shaped.
17. The anchor as claimed claim 1 wherein said through aperture is adapted to receive multiple reinforcing members.
18. The anchor as claimed in claim 1 wherein the aperture has at least two lobes.
19. The anchor as claimed in claim 18 wherein the two lobes are connected by a slotted channel.
20. The anchor as claimed in claim 18 wherein the lobe for receiving the lifting shackle is substantially circular in shape.
21. The anchor as claimed in claim 18 wherein the lobe for receiving the lifting shackle is substantially elongated circular in shape.
22. The anchor as claimed in claim 18 wherein the lobe for receiving the lifting shackle is substantially oval in shape.
23. The anchor as claimed in claim 18 wherein the lobe for receiving the lifting shackle is substantially pear shaped.
24. The anchor as claimed in claim 18 wherein the lobe for receiving the lifting shackle is substantially rounded square in shape.
25. The anchor as claimed in claim 18 wherein the lobe for receiving the lifting shackle is substantially teardrop in shape.
26. The anchor as claimed in claim 1 wherein the aperture is substantially keyhole in shape.
27. The anchor as claimed in claim 1 wherein the aperture is substantially elongated keyhole in shape.
28. The anchor as claimed in claim 1 wherein the aperture is substantially teardrop in shape.
29. The anchor as claimed in claim 26 wherein the anchor has an additional aperture for receiving a reinforcing member.
30. The anchor as claimed in claim 27 wherein the anchor has an additional aperture for receiving a reinforcing member.
31. The anchor as claimed in claim 28 wherein the anchor has an additional aperture for receiving a reinforcing member.
32. A concrete element including at least one of the anchors as claimed in claim 1.
33. A method of lifting a concrete panel in which a lifting anchor has been embedded, said anchor having a single aperture shaped to simultaneously receive both a lifting anchor and a reinforcing member, said method comprising the steps of:
- (i) passing a lifting anchor through said aperture, and
- (ii) lifting said shackle to transfer load directly to said reinforcing member and thereby raise said panel.
34. A method of lifting a concrete element incorporating at least one of the anchors as claimed in claim 1.
Type: Application
Filed: Feb 21, 2007
Publication Date: Aug 21, 2008
Applicant: Woodstock Percussion Pty Ltd (Epping)
Inventor: Rod Mackay Sim (Epping)
Application Number: 11/677,421
International Classification: E04G 21/14 (20060101);