AU2008329539B2

AU2008329539B2 - Improved lifting link

Info

Publication number: AU2008329539B2
Application number: AU2008329539A
Authority: AU
Inventors: Rod Mackay Sim
Original assignee: Leviat Pty Ltd
Current assignee: Leviat Pty Ltd
Priority date: 2007-11-29
Filing date: 2008-11-19
Publication date: 2014-12-11
Anticipated expiration: 2028-11-19
Also published as: WO2009067733A1; NZ585932A; AU2008329539A1

Abstract

A lifting link (101) for anchors (106) embedded in a concrete panel (9, 10) is disclosed. The lifting link has an inverted T-shaped slot (125) with a mouth (124) at one end and a blind end (137). The slot has a well (258) sized to receive the head (105) of the anchor and positioned adjacent the blind end (137). Preferably the well is formed by a discontinuity (251) in the side surfaces (132) of the slot. A method of lifting a concrete element is also disclosed.

Description

WO 2009/067733 PCT/AU2008/001708 1 Improved Lifting Link Field of the Invention The present invention relates to a releasable lifting link for connection to a load. In particular the invention relates to a lifting link for connection to an anchoring element 5 embedded in a prefabricated concrete element to enable it to be safely lifted, transported and manoeuvred without damage. Such lifting links for anchors embedded in concrete elements are known and widely used to facilitate the lifting of prefabricated concrete elements. 10 More particularly the present invention relates to a link for attachment to an embedded anchoring element, said link being of a substantially spherical form, truncated laterally and incorporating a substantially central opening through which may be passed an attachment element to couple the link to the hoisting hook or lifting chains. 15 Background Art Releasable lifting clutches for connection between embedded lifting anchors and the hoisting chains are known. The first such of such devices was disclosed in US Patent 3499676 (Haeussler) and comprised a one piece coupling unit with a generally 20 spheroidal socket at one end formed with an arcuate channel adapted to receive the head of the anchor extending arcuately through approximately 1800 and a second end taking the form of a means of coupling to a hoisting chain. This device was found to be unsuitable for applications where the direction of force 25 changed during the lifting process such as is found during rotation of panels. This problem was resolved through the development of a two piece clutch having two parts, a link part for connection to the embedded anchor pivotable about a second shackle element for connection to the hoisting system. The shackle element passes through a transverse aperture in the body of the link part about which the link part 30 may pivot to enable connection to the anchor element. This type of clutch was disclosed in US patent 4173367 (Haeussler). The link on this type of clutch connects to the head of an anchor and has the form of a generally WO 2009/067733 PCT/AU2008/001708 2 spherical body truncated in a direction parallel to the internal arcuate slot which connects to the head of the anchor element. The truncation of the spherical link part permits the use of clutches to connect with anchors located in truncated spherical recesses, which is advantageous in making connections to relatively thin concrete 5 building panels. The anchoring element is cast within a surrounding recess such that the spherical attachment head of the anchor lies below the surface of the concrete thereby protecting it from damage. The recess has a substantially hemispherical form or a 10 truncated hemispherical form to enable the positioning of anchors in the edges of thin concrete panels thus providing sufficient distance from the fragile edge of the concrete panel and the laterally truncated edge of the recess surrounding the anchor. Known links have a T shaped arcuate slot for connection to the head of the lifting 15 anchor which extends through an angle of approximately 90 degrees from an entry mouth of the T shaped slot which lies substantially in the plane of the concrete surface. The link is attached to the head of the anchor by rotation of the link body about its central axis to a position which enables the head of the anchor to be entered into the entry mouth of the arcuate slot. The link is then finally engaged by rotation 20 about its central axis until the anchor head abuts the interior end wall defined by the end of the arcuate slot. Known lifting links incorporate a generally radially extending actuating arm which has a lower surface which abuts the concrete surface when the link has been rotated to 25 its fully engaged position, closed over the anchor head. The upper surface of the radial arm provides an abutment surface to engage with a horizontal bar provided on the pivotable shackle element of the lifting clutch. The horizontal bar of the shackle element is positioned so as to prevent the through passage of the radial arm which restricts the range of the rotation of the link, thereby minimising (but not completely 30 eliminating) the risk for unwanted disconnections during lifting. Unwanted disconnections resulting from the unrestrained rotation of the link with respect to the anchor head are well known and some known links incorporate a restriction adjacent to the opening of the arcuate slot. This restriction takes the form WO 2009/067733 PCT/AU2008/001708 3 of a convex upward bulbous section which leads into the arcuate path of the internal slot and which limits the passage of the anchor head into and out of the arcuate slot. For certain applications it would be desirable and more economical to use a link 5 without the second shackle element of known lifting clutches, directly attaching the link to a chain or the eye of a wire rope sling. Unfortunately, known links are not safe to use in this manner because there is no restriction on the rotation of the link. A further problem which arises as a result of rotation of the link under load is that the 10 rotation results in the transfer of the lifting load through the head of the anchor at some distance between the end of the slot and its opening. This results in a cantilevered loading situation in the truncated side walls of the link between the point of load and the closed end of the slot. Furthermore, in this position the anchor is no longer supported by the rear of the slot and is supported on the two sides resting upon 15 the lower arcuate surfaces of the cavity of the link. The load between the link and the anchor head is transferred as a shearing force through the sides of the head of the anchor and the wedging action of the anchor in the slot leads to a lateral displacement force acting outwardly upon the walls of the arcuate cavity of the link. 20 As the load is applied at increasing distances from the end of the slot, (i.e. closer to the opening of the slot) the additional bending moment resulting from the lever arm between the load and the end of the slot results in lateral bending of the side walls. Such bending has been known to enable the head of the anchor to slip from the link or result in overload bending failure of the side walls of the link. 25 This type of failure is particularly acute when anchors are placed in the edges of panels and the panels are rotated from the horizontal to the vertical position with the slot of the link perpendicular to the load. 30 Anchor failure as a result of these shearing forces is known and failure of the side walls of the interior cavity of known links has occurred. A method to prevent the movement of the anchor head from its optimum position was disclosed in US patent 4398762 (Haeussler) in which a secondly located locking 5175K-AU element was provided to prevent the movement of the anchor head. The disadvantage of this type of clutch is that it is mechanically complicated and prone to damage and fouling of the free passage of the locking element, rendering the clutch inutile. Genesis of the Present Invention The genesis of the present invention is a desire to provide an improved lifting link which may be used either in conjunction with a second shackle element to form a lifting clutch for attachment to a lifting hook, or for direct attachment to a lifting chain or sling, without a secondary shackle element. In either case the anchor head is maintained in its optimum position and thereby minimises the risk for disconnection or failure of the link or anchor as a result of unwanted rotation of the link. Summary of the Invention In accordance with the first aspect of the present invention there is disclosed a lifting link for concrete elements having an anchor located in a cavity and comprising a stem with its base embedded in the element and with a head at its distal end, said lifting link comprising a body having an above centre lifting aperture and a below centre generally arcuate downwardly opening blind slot, said slot having an interior sized to retain said head and an opening sized to accept said stem and obstruct said head, and said slot further having an entrance at one end sized to allow said head and stem to enter said slot, wherein said slot has a well therein spaced from said entrance, closely adjacent the blind end of said slot and shaped to receive said head to inhibit the movement of said head towards said entrance and contact said head on opposite sides thereof and at least one point intermediate said opposite sides. Preferably the lifting link is of a generally spherical shape truncated on two sides normal to a centrally located through aperture for connection to a second hoisting shackle element. The link preferably incorporates a centrally positioned and substantially T-shaped arcuate slot in a plane parallel to the truncated sides of the link and extending through a range of approximately 90 degrees. The T-shaped slot has an open end through which the head of the anchor may be passed and is closed at the other end to define an 4 5175K-AU abutment surface which is shaped to receive the head of the anchor when the link is in the fully engaged position and which supports the said anchor head on three sides. The internal shape of the T-shaped slot is preferably characterized by an arcuate cavity forming an upper arcuate surface defining the roof of the cavity, lateral side walls placed at such a distance apart as to enable the free passage of the large diameter of the spherical anchor head, two lower arcuate surfaces extending arcuately and essentially normal to the lateral cavity walls and which terminate in a radial slot, opening to the surface of the spherical link which provides the passage of the body of the anchor. The arcuate lower surfaces preferably incorporate a restriction adjacent to the opening of the arcuate cavity which faces convexly up toward the centre of the sphere, to further minimise disconnection. The radial slot preferably extends through an angle of substantially 90 degrees such that when the link is connected to the embedded anchor and rotated until the anchor shaft abuts the end of the radial slot, said anchor shaft is aligned to the central axis of the through aperture in the body of the link so as to provide vertical alignment of the axis of the anchor, the lifting shackle and an applied vertical load. This position describes the optimum location of the anchor within the lifting link. 5 WO 2009/067733 PCT/AU2008/001708 6 The lower arcuate surfaces of the cavity of the preferred embodiment incorporates a radial discontinuity such that the radial distance of these surfaces from the central axis of the sphere varies along the arcuate length of the cavity such as to define a greater radial distance in the region occupied by the anchor head when the link is in the fully 5 closed position with the anchor shaft axially aligned with the centre of lift and the anchor shaft substantially abutting the end of the radial slot and a lesser radial distance between such position and the opening of the slot which permits the entry of the anchor head to the slot. 10 The position of the discontinuity is located so as to restrict the movement of the link about the anchor such that the anchor is at all times supported on a surface of the internal cavity of not less than 180 degrees around the head of the anchor. That is to say that the movement is restricted to a distance less than the radial difference between the anchor head retained within the internal cavity and the shaft of the anchor 15 which passes through the radial slot. The effect of this radial discontinuity is to provide a well in which the anchor head is positively seated when the link is in the fully closed, optimum position. The discontinuity defines an abutment surface between the anchor head and the arcuate 20 surfaces of the internal cavity which limits the free translational rotation of the link about the anchor head during lifting. The disengagement of the link can only be achieved by positively relaxing the load and manoeuvring the link about the head of the anchor within the limiting arcuate interior wall of the recess. 25 The restriction to the arcuate movement of the anchor within the arcuate slot provided by the radial discontinuity ensures that the anchor is retained in the optimum support position, aligned with the centre of lift, and prevented from moving along the arcuate surface of the internal slot. The arcuate restriction thereby ensures that the lifting load is applied through the relatively thin side walls of the truncated link part at its 30 position of maximum strength, there being no additional bending forces induced in the side walls as a result of a cantilevered load caused by radial movement of the load toward the open end of the slot and wedging action by the anchor through the arcuate slot. The maintenance of the load in the optimum position improves both the security against shearing failure of the anchor head and side wall failure of the lifting link.

WO 2009/067733 PCT/AU2008/001708 7 A further aspect of the preferred embodiment is that the position of the radial discontinuity provides positive tactile and audible feedback to the operator indicating complete and full engagement as the link drops into position when the anchor head 5 moves into the discontinuity defined by the change of radial position. Another aspect of the preferred embodiment is that during lifting, the restriction to arcuate travel of the link about the anchor minimises movement of the radial arm of the link as a result of inertial or other external forces. The link may pivot about the 10 anchor head but the restriction to travel along the arcuate path ensures that the link remains closed over the anchor head in its optimum position at all times whilst the load is maintained, thereby improving safety. Brief Description of the Drawings 15 Preferred embodiments of the present invention will now be described with reference to the drawings in which: Fig. 1 is a perspective view of a prior art lifting link and its co-operating anchor embedded within a hemispherical recess in the face of a concrete surface, Fig. 2 is a perspective view of a prior art lifting link and its co-operating anchor 20 embedded within a truncated hemispherical recess in the edge of a concrete panel, Fig. 3 is a side elevation of a prior art link, Figs. 4 is a front elevation of a prior art link, Fig. 5 is a vertical section through the central axis of the sphere in Fig. 3, Fig 6 is a bottom view of the sphere connected to an anchor located within the slot 25 in its optimum position, Fig. 7 corresponds to Fig. 5 showing the link connected to an anchor embedded in. a hemispherical recess in the face of a concrete element, Fig. 8 is a vertical section through the centre of Fig. 4 showing the link connected to an anchor within a hemispherical concrete recess in the face of a concrete 30 element, Fig. 9 is the same as Fig. 8 however with the sphere rotated such that the anchor lies between the closed end of the slot and the open position, Fig. 10 is a bottom view of the sphere in the position indicated by Fig. 9 showing the anchor within the slot supported on two sides of the anchor head only, WO 2009/067733 PCT/AU2008/001708 8 Fig. 11 is section corresponding to Fig. 7, however, with an anchor located in the edge of a thin panel in a truncated hemispherical recess and with the lifting load applied through the link normal to the centreline of the internal cavity and the anchor axis, 5 Fig. 12 is a section corresponding to Fig. 7 and showing the lateral bending of the side walls of the internal cavity leading to release of the anchor head, Fig. 13 corresponds to Fig. 12, however, where the link has released after shearing failure of one side of the head of the anchor, Fig 14 corresponds to Fig. 12 where the link has released after bending overload 10 failure of one of the side walls of the internal cavity, Figs. 15-20 are equivalent views to those of Figs. 3-9 but illustrate the preferred embodiment of the present invention, Fig. 21 is equivalent to Fig. 20 but without the inclusion of the anchor, Fig. 22 shows the preferred embodiment of the present invention attached to an 15 anchor and subject to an inclined load, and Fig. 23 is an equivalent view to Fig. 19, however, illustrating the preferred embodiment of the present invention attached to an anchor located in a truncated hemispherical recess, rather than a spherical recess. 20 Detailed Description of the Preferred Embodiments As seen in Figs. 1-2 the prior art lifting clutch assembly IA is attached to hoisting chains (not illustrated) by a shackle 2 or similar element which passes through a central hole 3 in the truncated hemispherical body 4 of the lifting link 1 25 The known lifting link 1 is attached to the exposed head 5 of an embedded anchor 6 which is located within a recess 7 in a concrete element 8. One form of the recess is recess 7A illustrated in Fig. 1 and being of a generally hemispherical shape. The anchor 6 and recess 7A are located in the horizontal face 8 30 of the concrete element 9. Fig. 2 shows the exposed head 5 of an embedded anchor 6 located in another forn of the recess 7, namely a truncated hemispherical shaped recess 7B located in the edge 10 of a thin concrete panel element 11.

WO 2009/067733 PCT/AU2008/001708 9 As seen in Figs 3-8, the known link 1 has the form of a generally spherical body 4 with a transverse aperture 3 in an upper segment 4A of the body, which enables connection of the link 1 to the hoisting system by a shackle 2 or other connection 5 means. A lower segment 4B of the body generally lies below the surface 8 (Fig. 1) or 10 (Fig. 2) of the concrete surrounding the recess 7. The generally spherical body 4 is laterally truncated normal to the transverse aperture 3 to form two generally planar side faces 20 (Fig. 4). Known links have an arcuate slot 22 (Fig. 8) for connection to the head 5 of the lifting anchor 6. The arcuate slot 22 extends through approximately 10 150 degrees about the axis 23 (Fig. 3) of the link 1. The arcuate slot 22 is defined by a generally "U" shaped mouth section 24 (Fig. 4) to permit closure of the slot over the exposed head 5 of the anchor 6 within the recess 7 and a generally T-shaped slot 25 (Fig. 7) which extends through an angle of approximately 90 degrees from an entry point 26 (Fig. 8) which lies substantially in the plane of the concrete surface 8, 10. 15 The truncated sides 20 of the link 1 permit the connection of the link 1 to an anchor head 5 located in the truncated spherical recess 7B of Fig. 2 which is advantageous in the connection to relatively thin concrete building panels 11. 20 As seen in Fig. 8, the internal shape of the arcuate slot 22 is characterized by a generally arcuate cavity having an upper generally arcuate surface 30 defining the roof of the cavity, lateral side walls 21 (Fig. 5) placed at such distance apart as to enable the free passage of the head 5 of the anchor 6, and an end wall 38 and two upwardly facing, arcuate surfaces 32 (Fig. 5) extending arcuately from the end wall 38 25 of the cavity to the entry point of the slot 26. The arcuate surfaces 32 extend arcuately about the central axis 23 of the link body 4 from interior surface 21 of the side walls 33 to terminate at a radial slot 34, with inwardly facing vertical faces 34A opening to the surface 35 of the body 4 of the link, which provide passage of the shaft 27 of the anchor 6. The radial slot 34 extends from the entry point 26 approximately 30 90 degrees and terminates at an end wall 37 which defines an abutment surface for the shaft of the anchor 27 where the central axis of the shaft 27 of the anchor 6 is substantially vertical in Fig. 8 and directly below the central axis of the body 4 of the link 1. This position is illustrated in Fig. 8 and Fig. 6. Fig. 6 which shows the contact surface 39 of the anchor head 5 supported circumferentially over an angle of WO 2009/067733 PCT/AU2008/001708 10 approximately 270 degrees about the axis of the anchor by the arcuate surfaces 32 extending from the surface 21 of the side walls 33 and the rear of the arcuate cavity 38. This is the fully engaged position of the link 1 with optimum and maximum support of the anchor head 5 within the lifting link 1. 5 The arcuate surfaces 32 may terminate at a restriction element 36 adjacent to the opening 24 of the T- shaped arcuate cavity 25 which faces convexly up toward the centre 23 of the sphere, to minimise unwanted disconnection of the link 1 from the anchor head 5. 10 The link I is attached to the head of the anchor 5 by rotation of the link body 4 about its central axis 23 to a position which enables the head of the anchor 5 to be entered into the entry mouth 26 of the arcuate slot 22. The link 1 is finally engaged by rotation about its central axis 23 until the anchor shaft 27 abuts the end 37 of the 15 radial slot 34. Known lifting links incorporate a generally radially extending actuating arm 50 (Fig. 3) which has a lower surface 51 which substantially abuts the concrete surface 8, 10 when the link 1 has been rotated to its fully engaged position illustrated in Fig. 8. 20 The upper surface 52 of the radial arm 50 provides an abutment surface to engage with a horizontal bar 2A (Fig. 2) provided on the pivotable shackle element 2 of the lifting clutch assembly 1A. The horizontal bar 2A of the shackle element 2 is positioned so as to prevent the through passage of the radial arm 50 which restricts the 25 range of the rotation of the link so as to minimise the risk for disconnections during lifting. Known links may incorporate the restriction element 36 to limit the free passage of the anchor head into and out of the arcuate slot to help minimise the risk for 30 disconnection where rotation of the link I with respect to the anchor head 5 is otherwise unrestrained during complex turning and lifting operations. For some applications it would be desirable and more economical to use a link 1 without the shackle element 2 of known lifting clutches, by directly attaching the link WO 2009/067733 PCT/AU2008/001708 11 1 to the eye of a wire rope sling or similar device. Unfortunately, known links are not safe to use in this manner without the horizontal bar 2A of the shackle 2 which restricts at least to some extent the rotation of the link 1. 5 Figs. 9 and 10 illustrate the problem which arises as a result of rotation of the link 1 under an inclined lifting load "PI" at an angular direction "a" with respect to the axis of the anchor 6. The link rotates about its axis 23 which results in a rotational translation of the sphere along the arcuate surfaces 32 of the cavity 22. This rotation results in the transfer of the lifting load through the head of the anchor 5 at some 10 distance shown as "x" in Fig. 9 from the end 37 of the slot, which defines a lever arm between the point of support at the end of the slot 37 and the axis 6A of the anchor 6. This lever arm results in a cantilevered load being applied to the truncated side walls 33 of the link 1. Furthermore, in this position the anchor 26 is no longer 15 circumferentially supported over 270 degrees of its radial surface 39 (Fig. 7), instead being supported only by the arcuate surfaces 32 adjacent to the side walls 33 of the link 1. The contact surface 39 of the underside of the anchor head 5 is therefore reduced from approximately 270 degrees circumferentially about the anchor axis, to the two sectors 40 (Fig. 10) which bear upon the arcuate surfaces 32 of the link 1. 20 The two sectors 40 in aggregate amount to approximately less than half the full contact surface area 39. Thus the load between the link 1 and the anchor head 5 is transferred as a shearing force through the two sectors 40 of the anchor head. 25 Figs. 11-14 illustrate the effect of this overloading resulting from the rotation of the link 1 under load. A wedging action of the anchor head 5 in the slot 34 induces a lateral force "F" shown in Fig. 11 acting outwardly upon the walls of the arcuate cavity of the link, resulting in bending of the side walls 33 away from the centre of the 30 slot 34, thereby opening the width of the slot 34. Fig. 11 shows a situation where the widening of the slot 34 is just sufficient to allow the head of the anchor 5 to slip through the slot 34.

WO 2009/067733 PCT/AU2008/001708 12 Fig. 12 shows a situation where the widening of the slot 34 has reduced the contact sectors 40 sufficiently for the anchor head to fail by shearing of the sides 41 of the anchor head 5, thereby allowing the link 1 to disconnect from the failed anchor head 5. 5 Fig. 13 shows an overload bending fracture or failure of one of the side walls 31 of the link 1 as a result of excessive bending. Fig. 14 shows a bending failure of the side walls 31 of the link 1 which is a particular 10 problem when the side walls 31 of the link 1 are prised apart by the lifting load P being applied normal to the axis of the anchor 6 and the arcuate slot 25. This occurs when anchors are placed in the edges 10 of panels 11 and the panels 11 are intended to be lifted from a horizontal position to a vertical position with the slot 34 of the link 1 perpendicular to the load. 15 A method to prevent the movement of the link 1 from its optimum closed position with the anchor shaft 27 abutting the end of the radial slot 37 was disclosed in US patent 4398762 (Haeussler). This provided a second located locking element to prevent the movement of the anchor head. The disadvantage of this type of link is 20 that relies upon a separate locking element which may be prone to damage and fouling, rendering the link inutile. It is desirable to provide an improved lifting link having only one link element which may be used either in conjunction with a second shackle element or for direct 25 attachment to a lifting chain or sling. The lifting link includes a means to prevent rotational displacement of the link from its optimum closed position during lifting, regardless of the angle of inclination of the load, to substantially eliminate the risk for disconnection, failure of the link or the anchor. 30 In accordance with a first embodiment of the present invention there is disclosed in Figs. 15-22 a lifting link 101 for anchors 106 embedded in concrete elements 9, 11 (Figs. 1 & 2). In Figs. 15-22 the elements which correspond to elements illustrated in Figs. 1-14 have a designation number increased by 100. The lifting link 101 has the form of a generally spherical body 104 with a transverse aperture 103 in an upper WO 2009/067733 PCT/AU2008/001708 13 segment 104A of the body, which enables connection of the link 101 to the hoisting system by a shackle 2 or other connection means. A lower segment 104B of the body generally lies below the surface 108, 110 of the concrete surrounding the recess 107. The generally spherical body 104 is laterally truncated normal to the transverse 5 aperture 103 to form two generally planar side faces 120. The link 101 has an arcuate slot 122 for connection to the head 105 of the lifting anchor 106. The arcuate slot 122 extends through approximately 150 degrees about the axis 123 of the link 101. The arcuate slot 122 is defined by a generally "U" shaped mouth section 124 to permit closure of the slot over the exposed head 105 of the anchor 106 within the recess 107 10 and a generally T-shaped slot 125 which extends through an angle of approximately 90 degrees from an entry point 126 which lies substantially in the plane of the concrete surface 108, 110. The truncated sides 120 of the link 101 permit the connection of the link 101 to an 15 anchor head 105 located in a truncated spherical recess 107B which is advantageous in the connection to relatively thin concrete building panels 11. The internal shape of the arcuate slot 122 is characterized by a generally arcuate cavity comprising an upper generally arcuate surface 130 defining the roof of the 20 cavity, lateral side walls 133 placed at such distance apart as to enable the free passage of the head 105 of the anchor 106, an end wall 138 and two upwardly facing, arcuate surfaces 132 extending arcuately from the end wall of the cavity to the entry point of the slot 126. The arcuate surfaces 132 extend arcuately about the central axis 123 of the link body 104 from interior surface 121 of the side walls 133 to terminate 25 at a radial slot 134 with inwardly facing vertical faces 134A opening to the surface 135 of the body 104 of the link, which provide passage of the shaft 127 of the anchor 16. The radial slot extends from the entry point 126 approximately 90 degrees and terminates at an end wall 137 which defines an abutment surface for the shaft 127 of the anchor 106 where the central axis of the anchor 106 is substantially vertical in Fig. 30 20 and directly below the central axis 123 of the body 104 of the link 101. This position is illustrated in Fig 18 and Fig. 20. Fig. 18 shows the contact surface 139 of the anchor head 105 supported circumferentially over an angle of approximately 270 degrees about the axis of the anchor 106 by the arcuate surfaces 132 extending from the surface 121 of the side walls 133 and the rear of the arcuate cavity 138. This is WO 2009/067733 PCT/AU2008/001708 14 the fully engaged position of the link 101 with optimum and maximum support of the anchor head 105 within the lifting link 101. The arcuate surfaces 132 may, if desired, terminate at a restriction element 136 5 adjacent to the opening 124 of the T-shaped arcuate cavity 125 which faces convexly up toward the centre of the sphere 123, to minimise unwanted disconnection of the link 101 from the anchor head 105. The link 101 is attached to the head of the anchor 105 by rotation of the link body 104 10 about its central axis 123 to a position which enables the head of the anchor 105 to be entered into the entry mouth 126 of the arcuate slot 122. The link 101 is finally engaged by rotation about its central axis 123 until the anchor shaft 127 abuts the end of the radial slot 137. 15 The link has a generally radially extending actuating arm 150 which has a lower surface 151 which substantially abuts the concrete surface 108, 110 when the link 101 has been rotated to its fully engaged position illustrated in Fig. 20. The radial arm 150 provides a means of grasping the link 101 to enable it to be 20 engaged and disengaged by rotating the link 101 about the anchor head 105 within the recess 107. As best seen in Fig. 21, the arcuate surfaces 132 of the cavity 25 of the link 101 incorporate a radial discontinuity 250 which divides the surfaces 132 into two sections 25 132A and 132B. The former is that part of the surfaces 132 extending from the rear 138 of the cavity 125 to the discontinuity 250. Section 132B is that part of the surface 132 extending from the discontinuity 250 to the either the commencement of the restriction 136, or where no such restriction exists, to the entry point 126 to the cavity 125. 30 The radial extent of section 132A from the centre 123 of the body 104 of the link 101 is greater than that of section 132B. There is provided a short transition surface 251 between the two sections 132A and 132B which effectively defines an angled step linking the two sections together to make the surface 132 continuous.

WO 2009/067733 PCT/AU2008/001708 15 The position of the discontinuity 250 is located at a distance from the rear of the slot 137 so as to restrict the movement of the link 101 about the anchor head 105. Thus the contact area 139 of the underside of the anchor head 105 is at all times supported 5 by the surface of the internal cavity 132A. This support is preferably approximately 270 degrees, but is not less than 180 degrees, circumferentially around the head 105 and the longitudinal axis of the anchor 106. That is to say that the movement of the head 105 is restricted to a distance less than the radial difference between the anchor head 105 retained within the internal cavity 125 and the shaft 127 of the anchor which 1 Q passes through the radial slot 134. As seen in Figs. 21 and 22 the effect of the radial discontinuity 250 is to form a well 258 in the internal arcuate surfaces 132, extending over the length of the section 132A in which the anchor head 105 is positively seated when the link 101 is in the fully 15 closed optimum lifting position. The transition surface 251 defines an abutment surface between the anchor head 105 and the arcuate surface 132B of the internal cavity 125. This abutment surface prevents the anchor head 105 from moving past the discontinuity 250 when inclined loads are applied through the link 101 to the anchor 106. The effect of the discontinuity under the application of an inclined load "PI" is to 20 allow the link 101 to pivot about the anchor head 105 on the abutment surface 251 instead of allowing rotational translation of the link 101 around its central axis 123. The anchor head 105 is therefore retained in the optimum closed position for lifting regardless of the lifting load direction applied to the link 101. 25 The disengagement of the link 101 from the anchor head 105 can only be achieved by positively relaxing the load and moving the link 101 radially downwards along the anchor shaft 127 so as to allow the anchor head 105 to move beyond the well 258 and the discontinuity 250 and rotate about the surface 132B. 30 A second aspect of the restriction to the arcuate movement of the anchor head 105 within the arcuate slot 125 provided by the radial discontinuity 250 is as follows. Because the anchor is retained in the optimum support position, aligned with the centre of lift, and prevented from moving along the outer arcuate surface 132B of the internal slot, the lifting load is applied through the relatively thin side walls 133 of the WO 2009/067733 PCT/AU2008/001708 16 link 101 substantially at the position of their maximum strength, without inducing significant prising and outward bending forces in the side walls 133. This improves both security against shearing failure of the anchor head 105 and failure of the side wall 133 of the lifting link 101. 5 A further aspect of this arrangement is that the radial discontinuity 250 provides positive tactile feedback and audible feedback to the operator indicating complete and full engagement of the link 101 in its optimum position for lifting with respect to the anchor 106 when the anchor head 105 drops into the well 258. As the anchor head 10 105 moves from section 132B to 132A of the arcuate surface 132 it makes a noise and the dropping movement can be felt via handle 150. A still further aspect of this arrangement is that during lifting, the restriction to rotational translation of the link 101 about the anchor 106 minimises movement of the 15 radial arm 150 from the surface of the concrete 108, 110 providing a visual confirmation that the link 101 is properly engaged at all times during the lifting operation, thereby improving safety. Fig. 23 shows that the link 101 can be conveniently used for lifting anchors located 20 within a truncated recess 107B. An aspect of this arrangement is that the side walls 133 of the link 101 are increased in thickness between the spherical outer surface 135 of the body and a point 145 at some lesser radial distance from the centre 123 of the body 104 of the link 101. The effect of this thickening is to increase the bending strength of the side walls 133 when the link 101 is loaded in a direction perpendicular 25 to the arcuate cavity 125. The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention. 30 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. A lifting link for concrete elements having an anchor located in a cavity and comprising a stem with its base embedded in the element and with a head at its distal end, said lifting link comprising a body having an above centre lifting aperture and a below centre generally arcuate downwardly opening blind slot, said slot having an interior sized to retain said head and an opening sized to accept said stem and obstruct said head, and said slot further having an entrance at one end sized to allow said head and stem to enter said slot, wherein said slot has a well therein spaced from said entrance, closely adjacent the blind end of said slot and shaped to receive said head to inhibit the movement of said head towards said entrance and contact said head on opposite sides thereof and at least one point intermediate said opposite sides.

2. The link as claimed in claim 1 wherein said well is formed by a discontinuity in the base of said slot.

3. The link as claimed in claim 2 wherein said discontinuity is spaced from the blind end of said slot by a distance corresponding to the size of said head.

4. The link as claimed in any one of claims 1-3 wherein said stem is substantially cylindrical, said head is substantially cylindrical being substantially co-axial with said stem and of greater diameter, and said slot is generally T-shaped when viewed in transverse cross-section.

5. A lifting link as claimed in any one of claims 1- 3 wherein said head and well are substantially cylindrical and wherein said slot has a floor shaped to receive said head and inhibit the movement of said head towards said entrance.

6. The link as claimed in claim 5 wherein said well is formed by a curved discontinuity in the base of said slot.

7. The link as claimed in claim 6 wherein said discontinuity is spaced from the blind end of said slot by a distance corresponding to the diameter of said head.

8. The link as claimed in any one of claims 5 - 7 wherein said stem is substantially cylindrical, said head is substantially co-axial with said stem and of greater diameter, and said slot is generally T-shaped when viewed in transverse cross-section.

9. A method of lifting a concrete element having an anchor located in a cavity and comprising a stem with its base embedded in the element and with a head 5175K-AU 17A at its distal end, said stem being engagable with a lifting link as defined in any one of claims 1-8 above, said method comprising the step of: a. engaging said head with said well prior to raising said lifting link.

10. A concrete element having an anchor located in a cavity of said element, said anchor comprising a stem with its base embedded in the element and having a head at its distal end, said anchor being engaged with a well of the lifting device as defined in any one of claims 1 - 8.

11. A lifting link substantially as herein described with reference to Figs. 15-23 of the drawings.

12. A method of lifting a concrete element, said method being substantially as herein described with reference to Figs. 15-23 of the drawings.

13. A concrete element having an anchor located in a cavity of said element, said anchor comprising a stem with its base embedded in the element and having a head at its distal end, said anchor being engaged with a well of the lifting link as defined in claim 11. Dated this 23rd day of October 2014 WOODSTOCK PERCUSSION PTY LTD By: FRASER OLD & SOHN Patent Attorneys for the Applicant 5175K-AU