AU2006201337B2

AU2006201337B2 - Cast-in anchors

Info

Publication number: AU2006201337B2
Application number: AU2006201337A
Authority: AU
Inventors: Robert Urquhart Connell; Geoff Fletcher
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2005-04-07
Filing date: 2006-03-30
Publication date: 2012-02-02
Anticipated expiration: 2026-03-30
Also published as: AU2006201337A1

Abstract

P:\OPER\RSHW 27443 20-CAP. doc.29/03M06 - 18 An anchor for embedment into a concrete component, has a head via which load is applied to the anchor in use and an anchoring formation provided by at least one leg extending 5 from the head and profiled along an edge thereof so as to lock into the surrounding concrete. The profile is formed by a series of longitudinally spaced formations each of generally saw-toothed shape with a leading edge of each formation inclining towards the head such that on application of a pulling load to the head the leg will lock tighter into the concrete with increasing load. In one form the anchor is a lifting anchor and having a pair of such legs extending from the head which is adapted for releasable engagement with lifting equipment, and the profile is formed along an inner edge of each of the legs. 15 In an alternative form the anchor is a plate anchor in which the head of the anchor is formed by a plate and a set of such legs extends from each of two opposite sides of the plate transversely to the plane of the plate. Each set of legs comprises at least two parallel legs and the profile is formed along an inner edge of each of said legs. -6 2\\ 16 /2

Description

Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT (ORIGINAL) Name of Applicant: Cetram Pty Limited Actual Inventors: Geoff FLETCHER Robert Urquhart CONNELL Address for Service: DAVIES COLLISON CAVE, Patent Attorneys, 1 Nicholson Street, Melbourne, Victoria 3000. Invention Title: "Cast-in anchors" Details of Associated Provisional Applications Nos: 2005901724 7 Aril 2005 2005903846 20 July 2005 2006900092 9 January 2006 The following statement is a full description of this invention, including the best method of performing it known to us: Q:\OPER\RSH\Jan 06 - June 06\12744320-89.doc - 30/3/06 P:\OPER\RSH\I 2744320-CAP.do-29/03/6 CAST-IN ANCHORS The present invention relates to anchors intended to be incorporated into a concrete component prior to casting, for example lifting anchors to provide a lifting point by which 5 the component can be lifted during subsequent erection, and anchors for providing a fixing point for other components post-erection. Concrete lifting systems for lifting of concrete panels, beams and other components typically involve the use of lifting anchors incorporated into the component during casting, 10 with the head of the anchor being encased within a removable or disposable hollow void former to form within the surface of the component a recess within which the head of the anchor lies for releasable coupling to lifting equipment. Different types of lifting anchor are required for different components, loads, and type of 15 lift. Figure 1 shows an anchor which has been widely used for edge lifting of concrete panels although it can also be used for edge lifting of other components. As shown in Figure 1 the anchor comprises opposed parallel legs 2 of wave like or meandering form extending from a head 4. The particular head shown is designed for use with a releasable lifting clutch in the form of a ring clutch having an arcuate locking bolt received within an 20 eye 6 in the head and which remains exposed within the recess after casting. Typically, this type of anchor is formed from a thick metal plate using non-contact high energy cutting means such as a laser beam or plasma arc. As mentioned, anchors of the type shown in Figure 1 have a principal utility in the edge 25 lifting of concrete panels and in that usage the anchor is installed within the panel such that it traverses the thickness dimension of the panel with each of the two legs 2 lying adjacent to the respective faces of the panel. The two legs 2 lie either side of reinforcing mesh in the central median plane of the panel and one or more shear bars or tension bars are incorporated into the apertures 8 shown in the head in order to tie the anchor into the 30 reinforcing structure of the panel; the details of the actual tie-in will depend on the actual loading to which the anchor is to be subjected and also to the type of lift which can be C-\NRPortbl\DCC\PLW\47553_1.DOC-23/i2/201" -2 either straight edge lift or edge lift with tilt-up. When installed, there is a relatively small thickness of concrete between each leg 2 and the adjacent face of the panel. During lifting, the meandering profile of the leg interacting 5 with the concrete to the inside and outside of the leg provides on the leg opposing lateral forces which are normally in equilibrium in order to prevent lateral deflection of the leg. However a potential failure mode with this type of anchor arises if the strength of the concrete to the outside of the leg is insufficient to withstand the forces acting on the leg from its inner face and acting in a sense to force the leg outwardly. If such failure were to 10 arise, the leg would be deflected outwardly and would "burst through" the adjacent face of the panel. In order to avoid this type of failure, existing anchors of this type are designed with legs which are sufficiently long to provide load distribution over a long leg length such that "burst through" in the circumstances just described, should not arise. 15 With existing anchors of this type, the need to produce the anchor with relatively long legs increases the material costs and also can sometimes complicate the installation of the anchor prior to casting. According to one aspect of the present invention there is provided an anchor for 20 embedment into a concrete component, the anchor having an anchoring formation provided by at least one leg so profiled as to lock into the surrounding concrete, the profiling being formed by a series of formations each of generally saw-toothed shape and arranged longitudinally along the leg, with a leading edge of each formation inclining towards the head, the profile being such that when load is applied to the anchor in the axial 25 direction of the leg, the resultant of the forces acting on the leg is such that there is no, or substantially no, component of that force acting in a sense to deflect the leg laterally outwardly towards an immediately adjacent face of the concrete component.

C \NRPonblWCC\PLWW67553 I DOC-23/122011 -3 Particularly advantageously the profiling of the leg is such that the resultant of the forces acting on the leg acts laterally inwardly in a direction towards the other leg. 5 With the configuration defined above, the outer edge of the leg can be kept straight and this is of particular advantage when the anchor is being cut out of thick metal plate by laser beam or plasma arc as cutting in a straight line is able to be accomplished significantly more quickly than when cutting along a complex path. It is however within the scope of the invention for the outer edge of the leg also to be suitably profiled. 10 Accordingly, according to yet another aspect of the present invention there is provided a lifting anchor for embedment into a concrete component, the lifting anchor having a head for releasable engagement with lifting equipment and generally parallel legs extending from the head portion, wherein the anchor is cut from metal plate material using a high 15 energy non-contact cutter, the outer edge of each leg is cut along substantially its entire length with a straight cut, and the inner edge of each leg is cut to form the profile which locks with the surrounding concrete. According to another aspect of the invention there is provided an anchor for embedment 20 into a concrete component, the anchor having an anchoring formation provided by at least one leg so profiled as to lock into the surrounding concrete, the profiling being formed by a series of formations each of generally saw-toothed shape and arranged longitudinally along the leg, with a leading edge of each formation inclining towards a head of the anchor such that on application of a pulling load to the head, the leg will lock tighter into the concrete 25 within increasing load. According to another aspect of the invention, there is provided a lifting anchor for C:NRPonbIL\DCC\MLW\.7553_1 DOC-23/12/2011 -4 embedment into a concrete component, the lifting anchor having a head with an eye for releasable engagement with lifting equipment, and generally parallel legs extending from the head, each leg being profiled along an inner edge thereof so as to lock into the surrounding concrete, the profiling being formed by a series of formations each of 5 generally saw-toothed shape and arranged longitudinally along the leg, with a leading edge of each formation facing upwardly towards the head and inclined at an acute angle to the axis of the leg. When using an anchor as described above, a tension bar to increase the load capacity of the 10 anchor can be installed between the two legs adjacent to the underside of the head but without actually physically contacting the head as there will be load transmission between the tension bar and the head via the intervening concrete. The inventive principles discussed above in relation to anchors having a pair of generally 15 parallel legs are also applicable to an anchor having a single leg or other elongate anchoring formation projecting from the anchor head. Although the present invention in some aspects is primarily applicable to lifting anchors, it is also applicable to other forms of cast-in anchor. 20 When applied to a plate anchor each leg extends transversely to the plane of the plate of the anchor with one or more legs extending from each of two opposite sides of the plate. The legs are formed integrally with the plate by cutting from metal stock and then bending the legs. 25 Preferably, the legs extend substantially perpendicularly to the plane of the plate as this is the most economical option to obtain the required embodiment depth, although in C:\NRPorblOCC\PLWW407553_ .DOC-23/12/2 I -5 alternative versions, the legs could be inclined to the perpendicular by up to approximately 300 in either direction. The plate may include a threaded fixing point. In one form, this can be formed by a nut 5 welded to a rear surface of the plate in alignment with an aperture and enclosed within a separate void former, for example in the form of a plastics cup, attached to the rear side of the plate. In another form, the threaded fixing point can be formed by a rearwardly projecting integral tubular structure produced integrally with the plate by a burst extrusion process which may result in the tubular structure being of increased thickness with respect 10 of that of the remainder of the plate. The tubular structure is then tapped and is enclosed within a separate void former, for example formed by a plastics cup attached to the rear side of the plate. Although these methods providing a threaded fixing point have significant utility in a plate 15 anchor formed with integral anchoring legs designed in accordance with the principles P:\OPER\RSH\l2744320-CAP.doc-29/0306 -6 discussed above, they also have utility in more conventional forms of plate anchors such as those with anchoring formations formed by lengths of reinforcing bar bent into U shape and welded to the rear of the plate. 5 Accordingly, a yet further aspect of the invention provides a plate anchor for embedment into a concrete component, wherein the plate of the anchor has a fixing point formed by a threaded formation enclosed within a separate void former attached to the plate. The threaded formation may be formed by a nut welded to the rear side of the plate or by 10 an integral tubular structure extending to the rear of the plate and formed by burst extrusion and subsequently threaded. In either case, the void former can be formed by a separate plastics cup attached to the rear of the plate, for example by adhesive. Embodiments of the invention will now be described by way of example only with 15 reference to the accompanying drawings in which: Figure 2 is a view from the front of a lifting anchor in accordance with a preferred embodiment of the invention; Figure 3 is a perspective view of the anchor shown in Figure 2; Figure 4 is an enlarged detail showing a modified form of profiling applicable to 20 the inner edge of each leg of the anchor shown in Figures 2 and 3; Figures 5 to 7 are fragmentary views of anchors of the type shown in Figures 2 and 3 but with profiling along the outer edge of each leg; Figure 8 shows a modification to the anchor to accommodate further reinforcement in a concrete panel; 25 Figure 9 shows schematically a modified anchor having only a single leg; Figure 10 is a perspective view of a plate anchor; Figure 11 is a side view of the anchor shown in Figure 10; and Figure 12 is a plan view showing the plate anchor after cutting from metal plate material and prior to bending of the legs. 30 The anchor shown in Figures 2 and 3 is of the general type shown in Figure 1 with a head P:\OPER\RSHi\l 2744320-CAP.doc-29/03/06 -7 4 for coupling to lifting apparatus and a pair of substantially parallel legs 2 extending from the head 4. The particular head 4 shown is designed for co-operation with a lifting clutch in the form of a ring clutch with an arcuate locking bolt received within the eye 6 although it is to be understood that the head 4 could be of a different detailed design for use with 5 other types of lifting apparatus. As with the prior anchor, the anchor is cut from thick metal plate by laser beam or plasma arc cutting. In the particular form shown, the eye 6 is also laser or plasma cut as part of a continuous cutting operation as described in our patent 751863. However the eye could alternatively be formed by a separate stamping operation after cutting the anchor. 10 In the conventional wave profile in the anchor in Figure 1, the profile at the inner edge of the leg engenders, when the anchor is under load during edge lifting, a reaction with the surrounding concrete, the resultant of which is in a laterally outwards direction. Conversely, the profile at the outer edge of the leg engenders with the surrounding 15 concrete a reaction the resultant of which acts in a laterally inwards direction. In contrast, in the anchor shown in Figures 2 and 3, each leg 2 is provided along its inner edge with a series of spaced profiles which lock into the concrete but which are so shaped that the resultant of the reaction between these profiles and the surrounding concrete when the anchor is under lifting load has no, or substantially no, component in a laterally outwards 20 direction. To the contrary, the resultant of the reaction may have a component acting in a laterally inwards direction although this might not be particularly significant. As shown, each sequential series of profiles consists of an upper generally straight portion 12 inclined laterally outwardly in a downwards direction (in other words a direction away from the head 4) merging into a portion 14 which is inclined upwardly to face the head 4 and 25 laterally inwardly. It is this latter portion 14 which locks into the concrete under load and it is this portion that principally takes the loading between the leg and the surrounding concrete. It will be understood that as a result of the inclination of the load-carrying locking portion 14 upwardly and laterally inwardly the resultant of the forces acting on the leg as a result of the inter-engagement will act laterally inwardly, in other words away 30 from the adjacent face of the panel. This not only avoids "burst through" of the leg into the panel face under load but also causes the leg to lock tighter into the concrete as the load P:\OPER\RSH\l2744320-CAP doc.29/036 -8 increases. From what is shown in Figures 2 and 3 and also Figures 4 to 12 to be described subsequently, it will be understood that the profiling can be described as being formed by a series of formations of saw-tooth like shape with the leading face thereof which represents the locking portion facing towards the head of the anchor. 5 In the form shown, the portion 12 merges into the load-carrying locking portion 14 via an arc 16 of large radius which actually continues so as to form the locking portion 14. In addition to the basic requirement of shaping the profile to achieve the type of locking action discussed above, it is also in practice necessary to ensure that the profile is able to 10 be cut efficiently using laser or plasma cutting techniques and this may result in some variation from that shown. For example, in the detail shown in Figure 4 the locking portion 14 is more rectilinear in shape and merges at its lower end with the end of the downwardly inclined portion 12 via a small radius 18, and its upper end merges with the upper end of the following downwardly inclined portion 12 by a similar small radius 20. 15 In one example the angles included between the portions 12 and 14 are the order of 15*. It is to be understood that the invention is not restricted to the particular profiles shown and other profiles which lock into the concrete without engendering a resultant laterally outwards reaction on the leg could alternatively be used. Examples of other forms of 20 profile are shown with reference to the embodiments of Figures 8 to 12. As the inside leg profile is such that the leg is not required to be of a length to avoid the "burst through" condition previously described, the requisite load can be carried using shorter legs than was necessary in a comparable anchor of the form shown in Figure 1. 25 Accordingly the material costs for the anchor are reduced and also installation may be quicker in some circumstances. Preferably, each leg 2 progressively tapers in width towards its lower end. Therefore, the upper part of each leg which carries the maximum part of the load can be made of 30 increased width and this is offset by the reduced width at the lower end. This is of significance in terms of material costs as anchors of this type are typically cut out of the P:\OPER\RSH\I 2744320-CAP.doc-29/03M06 -9 metal plate in an inverted interlocking array whereby during cutting, the leg of one anchor is cut out of the plate material between the two legs of a second anchor inverted with respect to the first. 5 Due to the locking interaction with occurs between the surrounding concrete and inside leg profile as described, it is not necessary to profile the outer side of the leg and in fact it is particularly preferred that the outside of the leg is straight as shown, as this significantly facilitates manufacture as a straight cut using a laser or plasma cutting machine can take place much more quickly than cutting along a path involving continual changes of 10 direction. Although it is particularly preferred that the outer edge of the leg is straight for the reasons just discussed, nevertheless it is within the scope of the invention for the outer edge of the leg to be profiled to further improve the lock with the concrete and possible forms of 15 profiling for the outer edge are shown in Figures 5 to 7. It is to be noted that none of these outer edge profiles are such as to engender a laterally outwards reaction force on the leg and in fact those shown in Figures 6 and 7 will engender a laterally inwards reaction to add to that engendered by the profiling of the inner edge. 20 Although preferred embodiments of the present invention use an inside leg profile which does not engender an outwards lateral reaction and a straight outer edge profile which facilitates cutting of that edge, it is envisaged that a straight cut outer edge could, due to its manufacturing advantages, have utility in an anchor shaped along its inner edge with a more conventional meandering or wave like profile such as that shown in Figure 1. In that 25 case however it is likely that the overall leg length may need to be increased somewhat to ensure that "burst through" can not occur having regard to the reduced counteracting forces which will be present in this mode. Figure 8 shows a variation in which the apertures 8 in the anchor head are lengthened so 30 that each can accommodate two reinforcing bars, specifically a shear bar and an upper perimeter bar of the panel itself. This modification would also have applicability to other P:\OPER\RSH\I2744320-CAP.doc-29103f6 - 10 forms of anchor such as that shown in Figure 1. Figure 8 shows the anchor head 4 as being of extended length to accommodate an aperture 22 beneath the eye 6 for receiving a tension bar to increase the load capacity of the anchor 5 and this variation can apply to all of the anchors described herein. However as a result of the locking action of the legs relative to the concrete between the legs as previously discussed, and which provides a different type of failure mode for the anchor in relation to that of prior anchors as shown in Figure 1, a tension bar can, alternatively, be installed between the two legs within the upper part of the space between the two legs as it is not, 10 now, necessary for there to be physical interaction between the tension bar and the anchor itself in order to achieve the required effect. It follows from this that the higher loading capacity achieved when the tension bar is installed between the legs does not require the use of a larger head with the aperture for the tension bar. This not only reduces material costs but also it reduces manufacturing costs as the tension bar aperture is no longer 15 required. Figure 9 shows a variation in which the anchor only has a single leg 2 profiled in accordance with the principles described above. As shown, the leg is positioned asymmetrically relative to the anchor head 4 so that its straight edge will lie closer to the 20 adjacent face of the panel than will its profiled edge. This asymmetry also allows pairs of anchors to be produced in inverted relationship as shown with minimal wastage of material. This form of anchor can be cut in this way from a metal plate by laser beam or plasma arc cutting, or it could also be punched from flat bar. 25 The principles described above are also applicable to other forms of cast-in anchor such as plate anchors for providing fixings for use post-erection of the concrete component, for example panel-to-panel fixings and connections for beams. Current forms of plate anchor generally comprise a plate with lengths of reinforcing bar bent into U shape and welded to the rear of the plate; a threaded fixing point may be provided by an internally threaded 30 ferrule welded to the rear of the plate in alignment with an aperture in the plate.

P:\OPER\RSH I2744320-CAP.dc-29/0306 - 11 With reference to Figures 10 to 12, a plate anchor constructed in accordance with the principles of the present invention is formed with sets of anchoring legs extending from opposite edges of a plate 30 transversely to the plane of the plate. In the embodiment shown each set of legs has three legs, two outer legs 32 and an intermediate leg 34 5 although in other versions having reduced load requirements and of reduced size each set of legs may consist just of the two outer legs. It is also conceivable that just a single leg equivalent either to the leg 32 or the leg 34 could be provided at each side of the plate 30 in further versions of the anchor. The inner edge of each outer leg 30 is profiled in the manner previously described as are both edges of the intermediate leg 34; as shown, the 10 outer edge of each leg 32 is straight. The plate anchor with integral legs is cut from metal plate of required thickness (see Figure 12) and the legs are then bent so as to extend substantially perpendicular to the plane of the plate. It will be noted that in the preferred embodiment the two sets of legs are 15 asymmetrically arranged with one set laterally offset relative to the other set. As a result of this asymmetry, successive anchors can be cut from the plate with a minimum of wastage as the legs of one anchor are cut from the material lying between the legs of adjacent anchors. 20 Although it is preferred that the legs are bent so as to extend substantially perpendicular to the plane of the plate as this is the most economical option to provide a required embedment depth for a given leg length, it would be feasible for the legs to be inclined by up to approximately 300 in either direction relative to the plane of the plate. In that case for the same embodiment depth, the legs would then be commensurately longer whereby 25 the amount of concrete engaged would be increased thereby increasing the load-bearing capacity of the anchor. In the embodiment shown, the plate anchor provides a threaded fixing point provided by a nut 36 welded to the rear of the plate 30 in alignment with an aperture 38 cut into the plate. 30 The nut lies within a plastics cup 40 attached to the rear of the plate, for example by adhesive, and which acts as a void former behind the nut to form a void in the cast concrete P:\OPER\RSH\I2744320-CAP.doc-2903/06 - 12 and into which a threaded fastening can extend. Alternatively, the plate 30 can be subject to a so-called burst extrusion process which forms a rearwardly projecting integral tubular structure of increased thickness which can then be tapped to receive a threaded fastener. This, likewise, is associated with a plastics cup attached to the rear of the plate and acting 5 as a void former. It is to be understood that the presence of a threaded fixing is not essential although it will be required in some situations. If it is required, it's provision either by the nut welded to the rear of the plate or the tapped burst extrusion in conjunction with the plastic void former will provide a reduced cost option in relation to the incorporation of an internally threaded ferrule in accordance with current practice. It is 10 therefore envisaged that these methods of providing a threaded fixing point in a cast-in plate anchor would also have benefit in more conventional plate anchors in which anchorage within the concrete is achieved by bent lengths of reinforcing bar welded to the rear of the plate. 15 The embodiments have been described by way of example only and modifications are possible within the scope of the invention. Throughout this specification, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the 20 inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

1. An anchor for embedment into a concrete component, the anchor having an anchoring formation provided by at least one leg so profiled as to lock into the surrounding 5 concrete, the profiling being formed by a series of formations each of generally saw toothed shape and arranged longitudinally along the leg, with a leading edge of each formation inclining towards the head, the profile being such that when load is applied to the anchor in the axial direction of the leg, the resultant of the forces acting on the leg is such that there is no, or substantially no, component of that force acting in a sense to 10 deflect the leg laterally outwardly towards an immediately adjacent face of the concrete component.

2. An anchor for embedment into a concrete component, the anchor having an anchoring formation provided by at least one leg so profiled as to lock into the surrounding 15 concrete, the profiling being formed by a series of formations each of generally saw toothed shape and arranged longitudinally along the leg, with a leading edge of each formation inclining towards a head of the anchor such that on application of a pulling load to the head, the leg will lock tighter into the concrete within increasing load. 20

3. An anchor according to claim I or claim 2, wherein the anchor is a lifting anchor having a head for releasable engagement with lifting equipment.

4. An anchor according to claim 3, wherein the anchor has a single such leg. 25

5. An anchor according to claim 3, wherein the anchor has a pair of said legs, the legs being generally parallel and each leg having the said profile on its inner edge.

6. An anchor according to claim 5, wherein the outer edge of each leg is substantially straight. 30 CNRPonblDCCPLW\406553_l DOC-23/1212111 - 14

7. A lifting system using a lifting anchor according to claim 5 or claim 6 installed into a concrete component, a tension bar being mounted between the legs of the anchor beneath the head but without physical contact between the tension bar and the head. 5

8. An anchor according to claim 1 or claim 2, the anchor having at least one set of said legs, the legs of the set being generally parallel.

9. An anchor according to claim 8, wherein the anchor is a plate anchor of which the head is formed by a plate which provides a fixing point and the legs extend transversely to 10 the plane of the plate.

10. An anchor according to claim 8, wherein the anchor is a plate anchor and each leg extends transversely to the plane of the plate of the anchor, a respective set of said legs extending from each of two opposite sides of the plate. 15

11. An anchor according to claim 9 or claim 10, wherein the legs are formed integrally with the plate by cutting from metal stock and then bending the legs.

12. An anchor according to any one of claims 9 to 11, wherein the legs extend 20 substantially perpendicularly to the plane of the plate or are inclined to the perpendicular by up to approximately 300.

13. An anchor according to any one of claims 9 to 12, wherein the plate includes a threaded fixing point formed by a nut welded to a rear surface of the plate in alignment 25 with an aperture and enclosed within a separate void former.

14. An anchor according to any one of claims 9 to 12, wherein the plate includes a threaded fixing point formed by a rearwardly projecting integral tubular structure produced integrally with the plate by a burst extrusion process and then tapped, the tubular structure C:\NRPortbIWlCC\PLW4067553_ DOC-23/1212011 - 15 being enclosed within a separate void former.

15. A lifting anchor for embedment into a concrete component, the lifting anchor having a head with an eye for releasable engagement with lifting equipment, and generally 5 parallel legs extending from the head, each leg being profiled along an inner edge thereof so as to lock into the surrounding concrete, the profiling being formed by a series of formations each of generally saw-toothed shape and arranged longitudinally along the leg, with a leading edge of each formation facing upwardly towards the head and inclined at an acute angle to the axis of the leg. 10

16. A lifting anchor according to claim 15, wherein the anchor is cut from metal plate material using a high energy non-contact cutter, and the outer edge of each leg is cut along substantially its entire length with a straight cut. 15

17. A lifting anchor substantially as hereinbefore described with reference to Figures 2 to 4, Figure 5, Figure 6, Figure 7, Figure 8, or Figure 9 of the accompanying drawings.

18. A lifting anchor according to claim 15, having along the inner edge of each of its legs profiling substantially as hereinbefore described with reference to Figures 4 or 8 of the 20 accompanying drawings.

19. A plate anchor substantially as hereinbefore described with reference to Figures 10 to 12 of the accompanying drawings.