AU2010273162A1 - Concrete lifting anchors - Google Patents

Abstract

A shear bar for an edge lift anchor for a concrete panel, the shear bar being a bar shaped to provide a central portion to engage an upper edge of the lifting anchor when installed in the panel and legs inclining downwardly from each end of the central portion, the underside of each leg being profiled to lock into the surrounding concrete, the profiling being formed by a series of longitudinally spaced formations each of generally saw-toothed shape with a leading edge of each formation facing towards the central portion such that on application of shear load to the shear bar the leg will lock into the concrete with a generally compressive loading being applied to the concrete in the zone between the two legs.

Description

WO 2011/006188 PCT/AU2010/000830 CONCRETE LIFTING ANCHORS The present invention relates to anchors for use in the lifting of cast concrete products such as wall panels during the erection thereof. More particularly the invention relates to shear 5 bars for use with edge lift anchors. In the fabrication of precast concrete wall panels either at an offsite casting yard or onsite, it is necessary to lift the panel from the horizontal configuration in which it is cast to a vertical configuration for transportation and/or erection. For offsite casting and for some 10 onsite casting, lifting of the panel takes place from the edge of the panel which is the upper edge in the erected condition of the panel. For this purpose so-called edge lift anchors are incorporated into the reinforcing structure of the panel prior to casting. During casting the head of the anchor is encased within a removable or disposable void former to form within the edge surface of the panel a recess within which the head of the anchor lies for 15 releasable coupling to lifting equipment. Various forms of edge lift anchor are currently available. At the commencement of edge lifting when the panel is in its horizontal configuration following casting, the anchor is subject to a substantial shear loading in a direction transverse to the upper face of the 20 panel. In order to resist that shear loading, the anchor is associated with a shear bar which engages the upper edge of the anchor body. Conventionally, the shear bar is formed from a length of reinforcing bar, and thereby of substantially circular cross-section appropriately bent to overlie the upper edge of the body of the anchor and to extend further into the depth of the panel. The shear bar must be of an adequate size to carry and distribute the 25 loading. In this regard the potential failure mode of conventional shear bar is that of a so called failure cone of concrete extending from the outer edges of the bar to the upper surface of the panel. The concrete zone directly beneath the bar is basically under a tensile loading and as such does not assist in load distribution between the shear bar and the panel. In other words the bar does not lock into the concrete below it and it interlocks with the 30 concrete above it by virtue of its shape and the frictional bond strength between the WO 2011/006188 PCT/AU2010/000830 -2concrete and the surface of the bar. At the commencement of lifting, the concrete above the bar which acts to resist upwards movement of the bar, is placed in tension and does not provide high resistance. The size of the shear bar needs to be such as to allow for this. 5 The present invention relates to a shear bar which locks into the concrete in a more effective way than does a conventional shear bar. According to the present invention there is provided a shear bar for an edge lift anchor for a concrete panel, the shear bar being a bar shaped to provide a central portion to engage an 10 upper edge of the lifting anchor when installed in the panel and legs inclining downwardly from each end of the central portion, the underside of each leg being profiled to lock into the surrounding concrete, the profiling being formed by a series of longitudinally spaced formations each of generally saw-toothed shape with a leading edge of each formation facing towards the central portion such that on application of shear load to the shear bar the 15 leg will lock into the concrete with a generally compressive loading being applied to the concrete in the zone between the two legs. In a preferred embodiment, the bar is of a generally flat cross-section configured so that a large area surface of the bar faces upwardly to the upper surface of the panel in its installed 20 position prior to lifting of the panel. Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a perspective view showing an edge lift anchor having a shear bar in 25 accordance with the invention installed thereon; Figure 2 is an end view; Figure 3 is a plan view; Figure 4 is a side view; Figure 5 is a fragmentary end view similar to Figure 2 and to an enlarged scale to 30 better illustrate the detail of the locking formations of the shear bar; WO 2011/006188 PCT/AU2010/000830 -3 Figure 6 is a view similar to Figure 1 but having a shear bar formed to a different configuration; and Figure 7 is an end view. 5 Figures 1 to 4 show an edge lift anchor 2 in its installed position for lifting of the panel from its casting configuration in which the upper face of the panel is horizontal. The anchor has a head 4 for coupling to lifting apparatus, and an anchoring portion in the form of a pair of substantially parallel legs 6 extending from the head 4. The particular head 4 shown is designed for cooperation with a lifting clutch in the form of a ring clutch and an 10 arcuate locking bolt received within the eye of the head, although it is to be understood that the head could be of a different detailed design for use with other types of lifting apparatus. The legs 6 are profiled along their inner edges with a saw tooth profile so as to lock into the surrounding concrete but it is to be understood that the legs may have any other form of profile to achieve that purpose and the anchoring portion may be even be of a form which 15 does not use two parallel legs. In the embodiment illustrated in which the legs 6 are profiled along their inner edges with a saw-tooth profile, it is preferred that the detailed profile is as described in patent application 2006201337 the disclosure which is incorporated by reference. As disclosed in 20 that application the profiling is 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. That leading face is inclined towards the head such that on application of a pulling load to the head the formations will cause the leg to lock tighter into the concrete with increasing load and will not deflect laterally outwardly under the effect of forces 25 acting on the formations when under load. In practice, the inclination of the leading edges of the saw-tooth formations will apply a laterally inwards force to each of the two legs whereby the concrete between the two legs will be under a compressive loading. The anchor of the general type shown with parallel legs or of other forms without parallel 30 legs is formed from thick metal plate by cutting and/or pressing techniques as will be well WO 2011/006188 PCT/AU2010/000830 -4 understood by persons skilled in the art. It is orientated in the panel in its casting configuration with an upper edge substantially parallel to the upper face of the panel. In the embodiment shown, the head 4 of the anchor is stepped inwardly relative to the anchoring portion, the step being designated 4a in the drawings. A metal shear bar 8 5 engages the upper edge of the head 4 adjacent the step 4a as is clearly shown in Figures 1 and 4 although in an alternative the edge of the anchor can be provided with a recess of appropriate shape at the base of the head to receive and locate the shear bar. The shear bar 8 is principally of flat cross-section and is shaped to extend across the upper 10 edge of the head 4 and then extends downwardly at each side of the head 4 to form downwardly inclined portions or legs 8a embedded more deeply within the thickness of the panel. Outer portions 8b of the bar extend laterally outwardly (horizontally) so as to lie substantially parallel to the surface of the panel. The use of flat bar of this form with its large area surface facing upwardly to the upper face of the panel provides a large surface 15 area which is better able to carry the shear loading than an equivalent shear bar of round cross-section. It will be noted that the underside of each of the downwardly inclined legs 8a is formed with saw-tooth profiling which is similar to that of the legs 6 of the anchor and is 20 configured to operate in fundamentally the same way. In particular and with reference to Figure 5, each of the saw-toothed formations has a leading edge 10 inclining towards the central portion 8c of the shear bar 8 where the bar engages the edge of the anchor 2 so that when shear load is applied to the bar 8 when the panel is being raised from its horizontal configuration assumed during casting, the saw-toothed formations will lock more tightly 25 into the concrete. The inter-action between the legs 8a and the concrete as a result of these formations on their underside creates a laterally inwards force whereby the concrete in the zone between the two legs 8a is subject to a compressive loading. Due to this compressive loading, strong anchorage is achieved between the legs 8a of the shear bar 8 and the underlying concrete and this anchorage provides a substantial supplement to the effects 30 provided by the large surface area of the bar facing upwardly towards the upper face of the WO 2011/006188 PCT/AU2010/000830 -5 panel. As a result the load resistance provided by the shear bar is substantially greater than that of an equivalent conventional shear bar. This provides significant advantages. For a required load bearing capacity the shear bar can be smaller than would be necessary when a conventional shear bar is used thereby reducing material costs. Further, although 5 conventional shear bars enable the panel to be lifted before it has cured to full strength, the shear bar of the preferred embodiment enables, by virtue of the compressive loading, the panel to be lifted at lower part-cured strengths; thereby the panel can be lifted earlier following casting, thus providing for improved efficiency for both off-site and on-site casting. 10 Figures 6 and 7 show the shear bar 8 with its legs 8a more steeply inclined than in the previous embodiment, and may be applicable principally for use for lifting smaller components where the load resistance requirements are reduced. It will be appreciated that the bar of Figures 6 and 7 uses less material than that of the previous embodiment. 15 The embodiments are described by way of example only and modifications are possible within the scope of the invention.

Claims (6)

1. A shear bar for an edge lift anchor for a concrete panel, the shear bar being a bar shaped to provide a central portion to engage an upper edge of the lifting anchor when 5 installed in the panel and legs inclining downwardly from each end of the central portion, the underside of each leg being profiled to lock into the surrounding concrete, the profiling being formed by a series of longitudinally spaced formations each of generally saw toothed shape with a leading edge of each formation facing towards the central portion such that on application of shear load to the shear bar the leg will lock into the concrete 10 with a generally compressive loading being applied to the concrete in the zone between the two legs.

2. A shear bar according to claim 1, wherein each of the legs has an outer end portion extending substantially horizontally. 15

3. A shear bar according to claim 1 or claim 2, wherein the shear bar is of rectangular cross-section having opposed large area faces and opposed smaller area faces and is so configured that the central portion engages the edge lift anchor with one of its large area faces. 20

4. In combination, an edge lift anchor having a head portion for coupling to lifting apparatus and an anchoring portion extending from the head portion, and a shear bar according to any one of claims 1 to 3, the central portion of the shear bar being engageable with an upper edge of the anchor. 25

5. A combination according to claim 4, wherein the upper edge of the anchor has a planar portion engageable by the central portion of the shear bar.

6. A combination according to claim 4, wherein the upper edge of the anchor is 30 shaped so as to locate the shear bar.