CONCRETE LIFTING ANCHORS

ANCRES DE LEVAGE DE BETON

English 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.

French Abstract

L'invention concerne une barre de cisaillement pour une ancre de levage de bord pour un panneau de béton. La barre de cisaillement est une barre comportant une partie centrale destinée à venir en contact avec un bord supérieur de l'ancre de levage lorsqu'elle est disposée dans le panneau et des pieds inclinés vers le bas à partir de chaque extrémité de la partie centrale, la face inférieure de chaque pied étant profilée pour être bloquée dans le béton environnant, le profil étant constitué par une série d'éléments espacés longitudinalement, chaque élément présentant une forme générale en dents de scie et un bord avant faisant face à la partie centrale de sorte que, lors de l'application d'un effort de cisaillement sur la barre de cisaillement, le pied se bloque dans le béton, une charge de compression étant appliquée sur le béton dans la zone située entre les deux pieds.

Claims

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CLAIMS
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
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.
2. A shear bar according to claim 1, wherein each of the legs has an outer end
portion
extending substantially horizontally.
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.
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.
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
shaped so as to locate the shear bar.

Description

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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
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
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
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
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
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
concrete above it by virtue of its shape and the frictional bond strength
between the

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concrete 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.
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
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
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
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
better illustrate the detail of the locking formations of the shear bar;

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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.
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
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
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
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
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
legs is formed from thick metal plate by cutting and/or pressing techniques as
will be well

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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
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
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
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
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
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
provided by the large surface area of the bar facing upwardly towards the
upper face of the

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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
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.
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.
The embodiments are described by way of example only and modifications are
possible
within the scope of the invention.

Representative Drawing