Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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EXPANSION ANCHOR
The present invention relates to an expansion anchor and more particularly to
an
expansion anchor for temporarily anchoring a brace or other component in
building
construction.
In the construction of a building structure using precast concrete panels, the
panels are
temporarily supported on site by braces until the panels are physically
connected into, and
become an integral part of, the building structure. Typically, two braces are
used to
support each panel to resist wind loading acting to cause the panel to fall
over. Usually,
the upper end of the brace is fixed to the panel by bolting into a ferrule
which is
incorporated into the panel during casting. The lower end of the brace is
usually fixed into
the horizontal slab which i-nay either be on the ground, or suspended if a
niulti-storey
application, using a masonry anchor of expansion type which, for this purpose,
is termed a
brace anchor. Brace anchors may also sometimes be used for fixing the upper
ends of the
brace to the panel in circun~ stances where that is the preference of the
engineer or builder
or when the cast-in ferrule has been incorrectly installed.
Most commercially available braces are of similar construction and have at
each end a
steel anchor plate of between 12 and 20mm in thi.clcness (depending on
construction) with
a slot of approximately 22 to 24nim in width for receiving the brace anchor or
ferrule bolt.
Following a number of panel collapses from wind loading through failure of the
brace
anchors, an Australian Standard (AS 3850-2003) was introduced to prescribe
ininimuni
performance reGuirenients for anchors used as brace anchors. Although there
are
currently available a number of expansion anchors which meet these standards,
none are
specifically designed for tha.t usage and, as a result, compromises have to be
made when
using these anchors. In particular, expansion anchors are conventionally
designed for
permanent installation. When used as a temporary brace anchor, significant
difficulties
can arise both in releasing the anchor to permit removal of the brace and then
in the
actions necessary to ensure that remaining parts of the anchor do not project
beyond the
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surface of the slab, involving either the use of an angle grinder to cut any
projecting parts
flush with the base or tapping any projecting parts flush with the surface and
which might
compromise the integrity of a waterproof membrane underneath the slab.
Moreover, the
across-flats (AF) head size of bolt heads of suitable currently available
expansion anchors
is less than the width of the anchor slot incorporated into the base plates of
currently
available braces with the result that the washer installed between the head
and the anchor
plate will bend and rnust take the full fixing load in this mode.
According to one aspect= of the invention there is provided an expansion
anchor for
temporarily anchoring a component to concrete structure, the anchor having a
bolt with a
threaded shank which mat,--s with an internally threaded expansion cone, an
expansion
sleeve which cooperates with the expansion cone whereby the expansion sleeve
is
expanded into anchoring engagement with the wall of a hole drilled into the
concrete
structure as the cone is dravvn into the sleeve by rotation of the bolt, means
for forming an
anti-rotation mechanical interlock with the wall of the hole in order to
prevent rotation of
the cone to permit release of the bolt after setting of the anchor, and a
spacer arrangement
between the expansion sleeve and outer end of the bolt shank, the spacer
arrangement
consisting of or including a spacer sleeve having an inner end portion adapted
to lie within
the outer end portion of the hole when the anchor is set such that after
subsequent removal
of the bolt and the component, the spacer sleeve projecting from the concrete
structure can
be removed from the outer part of the hole.
In a preferred embodiment of the invention the spacer arrangement includes an
inner
sleeve between the spacer sleeve and expansion sleeve. Advantageously the
inner sleeve
is of a structure which permits axial collapse of the sleeve during setting of
the anchor to
provide a pull-down effect.
In alternative constructions the expansion sleeve itself may include structure
which
provides a pull-down effect or otherwise may be of a length such that the
inner spacer
sleeve is not required, in which case the outer spacer sleeve will directly
follow the
expansion sleeve on the shank of the bolt and thereby provide the spacer
assembly.
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Particularly advantageously the bolt shank is of stepped diameter with the
expansion cone
being mounted on the smaller diameter portion of the shank and the spacer
sleeve lying
on the larger diameter portion of the shank.
In one particularly preferred practical embodiment of the invention, the outer
end of the
spacer sleeve abuts against the head of the bolt via a metal washer and a low
friction
washer, and the bolt head is a hex head of 30mm width across-flats (AF) with
the outer
dia:neter of the expansion sleeve and spacer sleeve being substantially 20mm.
This means
that when the anchor is used with currently available braces having a slot of
between
approximately 22 and 24rr.im in the anchor plate, the head of the anchor will
span the
entire width of the slot and the underlying metal washer will not be subject
to load
transmission by bending.
In order to provide the anti-rotation lock to facilitate release of the bolt
while the
expansioii cone is held against rotation under the applied torque, the
expansion cone is
preferably formed to a size such that it is an interference fit within the
hole with
formations which. broach into the wall of the hole during insertion of the
anchor to
provide a physical anti-rotaiion lock. In one form, these formations can
consist of rib-like
projections although other formations which achieve the required interlock
during
insertion can alternatively be used. In a further alternative the expansion
sleeve could be
provided with the anti-rotation formations which broach into the wall during
insertion;
since, when the anchor is set, the expansion cone will be wedged very firmly
into the
expansion sleeve, rotation of the expansion cone will thereby be prevented.
According to another aspect of the invention there is provided a temporary
anchorage
between a concrete stnicture and an anchor plate of a brace, said anchorage
being
provided by an expansion arichor as defined above extending through the anchor
plate into
a hole drilled into the structure, wherein the spacer sleeve is of such a
length that its outer
end is substantially flush with the upper surface of the anchor plate and its
lower end
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extends into the hole to a depth which permits ready removal of the spacer
sleeve after
removal of the bolt and anchor plate.
According to another aspect of the invention there is provided an expansion
anchor
providing a temporary anchorage for a component during the construction of a
building,
the anchor being set into a hole drilled into concrete structure by expansion
of an
expansion sleeve of the anchor, the anchor having an anchor bolt which is
releasable and
removable after setting the anchor to permit removal of the component, and the
anchor
further having a spacer sleeve between an expansion sleeve and head ef the
bolt and which
is located only in the outer part of the hole so as to be easily removable
after removal of
the bolt so that no remaining part of the anchor then projects from the hole.
An embodiment of the inv ntion will now be described by way of example only
with
reference to the accompanying drawings in which:
Figure 1 is a perspective view of an expansion anchor in accordance with a
preferred embodiment of the invention;
Figure 2 shows the component parts of the anchor;
Figure 3 is a cross-section showing the anchor in its installed position to
act as a
temporary anchor for a brace;
Figure 4 is a sectiori similar to Figure 3 showing the anchor after the bolt
and
brace have been removed; arid
Figure 5 shows schematically the removal of the outer spacer sleeve which
remains projecting after rem.oval of the bolt and brace.
With initial reference to Figures 1 and 2, an expansion anchor specifically
designed as a
temporary brace anchor comprises a bolt having a stepped shank 2 of which the
inner,
smaller diameter, end portion 2a is tlu-eaded (the thread is not shown in
Figure 2) to
receive an internally threadeci cone nut 4 forming an expansion cone. An
expansion sleeve
6 is mounted on the smaller diameter portion 2a for cooperation with the cone
nut 4 in
conventional manner. A spacer assembly interposed between the expansion sleeve
6 and
washer 8 adjacent the head 10 of the bolt is, in the embodiment shown, of two
part
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construction having an inner spacer sleeve 12 and an outer spacer sleeve 14.
In the
particular embodiment shown, the inner sleeve 12 is formed with a series of
apertures 16
which form within the sleeve inclined struts 17 able to deform when axial
loading is
applied to the sleeve during setting of the anchor within the hole so as to
result in a
contraction in the axial length of the sleeve which facilitates so-called
"pull-down" to
ensure that the anchor is able to draw the brace anchor plate down to the
concrete slab and
anchor it fimzly. A pull-down action of this type is described in greater
detail in
Australian patent no. 559285 and Australian patent no. 697330. In the
embodiment
shown, the apertures within the sleeve 12 are of thc general shape described
in Australian
patent no. 697330 although it is to be understood that other constructions of
sleeve which
provide a pull-down effect could alternatively be used. It is to be noted that
although it is
preferred to form this inner sleeve to provide a pull-down effect this is not
essential to the
working of the invention and in other constructions an inner spacer sleeve
without that
capacity could alternatively be used.
The larger diameter end of the cone nut 4 is formed with a series 9f; flats 18
around its
peripheral surface which define longitudinal locking ribs 20. This end of the
cone nut 4 is
dimensioned so that the ribs 20 are an interference fit within the hole into
which the
anchor is fitted and thereby during installation of the anchor they will
broach into the
concrete to provide a mechanical interlock between the cone nut 4 and concrete
in order to
prevent rotation of the cone nut within the hole. As a result of this anti-
rotation interlock
the bolt is readily able to be released by unscrewing from the cone nut when
it is required
to remove the brace.
Preferably, a low-friction washer 21 for example of PTFE is incorporated
between the
bolt head 10 and main washer 8 to reduce so-called static friction acting on
the bolt head
during setting of the anchor and thereby to ensure that more of the torque
applied to the
bolt head is translated into expansion of the expansion sleeve and hence
setting of the
anchor within the hole.
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The installed condition of the brace anchor is shown in Figure 3. The anchor
is inserted in
its assembled form through the anchor plate 22 of the brace into the hole
predrilled into
the concrete slab 24 so that the underside of the washer 8 and outer end of
the outer spacer
sleeve 14 are flush with the upper surface of the anchor plate 22 and the bolt
is then
tightened to a specified torque in order to set the anchor in the usual way.
As previously
mentioned, the anchor plates of currently available braces are of a thickness
which varies
between approximately 12 and 20mm depending on its method of construction. The
length
of the outer spacer sleeve 14 is greater than the likely maximum thickness of
base plate,
but not significantly so, so that its inner, lower, end will lie within the
upper part of the
hole in the slab 24. As a result of this, when the anchor bolt and brace have
been removed,
the projecting part of the spacer sleeve 14 which only extends a relatively
short distance
into the hole, the extent of penetration depending on the actual thickness of
the anchor
plate with which the anchor has been used, can readily be removed by knocking
the sleeve
sideways or even by kicking it out (see Figures 4 and 5). The rest of the
anchor consisting
of inner spacer sleeve, expansi.on sleeve and cone nut will remain within the
hole but
beneath the surface of the slab. The end of the hole is then sealed with a
suitable filler.
The bolt is formed with a particularly large head 10 such that it is able to
fully span the
slot width of currently available braces, typically a slot width of 22 to 24mm
as previously
mentioned. In one practical example, with a bolt shank diameter of 20mm the
head size is
30mm across flats (AF) so that the underlying washer 8 will be subject to a
direct
compressive loading, not a'bending loading. The 30mm AF head also corresponds
to the
head size of inetric M20 threaded bolts as would typically be used with cast-
in ferrules at
the upper end of the brace so that an installer can thereby use the same
socket for fixing
both ends of the brace. Mo:eover the head size, being unusually large for an
expansion
anchor of this size will be r adily identifiable from simple inspection when
installed and
the head will also carry special identification markings to identify that the
anchor is a
specially designed brace anchor. Both of these aspects will ease the problems
of on-site
inspection by work-safety personnel to ensure that the correct anchors are
being used. It
will of course be understood that the anchor can be used both for fixing the
lower end of
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the brace to the slab and the upper end to the concrete panel if required
instead of a cast-in
ferrule.
Although the anchor has principally been described in terms of the temporary
anchorage
of a brace, the anchor also has applicability to other anchoring situations
which arise in
building construction where a temporary anchorage is required, for example
balustrades,
guard rails, hand rails, and scaffolding.
The embodiments of the invention have been described by way of example only
and
modifications are possible within the scope of the invention.
