Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a reinforcing
bar coupling.
In our Published British Patent specification No.
2220241 we describe a coupl~r for reinforcing bars which
utilises a sleeve having threaded holes to receive
correspondingly threaded engagers (bolts) which serve to
join reinforcing bars in conjunction with radial spaced
engagers which are ribbed to dig into the sleeve and
reinforcing bars. By these means a mechanical coupling
can be achieved which has a tensile strength at least
equal to the ultimate tensile strength of the
reinforcing bar. The wall thickness of the sleeve has
to be sufficient to avoid canting of the bolts when the
coupling is under tensile load. In addition the radial
loading which can be imposed by the bolts is a function
of the yield strength of the sleeve material and this
determines how many bolts will be required to achieve a
desired ultimate tensile strength. Previously we have
utilised a vanadium ~FS (hot finish sleeve tube)
material for the sleeve.
The present invention arises from our endeavour
to provide an equivalent streng~h of coupling at reduced
cost.
Accordingly, the present invention provides a
coupling fitting for making joints in reinforcing bars
or wires for structural concrete, comprising a sleeve-
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like device having means for locating it over and aboutportions of said bars or wixes adjacent said design
joint with clearance to saicl bar or wire portions,
whereln the means -for locat:ing comprises for each
portion engagers at radial spacings relative to the axis
of bars or wires to be joinedl one OI which engagers for
each portion is positively ad~ustable at emplacement
through the side wall of the device and the other
engagers comprise radially spaced ribs which are
profiled to key into at least the bars or wlre portions,
and in which the positively adjustable engager is
received in threading of or associated with the sleeve
and in which the threading has a higher yield strength
than the sleeve material.
In one embodiment the sleeve has a hole which
receives an insert having said threading. In another
embodiment, threading formed directly in the sleeve and
is subject to localised hardening. Usually there will
be more than one positively adjustable engager employed
for each portion and a respective threading for each.
The number used is dictated by the size of the bars or
wires being joined and the required tensile load. For
couplers of equivalent tensile strength to those
described in our above patent specification costs are
reduced by using inserts which have a higher yield
strength than the sleeve material, and by this means the
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sleeve material can have a lower material specification.
For example yield strength may be reduced from say
460N/mm2 to 360N/mm2. For exam~le ~FS instead of
vanadium ~S. The higher the yield strength of the
insert, say with YS in the range 800 to lOOON/mm2,
allows higher bolt radial loads to be utilised and this
in turn allows a smaller number of bolts to be utilised
and therefore the sleeve length can be decreased. A
further advantage arises from the ability to reduce the
wall thickness or the sleeve without impairing the
resistance to can~lng of the bolts by having the inserl
longer than the wall thic]~ness of the sleeve. A
preferred embodiment of insert has a cylindrical part to
be received in the hole of the sleeve and an enlarged
flange to one end having a shoulder which engages with
an inner bore of the sleeve. The flange prevents the
insert from pulling out under the action of the positive
engager and also serves to stabilise the insert to
further prevent canting. Alternatively, the enlarged
flange may be dispensed with where the insert comprise a
frusto-conical sleeve engaging with the correspondingly
tapered hole of the sleeve. By this means there is a
wedging action between the insert and the sleeve on
introducing the positive engager.
In one embodiment we use an insert having a yield
of 850 newtons per mm2 and conveniently the flange has a
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major axis longer than its m:inor axis and in use the
major axis is aligned with the longitudinal direction o
the coupling.
The present invention will now be described
further by way of example only ~ith reference to the
accompanying drawings, in which:-
Figure 1 is a plan view of a coupling accordingto the present invention,
Figure 2 is a cross section on A-A of Figure 1,
Figure 3 is a cross section on B-B of Figure 2,
Figures 4 and 5 are side and plan views of an
insert as used in the coupling, and
Figure 6 is an end view of an alternative
embodiment of sleeve.
Referring to the drawings of Figures 1 to 5, a
coupling fitting for use in securing togethe~ ends of
reinforcing bars or wires for subsequent embedment in
structural concrete, comprises a tubular sleeve 1 having
an internal diameter such as to fit about end portions
of bars or wires in spaced relation thereto.
The sleeve is constructed symmetrically about
its mid point and in the illustrated embodiment has, for
each half, three holes 3 through the wall of the sleeve
which receive a respective threaded insert 4 having a
threaded bore 5 to receive positively adjustable
engagers, in the form of threaded screws or bolts 7.
The holes 3 are spaced along the length of the coupling.
The inserts have a yield strength of at least 800N/mm2
whilst the sleeve will have a lowe~ yield strength
typically less then 460N/mm2 and more usually in the
region of 360N/mm2. The bolts are preferably cap screws
and with a reduced shank as at 8 so that the head shears
off at a predetermined toraue on screwing them in place.
The end of the bolt 7 is formed with indentation means 9
to penetrate into the bar or wires on doing up, either
as a tapered point, or a convex or concave formation
providing either a biting point or an annular bitins
edge. The bolts are hardened to 52 Rockwell C.
The inserts are illustrated further in Figures 4
and 5 and comprise a cylindrical sleeve portion 19
dimensioned to fit in the holes 3 as push fit and one
end of the sleeve has an enlarged flange portion 21. In
the illustrated embodiment the flange portion is
generally elliptical with its major and minor axis
dimensions larger than the diameter of the cylindrical
portion 19 so as to provide a shoulder 22 which, when
the insert is placed in the hole 3, engages against the
inner wall of the sleeve. The major axis is aligned
with the longitudinal axis of the coupling. In one
embodiment the inserts are made from a material having a
yield strength of the order of 850 newtons per mm2 and
the sleeve is made from a HFS specification material.
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It will be seen from Figure 2 that the length of the
threaded holes 5 is greater than the wall thickness of
the sleeve and this allows an increased radial loading
to be emploved on the bo]ts without the threads stopping
whilst utilising a reduced wall thic}cness for the
sleeve.
In the illustrated embodiment, two longitudinal
ribs 13 are provided acting as radial engagers to which
the bar or wire portions abut in use. The ribs are
spaced apart circumferentially by angle A, preferably of
the order of 120. The ribs are positioned straddling
the axis 15 of a positively adjustable engager 7 and in
the opposite half of the sleeve. In the illustrated
embodiment the ribs run substantially the length of the
sleeve with soft tack welding 17 at each end which
provides a convenient means of locating the ribs to the
sleeve longitudinally and circumferentially during
emplacement before doing up of the positi~ely adjustable
engagers. The ribs are profiled to both sides in the
illustrated embodiment so as to key into the wires and
the sleeve when tightening of the positively adjustable
engagers.
In use the coupling sleeve is fitted over and
about adjacent ends (butting up to one another for a
straight sleeve) of the coupllng bars or wires to be
jolned so centering the bars within the sleeve and
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causing the radial engagers to key into the bars, also
the sleeve where the ribs are profiled to both sides.
The ends of the positively adjustable engagers also bite
into the bars. The bolts shear off at the outer surface
of the sleeve at a torque determined to give required
cooperating engagement of the engagers with the bar
and/or sleeve. Such an arrangement provides the
required mechanical strength. Increased radial loading
of the bolts is made possible by the use of higher yield
strength material for the inserts but this means the
number of bolts required for each half of the coupling
can be reduced for a given coupling strength. This also
facilitates reduction of the length of the coupling.
The invention has been described with reference
to straight put joint in which a straight sleeve is
employed. This is probably the most common joint
configuration, but the invention also extends to sleeve-
like devices for coupling bars or wires dt angles to one
another by suitable configuration of the sleeve to
receive appropriately orientated ends of bars or wires.
The arrangement of the combination of two
profiled engagers (ribs) and positively adjustable
engagers (bolts) may also be produced using a casting.
A suitable end section is shown in Figure 6. In this
~5 case the sleeve threads 5' and the rib profiles 13' are
integral with the sleeve 1' and are hardened to 52
208B9~
Rockwell C units by induction heat treatment and water
quenching. As an alternative to hardening the threaded
holes, the aforedescribed inserts may be used as already
described above.
