Where the reinforcement in a section is congested, mechanical couplers may be
used to good effect. There are two distinct types of mechanical couplers (see
CIRIA 92 Reinforcement connector and anchorage methods):- tension couplers

  • compression couplersUnless specified otherwise tension couplers should be
    used. It should be noted that the cover provided for couplers should be that
    specified for the reinforcement. The notation used on the drawings and schedules
    for any special end preparation requirements is given as �E� just before the
    mark. Couplers are mainly tested in tension, but as required, may be tested
    under compression, cyclic and fatigue regimes. In the UK couplers should be
    supplied by a company holding a valid third party technical approval (e.g. CARES
    UK, BBA etc) and should be processed by fabricators being a member of the CARES
    UK third party certification scheme or equivalent.

Several types of coupler are available for tensile and compressive bars. Below
is typical examples of commonly available couplers.

Tyically available mechanical couplers

Lap joint in tension including a fourth bar### Type 1: Couplers with parallel
threadsThreads can be cut, rolled or forged. There are two variations to this
type of coupler. Type 1a uses reinforcing bars with the threaded portion having
a smaller diameter than the rest. Type 1b uses bars with the threaded portion
having a cross sectional area equal or greater than the nominal size. The former
is rarely used since the load capacity is reduced; the latter which maintains
the parent bar load capacity is widely used. An alternative to Type 1 also
includes a variant where one end of a parallel threaded coupler is swaged on to
a bar. The parallel (Type 1) couplers also have transitional and positional
variants. The transitional coupler allows two bars of different size to be
joined. The positional coupler usually comprises two halves joined by a parallel
thread and lock nut arrangement.

Type 2: Couplers with taper-cut threads
This system consists of an internally threaded metal coupler with a tapered
thread, and matching tapered bars. Due to its ability to meet the majority of
the structural building applications it is popular. The standard tapered coupler
can only be used in situations where the continuing bars can be rotated. This is
not always practical and more sophisticated tapered couplers have been developed
which allow the joining of bars that can not be rotated, and the joining of bars
where the continuing bar can neither be rotated nor moved (e.g. L-bars). below
some examples of positional and transitional couplers.

Type 3: Couplers with integral threads over full length bar
High yield reinforcing bars are specially manufactured with helical deformations
along the full length of the bar. The deformations form a continuous coarse
thread onto which an internally threaded coupler can be screwed. Locknuts are
used at either end of the coupler to prevent slippage on the coarse threads. A
turnbuckle system for when the continuing bar cannot be rotated is not
available, but the coupler can be completely threaded onto one bar and then run
back onto the continuing bar to form the joint.

Type 4: Metal sleeves swaged onto bars
A seamless malleable steel sleeve is slipped over the abutting ends of two
reinforcing bars. The sleeve is then swaged (deformed) onto the ends of the bars
using a hydraulic press. This action effectively splices the bars together. The
process can be carried out wholly in-situ. The hydraulic press compresses the
sleeve laterally onto the bars and several �bites� are usually necessary to
cover the whole joint.

Sufficient working space must be available around the bars to enable the
hydraulic press to swage onto the bars. In addition, swaging equipment for large
diameter bars (H40 and greater) may require mechanical support for safe
operation. It is therefore important to take this into account in likely
construction sequencing and detailing reinforcement in confined areas.

Example of swaged coupler### Type 5: Threaded couplers swaged onto the ends of
reinforcing barsIn this system two malleable sleeves which are threaded
internally for half their length are joined together by a high tensile threaded
stud. The unthreaded parts of the sleeves are hydraulically swaged on the two
ends of the bar to be joined. These ends can be screwed together using the
threaded stud. The swaging process can be performed by the fabricator prior to
arrival on site, in a stockyard at the site, or in-situ. For the latter method
it must be ensured that
there is sufficient working space around the bars. Connection of the bars with
the threaded stud is performed in-situ.

Type 6: Wedge locking sleeves
This system can be used for connecting compression bars only. The bars to be
joined together are held in concentric bearing by the lateral clamping action of
a sleeve and wedge. The sleeve is cylindrical in shape, with a wedge-shaped
opening. This opening has collared-shaped flanges, onto which a wedge-shaped
piece of metal is driven. This action compresses the sleeve laterally and so
clamps the bars together. It is very important that the bar faces are cut
accurately and aligned to within a 3° maximum angle tolerance.

Type 7: Couplers with shear bolts and serrated saddles
This type of coupler system has been available in the UK since 1986 and is now
widely used. The system does not require rebar threading and consists of a steel
coupler with a line of �lockshear� bolts running along its length. The two bars
to be joined are placed inside the coupler on two hardened serrated steel
locking strips, �saddles�, using ratchet wrench or electric or air powered nut
runner, which forces the bars against the longitudinal saddles. As this happens,
the serrated saddles bite into the bar and wall of the coupler. When the
predetermined tightening torque for the bolts is reached, the bolt heads shear
off leaving the installed bolt proud of the coupler. This provides a visual
check of correct installation. This coupler has proved useful in refurbishment
work, joining pile cage steel to pile caps and where couplers are required with
minimum lead time. They are, however, relatively bulky couplers requiring space
for sockets to tighten bolts. This should therefore be taken into account in
considering concrete placement. Often reduced aggregated concrete is required in
congested areas.