Field of the invention
The present invention relates to an improved mechanical coupler for end-to-end
connection of bars/rebars in concrete construction site without turning their
ends, or welding. The present invention also relates to a process of and-to-end
joining of bars/rebars in concrete construction site. The coupler of the current
invention can be also be used to connect bars/rebars of different diameters.
Background of the invention
Rebars are used to strengthen concrete structures. Huge quantities of rebar are
utilized in modern reinforced concrete construction. Rebars are generally
manufactured in 5-15 metre length or other convenient length for transportation.
Hence, it becomes necessary to connect a large numbers of rebar ends
longitudinally at the construction site to fulfill higher length requirement. The
connection can be done by three routes for example, lap splicing, welding and
mechanical coupling.
The lap splicing is a traditional technique to join rebars of lower and medium
diameter. A splice is made by lapping one of the plurality rebars over another
with a length sufficient to transmit forces and tied tightly with metallic wires.
However, this technique results in wastage of a large quantity of rebars due to
over-lapping. Further, cross-sectional area of a lap splice is more than double
that of a single rebar. This larger cross-sectional area over a considerable length
leads to restricted flow of concrete and poor filling.
Welding method is used for rebars with larger diameter (usually higher than 16
mm). Two rebar ends are axially aligned and electric arc welding technique is
generally used to join wieldable steel grades. However, exact axial alignment of
two rebar ends at the

construction site is difficult to determine. This directly affects the load bearing
capacity of the welded joint. Rebars are generally produced by thermo
mechanical treatment (TMT) to achieve unique microstructure throughout its
cross section. A ferrite-perlite phase forms at the core while a comparatively hard
tempered martensite is obtained at the surface. This microstructural combination
results in high strength without sacrificing the ductility. However, if two rebars
are joined by welding, high temperature in the process changes the unique
microstructure and adversely affect its mechanical properties.
In comparison to the two known techniques, the prior technique of mechanical
coupling for end connection of rebars is easier primarily for the reason that axial
alignment of rebar ends is not a problem. Accordingly, mechanical coupling has
become popular now a days. Four types of mechanical coupling are discussed
below:
(a) Steel sleeve with two converging sides: In this type of mechanical coupling,
two steel sleeves with two converging side is positioned in such a way that the
rebar ends make a substantially equal distance from the sleeve ends, and a
series of cone-pointed screws are then tightened along the sleeve length such
that the screw ends indent the surface of the rebar.
Limitation: Heads of the screw normally shear off at higher tightening torque.
This mechanical coupling technique can be successfully applied in soft material
but for high strength material and higher diameter bar this technique becomes
practically unfeasible due to huge sleeve length and large number of screws.
(b) Jaw assembly with interior teeth: A sleeve with interior teeth, two end-
locking collars and assembling machine are required for this kind of mechanical
coupling. The external sides of the rebar ends are held by the jaw assembly with
interior teeth. In both the ends, tapered locking collar constrict the jaw
assembly. The end collar remains in place, thereby locking the jaw assembly
after removal of the tool.

Limitation: A special assembling machine is required to perform jaw assembly
coupling and as a consequence assembly process is highly energy consuming.
Assembly operation inside the framework at construction site is a really
challenging job.
(c) A sleeve pipe clod swaged on the two rebar ends: In this type of mechanical
coupling process, a deformable soft hollow sleeve pipe and cold swaging
machine are required. The thickness of the sleeve pipe is determined such that it
is sufficient to transfer the required load from one rebar to another. The inner
diameter of the sleeve pipe is equal to the outer diameter of the rebar. By
application of sufficient clamping force, the smooth inner surface of the sleeve
pipe gets deformed and the impressions created in its inner surface engage with
the ribs of the outer surface of the rebar.
Limitation: Impressions on the inner surface of the soft sleeve pipe can carry low
loads as it deforms very easily. Therefore, to connect the steel rebars with higher
diameter, a large sleeve pipe is required which leads to higher cost and becomes
difficult to handle. Instead of soft sleeve pipe, a hard one cannot be used
because in that case, the ribs of the rebar also get deformed and the impression
on the inner surface of the sleeve pipe become very small which reduces the
effectiveness of the coupling.
(d) Internally threaded sleeve: Edge preparation of the rebar ends and an
internally threaded sleeve is required for this type of mechanical coupling. The
first step of edge preparation comprises heating and compressing the rebar ends
to increase their diameter and then threading is done on them. Next, the
internally threaded sleeve is employed to assemble the rebar ends.
Limitation: The processes of threading on rebars ends are cumbersome and time
consuming. Threading on rebar ends and also on the sleeve coupler becomes
costly.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved mechanical
coupler for end-to-end connection of bars/rebars in concrete construction site.
Another object of the invention is to propose a process of and-to-end joining of
bars/rebars in concrete construction site.
Still another object of the invention is to develop a mechanical coupler that can
join bars/rebars of different diameters.
Another object of invention is to propose a mechanical coupler that does not
need bending, turning and welding of bars/rebars for mechanical coupling.
Summary of the invention:
Accordingly, in a first aspect of the invention, there is provided an improved
mechanical coupler for end-to-end connection of bars/rebars in concrete
construction site without turning their ends, or welding, which allows a quick
end-to-end connection of bars / rebars. In a second aspect of the invention,
there is provided a process of and-to-end joining of bars/rebars in concrete
construction site, which enables immediate axial end-to-end connection of rebars
at the construction site. The mechanical coupler of the invention basically
comprises two separable funnel shaped components, wherein the corresponding
coupling method is a two-step process. In the first step, preparation of two ends
of the rebar which need to be connected is undertaken, including insertion of
half-couplers, followed by increasing the cross-sectional area by one of cold
forging, hot forging, and compressing of the bar ends. In the second step, the
bar ends are assembled by tightening the two halves of the coupler. The bulge
portion at the bar ends gets inter-locked within each funnel end of coupler halves
and carry the loads. The

load is transferred from one bar to another through the coupler halves which are
held together by threaded ends.
Brief description of the accompanying drawings:
For the purpose of illustrating the invention, the drawings are listed below.
Figure 1: Schematic of preparation of bar ends (a) preparing bar ends (b)
forging or hot compression of the bar ends, and (c) bar ends after edge
preparation
Figure 2: Schematic of a coupler fitting (a) placing of two bar ends (b) Full
coupler assembly.
Figure 3: Schematic cross sectional view of two coupler halves (a) first half (b)
second half
Details description of the invention:
According to the invention, bar / rebar ends are connected by a two-step
coupling technique. In the first step, preparation of bar ends is done after
inserting halves of the mechanical coupler appropriately. The schematic of bar
end preparation is depicted in figure 1. Cross section of the bar ends are made
larger (bulging of ends) by any known kind of operations for example, cold
forging, hot forging, compression of bar ends. Proper bulging of the bar ends is
necessary for higher efficiency of the inventive mechanical coupling.
Different components of the coupler assembly are identified in figure 2. Figure
2(a) depicts the alignment of the bulge portions C and D of bars A and B to be
coupled. E and F are the tapper or vertical edges of the bulge sections C and D.
Figure 2(b) shows schematic diagram of coupler assembly where G and H are
the two coupler halves.

Details of the coupler halves G and H are shown schematically in figure 3. Each
half of the coupler is inserted in the bar preferably before the end preparation.
After the end
preparation, the first half-coupler G should be positioned on rebar A end in such
a manner that the portion C of the bar resides in a cavity J of the coupler G and
edge E of the bar A matches with edge K of the coupler G. Similarly, the second
half-coupler H is placed on an end of bar B such that the bulge portion D resides
within a cavity N and the edge F of the bar B sits on an edge 0 of the coupler H.
In coupler halves G and H, portions L and P are threaded for assembly. During
assembly, L and P threads are interlocked and transfer the loads. Therefore, load
transferring portions are: edge E of bar A, edge K of coupler G, edge F of bar B,
edge 0 of coupler H threads L and P of coupler G and H respectively. For this
reason, dimensions of those portions are determined during designing process
on the basis of load carrying capacity.
The cavities of coupler halves can be varied as per the diameters of the
bars/rebars that need to be joined.
The mechanical coupler for longitudinal connection of bars/rebars has a number
of advantages such as:
(i) easy to install and disassembly at site;
(ii) Bars having different diameters also can be assembled
(iii) fabrication cost is low;
(iv) time required for installation is minimum;
(v) Provides a very strong bond between the bars/rebars;
(vi) no welding is required at the construction site;
(vii) no welding required during fabrication;

Further, the mechanical coupler of the current invention can be used to connect
bars/rebars of different diameters. The invented mechanical coupler for joining
bar / rebar can be easily installed. At the beginning, two bar ends of A and B are
prepared for coupling by increasing the end cross sectional area (bulging of ends
C and D of bars A and B, respectively). Then each coupler half is inserted in
respective bar ends such that the mouth of the funnel shaped coupler half
remains in the direction of bulge end of the bar. Two bar ends A and B are
placed in concentric and axially aligned positioned, and bulge portion C and D
touches each other. Next, the threads on the mouths of the funnel shaped
coupler halves are tightened and coupler halves become united to firm
mechanical joint.

We claim:
1. An mechanical coupler for end-to-end connection of bars/rebars, the
coupler comprising:
- a first half (G) having substantially a shape of a funnel, and having an
edge (K), a threaded portion (L), and a cavity (J);
- a second half (H) having an identical shape that of the first half (G), and
having an edge (0), a threaded portion (P), and a cavity (N),
wherein a first rebar (A) and a second rebar (B) to be joined each has bulge
portions (C,D), each bulge portions (C,D) comprises one of tappered and
vertical edge (E,F), wherein the first half-coupler (G) is positioned on edge-
prepared end of the first rebar (A) such that the bulge portion (C) residing in
the cavity (J) and the vertical edge (E), wherein the second half-coupler (H)
is placed on edge-prepared end of the second rebar (B) so that the bulge
portion (D) accommodated within the cavity (N) and the tapered edge (F),
and wherein the threaded portions (L,P) of the half-couplers (G,H) are
interlocked to transfer loads.
. 2. The mechanical coupler as claimed in claim 1, wherein bars/rebars to be
joined are of different diameters.
3. The mechanical coupler as claimed in claim 1, wherein bars/rebars to be
joined are of same diameters.
4. A process of end-to-end joining of bars/rebars, comprising :-

- bulging ends of the bars/rebars;
- inserting each coupler half to respective bar/rebar ends so that the front
portion of the funnel shaped coupler-halves remain in the direction of
bulge ends;

- placing the bars/rebars in concentric and axially-aligned position with the
bulged portions touching each other; and
- tightening the threaded portions of the coupler-halves to form a
mechanical joint between the bars/rebars.
5. The process as claimed in claim 4, wherein bulging is performed by
operations such as cold forging, hot forging, compression of bar/rebar
ends.

ABSTRACT

A mechanical coupler is provided for connecting ends of bars and rebars
longitudinally. The coupler can be used to connect bars of different diameter
also. The coupling process involves two steps. In the first step, bar ends to be
coupled are bulged through forging process. In the second step, mechanical
coupler halves are assembled tightly for connecting the ends. Two mechanical
coupler halves are funnel shaped and have threads at the mouth of the funnels.
During tension, bulge ends of the bars get locked in the narrow end of the funnel
and carry loads. Slackness of the coupler assembly can be eliminated by proper
tightening the threads of the mouth of the funnel shaped coupler.