THERMO MECHANICALLY TREATED (TMT) BAR WITH IMPROVED SURFACE RIB
PATTERN PROFILE AND THE METHOD FOR MANUFACTURING THE SAME.
FIELD OF THE INVENTION
The present invention relates to a ribbed Thermo Mechanically Treated (TMT) bar with
improved surface rib pattern profile for high adherence, particularly for reinforcements
for concrete or welded mesh, deformed by hot rolling and equipped ribs inclined with
respect to the central axis. More particularly, the present invention is directed to
developing TMT bars having higher bond strength (200% pull out load w.r.t. plain round
bars Min.) properties of said TMT rebars through optimizing design of surface
longitudinal and transverse ribs.
BACKGROUND ART
It is well known in the related art that thermo mechanically treated steel reinforcement
bars are being used in RCC application. It has also been experienced in the art that
considering the safety aspect of such construction, there had been a need to develop
steel materials with even higher bond strength with same section for the TMT bars to
suit application in RCC/tunnel structures.
It is thus the intent of the present invention to overcome the limitation of the existing
TMT bars used for RCC structures and also as rock bolts for mines or roof support
system or the like, by developing a new surface rib pattern profile of steel TMT rebars
capable of ensuring higher bond strength with concrete or other grout material for
composites. Such high bond strength rebars is developed and produced by selectively
controlling mass of transverse and longitudinal surface ribs of the steel bar material and
on the other hand optimizing the process of roll cutting for hot deformed rebars to
thereby obtain desired resistance to pull out through composite thereby achieving
desired superior bond strength properties in the end products.
In the Prior Art an European specification EP399910B1 by ACOR ACIERS DE
CONSTRUCTION RA discloses a ribbed steel rod with high adherence, particularly for
concrete reinforcements, which is deformed by cold rolling and provided, by cold

working, with ribs which are inclined with respect to the axis of the rod and disposed
between narrow longitudinal straight portions which are not ribbed, comprises four
narrow longitudinal straight portions which are not ribbed between which are disposed
four series of ribs inclined with respect to the axis of the rod.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to developing a Thermo
Mechanically Treated (TMT) rebar for application as reinforcement bar in RCC structure
and as rock bolt bar in roof support system for underground mines and tunnel
construction and the like.
According to yet another object of the present invention is directed to developing a TMT
rebar with higher bond properties.
A further object of the present invention is directed to developing a TMT rebar which
would be capable to providing higher resistance to pull out load in composite state with
optimum distribution of rib mass through surface deformation during hot rolling process
without adversely affecting the physical strength properties of TMT rebars
A still further object of the present invention is directed to developing a TMT rebar which
can maintain the composite action with surrounding concrete which is required to
transfer load between the concrete and steel.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to optimization of geometry of
surface ribs on curved surface of TMT round bars which are intentionally formed in the
process of hot rolling for the purpose of providing anchorage with surrounding cement
concrete. These surface deformation are categorized in two parts namely longitudinal
rib and transverse ribs (Fig 2.a). Straight longitudinal ribs are in the direction parallel to
the axis of bars caused due to filling of optimum material in gaps between top and
bottom roll during rolling process and curved transverse ribs are formed by making
indentation on top and bottom rolls during rolling process. The process of cutting
angular indentation on top and bottom rolls which causes transverse ribs on surface of

bar and adjusting roll gaps so that an optimum geometry of ribs are formed which
provided better anchorage is the main highlight of invention.
Therefore such as herein described it is an improved surface rib pattern profile thermo
mechanically treated (TMT) bar with high bond strength comprising of two
parallel longitudinal ribs along the diameter and a plurality of parallel spaced
transverse ribs disposed between longitudinal ribs inclined relative to the
axis of the rod and that the transverse are equidistant between each other
and are oriented with the same angular orientation and equal spacing with
respect to the longitudinal rib of the rod.
Further a process of manufacturing the said improved surface rib pattern profile thermo
mechanically treated (TMT) bar with high bond strength comprising the steps of:
making a steel billets from liquid steel of desired chemical composition;
hot rolling of billet in to round steel bar of desired diameter;
making longitudinal and transverse ribs as per specified geometry on the surface of
round bars by passing through a set of rolls in hot condition; and
quenching through water spraying and then cooling at ambient temperature to obtain
desired microstructure in the cross section.
The present invention and its objects and advantages are described in greater details
with reference to the following accompanying non limiting illustrative figures.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1 illustrates a pictorial representation of rib profile of TMT rebars in accordance
with the present invention;
Figure 2a illustrates the schematic diagram of one side of TMT rebars showing
transverse ribs, longitudinal rib, spacing of ribs and inclination angle of transverse rib
which have also been optimized in accordance with the present invention;
Figure 2b illustrates the sectional Area (Atr) of Transverse Ribbon round curve surface
of TMT rebars which is parabolic in shape in accordance with the present invention;

Figure 3a illustrates the mould of bond strength for pull test specimen where a helical
reinforcement is kept to prevent rupture due to excessive hoop during test in
accordance with the present invention;
Figure 3b illustrates the Pull test specimen cast with concrete and ribbed bar at centre
in accordance with the present invention;
Figure 4 illustrates the Pull test as per IS: 2770 at National Test House, Kolkata in
accordance with the present invention.
DETAILED DESCRIPTION
As herein disclosed, the present invention relates to a ribbed Thermo Mechanically
Treated (TMT) bar with improved surface rib pattern profile for higher adherence with
surrounding cement or grout material. The high bond strength TMT bar according to the
invention ensures high composite action ensure favouring wide scale application such
as reinforcement bar in RCC structures or as rock bolts for effective roof support in
underground mines or tunnel construction. The modified ribbed TMT bars have
application particularly for reinforcements for concrete, in general.
Thus, as can be seen in Figure 1 and 2, regardless of the series of ribs considered, the
ribs of two series longitudinal rib and transverse rib are shifted in axially and are
oriented with the same distance Str and at an angle to longitudinal ribs example 70 °,
relative to axis of the rod. The schematic diagram of one side of TMT rebars shows the
transverse ribs, longitudinal rib, spacing of ribs and inclination angle of transverse rib
which have been optimized. The ribbed TMT rod according to the invention have a
profile which, apart ribs is very close to a circular profile (Figure 2).
The optimization of geometry of surface ribs on curved surface of TMT round bars
which are intentionally formed in the process of hot rolling for the purpose of providing
anchorage with surrounding concrete. These surface deformation are categorized in two
parts namely longitudinal rib and transverse ribs (Fig 2.a). straight longitudinal ribs are
in the direction parallel to the axis of bars caused due to filling of optimum material in
gaps between top and bottom roll during rolling process and curved transverse ribs are
formed by making indentation on top and bottom on the final set of rolls during rolling
process. The process of cutting angular indentation on top and bottom rolls which

causes transverse ribs on surface of bar and adjusting roll gaps so that a optimum
geometry of ribs are formed which provides the maximum resistance to all of the
stresses exerted on the rod while pull out.
Each rib has, in section along a plane perpendicular to the axis of the rib with a
substantially trapezoidal / parabolic profiled flanks inclined at an angle 65 - 70 degrees
with respect to the longitudinal rib and more preferably to 68 degrees. The Space with
transverse and longitudinal rib = 0.15D max and more preferably 0 mm.
The height of the ribs, the width of the ribs in the middle thereof and the pitch or spacing
between two successive ribs, is defined in according to the nominal diameter of the
TMT rod. The values of rib profile geometry have been obtained though optimization of
available rib mass to maximize the resistance while pulling out in the concrete
embedded condition.
The High bond strength TMT bars as disclosed herein have optimum distribution of rib
mass on surface of TMT rebars ensuring excellent composite action with concrete and
provide bond strength of over 200% compared to that of plain round bars at a interfacial
slip of 0.25 mm when measured in accordance to BIS test conducted as per IS 2770.
The mould of bond strength for pull test specimen where a helical reinforcement is kept
to prevent rupture due to excessive hoop during test. The Pull test specimen cast with
concrete and ribbed bar at centre is shown in Fig 3. Test has been carried out at at
National Test House, Kolkata in a Pull-Off machine shown in Fig 4.
The process of manufacturing ribbed steel wire with high adherence, particularly for
concrete reinforcement, as disclosed herein by means of rolling a billet in hot condition
by passing through a series of rolls where adequate reduction in section size is
achieved by applying mechanical force. In this process, billet is rolled into round bars of
desired size. Indentation and grooves are made at predefined interval in the final set of
rolls which generates longitudinal and transverse ribs on the surface of the round bars.
The TMT bars are subsequently quenched and then tempered at ambient temperature
to obtained desired micro-structural properties in the cross-section of bars. The

optimization of rib geometry is key parameter for achieving maximum bond strength
value when the round TMT bars is embedded or grouted in cement or concrete.
Observed Test Results:
Bond strength test was conducted at National Test House, Kolkata in accordance to
IS: 2770 (Fig 4) wherein the bond strength was found to be 109% more than plain
round steel bars. The specified value for deformed bars is 80% over plain round
bars. This clearly indicates the effectiveness of newly designed rib pattern of SAIL
TMT rebars.
For example, the annexed table the values of different parameters for different nominal
diameters on ribbed steel high adhesion produced according to the invention and to
define the values of projected area corresponding to ribs.


Numerous modifications may be made to the present invention, which still fall within the
intended scope hereof. Thus, it should be apparent that there has been provided in
accordance with the present invention a method that fully satisfies the objectives and
advantages set forth above. Although the invention has been described in conjunction
with specific embodiments thereof, it is evident that many alternatives, modifications
and variations will be apparent to those skilled in the art. Accordingly, it is intended to
embrace all such alternatives, modifications and variations that fall within the spirit and
broad scope of the appended claims.

WE CLAIM:
1. An improved surface rib pattern profile thermo mechanically treated (TMT) bar
with high bond strength comprising of two parallel longitudinal ribs along the
diameter and a plurality of parallel spaced transverse ribs disposed between
longitudinal ribs inclined relative to the axis of the rod and that the
transverse are equidistant between each other and are oriented with the
same angular orientation and equal spacing with respect to the longitudinal
rib of the rod.
2. An improved surface rib pattern profile thermo mechanically treated (TMT) bar as
claimed in claim 1, wherein the angle of the transverse rib is in the range of 65 degrees
to 70 degrees with respect to the longitudinal rib.
3. An improved surface rib pattern profile thermo mechanically treated (TMT) bar as
claimed in claim 1, wherein the angle of the transverse rib is preferably 68 degrees.
4. An improved surface rib pattern profile thermo mechanically treated (TMT) bar as
claimed in claim 1, wherein the space between the transverse rib and longitudinal rib is
0.15D(max).
5. An improved surface rib pattern profile thermo mechanically treated (TMT) bar as
claimed in claim 1, wherein the space between the transverse rib and longitudinal rib is
preferable 0 mm.
6. An improved surface rib pattern profile thermo mechanically treated (TMT) bar as
claimed in claim 1, wherein transverse round curve surface of TMT rebars is trapezoidal
/ parabolic in shape.
7. An improved surface rib pattern profile thermo mechanically treated (TMT) bar as
claimed in claim 1, wherein the optimum distribution of rib mass on surface of TMT
rebars ensures excellent composite action with concrete and provide bond strength of
over 200% compared to that of plain round bars at a interfacial slip of 0.25 mm when
measured in accordance to BIS test conducted as per IS: 2770.

8. An improved surface rib pattern profile thermo mechanically treated (TMT) bar as
claimed in claim 1, wherein the height of the ribs, the width of the ribs in the middle
thereof and the pitch or spacing between two successive ribs, is defined in according to
the nominal diameter of the TMT rod.
9. A Process of manufacturing improved surface rib pattern profile thermo
mechanically treated (TMT) bar with high bond strength as claimed in claim 1,
comprising the steps of:
making a steel billets from liquid steel of desired chemical composition;
hot rolling of billet in to round steel bar of desired diameter;
making longitudinal and transverse ribs as per specified geometry on the surface of
round bars by passing through a set of rolls in hot condition; and
quenching through water spraying and then cooling at ambient temperature to obtain
desired microstructure in the cross section.
10. An improved surface rib pattern profile thermo mechanically treated (TMT) bar
with high bond strength substantially as herein described.
11. A process of manufacturing improved surface rib pattern profile thermo
mechanically treated (TMT) bar with high bond strength substantially as herein
described.