Welding in reinforcement steel

1. 1
REINFORCEMENT
welding
Amardeep Singh

2. 2
WELDING OF REINFORCEMENT
• IS : 1786 allows the chemical composition and carbon
equivalent to be limited so that the material can be
readily welded by conventional welding procedures.
• Material not conforming to these limits is generally
difficult to weld for which special care and
precautions will have to be exercised.
• IS : 9417 may be followed for welding in Cold Worked
Steel Bars
Is welding in reinforcement allowed ?

3. 3
WELDING OF REINFORCEMENT
• For guaranteed weld ability, the Carbon Equivalent, CE using the
formula
CE = C+ Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
shall not be more than 0.53 percent, when micro alloys/low alloys are
used.
CE = C+ Mn/6
• Carbon Equivalent, CE using the formula
shall not be more than 0.42 percent when micro alloys/low alloys are not
used.
Where,
CE = Carbon Equivalent, C = Carbon, MN = Manganese, Cr = Chromium, Mo = Molybdenum, V =
Vanadium, Ni = Nickel and Cu = Copper
Refer MTC of reinforcement Steel for values

4. 4
WELDING OF REINFORCEMENT
• The parent metal shall be of guaranteed weld able quality of
steel conforming to IS : 1786 according to its CE.
• Electrodes used shall conform to IS : 814 – part 1.
Requirement :-
• Sometimes welding is required at limited working spaces.
• In piles where reinforcement cage bars get damaged while
cutting the pile heads.
• Where structure need to extended for any reason.
• In TG Deck slab where the reinforcement is much congested and
working space is less.
• Fixing of steel structural members in concrete.

5. 5
WELDING OF REINFORCEMENT
• Cold-worked steel bars shall be either butt welded or lap welded. Butt
welding may be carried out either by flash butt, gas pressure or by
shielded metal arc welding process. Lap welding may be carried out by
shielded metal arc welding process.
• Bars of unequal diameter may be welded. However, in case of butt
welding, the difference in, diameter of bars shall not exceed 5 mm.
• The untwisted ends must be removed before welding and the surface of
the ends of the bars to be welded shall be clean and free from rust,
paint, grease and/or other contaminants which are likely to affect the
quality of weld.

6. 6
WELDING OF REINFORCEMENT
• Butt-welds by metal arc welding process are normally adopted to join bars of thickness
more than 20 mm.
• The ends of the bars to be welded should be placed in proper alignment in clamps so that
bent or eccentric joints do not result.
• Flash Butt Welding of Cold-Worked Bars
The bar ends shall be uniformly pushed against each other from the moment of contact to the
up-setting. The transformer regulator should be so set that that current at contact area is
between 80 to 90 A/mm2.
If the capacity of butt welding machine or the available power is not sufficient to take the
load for welding from cold, welding may be done after preheating. Satisfactory joints with only
slight reduction in original strength of the bar can be achieved with a current density up to 25
A/mm2.
• Butt-Welding by Shielded Metal Arc Welding Process
Welding electrodes with flux covering of Type 3 or Type 6 of IS 815 : 1974
The size of electrodes depends upon the position of the bead and thickness of the bar to
be welded. The root runs should be made with electrodes of size not exceeding 2’5 mm. For
successive beads, the size of the electrodes should be progressively increased so that in the top
bead, the electrode size does not generally exceed 3.15 mm for 20 mm bars and 5 mm for 40
mm bars.
The temperature of the bars at a distance of about one bar diameter from the joints shall
not exceed 300°C immediately after the bead is made. Before commencing the next bead, the
temperature shall not exceed 250°C.
Butt Welding

7. 7
WELDING OF REINFORCEMENT
• Butt Welding by Gas Pressure Welding Process
Gas pressure welding is basically a hot forging process of joining the two bars end to end.
The bar ends are heated by a multi-nozzle burner using oxy-acetylene flame and fused by
forcing the two bar ends against each other under pressure to effect a solid phase welded joint.
Butt Welding

8. 8
WELDING OF REINFORCEMENT
Butt Welding

9. 9
WELDING OF REINFORCEMENT
• Lap Welding of Cold-Worked Bars
Lap joints may be made in cold-worked bars of all sizes. They are preferred when access for
welding is from one side only, and while connecting prefabricated units. Use of electrodes with
flux covering of Type 3 or Type 6 of IS 815 : 1974
The surface of the bars to be welded shall be clean and free from rust, paint, grease and/or
other contaminants.
Lap Welding
Rebar Diameter vs. Electrode size
Sr. No Nominal Diameter of Bar (mm) Size of Electrode max
(mm)
1 Up to and including 10 mm 2.5
2 Over 10 up to and including 18 mm 3.15
3 Over 18 up to and including 28 mm 4.0
4 Over 28 mm 5.0

10. 10
WELDING OF REINFORCEMENT
Lap Welding

11. 11
WELDING OF REINFORCEMENT
Lap Welding

12. 12
QUALITY CONTROL TESTS
• Tensile test : Specimens with a free length between grips about 20d should he used. The
selected pieces when subjected to a tensile test shall have tensile strength not less than 90
percent or the actual tensile strength of the bar but in no case less than 485 MPa for grade
Fe 415 and 545 MPa for grade Fe 500 of IS 1786. The fracture shall not take place in the
weld joint.
• Bend test : The welding flash or reinforcement shall be removed at the point where contact
is made with the mandrel. The welded joint shall be capable of being bent to an angle of 60
degree around a mandrel of diameter specified below, before any crack appears:
Sr. no Nominal Diameter of Bar
(mm)
Diameter of
mandrel ( mm)
1 Up to 5 d
2 Over 7 d
Butt Welding

13. 13
QUALITY CONTROL TESTS
• Tensile test : The free specimen length between grips must be between 25 d and 30 d where
d is the nominal diameter of the bar. The breaking load shall not be less than the
guaranteed load in accordance with IS 1786 required to fracture the bar.
Lap Welding

14. 14
PRECAUTIONS IN REINFORCEMENT BARS
The reinforcement bar should not cut with
flame because when it is heated and air
cooled the surface will be lost and strength
of bar will approach to center of bar. Loss
of strength is the reason to restrict the
cutting of bar with flame.
The bending of bar should be done in
correct radius of mandrel because tighter
the bend greater the strains around the
bar. The bend diameters should be
followed as per IS : 2502 to maintain
ductility and practical construction
operations.

15. 15