4.3 Welding of Reinforcement Bars
IS 456 Recommendations for welding splices:
Clause 26.2.5.2 of IS456:2000, provide the guideline for strength of weld based
on the test results w.r.t the parent bar.
Splice for Compression Bar: For welded splices and mechanical connection, 100
percent of the design strength of joined bars.
Splice in Tension Bars:
- 80 percent of the design strength of welded bars (100 percent if welding
is strictly supervised and if at any cross- section of the member not more
than 20 percent of the tensile reinforcement is welded). - 100 percent of design strength of mechanical connection.
IS 9417: 1989 Recommendations for Welding Splices:
Welding cold worked steel bars confirming to grade Fe500 of IS 1786:2008 shall
be either butt welded or lap welded. Lap welding of the bars is not covered in
this technical note. Further, code recommends butt welding shall be carried out
either by
- Flash butt,
- Gas pressure or
- By shielded metal arc welding process.
Also, guideline for quality control by selection of test specimen, testing requirements
and limiting values have been provided in relevant clauses.
Based on ease of process, handling of equipment and in-situ placement of
reinforcement bar & its welding consideration, Gas pressure welding is covered in
this technical note.
Gas Pressure Welding of Bars: Gas pressure welding adopts the method of
heating the steel joints by the combination of oxygen and acetylene gases, when
the temperature reaches the plastic state, then putting pressure on the joints to
crimp the steel joints together.
The equipment for gas pressure welding comprises of the following:
- Oxygen and acetylene gas cylinders with regulating values etc.
- Multi nozzle burner: The burner consists of a blow pipe with 4 or more
nozzles. The nozzles shall be so arranged to ensure uniform heating of the
bar surface. The burner shall provide the stable flame during heating and
the heating capacity shall be appropriate to the size of bar. - Clamping Unit: The clamping unit shall grip the bars well.
- Pressurizer: Pressurizer shall be either hydraulic or mechanical and either
manually operated or electrically driven. The pressurizer shall be capable of
maintaining the uniform axial pressure.