Welding of reinforcement bar steel
Welding reinforcement offers advantages over conventional tying. Welds provide rigid connections that do not work loose during handling of the reinforcement or placing of the concrete. They are particularly advantageous for pre-assembled reinforcement cages, such as for piles, diaphragm walls, columns and beams.
The standard specifications for reinforcing bars referred to in Material Specification 539, (ASTN A 615, A 616, and A 617) are based on physical properties and do not specify the chemical composition of the steel. Since weldability is dependent upon chemical composition, bars may conform to these specifications yet not be weldable. If bar splices are to be welded, Material Specification 539 still applies, but the construction details must specify in addition that the bars be of weldable steel.
Welding electrode/ wire for Rebar or reinforcement bar
Most of the rebar materials are carbon-manganese bases. They can be successfully welded using ER70S-6 when welding with the GMAW process. E7018 or E6013 types electrodes are mostly used with shielded metal arc welding or SMAW welding process.
Table 5.1 in AWS D1.4 provides the requirements for filler metal needed to weld the rebar. An example would be the method for A615 grade 60 rebar. If the method of welding was SMAW, an electrode of E9015-X, E9016-X, E9018-X or E9018M would be used. If using the GMAW method, an electrode of ER90S-XXX or E90C-XXX would be required. If two different bar grades or specifications are welded together, the electrode for the rebar with the higher tensile strength is used. For example, if an A706 grade 60 bar is welded to a A615 grade 60 bar, the electrodes required for the A615 grade 60 are used. This is because the tensile strength of the A615 rebar is 90,000 psi while the A706 rebar is only 80,000 psi.
Materials Specifications for Rebar or reinforcement bar
ASTM A615 , A 616, and A 617, ASTM A706
Code/ Standard for Reinforcement bar welding
1. BS 7123:1989 Metal arc welding of steel for concrete reinforcement
2. BS 5135:1984 Process of welding of carbon and carbon manganese steels
3. AWS D 12.1, Recommended Practices for Welding Reinforcing Steel, Metal Inserts, and Connections in Reinforced Concrete construction
4. ACI CODE-318-19: Building Code Requirements for Structural Concrete and Commentary
5. ISO 17660-1:2006 Welding — Welding of reinforcing steel — Part 1: Load-bearing welded joints
7. BS 8548:2017 Guidance for arc welding of reinforcing steel
Selection of welding process for Reinforcement bar welding
The welding processes for pre-assembly of reinforcement bar welding are:
- Shielded metal arc welding
- Gas Metal arc welding or MIG/ MAG
- Resistance spot welding
Welding Procedure for Reinforcement bar or rebar welding
Welding procedures should be specified in the construction details. They will depend upon the kind of splice, the size of the bars, the composition of the steel, the position and accessibility of the welds, the atmospheric temperature, and other factors. Procedures and workmanship should conform to Section 4 of AWS D 12.1, “Welding Reinforcing Steel, Metal Inserts and Connections in Reinforced Concrete Construction” and Section 4 of AWS D 2.0, “Specifications for Welded Highway and Railway Bridges.
If thermit welding is to be used, procedures should conform to the recommendations of the manufacturer of the materials. The thermit powder must be of a composition that will produce weld metal of strength and ductility comparable with that of the bars being spliced, and the quantity used must be sufficient to fill the splice mold and fuse the ends of the bars.
For British or European applications, Full details of the correct procedure are contained in BS 7123:1989 Metal arc welding of steel for concrete reinforcement, BS 8548 & ISO 17660 series.
TACK WELDING OF REINFORCED BARS ORREBARS
The sizes specified in BS 7123 for tack welds in the form of lap joints are a minimum throat thickness of 4mm and a length of at least 25mm. This requirement was met by the defective welds which had been made with basic covered electrodes but the 32mm diameter BS 4449:1979 Grade 460 bars had not been preheated before tack welding. Chemical analysis showed the steel to contain 0.28%C and 1.2%Mn with a carbon equivalent of 0.51% which is the maximum allowable CE for this grade of reinforcing bar. The welds had throat thicknesses of 6mm minimum which according to BS 5135:1984 Process of welding of carbon and carbon manganese steels corresponds to an arc energy of 2.2kJ/mm.