I am State DOT engineer responsible for concrete pipe fabrication. Historically, little attention was given to the welding process associated with producing a lap weld on the cages used to reinforce concrete pipes. The reinforcement is typically ASTM A185 with a yield strength of 65 to 75 ksi. Table 5.1 in D1.4 only addresses reinforcing bars and not welded wire reinforcement. My assumption is that a 90 series electrode would be required however due to the higher yeield strength of the material. Am I correct? My question is posed because the majority of the industry is using a 70XX electrode. Who is correct?
bh:
1.) The ASTM specification you referenced is for Steel Welded Wire Fabric. This material is composed of ASTM A82 steel wire. These are code approved materials, but also require qualification. Mechanical testing of the wire or fabric would be required by the applicable ASTM specification for these products. Metallurgical testing to determine the CE value and chemical composition is required if welding to reinforcing bars. [D1.1-98, 1.3.1]
2.) Undermatching filler metal is quite common, particularly with reinforcing bars. I have inspected a number of projects were undermatched filler metals were specified by the RDP for reinforcing steel. The determining factor (at least from my limited experience and perspective) has been design/application requirements. Here, E7018M electrodes are the norm. Please note I stated this is a practice by the local design community. [D1.4-98, 5.1.1]
3.) I don't think there is a right or wrong answer to your question, it would be project or site specific (by the RDP or governing jurisdiction) where matching or undermatching filler metals would be sufficient.
If the wire mesh is used to reinforce concrete pipe, and loading is primarily in the hoop direction or tranverse to the pipe run, lap welding the ends may serve more to hold the ends of the mesh in place till the concrete cures. Aren't the pipe sections usually fitted end-to-end with no permanent joint? Also, if you have a larger cross section through the length of the lap weld than through the wire diameter alone, can't you use a lower strength weld material and increase the weld length to obtain the same load carrying capacity? I'm a little rusty on this stuff. Someone correct me if this is wrong.
Marty
I think Marty explained it better than I did (with all the code babble).
Increase the effective area of the undermatched weldmetal will permit undermatching filler metal. Common design practice. Good catch.
Another consideration when looking at under-matched filler metals, is that usually the tensile strength would not be the limiting factor, but rather the yield strength. (Where it starts yielding first, is generally where it will break.)
As such, as-welded weld metals have a distinct advantage. They generally yield at around 80% of tensile strength. (UTS) Most base metals yield at around 65% of UTS. This means that you can have a "weaker" filler and it will still not break on the welding.
Hope this helps
Regards
Niekie
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