Welded Reinforcement Exposed To Earth 1

[RFreund]

Should a special coating be applied, if so, what?

Basis of question:
Rebar ties together a foundation wall back to a deadman. The proposed weld would be made to overlapping rebar in the soil between the deadman and foundation wall.
This is not the original detail just FYI.

EIT

http://www.HowToEngineer.com

 

[TXStructural]

Rebar is not the right material to use for this application, and field-welded bar will tend to rust unless properly protected. Normally, it is the alkalinity of concrete that protects the bar from corrosion, but you do not have this in soil. It is not good practice to extend embedded reinforcement into soil, since this creates pathways for corrosion to enter the concrete.

That said, depending on soil type and exposure, either galvanized or epoxy-coated would work, but not if you intend to weld the bar. You should only consider the detail you suggest for temporary use.

 

[RFreund]

Right, that was my concern. This actually is something a contractor built, inspector catches it and now wants an 'ok'.

I suppose they could drill through the concrete and use some stainless steel threaded rods and plates?

EIT

http://www.HowToEngineer.com

 

[TXStructural]

Yes, but then the vulnerability to corrosion and resultant splitting/spalling forces on the concrete at each end is not resolved. The stainless would likely be less likely to corrode (depending on steel spec and grade, and soil/exposure.

If the contractor did not weld in accordance with AWS D 1.4, then the welds are not structurally qualified. If the bars are ASTM A706 (weldable) rebar and were properly welded, then the simplest solution might be to excavate at least 3 inches below the bars, form sides with adequate cover around the bars, and pour a concrete strip along the length of bar to provide passivation and protection for the bars. Be sure the bars are clean, and the concrete is of good quality and properly consolidated.

If this is near a road which is salted, near a coast, or there are other reasons you expect severe corrosion, you could require stainless or epoxy-coated threaded bars. Not an endorsement of a brand (they are not a CRSI member), but DYWIDAG does sell epoxy-coated threaded bars, couplers, and accessories for soil nails and similar uses. Their couplings and nuts can be used as you describe (drill, through-bolt, and connect) and the epoxy-coated bars should work well even in corrosive exposures.

 

[PT999]

Its unlikely that your contractor followed AWS D1.4 (Structural Welding Code - Reinforcing Steel) requirements, if he did this without any engineering input. The requirements include knowing carbon equivalency from material reports, using proper welding rods for the rebar, using approved welding procedure called WPS, maintaining electrodes in ovens at the site and much more.

So approving this work would never fly if an experienced AWS welding inspector (CWI) actually reviewed your contractor's work carefully. And if this work failed, that is exactly likely to happen.

 

[msquared48]

The rebar should have been encased in a concrete grade beam.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com