[TowerTalk] Tack welding rebar

N3AE n3ae at comcast.net
Sat Jan 4 12:50:47 EST 2014

A local metal fab shop a few miles away told me they prefer tack welding rebar cages because wire-tied cages don't hold shape well in transit. Not sure I buy into that, particularly if diagonal bracing is used, but that's what they told me. 

The discussion did raise some questions for this novice tower installer. Hoping to put in a base this spring for a UST TX-472 (4x4x7 cage ...probably weighs about 250 - 300 lbs). 

1. If the cage is constructed near (not in) the hole, what's the best way to rig it for lowering it in with a backhoe? Seems to me that just tying some lift straps to the top horizontals at the four corners might pull the cage out of shape or pull the horizontals off, particularly if wire-tied vs welded. 

2. There's another rebar cage fabricator further north that has automated machinery for cutting and bending. Would it be feasible to have them just cut and bend the pieces, toss them in my pickup truck and construct the cage on-site? Reason I ask is I'm not sure if building a cage requires measuring and cutting as you go to deal with tolerances. I would guess the fabricator's automated machinery would hold better tolerances on bend radius and bend location than manual tools in the hands of a novice builder. 

3. What's the proper way to electrically bond the tower anchor bolts to the cage to get a good Ufer ground? The anchor bolts are galvanized. 

4. Not really a question, but it's annoying that UST requires a 7 ft deep cage. From what I understand, rebar stock typically comes in 20 ft lengths. If the depth was 6 ft 8 inch, you could get 3 vertical pieces out of that 20 ft stock. Perhaps a practical reason for asking about required rebar lap splice overlap if you have to extend a length. 

Thanks & 73 

Shawn - N3AE 

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