[TowerTalk] Rebar Cage for Foundation

[Donald Chester]

On 5/4/2017 3:10 PM, Wes Stewart wrote:
> IMHO, the rebar in steel-reinforced-concrete is there to constrain the
> concrete under tension.  It's not there to anchor the tower. Generally
> speaking, welding isn't a good idea either, unless rebar graded for
> weld-ability is used (Grade "W").  The stuff you buy at Home Depot is
> probably Chinese made and of questionable quality.

I used big-box store re-bar stock for the cages when I put up my tower 35 years ago, but the quality was probably better then.  I tack-welded the cages together, just enough to hold the pieces in place while I set the cage in the hole.  I have heard it said that you should never weld re-bar, but I can't see what harm a small tack-weld could possibly do.  I can understand it not being advisable to solidly weld the pieces together so that the entire pieces at the joints get red hot all the way through. In any case, the tower has been up for 35 years and the concrete anchors and piers haven't fallen apart yet.

I suspended my cages in place using about 16 gauge non-galvanised steel bailing wire attached to scrap pieces of water pipe laid across the top of the hole, with enough clearance between the pipes to allow the concrete to be poured without knocking anything out of alignment.  I didn't trust resting the cage on concrete bricks or piers, not sure if the concrete could be guaranteed to completely cover and seal the re-bar away from the soil.  Once the concrete was poured I used a pair of wire cutters and reached down a  couple of inches into the wet concrete and clipped the wires, then  smoothed over the top surface of the concrete where I had inserted the cutters.  Once concrete is poured, the re-bar isn't going anywhere; in fact it would be difficult to forcefully displace it.  It certainly won't  sink to the bottom.

I didn't use concrete forms; just dug the holes to size and filled them with concrete, except for one where a heavy rain a couple of days before had collapsed the sides of the hole.  I had to dip out the mud and build a form for that anchor, because my hole had turned into a  shallow crater filled with mud with the consistency of chocolate pudding.

When the holes were all filled, the guy in the concrete  truck asked me where I wanted him to dump the left over concrete.  I thought they would take it back where they had some place to mix it with water and dump it, but no, it was all mine and he said they had to empty the truck before going back to town.  Instead of having them dump it  at the edge of the field somewhere where it would turn into an immovable boulder, I told the guy to use what was  left to top off the two holes that hadn't collapsed in the flood.  The piers were to be buried two feet below grade, but the ones they topped off came up to about 4" from the surface.  I decided that wouldn't hurt anything, if anything make the piers stronger, and since they would still be covered with dirt, better to have the extra concrete as part of the anchors than out in the field somewhere to be in the way for all eternity.


Don k4kyv