At 02:56 AM 6/20/2003 +0000, Paul Playford wrote:
>I am under the impression that the rebar cage should be tied, not welded.
>de Paul, W8AEF
Found on the web (no guarantee of validity, etc.):
Regarding my recent query as to whether it is better to weld the rebar cage
for a tower base or to tie it together with wire:
There were 15 or 20 responses. Many were of the "I always/never ...
weld/tie rebar in tower base" flavor. A few pointed out that (1) Rohn
specifically prohibits welding rebar cages and embedments in their plan
drawings but that on the other hand (2) Triex sells pre-welded rebar cages.
However, the biggest revelation was a bit of serendipity, as someone pointed
out to me that there is a column from KI7NF (PE and ARRL VCE) on pg. 79 of
4/96 QST that addresses this exact issue. His recommendations against
welding rebar have to do with the uncertain metallurgical makeup of rebar
purchased from most sources and the difficulty in making a proper strucural
weld without a low-hydrogen welding rod and the correct type of welding rig
(not the garden variety type apparently). However, he does go on to state
that if your purpose in welding a cage is _NOT_ structural, but rather
electrical (continuity to minimize arcing/or for ufer grounds), then you are
free to go on your merry way as long as you provide some other structural
joint, i.e. his tied wire "lap splice" method.
As far as Triex providing pre-welded cages, I'm guessing that they have a
certified welder on staff with the proper equipment and that they are
certain of the makeup/carbon content of the rebar that they use.
One respondent told me to cadweld the joints and another mentioned brazing
the joints instead of welding them.
The net result is that I will definitely tie my cages, and maybe weld the
non-Rohn cages as well this summer as I begin construction of my new
station. Thanks to all for their responses.
de Pete, AD4TU
Pete's comments make sense...
I've also seen some comments to the effect that rebar is not manufactured
to be weldable (that is, the alloy, temper, etc.), so the structural
quality of a welded joint is uncertain, even if low hydrogen rods, etc.