There are various grades of rebar. All rebar is some form of steel so it
can bee welded. The trick is the resulting microstructure of the welded
area.
Some grades of rebar have guarenteed metalurical composition and are
weldable and produce a very ductile micro structure. Some rebar is made
of recycled Toyotas which are made of recycled beer cans which are .....
The cheap stuff you get at you local Home Depot is the latter. It
typically high in carbon which when welded turns brittle and provides a
site for cracks to start.
When I was working as an engineer for a crane company, the rule of thumb
was the a welded joint would only support 10,000 psi stress in a fatigue
application. General structual steel is 36,000 psi yield or 18,000 psi
in fatigue, and Core-Ten is 50,000 and T-1 Steel was 100,000. Most rebar
is between 30,000 and 40,000. But stike an arc on any of them, and you
could only count on 10,000 psi, less if you get a brittle weld.
You always want to place the weld in as low a stress location as
possible, so you can take advantage of the strength of the parent
material. Weldment design is a definite art and there have been books
written about it. Some of the best were writen by the Lincoln Arc
Welding Foundation. I assume you have heard of Lincold Welders - same
people.
My personal recommendation is to overlap the bars to length of 18
diameters for strength, use lots of twisty wire ties, grind the rebar to
bare metal where you want to braze copper to it, and not do a lot of
welding unless I absolutely have too. (I worked my way through college
as welder on pressure vessels, so I do know how to weld.)
In the event of lightning strike, the twisty wires will carry a lot of
current, there will be some carbonization of the concrete where the
curent flows form bar to bar, but it won't explode.
de n0yvy steve
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