Think about this once. The purpose of copper (or any) pipe is to
transfer water or another liquid. If you fill it with a solid, how in
the hell is a liquid going to get thru?
You get an "F" in basic science.
Back to science class you go !!!
Bottom line................a 16ft span (if only supported at the ends)
is way too far for a 3/4" copper tube (.875 od & .745 id)
just under self weight I estimate a center point sag of about 5".
An 1 1/2" or 2" tube would be more appropriate.
Fiberglass kits would be so easy for this project.
You can use just the liquid with the hardener added or you could fill
the liquid with the fiberglass cut into small pieces for super
strength. Either one will work.
Use the biggest pipe you can. SInce copper pipe typically
comes in 10' lengths, you're probably going to need
a connector in the middle. Hopefully, you can add a
third support here.
Don't use Rebar. Run aircraft cable down the pipe, then fill the
pipe with cement with fine aggregate. Then pre-stress
the pipe with about a 1" camber, blocking it in place on the floor,
and crank the shit out of the aircraft cable. Let this dry
for about 3 days. When you put this up, set the camber so that
it crowns up. In order for this arch to collapse, the ends have to
move apart. If you can rigidly constrain them you MIGHT be
ok. Be warned, however, that a weight on the top of
a 1" high, 16' long arch has a huge mechanical advantage, so
you're not going to resist the sideways thrust with a couple
10-penny-nails and a block of wood. You want big-ass steel brackets.
Considering the small diameter of hte tubing, won't the cement just crack
with a little bump or stress? Your idea is far better than just filling the
tubing, but it does not it seems as though there is much room for a strong
shear section of concrete.
The concrete isn't there as a beam-member, it's there mostly to
keep the cable from moving around, and partly to keep the
tube from collapsing. I do agree that there's a good chance this
won't work, but it's the best I could come up with, given the
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