Re-bar ties, the 5 1/2" or 7 1/2" usually are readily available from any
lumber yard or homecenter. Usually they are sold in rolls of 1K....and they
are cheap....they are malleable metal waiting for you to twist it and deform
it. They are probably rusting by the time you get them home....this is not a
problem.
Two years of Architecture taught me that the purpose of the ties is not to
bond the steel together, but to ensure the steel's ultimate correct placement
within the pour of concrete......
By forming all the rebar into a cage where everything is tied to everything
else it is "self-supporting" - hopefully this cage is properly placed with
the bar in from the edge of the pour so it is well covered. Do not rest this
cage on the ground....jack it up on some concrete blocks/rocks/bricks so the
concrete will flow under it giving it coverage on the bottom as well as the
side and the top. I recommend the cage be constructed out of the hole and
then with some help from a buddy be lowered into place. You probably have
seen big cages on high rise sites or on road work where they are building
overpasses.
The miracle of reinforced concrete for construction is that both the steel
and the concrete have almost identical rates of expansion and contraction as
temperature changes...imaguine the mess if they didn't, especially you guys
in MN! The steel's function is "tension" (it is tough to bend or alter in
shape) and the concrete's duty is "compression" - you can, for example,
drive your car on it. A nice side feature tower building CONTESTERS need
more than anything else is it is very heavy!
As has already been elucidated (what a great word) by our resident tower
expert K7LXC (thanks for the great input here, Steve), if your tower is
already going to have a grounding system you won't be in the situation where
Lightening's energy is looking for a path and in desperation arcs through the
concrete over to another piece of rebar.
Last I checked at retail a bar tie is less than a penny a piece....use
lots...and once you get the hang of the twister you will find it can be fast
- hopefully this won't be when you get to hole number four after wrestling
with linemans pliers on the other three!
....on another concrete note: The piece on concrete fastners and epoxies from
VR6BG was right on....look for similar home owner non-commercial user sized
packages of the Epoxy that come in a double barreled syringe, saw those
barrels off and squeeze! This stuff is frequently placed near where the metal
lumber connectors are, as that wood will probably need to eventually be
anchored to concrete. I have seen this stuff at most home centers here in
Florida.
Good topic, hope we have more tech stuff...that is the part I value more than
anything WN4KKN offers us the ability to share by his support of The Contest
Reflector....thanks Trey.
73,
Jim K1ZX
|