TT:
This advice against using common face brick to support rebar cages
reminded me - I did not use such brick in my tower's foundation. I actually
used the gray cement/concrete brick. I was reminded when I looked more closely
at the photo link from my earlier e-mail. The brick there is light gray and
not face brick.
So let me correct my earlier advice - Instead of using dobi blocks to
support rebar cages, one can use CEMENT bricks. Just make sure the rebar cage
does not slip off the bricks once the pouring starts.
73 de
Gene Smar AD3F
On 12/16/14, Grant Saviers wrote:
The chairs most commonly used are plastic, so no rust concerns with
them. And no chance they will wick moisture. The "trick" is to use
enough of them to provide enough support if the rebar is stepped on or
has some load on it. I used 1 for about every 2 sq ft of base area.
There are several different styles, pick the right one for the rebar #
being used and that look stronger. I used the 3" high which is the code
for rebar to earth separation.
Concrete "block" can be very porous and not water tight, at least many
were in a basement I once owned.
Grant KZ1W
On 12/16/2014 6:08 PM, edk0kl@centurytel.net wrote:
> I'm not sure tying the legs of a tower to a concrete base by putting
> part of it in concrete. Most big towers taper down to a small point.
> That point rests on some iron tied to the concrete. The guyed tower is a
> moving load, putting the rotational or lateral force puts stress on the
> base and could not be a good thing. Maybe I over think ...
>
> In any event, rebar should never rest red brick, porous material transmitting
> water to the iron. Same thing for "chairs" they inevitably attach to the
> iron, in time the rust keeps on going up the iron. "Chairs" are made
> to keep the iron off the plywood form in a building or bridge molding
> NOT on gravel, etc. Best thing is concrete block, same stuff the concrete
> is. On my tower we suspended the foundation in the concrete with a
> horse on the ground over the form. The form is 10ft square using 2x4
> and ordinary steel tie wire.
>
> Don't forget to leave a drainage hole, slot, whatever for the condensation to
> drain out of the leg.
>
> Good Luck! We're all counting on you
>
> 73!
>
> ed K0KL
>
>
>
>
>
>
>
> ----- Original Message -----
> From: "Bill Aycock" billaycock@mediacombb.net>
> To: jbwolf@comcast.net, towertalk@contesting.com
> Sent: Tuesday, December 16, 2014 6:59:10 PM
> Subject: Re: [TowerTalk] : Nube rebar question
>
> Jim-
> Your terminology has confused me. Can you describe what you mean by a "Roof
> Mount"?
> Thanks--Bill--W4BSG
>
> -----Original Message-----
> From: James Wolf
> Sent: Tuesday, December 16, 2014 6:17 PM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] : Nube rebar question
>
> Gentlemen,
>
> I'm baffled that so many of us put part of a tower in the cement base when
> installing a guyed tower.
> I know I've said it here before, but on most guyed towers, why not use a
> simple roof mount? Put threaded rods in the cement that rise enough to bolt
> to the roof mount so it won't turn or twist.
>
> Reasons to consider this:
>
> - No drainage to worry about in the tower section below ground level.
> - Weep holes should be or can be made in the roof mount where they can be
> easily inspected and cleaned out.
> - You are not locked into changing to a different tower later in life -
> assuming the cement base will handle it.
> - You don't have to worry about getting the tower section in the cement
> exactly vertical.
> - For those who worry about lightning cracking the base, there would be a
> lot less chance of it. [maybe an old wives tale by now].
> - It's probably less expensive.
> - It's certainly simpler.
>
> I installed my 120 ft. of Rohn 45 with a roof mount 25 years ago and I've
> seen no issues.
>
> Can anyone provide a good reason not use a roof mount for these
> installations? I would be very interested.
>
> Jim - KR9U
>
>
>
> ___________________
>
> On Tue,12/16/2014 9:27 AM, Kent Olsen wrote:
>> What do you do in the bottom where the rebar sits on the dirt? Is this
> just a sacrificial bit?
>
> A layer of gravel at the bottom of the hole. If you put the bottom section
> of the tower into the concrete pour as many of us do, the layer of gravel is
> important for another reason -- it provides drainage for water that comes
> down the legs of the tower.
>
>
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