[TowerTalk] New Tower Construction - Questions
Dan Evans
n9rla@yahoo.com
Thu, 31 Aug 2000 14:26:39 -0700
Hi All
I have been enjoying this new tower construction thread. I recently
subscribed to the list because I intend to put up a small tower soon and
wanted to learn more about it, wish I had joined a long time ago!
Are the "Rohn specs" available on the web?
Thanks,
Dan
Dan Evans
N9RLA
Scottsburg, IN {EM78}
1/2 of the N9RLA /R no budget Rover Team
Check out the Rover Resource Page at:
http://www.qsl.net/n9rla
----- Original Message -----
From: "John D. Farr" <johnfarr@ro.com>
To: <K7LXC@aol.com>; <aa4lr@radio.org>; <towertalk@contesting.com>
Sent: Thursday, August 31, 2000 11:23 AM
Subject: RE: [TowerTalk] New Tower Construction - Questions
>
> Gentlemen
>
> I would be careful about adding rebar. Rohn does not specify any for a
guyed
> 25G tower. Apparently, casting the base section into concrete per their
> specifications is adequate. I have not read TIA/EIA-222-F, but I have read
> and understood the concrete code, the ACI 318-95. This code specifies a
> maximum amount of steel to use. The maximum allowed is 75% of a "balanced"
> strain condition in the cross section. "A balanced strain condition exists
> at a cross section when the maximum strain at the extreme compression just
> reaches 0.003 simultaneously with the first yield strain f_y/E_s in the
> tension reinforcement". In English, this means that you want the steel to
> fail well before the concrete. This is because the steel gives lots of
> warnings before it parts where the concrete gives none at all. I know of
no
> exceptions to this rule. One should never over reinforce concrete.
>
> Development length is the length of embedded rebar required such that in
> tension or compression, the full strength of the bars can be achieved
> without the bar slipping in the concrete. If Rohn is using the base
section
> as rebar, you should not coat the base section prior to pouring the
> concrete. The ACI allows only for uncoated bars and epoxy coated bars. I
> would imagine that there is a specification for the epoxy used. The
> development length is increased by a factor of 1.5 for the epoxy coated
> bars. I have heard of sealing the area where the base section enters the
> concrete with roofing pitch. I don't see a problem with that.
>
> The long and the short of it is that you should build the foundation per
> Rohn's specifications. A detailed knowledge of the governing codes (I'm
not
> sure that the ACI governs in tower bases) is required to make changes.
>
> gl
> John
> KC4ZXX
>
> > -----Original Message-----
> > From: owner-towertalk@contesting.com
> > [mailto:owner-towertalk@contesting.com]On Behalf Of K7LXC@aol.com
> > Sent: Thursday, August 31, 2000 10:13 AM
> > To: aa4lr@radio.org; towertalk@contesting.com
> > Subject: Re: [TowerTalk] New Tower Construction - Questions
> >
> >
> >
> > In a message dated 08/30/2000 2:42:27 PM Pacific Daylight Time,
> > aa4lr@radio.org writes:
> >
> > > * I'm planning to embed a Rohn 25 tower section in the concrete
> > base. I'm
> > > unsure if direct contact with the concrete will cause corrosion of
the
> > > section. Should embedded tower sections be coated with some kind of
> > > protectant? Or would a protectant reduce the mechanical
> > coupling between
> > > the base and the tower? Is corrosion (other than pooling of
> > water in the
> > > legs due to improper drainage) not really a problem?
> >
> > Most everyone just sinks the section in the concrete as is.
> > OTOH W3LPL
> > had serious corrosion problems by doing that. Now he coats metal
surfaces
> > that'll be in the concrete with building tar. That might be a
> > 'belt-and-suspenders' approach but it'll sure take care of any potential
> > longterm problems.
> > >
> > > * I know I need a rebar cage in the base, but I'm fuzzy on the
> > details of
> > > how to construct it. This is a standard 2x2x4 foot base, and I
> > understand
> > > the rebar should be about 3" from the edges of the concrete. This
> > > translates into a 1.5x1.5x3.5 foot cage. I can see rebar at all the
> > > edges, how much is needed on the long faces? Are there
> > horizontal pieces
> > > on the way down each face? Spaced how often? How about spacing for
> > > vertical pieces? Are there pieces on the top and bottom faces?
> > Are there
> > > any pieces on the INTERIOR of the cage? Isn't there a problem
> > with rebar
> > > and tower section trying to occupy the same space with the interior
> > > elements?
> > >
> > You can add any rebar that you want - the specs are for the
> > MINIMUM size
> > and amount. If you want to add vertical pieces to hold everything
> > in place or
> > additional horizontals - go nuts.
> >
> > > * I plan to build a small wooden form to shape the top few
> > inches of the
> > > concrete base. Is there something you can put on wooden
> > surfaces to make
> > > the concrete not stick to it? This would make it easier to remove the
> > > forms later.
> > >
> > You can cover the parts of your wooden form that'll touch the
> > concrete
> > with motor oil. The forms will come off easily and the motor oil
> > won't affect
> > anything.
> >
> > Cheers & GL! Steve K7LXC
> >
> > --
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> >
>
>
> --
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