Brian:
The 3" clearance is not a recommendation that did not initiated with
ROHN, it is a part of the ACI 318-99 Building Code for Concrete, which
is adopted by all the building codes in the United States. The bars
when they rust will increase in diameter and cause the concrete to
crack.
Rohn's sections are galvanized and are more resistant to corrosion than
the mild bars. You can get rebar that is galvanized or epoxy coated but
the 3" still is the code requirement. I have put a lot of galvanized
handrail and other embedded items in industrial plants exposed to the
weather and other chemical enviroments and they tend to last a very long
time.
I agree that if the water table rises then there will be water in the
legs. Could be a problem if above the frost line. Frozen water in a
emebdded pipe can crack the concrete.
Foundations are supposed to be set with the bottom at the frost line,
according to the building codes. For corrosion to take place you need
oxygen and water, the soil ph assumed to be neutral. IF the soil pH is
acidic then things get tricky.
For the normal structural life of amateur towers I don't see too many
problems with the practice of extending the legs into the base gravel.
You really shouldn't put a foundation in location where the water table
is at the surface anyway.
Hank / KR7X
alsopb wrote:
>
> This practice recommended by Rohn has me a bit puzzled. Rebar in the
> concrete has to stop 3" from the end of the concrete on all sides.
> The reason given is that they will rust, disintegrate and form a
> cavity which weakens the base.
>
> I guess Rohn believes their towers legs never rust-- inside or
> outside.
>
> Is that true? I agree with wanting to keep water out of the legs.
>
> Also, if the water table rises above the base of the bed of rocks,
> doesn't it guarantee water being in the tower legs?
>
> 73 de Brian/K3KO
>
> Bill Coleman wrote:
> >
> > On 6/20/01 10:40 AM, Ward Silver at hwardsil@WOLFENET.com wrote:
> >
> > >
> > >The only problem I've had was that water got into the pipes (my fault) and
> > >had to be siphoned out. Put a cap on the pipes or fill them with cement
> > >(after you put the bolts in).
> >
> > Wouldn't it be better practice to place the pipes so they go through the
> > concrete base and into 4-6" of gravel for drainage?
> >
> > This is the typical practice for Rohn 25/45-type bases using either a
> > base section or embedding a full-length section.
> >
> > Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
> > Quote: "Not within a thousand years will man ever fly!"
> > -- Wilbur Wright, 1901
> >
> > List Sponsor: Are you thinking about installing a tower this summer? Call us
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> >
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>
> List Sponsor: Are you thinking about installing a tower this summer? Call us
> for information on our fabulous Trylon Titan self-supporting towers - up to
> 96-feet for less than $2000! at 888-833-3104 <A
> HREF="http://www.ChampionRadio.com";>
> www.ChampionRadio.com</A>
>
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List Sponsor: Are you thinking about installing a tower this summer? Call us
for information on our fabulous Trylon Titan self-supporting towers - up to
96-feet for less than $2000! at 888-833-3104 <A
HREF="http://www.ChampionRadio.com";>
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