I am not a specialist in metal work. However, I would be nervous about
heating metals. According to reference books, certain
types of metals are produced through a combination of alloying and heat
treatments during manufacture -- and the result has a
different strength and resiliency. If the material is subsequently re-heated
beyond a certain point, the structural properties of
the metal can be altered -- changing the strength and resiliency, possibly in a
way which we would not like for a structure like a
tower.
Since this tower was not installed in accordance with the K7LXC Prime
Directive (i.e., the base was not poured as per
manufacturer's instructions), if it was my station, I would correct the base to
comply with the manufacturer's instructions. In
this case, I would also check with a concrete specialist about how to pour an
additional cap in such a way as to eliminate the
boundary between the old concrete base and the new cap (which could allow water
to seep in and continue the rusting process).
In a previous life as a meteorologist, a group in my office at the National
Weather Service was doing a post-hurricane damage
review in North Carolina. Among the damaged sites, a number of high-rise
apartment and hotel buildings along the shore had been
swept off their foundations (pilings) and had to be condemned. These buildings
were of modern construction and had been built
compliant with the current code -- yet the pilings had sheared off cleanly. We
were puzzled why this occurred -- especially since
the hurricane was only mid-scale in strength and a modern structure should have
been fine. Quite by accident, one of the team
members was strolling along the beach during a lunch break and passed a
location where a new building's foundation was being poured.
The workers were also on lunch break... and the pouring of concrete had halted.
Our team member noticed that the breeze had blown a
fine layer of beach sand on top of the morning's concrete pour. Subsequent
research showed that this layer of sand was sufficient
to cause a discontinuity in the concrete column: a weak horizontal layer where
the column would shear off relatively easily.
Construction codes were subsequently changed to require a continuous pour
without stopping to eliminate this failure mode.
I gained a new respect for the importance of continuity in a block of
concrete.
-- Eric K3NA
-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of Chris BONDE
Sent: 2001 December 4 Tue 05:07
To: Dave Sublette
Cc: W9zr@aol.com; towertalk@contesting.com
Subject: Re: [TowerTalk] Looking for Ideas for Preserving Tower Legs
At 06:31 PM 2001-12-03 -0500, Dave Sublette wrote:
Long time ago iron by the blacksmiths was protected and called black
wrought iron. I think that the wat they protected the iron was to heat it
to almost red then quench it in tar. It had to be coated now and then with
molten tar. Now if you heated the legs with a propane tourch then put the
roofing compound on the legs while hot, this might be a good method of
protecting the legs.
Chris opr VE7HCB
>I coat the legs of my towers with roofing compound...black gooey stuff.
>Your idea of treating the legs, then filling the concrete up to above
>grade seems reasonable. I have actually removed a one yard base from the
>ground using railroad jacks. It wasn't too hard.
>
>73,
>
>Dave, K4TO
>
>W9zr@aol.com wrote:
>
>>I am running into a problem with my tower legs starting to rust and I am
>>looking for some ideas.
>>
>>Background:
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List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
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supporting towers up to 100 feet for under $1500!! http://www.anwireless.com
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