Rick:
Actually the concrete code specifies that for concrete cast
against and permanent exposed to earth; the minimum clear
cover is 3". For concrete cast in forms and subsequently
having exterior exposure; the minimum clear cover is 2".
Additionally, the clearances for walls, beams and slabs differ
depending on bar size and exposure, etc.
The reason is that concrete cracks and moisture can penetrate
and cause corrosion that will cause the rebar to expand and
spall the concrete and the structure will lose strength. The
anchor rods(bolts) protrude above the concrete surface and are
exposed to intermittent dry-damp cycles but not continuous
moisture exposure as if it were in the ground. This mitigates
somewhat the corrosion but does not eliminate it. It is also
visible for preventative maintenance.
Galvanizing provides longer service life with less
maintenance. In the long run if you had a lot of anchor bolts
in places that are difficult to see or even get to then
galvanized anchors is the way to go. It does add to the cost
of the anchor. This is a decision trade-off the owner of the
structure has to make. Either way the anchor will be
sufficient in load capacity if designed properly. It is a
matter of what your desired design life span for the structure
is, 15 years, 30 years, or whatever.
Regards
Lonberg Design Group, Ltd.
H.S. Lonberg, P.E.,S.E.
President
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Richard
(Rick) Karlquist
Sent: Friday, April 11, 2008 6:01 PM
To: K7LXC@aol.com
Cc: towertalk@contesting.com; geitaemort@sbcglobal.net
Subject: Re: [TowerTalk] Anchor bolts
Here's what I don't understand (as a non expert):
There are elaborate precautions to prevent rebar from
rusting: no rebar is allowed to be within an inch of
any concrete surface.
OTOH, the anchor bolts are allowed to poke up through
the top of the concrete and now you're telling us they
don't even need to be galvanized. FWIW, I have seen
a lot of apparently galvanized anchor bolts on traffic
signals and light poles.
Is there any logic here I am missing? Or maybe as
you say, the code is always right, whether it is logical
or not.
Rick N6RK
K7LXC@aol.com wrote:
>
> In a message dated 4/10/2008 8:38:30 P.M. Pacific Daylight
Time,
> towertalk-request@contesting.com writes:
>
>> Ok lets try again. I have a us tower that I purchased used
in excellent
> condition.I orderd anchor bolts from us tower,when they
arrived they were not
> galvinized nor were they bent at ninety degrees at the
bottom.Being my first
> tower this seems a little odd to me. Can any one elaborate
on this subject?
>
> Sure. You don't need galvanized (that's for another
application) and
> they don't need to be bent at the bottom. A welded nut at
the bottom
> accomplishes the same thing. A Professional Engineer
calculated what's required for your
> application and that's what meets the codes and calcs.
>
> Cheers,
> Steve K7LXC
> TOWER TECH -
> Professional tower services for hams
> US Tower factory authorized installer
> Installer of more SteppIRs than anyone else in the world
> Cell: 206-890-4188
>
>
>
>
>
>
>
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