[UK-CONTEST] Lattice tower information page

[Mike Harris]

G'day,

Having just recently gone down the route of installing a new base
plate mounted FLI HD 12M Versatower I'll add a few comments to Chris's
excellent guide:

Not sure about the recommendation to have steel stakes hammered into
the sides and base of the hole before pouring concrete.  This is not
thought to be a good idea because it allows for corrosion of the steel
within the concrete which can lead to failure and probably adds little
or nothing to the turn over resistance of the base when properly
retained within the ground.  All the reading I did, and consultation
with a local civil engineer and government design engineers suggested
that steelwork within the concrete shouldn't be any closer than 75mm
to any external surface, with the exception of the holding down bolts,
naturally.

I was disappointed with the length of the bolts supplied, I would like
to see them further than 1/3 of the way into the concrete base given
that it is only the mass of the concrete above that stops them
breaking out.  It is common to see in American tower base designs
(Rhone) bolts extending at least 2/3 into the concrete mass.  Also the
FLH design doesn't use any re-bar cage.  Re-bar supplies the tensile
strength of the mass, concrete itself doesn't have any tensile
strength worth considering and with wind forces on the tower, bolts
will be in tension which will be transferred to the concrete.
However, there must be hundreds of the FLI base design around without
problems.  I built a re-bar cage which added steel around the high
load bolt areas.

I used poly cones over my bolts which are then removed and allow the
bolts to move laterally, retained by the wash plates.  This allows
perfect alignment of the bolts with the mounting plate holes and is
shown in the FLI base drawing.  The resulting cone shaped holes are
then filled with grout.  Given that it is easy to make an appropriate
bolt setting jig I wouldn't bother going down this route again.

I used a chemical admixture to make the grout slightly expanding, this
counteracts the normal shrinkage as the mixture dries and makes for a
tight joint both around the bolts and under the base plate.

I also used a vibrator to pack the concrete tightly into the
foundation hole when pouring, poking it with a lump of wood isn't
really good enough.  I used  the same when we poured the footings for
our house.  It has to be used with care so as not to separate out the
concrete mix, only a few seconds at a time.

If anyone is interested I'm happy to gather up a collection of
pictures.

If you really want to get heavy with the subject, subscribe to the
"Tower talk" reflector.  American in content but these guys do things
big time, 200 foot towers, 4 x array stack, small stuff like that!

Never, never, ever skimp on the concrete.  Doing it right means you
sleep at night.

On the subject of post mountings.  Check out to see if one of the
utility companies or contractors has a pole hole borer truck, farmer
even.  These usually have a huge earth auger which can drill a 14 inch
diameter,or there about, hole.  Used one of these many years ago to
install a base post for an exhibition station tower in Nottingham.
Several of the club were Post Office Engineering (Telecom to
youngsters) so we hade the contacts!

Regards,

Mike VP8NO

On 24/10/2006 18:48:32, Adrian Rees (MW1LCR) (rees.a at btconnect.com)
wrote:
> Brilliant !
>
> Lots of really useful info for us guys just starting out with towers
> !
>
> Adrian MW1LCR
>
> -----Original Message-----
> From: uk-contest-bounces at contesting.com
> [mailto:uk-contest-bounces at contesting.com] On Behalf Of Chris Tran
> Sent: 24 October 2006 19:55
> To: uk-contest at contesting.com
> Subject: [UK-CONTEST] Lattice tower information page
>
>
> Hello all
>
> We all have differing ideas about how a crank-up tilt-over tower
> (e.g. a
>
> Versatower BP60) should be installed, but you might be interested to
> read my new, as yet unfinished, web-page on this subject :
> http://www.qsl.net/gm3woj/latticetower.htm
>
> When the rain stops I'll add more photos.  I'm doing 15m Single-op
> Single-band in WW SSB this coming weekend, so please give me a call
> !
>
> 73
> Chris
> GM3WOJ
> http://lists.contesting.com/mailman/listinfo/uk-contest