[TowerTalk] post in concrete ??

[Roger (K8RI)]

Paul Young wrote:
> Hi all,
>        I just got myself a 2nd hand 40ft tilt over tower.
> The base is post mount, and I need to set it into a 3ft SQ
> block of concrete. I don't have a sleeve to go over the 
> 6 inch box section that needs to go into the ground and
> was wondering if I covered it with 1 thick layer of a 
>   
If you wrap that much (1" thick) plastic  around the post it would be 
unstable.
A thin wrap, as others have said would still let the concrete grip 
tightly.  There are enough irregularities in the steel that it wouldn't 
come out of the concrete easily. IF and I have to emphasize the "IF" the 
irregularities are small enough you *might* be able to use hydraulic 
jacks to "jack" the post out of the concrete if it's wrapped a single 
layer of of 2 or 3 mil plastic. You'd probably need to have plates 
welded to the side of the post for the jacks to push against.  Most 
likely the only thing you'd gain would be the concrete would be easier 
to break off as it wouldn't be bonded to the post.

Are the outside dimensions actually 6"?   It's quite likely you can 
either find a stock size that will just fit over it, or have a sleeve 
fabricated from flat stock.  However that sleeve is going to be *heavy* 
if made sturdy enough that the concrete doesn't deform it to the point 
of being unable to pull the post out of the concrete. Also there is the 
problem of rust which could literally bond the post to the sleeve over 
time.  The sleeve would need to be snug, but still allow for coating 
with some type of rust prevention.

As an alternative, how about a pipe, or tube (Culvert section?) 
*slightly* larger than the post?  Pour the concrete around that, put the 
post into the pipe and pour sand into the area between the post and 
pipe.  Of course the pipe and post overlap would need to be long enough 
to provide  the required support.  The pipe and sand can provide a very 
rigid mount when done properly and IF allowed in your area.  This has 
been a preferred method of mounting small to medium size telescopes 
which are sensitive to vibration and where even a light wind can cause 
noticeable movement.

BTW I'm assuming this block of concrete extends more than 3' deep as I'd 
think a 3' cube would be insufficient to provide stability for even a 
tribander on a 40', self supporting pole.

I'm not a mechanical engineer but depending on your soil conditions I'd 
want the hole to be at least 5 to 6' deep. Even a small tribander 40 
feet up can exert tremendous leverage.

Good Luck and 73,

Roger (K8RI)
> plastic bag, Would I be able to remove the base out of the
> concrete block at a later date if needed ?
>
> Paul  G0HWC
>
>
> Check out my website  www.g0hwc.com / www.sstv.org.uk
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