[Boatanchors] Tower Construction

[telegrapher at att.net]

I always felt that the point where the tower attached to the concrete 
was going to be the weakest of points also.  A Rohn HDBX-56 i had back 
in Kansas was setting on 3 L shaped bolts down in the concrete.  I 
thought that if any corrosion or continuous vibration was to set in that 
those would be the places to fail.  I had a 5 element 10 meter beam and 
a 4 element 20 meter beam on top along with 40 and 80 meter dipoles. 
Winds back there could get up in the 70 mph + range with the storms that 
came through.  I put a guy wire made out of 3/8 in. stainless steel 
cable running North and SOuth off the tower.  Just for comfort lets say. 
  Never had any problems with it all the years it was up but i could 
certainly hear it rattle, flex and groan when we had big winds.

One night we had a thunderstorm come through. I'd just shut off the 
lights down in the shack and went to bed.  Laying there listening to the 
wind, rain and thunder.  All of a sudden i heard a loud "click"!  I knew 
immediately what had happened without getting out of bed.  Next morning 
before work i went down to the work area in the basement to see what had 
happened.  My Gonset communicator was a different color in places.  I 
talked it over with a buddy of mine and we decided that the only way to 
do anything with it was to relegate it to the trash can.  So be it.  One 
wall socket was blackened.  That was all.  very lucky indeed.

I currently just received a new Universal Aluminum tower that will soon 
go up, well maybe after the summer heat is over with in November.  It 
came with 3 quite heavy legs to be implanted in concrete.  Since we 
don't have the winds down here i probably won't put any guys on it but 
it will go into a big puddle of concrete.  First thing is to find 
someone who can or will attempt to dig the hole for it through this 
calichy.  Darn, it's tough to get through.

Interesting topic here.  I'll have a 5 element triband unit as well as 
my trusty 4 el. 20 meter beam up on top.  YOu better hear me then!  300W 
on Rtty ought to do a good job shouldn't it?

Larry
W0OGH


sdaitch at ibb.gov wrote:

> Al,
> 
> let me ask you a question about this, from another point of view.
> 
> In terms of bending moment capability at the base of the tower, does it make any difference at what point the embedded tower section comes out of the concrete block?
> 
> My initial reaction would be it would not make any difference, since the
> metal structure continues into the block, but the bending point (which should be close to or close to the top of the concrete) could be at a weak point (which I suspect might be between the horizonal braces of the truss section), thus depending on where the steel actually exits the concrete.  
> 
> Could you share with us a thought on this?
> 
> 73
> Sheldon
> WA4MZZ
> 
> 
> 
> ----- Original Message -----
> From: Al Parker <anchor at ec.rr.com>
> Date: Saturday, June 10, 2006 8:32 pm
> Subject: Re: [Boatanchors] Tower Construction
> 
> 
>>Hi Dave,
>>   Eddie's thoughts are a good guide, but realize that there are 
>>2 (at
>>least) things that need to be closely considered.
>> 1.  The soil and wind conditions at your QTH, and
>> 2.  What Rohn rates the tower sections for in an unguyed mode
>> 3.  How much stuff you're gonna hang on top of the tower
>> Your intial comment of "cementing a section" in is already in 
>>error, you
>>really mean "concrete".  And the amount of it needed depends upon 
>>the soil
>>conditions, and the wind  load on the tower.  I'd suggest, that if you
>>don't know a licensed Professional Engineer in your area that will 
>>helpyou, you should find out what Rohn suggests.  They won't be 
>>specific for
>>liability reasons, but should have some general guidelines for "normal
>>soil conditions."   Then get a local professional opinion.
>>   I am a P.E., and have twice installed a 55 ft self-supported 
>>tower for
>>myself, in 2 different QTH's.  At the first I needed to submit, to the
>>local building permit dept., engineering calculations (from the tower
>>mfgr) on the tower itself, and drawings of my proposed 
>>installation.  An
>>inspection of the rebar in the hole for the foundation was 
>>required before
>>the concrete was poured.
>>   Safety is the main concern in these things, failures can be 
>>hazardousto health.
>>73,
>>Albert W. Parker, P.E., W8UT
>>New Bern, NC
> 
> 
> 
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