[Boatanchors] Tower Construction

[Ron]

Most towers fail by rotation where the tower twists and changes the 
rigidity of the structure.  I think this was call the 4 moment if 
inertia but would need to look it up to be sure.

Placing a long shaft to mount the rotor 20 to 30 feet down the tower 
removes the torsional load on the whimpy upper sections and can place it 
on a lower heavier section.
My rotor is mounted just above the sections that have double crosses 
between the rungs that are better able to resist the rotational loads 
and the shaft clamp is not pinned so that it gives way when the loads 
get too high.

THe other part is that the junk that you hang up on the top will fly 
apart at about 80 MPH wreaking the antenna but possibly unloading the 
tower enough to allow it to survive.

---
Ron


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
>>    
>>
>
>
>_______________________________________________
>Boatanchors mailing list
>Boatanchors at mailman.qth.net
>http://mailman.qth.net/mailman/listinfo/boatanchors
>** List Administrator - Duane Fischer, W8DBF/W9WZE **   
>** For Assistance: dfischer at usol.com **         
>$$ For vintage radio info, see the HCI web site $$      
>http://www.w9wze.org    
>
>
>
>  
>