[TowerTalk] Non-Guyed Support for 80m Horizontal Loop at 35 feet

[Gene Fuller]

A couplele of quick notes on this thread.

For someone with a few years of antenna work ahead of them, and an interest 
in welding, check out your local school system nighttime adult ed classes.

For the tower without a big guy field, how about a "spreader" about half way 
up and guys that run from up near the top down to the spreader, then to down 
near the base. I haven't done the calculation but I'm sure you could pick up 
a fair increase in bending moment restraint for the mid section of the 
tower, then just be sure to reinforce the section(s) below the bottom return 
point because you would still have the same or a little greater bending 
moment below the return point. This would take a good analysis since it 
would also increase the columb loading, but it could result in smallet 
tubing and keep away from the extended guy field.  A good challenge if you 
should decide to hire an engineer. Possibly a naval architech who does mast 
designs.

Gene / W2LU

----- Original Message ----- 
From: "jimlux" <jimlux at earthlink.net>
To: "Grant Saviers" <grants2 at pacbell.net>
Cc: <towertalk at contesting.com>
Sent: Sunday, February 06, 2011 2:01 PM
Subject: Re: [TowerTalk] Non-Guyed Support for 80m Horizontal Loop at 35 
feet


> On 2/6/11 10:14 AM, Grant Saviers wrote:
>> Thanks Jim,
>>
>> A bit of an oops in my post, I hit send rather than save as draft.
>>
>> I was using buckling loosely as a term although for the really big poles
>> the standard does include column buckling and uses a segmented approach
>> for the taper for the wind load bending moments and stress.
>>
>> I haven't done a decent calc for the wind load stress, I need to refresh
>> some very old learning or find a java app :-) .
>
> One could probably use the flagpole guidelines and add a bit for the
> wires (which can have surprisingly high drag, given their small
> diameter.. back when I was interested in small plane/ultralight
> modeling, I was amazed to discover that a 1/4" cable had a lot more drag
> than a big 1"x3" strut)
>
>
>
>>
>> What would be really neat is for somebody with a bit more expertise than
>> I have to figure out several cost optimized self supporting poles for
>> wire antennas.
>
> It would make an excellent QST article, no? Maybe we could get some
> folks on this list to collaborate on such a thing.  It's a LOT of work
> to generate a finished article, but if the toil is divided up among
> several people, it's more tractable.
>
>
>  For example my steel supplier stocks 20' lengths, so they
>> would be good for 35' poles. One of the Metal Supermarkets or the like
>> has 24 footers, so they would be good for 42' or so. The question to be
>> answered is what is the cheapest pole design for some wind load (e.g.
>> 80mph) and say 200 lb of wire force at the top? Beyond 42' might be best
>> left to a Structural PE, soils engineer, and professional erector.
>>
>> I'm partial to square tube steel since the moments are higher than pipe
>
> Actually, for a given cost (i.e. weight of steel), round tube is your
> best deal. And larger diameter with thinner wall is better (that 4th
> power in the second moment, and why car drive shafts are hollow sheet
> metal tubes, etc.)
>
>> and there is a variety of wall thickness available for ease of
>> telescoping fits.
>
> Yes..
>
>
>  Also, the average ham could probably thru bolt the
>> joints rather than some structural welding.
>
> Yes. That makes the engineering a bit more complex.  I guess you could
> design/calculate based on holes with a lot of clearance, etc.
>
> While doing everything yourself is an admirable goal, sometimes it's
> better to hire someone to do a specialized task. And welding fits in
> that category.. A decent welding rig costs more than a drill, and you
> really need some real practice and training to do it right.
>
> The trick is in finding somewhere to get it done.  If your day job is
> working in a cube farm or managing the same, finding a welding
> fabricator isn't a simple task. You just don't even know where to start,
> because it's not like you want a whole building constructed, just an
> hour's worth of welding work for $50.
>
> So, an article about "how to find a structural welder for your antenna
> project" might be useful.  Around here (southern California) places that
> do motorcycle frames or race cars are one place. Lots of places that do
> decorative fences, but typically, those guys aren't necessarily who I'd
> hire to do something structural.  But it's one of those things that you
> can't do by googling.  It's a lot of phone calls, or going by the shop
> and asking "can you do this, or do you know someone who does?" and if
> you don't know where the shop is in the first place...
>
>
>
>
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