[TowerTalk] Guyed + self supporting /2 ??

[Jim Lux]

On 10/19/14, 11:55 AM, Hans Hammarquist via TowerTalk wrote:
> You are right, Doug
>
>
> When it comes to structures like towers you have to take in
> consideration the buckling effect. Just an extreme example; a long
> steel wire cable has no strength in compression but all its strength
> in tension. I am not sure what the story is with the legs in a
> tower.
>
>
Column loading (buckling) is often the limiting failure on lattice
towers (e.g. on a Rohn BX, I think buckling is the limit).

On Rohn 25, it's a bit different. Consider the vertical tubes: they're
basically 1.25" OD tubes that are 16 ga steel (0.065" wall thickness).
There are 7 or 8 segments in a 10 foot length (depending on how you
count), so they're 15 inches long.  A l/d of 12 definitely counts as a
"slender column".

The cross sectional area is 0.065*pi*1.225 or very close to 0.24 square
inch.

If it's 1026 steel, the tensile strength is about 70,000 psi, the yield
strength is 60,000 psi.  Elastic modulus is 28-30,000 ksi

So, the "crush strength" of that tube is about 15,000 lbs...

A round tube 1.25 OD and 1.12 ID has moment 0.085 in^4

If you figure this is a "clamped/clamped" boundary conditions, the
buckling load would be well over 200,000 lbs, so in the case of Rohn 25,
the vertical tubes will fail by crushing before buckling.



> Hans - N2JFS
>
>
>
> -----Original Message----- From: Doug Renwick <ve5ra at sasktel.net> To:
> 'Hans Hammarquist' <hanslg at aol.com>; Tower Talk
> <towertalk at contesting.com> Sent: Sun, Oct 19, 2014 2:41 pm Subject:
> RE: [TowerTalk] Fwd: Fwd: Guyed + self supporting /2 ??
>
>
> Well you are going to have to take that point up with sdsc.edu.
>
> "Metals like steel are elastic materials. Such materials are equally
> strong in compression as in tension. ... when subjected to very large
> forces, it is much stronger in compression than it is in tension."
>
> Doug
>
> I wasn't born in Saskatchewan, but I got here as soon as I could.
>
> -----Original Message-----
>
> Doug,
>
>
> I have to correct one of your statements: Any metal structure, in
> general, is stronger in tension than in compression. This doesn't
> change your point, though.
>
>
> Hans - N2JFS
>
>
>
> --- This email is free from viruses and malware because avast!
> Antivirus protection is active. http://www.avast.com
>
>
>
>
> _______________________________________________
>
>
>
> _______________________________________________ TowerTalk mailing
> list TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>