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@sasktel.net> To:
'Hans Hammarquist' <hanslg@aol.com>; Tower Talk
<towertalk@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@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|