Jim Lux wrote:
>>Since this has been discussed extensively before, I hesitate to
>>ask this....
>>
>>But I would really like to see an example (with a little analysis)
>>of a self support structure of ANY kind that is compromised by
>>sensible guy wires. By "sensible" I mean guy angles that are not
>>steep, and guy strand that is sized for the structure *top*, and
>>pre-tensioned at normal values. I'm really curious about this. I've
>>seen lot's of pronouncements, but little substance to support the
>>idea that self support structures should never be guyed. I fully
>>understand that some might be wary of the issues because of the
>>idea that encouraging overloading of towers might result, but this
>>is an interesting topic, academically.
> I think there has been some examples posted in the last couple years..
I sure haven't seen them.
> Off hand, here's the problem I would contemplate: Increased down force from
> the guy tension will increase the compressive load at the base. Whether
> it's a problem is another issue. A self supporting tower will be generally
> stronger than a guyed tower of the same height (because it has to support
> the bending loads, which manifest themselves as compressive loads at the
> base). When you guy, you're turning some of the bending moment into a
> tension in the guy.
Yes - with guys you convert almost ALL of the bending moment into
guy tension and straight downward force. The numbers (on a simplified
model) don't give any support to the "don't guy" mantra. IOW, the
increased straight downward force is minor, compared to what the
tower MUST be capable of, if it can survive the extreme compression
in the down-wind leg(s), unguyed.
Here's the way I look at it:
Consider a 100' properly guyed Rohn 45 tower. Now, while holding the
top face width at 18", slowly increase the size of the bottom of the
tower - to 24", then 48", then 10', then 100' - all the while, making
appropriate changes to the diagonals & horizontals of course.
I think it's obvious that when taken to the extreme (a pyramid), that
having 1/4" guys does not compromise the structure. So at what point
in the widening of the tower do you reach an unsafe condition? All
you are doing is *strengthening* the tower over the stock Rohn 45
configuration.
Steve K8LX
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|