In a message dated 4/9/2005 6:25:38 AM Pacific Daylight Time,
towertalk-request@contesting.com writes:
>> 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.
>> For the purpose of illustration, it might be reasonable to take a
parameter to the the extreme, to see where the fault line is. For
the life of me, I can't imagine what it is.
Okay, here are my thoughts.
First, the LXC Prime Directive - "DO what the manufacturer says" - is
still in effect.
The big problem with guying self-supporting towers is that the guys have
the potential to increase the leg compression preload when properly tensioned.
And as the leg capacity is the primary factor for tower strength, adding
additonal compressive force can lead to failure when a big windstorm blows
through
and the leg strength is exceeded.
Delhi towers are sort of a special case. Yes, they're the classic BX
design and include straight sections along with the tapered ones and, yes, the
manufacturer does say "Guy wires must be used for larger loads or if straight
sections are added".
No other self-supporting tower or manufacturer makes that kind of a
statement or suggests guying the tower. They're designed to be self-supporting
and
guying them goes against their engineering and design.
K8FU said:
>> As you may remember from earlier conversations I'm erecting a 100' self
supporting tower but am going to guy in two places basically for the safety of
the climbers, to make sure it would not fall across pwr lines, ensure it would
land on my neighbors property, and my own peace of mind.
The only real reason IMO for guying in this case is a safety concern -
"to make sure it would not fall across pwr lines". Fair enough.
In this case I would suggest guys that will tether it whereby there is
little or no tension on the guys and they would only provide some restraint
when
the wind is blowing. Not being an engineer I can only say that this is
intuitive but when the wind is blowing, the tether lines will be taking some of
the
wind pressure off of the tower legs and bringing it down the guy to the
anchor, thus relieving the leg of some of the compressive force.
In K8FU's case, 2 sets of guys is unnecessary to do this. One set 70-80
feet up should suffice since we're not holding the tower up - we're just
providing a safety tether.
Cheers,
Steve K7LXC
TOWER TECH -
Professional tower services for commercial and amateur
_______________________________________________
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.
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