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[TowerTalk] A Different Take On Guy Wires?

To: <towertalk@contesting.com>
Subject: [TowerTalk] A Different Take On Guy Wires?
From: notawc@juno.com (notawc@juno.com)
Date: Fri, 30 Apr 1999 15:39:49 -0400
All of this discussion over 60' of 45G?

Suspect Bill had the right idea yesterday about traffic on the reflector.

Norm



On Thu, 29 Apr 1999 21:15:28 -0700 Michael Tope <W4EF@pacbell.net>
writes:
> 
> David and Steve,
> 
> If I recall my statics from college correctly, the deflection for a 
> given applied load will 
> be different if the Young's modulus of the two materials is 
> different.  A tower can be thought 
> of as being analagous to a cantilever beam suspended between two 
> springs that are 
> pre-tensioned. When a side load comes along from the direction of 
> one of the guys, the 
> tension in that guy increases while the tension in the opposing guy 
> decreases. If the 
> stress/strain relationship in the two guys is
> linear, then the increase in force on the windward guy will equal 
> then decrease in
> force on the leeward guy. There will be an accompanying deflection 
> proportional to 
> the Young's modulus of the guy material. In practice, as long guy 
> deflections are small 
> in comparison to the allowable tower deflections, then as Steve 
> points out they are of 
> little practical consequence. All of the guyed towers that I have 
> climbed (both EHS and 
> Philly) are stable as a rock. I would guess allowable deflections 
> are at least an order of 
> magnitude below safe limits, perhaps much more (Rohn 25 is rate at 
> 6700 ft*lbs of 
> overturning moment). Interesting mental exercise though. 
> 
> Does anyone know if preload specs are driven mainly by side load 
> deflection limits
> or torsional deflection limits?
> 
> Mike, W4EF.................
> 
> -----Original Message-----
> From: K7LXC@aol.com [SMTP:K7LXC@aol.com]
> Sent: Friday, April 30, 1999 8:11 AM
> To:   davidc@bit-net.com; towertalk@contesting.com
> Subject:      Re: [TowerTalk] A Different Take On Guy Wires?
> 
> 
> In a message dated 99-04-30 10:34:42 EDT, you write:
> 
> > >      What tower flex? You mean torsionally? That'll happen no 
> matter what
> >  guy material you use.
> >  
> >  But is not Phillystran more flexible at the same tension than 
> EHS?  Thus
> >  would
> >  it not allow a little more sway under high wind gust conditions?
> >  
>       Flexible? That's not a term used in tower/guy specs. The 
> momentary 
> 'stretch' (if any - I'm not an engineer either) of these materials 
> is of no 
> practical consequence. I'm assuming of course that you follow the 
> manufacturer's specs in all cases. 
> 
> >  >      Vibration? Haven't run across that one before.
> >  
> >  Are not the strands of EHS more stiff (and-to-end) than 
> Phillystran, thus
> >  vibrations
> >  initiated at any point would be transmitted to anything 
> connected?  Or do
> >  the insulators  effectively deaden that?
> 
>       Even *if* measureable, it's of no practical consequence.
> >  
> >  >       Joint stress? Leg compression is the biggest factor in 
> tower 
> forces.
> >  > The leg joints are stronger than the rest of the leg.
> >  
> >  I was imaging the tower swaying a bit in 125-150mph gusts and 
> rocking 
> around
> >  the connecting bolts.  (Sounds like something from a song, 
> "rocking around
> >  the tower bolts, have a happy hurricane ..."  :-)  )
> >  
>      The whole tower structure is designed for different 
> windload/windspeed 
> scenarios and they DON'T rock.
> 
> >  >       While I don't have the technical data in front of me, if 
> you're
> >  asking
> >  > about possible elongation of EHS and Phillystran - for our ham 
> purposes
> >  they
> >  > are both small enough that you don't have to worry about it.
> >  
> >  Not permanent elongation but momentary under high stress moments?
> 
>        Even *if* measureable, it's of no practical consequence.     
> >  
> >  >      Here's a suggestion - use the EHS-with-insulators on the 
> bottom set
> >  and
> >  > 50% Phillystran/EHS on the top set. I think this'll reduce your 
> risk
> >  exposure
> >  > while giving you some Phillystran benefits.
> >  
> >  50%?  I would use a 4 guy top rather than three?  Will have to 
> explore 
> that.
> >  
>        What's a "4 guy top"? 50% refers to the top half of the guy 
> being 
> Phillystran and the bottom half being EHS w/insulators.
> 
>       Most of these questions that you are asking are things that 
> you are 
> perceiving that don't have any practical considerations. You're 
> over-thinking 
> the whole structure. Follow the manufacturer's instructions. If 
> you're 
> worried about Phillystran being more likely to be cut by things 
> flying 
> through the air - then use EHS w/insulators. And get an engineer 
> involved. 
> Everything else is background noise.
> 
> Cheers,   Steve  K7LXC
> 
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