Towertalk
[Top] [All Lists]

Re: [TowerTalk] Guyed + self supporting /2 ??

To: "Richard (Rick) Karlquist" <richard@karlquist.com>
Subject: Re: [TowerTalk] Guyed + self supporting /2 ??
From: <ve4xt@mymts.net>
Date: Wed, 15 Oct 2014 09:57:40 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
I'm curious, Rick, if your engineer addressed this question: to what extent 
does the warning to not have a fixed base on a guyed tower (use a pier pin 
instead) apply to the question of guying a self-supporting tower (which by 
design would have a fixed attachment to the base)?

Seems the issue of torsion would be the same, yes?

>From an initial design perspective, if you were planning a guyed tower, would 
>it make sense to pay extra for a freestander?

It seems the question of guying applies best to attempts to increase load 
factor of an existing freestanding tower. 

73, Kelly 
ve4xt

Sent from my iPhone

> On Oct 15, 2014, at 9:42, "Richard (Rick) Karlquist" <richard@karlquist.com> 
> wrote:
> 
> 
> 
>> On 10/15/2014 12:08 AM, Roger (K8RI) on TT wrote:
>> On 10/15/2014 1:28 AM, Richard (Rick) Karlquist wrote:
> 
>>> can cause it to try to tip the base because the part of the tower
>>> below the guys bends in a strong wind.  This is the fallacy involved
>>> in the idea of using just enough base to keep it from sinking into
>>> the ground.
>> 
>> This is not a fallacy!  Originally towers were designed to be strong
>> enough that this would not be a problem.  If properly guyed, it's still
>> not a problem.  With the proper guys there is very little bending moment
>> at the base.
> 
> The issue is not the strength of the tower, it is the stiffness.
> If not sufficiently stiff, the tower bows out away from the wind
> and will tilt the base if it is not big enough.  Maybe what you mean
> by "properly guyed" is to have multiple levels of guying.  Yes
> that might allow you to use a minimal base.  The whole advantage
> of using self supporting type sections in a guyed tower is that
> you don't need so many levels of guying.
> 
> 
>> That is a complicated issue, but the guys will even out the forces on
>> the base from wind, but they will INCREASE the load on the base. because
>> of their tension and wind load.
> 
> The compressive load on the base from the guys is less than what
> would have been the load in the self supporting case due to
> bending moment.  The issue is with tapering.  If the upper sections
> are very lightweight, they will not be able to handle the guy
> forces, even though they are less than the forces at the bottom.
> Simply because the bottom sections are much stronger.  The solution
> is to not taper until above the guys.
> 
>> In general, self supporting towers should not be guyed.  Guying reduces
>> the design load limits of the self supporting tower.  Crank up towers
>> should not be guyed as it can greatly increase the load on the tower
>> cables.
> 
> Actual modelling shows that guying can increase the load limits if
> properly applied.  In the crank up tower case, UST specifically
> says its OK to guy the base section.  The load on the base will
> be less than the self supporting case and in any event, the base
> is in compression and not be the weak link.
> 
>> 
>> Is the tower base designed to support the additional weight?  Guying the
>> base is the same as adding additional weight to the tower.
>> 
>> When changing the installation of a tower to something different than
>> the manufacturers recommendations, it's wise to seek that companies
>> input as well as a certified engineer.
>> 
>> 73
>> 
>> Roger (K8RI)
> 
> I have a certified engineer doing the modelling.  I'm just reporting
> here what he is telling me.
> 
> Rick N6RK
> _______________________________________________
> 
> 
> 
> _______________________________________________
> 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

<Prev in Thread] Current Thread [Next in Thread>