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Re: [TowerTalk] Legs of a 60' piece of tower being dragged while being l

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Legs of a 60' piece of tower being dragged while being lifted
From: john@kk9a.com
Date: Mon, 17 Oct 2016 11:53:58 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
The weight is irrelevant.  A skilled crane operator can move the boom as
it is being lifted leaving the section on the ground as a pivot point. 
Of  course if someone wishes to build a slide or use a loader to move
the base as it is being lifted that is perfectly fine, but I won't be
doing this. 

John KK9A 

On 2016-10-17 10:23, Grant Saviers wrote:

> Perhaps a non-issue for your situation, but for me it wasn't.  20' to 60' 
> sections of Rohn 65 with K0XG rings weighed in between 600# and 1800#.
> 
> A free body drawing shows the problem.  A crane cable hook is a pivot point, 
> virtually no resistance to torque.  Same with slings. The tower section(s) 
> being lifted have a center of gravity somewhere along its length.  Where 
> depends on what other than a plain tower section is the section.  With two 
> rings on some sections, I could find the balance point only by trial and 
> error, ie single sling on a leg until it balanced.
> 
> The further the center of gravity is from the hook at the top, the larger the 
> moment is on the section, trying to swing it under the hook point.  So even 
> if the crane op swings the boom tip directly above the tower top as he lifts, 
> there is still that moment. Perhaps by swinging the boom tip further towards 
> the section base a force can be added to cancel what gravity is doing.  
> However, that offset will be different if the sections are different re their 
> center of gravity.  The geometry of boom tip vs hook position also varies as 
> the boom is swung, so the boom top height would need to change.  This could 
> be pretty difficult to pull off.
> 
> Rings on towers really complicate the lifts since the tower section needs to 
> be assembled on the ground, off the ground on heavy duty supports, not HD or 
> HF saw horses.  My 4400# capacity fork lift with a boom extension could not 
> lift some single sections to vertical for testing mounted rings, so I rented 
> a 8,000# shooting boom fork lift.  My regular forklift was used to manage the 
> bottom of the sections as they swung.    So as soon as the lift starts, the 
> section swing force wants to tip over the far support.  To avoid that the 
> section was first suspended with slings off the supports at both ends.  We 
> got this done slowly and carefully since the shooting boom fork position 
> (lifting and extending at the same time to keep the forks over the section 
> top) and forklift motion needs to be in sync.  Once vertical the lower slings 
> were removed and the section set vertically with the shooting boom, but with 
> some tension as a safety support.  After the rings were tested (can only do
  this
with the section vertical), the process was reversed to place the section back 
on the supports.  Not a "no sweat" process.
> 
> The sure/safe way to go for larger towers is to keep the boom tip as directly 
> over the section top as possible and rig for the base to swing or drag.
> 
> Grant KZ1W
> 
> On 10/17/2016 5:09 AM, john@kk9a.com wrote: 
> 
>> I have used a crane many times and I still say that this is a non-issue.
>> Is it addressed in K7LXC's book?  Please read my post:
>> http://lists.contesting.com/archives//html/Towertalk/2016-10/msg00141.html
>> 
>> John KK9A
>> 
>> To:    "tower" <towertalk@contesting.com>
>> Subject:    [TowerTalk] Legs of a 60' piece of tower being dragged while
>> being    lifted
>> From:    "StellarCAT" <rxdesign@ssvecnet.com>
>> Date:    Fri, 14 Oct 2016 07:58:44 -0400
>> 
>> So Fred pointed this out ... I hadn't considered it up until then... is it a
>> problem to just allow the legs drag in the dirt while the 60' piece with
>> rotating ring attached (~850#) is lifted? Is there ANY chance the legs will
>> deform making it impossible to mate it to the tower? I don't have access
>> to an
>> end loader or any other piece of heavy eqmt ... I thought, and this might
>> sound
>> silly, a dolly ... those cheap(er) ones - seem to be rated at 600# ... if I
>> could get enough guys to lift the end and put that under the end - then we
>> could pull it along as the crane goes up.... although the ground is really
>> rough so that is doubtful... it would probably get stuck and the legs drop
>> off
>> which would be far worse than just having them drag on the ground ...
>> experiences anyone?
>> 
>> Gary
>> 
>> _______________________________________________
>> 
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