[TowerTalk] Anchors less than 80 per cent from the bases of a tower

[kr7x at comcast.net]

Bill,Jim,List and original poster:
You are correct as you move the guys inward the vertical component of the guy force increases and the horizontal component decreases. This increases the vertical load in the tower. The load could get to the point of buckling the tower by exceeding the allowable load for an individual leg or the whole tower cross section depending on the guy spacing.
This installation can be done however with careful engineering. I have engineered an Rohn 45g tower on a similar width lot that was 80 feet in height. It was designed for 80 mph and exposure "B" (UBC). It had elevated guys with the guy point being at 7' above the finished grade. It carries a KT34 and a Shorty 40.
With 5' set backs and an 80 foot wide lot the max 3 guy radius would be 40' or 33% of the height. If you were to use 4 guys then the max radius would increase to 49.5' or 41% of the height. It can be done, the guy anchors, tower section and base would have to be carefully reviewed for the loads. Even with 4 guys you have to look at all the lateral force being carried by one guys set. It would be an adventure to climb but would be safe.
The short answer is that it could be done, but with care.
If this were to proceed I would recommend 45g, as a minimum, .elevated anchors, and having the installation engineered by a competent structural engineer.
.Regards
Lonberg Design Group, Ltd.
Hank Lonberg, P.E., S.E. / KR7X
President

-------------- Original message -------------- 

> 
> Pulling the guys in closer also increases the vertical loading on the tower, 
> which may require increasing the size of the tower foundation, and/or 
> checking to make sure that the tower won't buckle. All in all, fooling with 
> the guys on a marginal design probably isn't something to be taken on 
> casually.........de Jim Lux 
> _______________________________________________ 
> 
> There is a lot of truth to that statement. Around here one of the local 
> broadcast towers constructed of Rohn 55 is guyed no more than 45-50 per cent 
> from the base...if that. In addition, it is guyed four ways instead of three, 
> obviously to counter space limitations. A local, who has climbed quite a few 
> towers, had a chance to go up the tower for maintenance. He said being on 
> the tower was 'very exciting' and did not want to do it again. 
> 
> To pull the guys in a couple per cent is probably no big deal, but probably 
> to 45-50 per cent is not a wise thing to do. Instead of lots of force being 
> pulled outward to stabilize, the main force is now transferred downward. 
> This certainly doesn't help to counter lateral pulls from the wind and, as Jim 
> said, increases the load on the base. 
> 
> Bill K4XS 
> 
> _______________________________________________ 
> 
> 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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