[TowerTalk] How many tower sections i can install??

[Patrick Greenlee]

Good stuff Gerald.  Douglass may want to also consider placing the base 
of the tower above or quite near to a load bearing interior wall even 
though that might mess with the symmetry of a centered location guy 
wise.  Depending on the strength of the roof in the centered 
configuration and on the interior layout of the residence a thrust 
member (column) located below the tower base could be used to carry the 
vertical download through to the (assumed) concrete slab floor. (Also 
assuming this is a single story home although in theory depending on 
layout another thrust member on the ground floor could be used as well.)

If there are tower sections to spare put one under each guy to change 
the angle of the guy and get more strength to oppose wind loading with 
less down thrust on the tower. There is no free lunch and each of these 
"guy helpers" will have some down thrust directed through them 
vertically to the roof but much less than that of the tower itself.

Patrick        NJ5G

On 8/26/2015 10:22 AM, TexasRF--- via TowerTalk wrote:
> Hi Douglas, you can achieve a a greater guy point distance by using four
> guys instead of three. You would not want the guy to guy angle to exceed 120
> degrees in any case.
>   
> Your roof dimensions would allow guy to guy angles of 120, 60, 120 and 60
> degrees. With the tower mounted in the center of the roof and assuming the
> anchors are at the edge of the roof, a guy to guy angle of 120 degrees,  the
> distance would be 20.0 ft to the anchor. The distance between anchors
> would be 34.6 ft, 20 ft, 34.6 ft and 20 ft.
>   
> So, in this case, you could guy the tower a couple of ft below the top and
> three 10ft sections would have a anchor/height ratio of 66.66%.
>   
> We typically use an 80% ratio mainly because that is the number Rohn
> specifies for all of their tower models. It is a good compromise between load
> capacity and space required.
>   
> Considering that these towers are used up to 180ft in height or more, it is
>   reasonable to move anchor points inward for reduced heights. The issue in
> doing  this is that Rohn has no published data for doing this. The wind load
> rating has  to be reduced and it takes engineering skills to properly do
> the calculations.  It is not rocket science however.
>   
> I would be concerned about possible roof damage as much as the tower  surviv
> al. It is conceivable that using the roof edge as a turning point for the
> guy and then a ground anchor would be stronger. Something else that would
> benefit from an engineers blessing.
>   
> 73,
> Gerald K5GW
>   
>   
>   
>   
>   
> In a message dated 8/25/2015 9:14:22 P.M. Central Daylight Time,
> co8dm at frcuba.co.cu writes:
>
> Hi,
>
> I would like read your ideas.
>
> I have few 10 ft  section of a tower (it is like a Rohn 25G).
>
> I would like install few  section over some part of my roof...The roof is
> concrete...as you know many  house in the Caribbean has concrete roof ...it
> is 24ft by 40ft...so, i have  calculating and the distance from the base to
> the guy anchors is 14 ft  !!!
>
> I know the distance from the base to anchor points is 70 % of the  tower
> height...so, 70% of 20 ft is 14ft, that´s mean 2 tower sections...right
> ??...Is it possible install 3 sections adding more guy´s set  ???
>
> Thanks,
>
> 73....Douglas,  CO8DM
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