Seems to me the question of where to tie the upper pull ropes depends on the
position of the tower.
If it's alongside the building, you should be good to tie it at the top and
pull. If it's laid out extending away from the building, it becomes a
question of enclosed angle vs. force required to lift.
The tower is going to weigh at least 240 pounds (40lb per section x 6
sections), and the effective weight will increase as the enclosed angle goes
down. Even from directly above the top of the tower, you might find that to
be more than even a few people can pull up.
You might want to pull up the first 50 feet and then attach the last section
from the roof.
As for the ground rod: isn't the lightning just as likely to travel to the
base of the tower, into the butterfly fasteners and then on into the
concrete anyway?
And hasn't it been shown that exploding concrete bases are a myth?
Especially when you consider designs for concrete-encased ground rods?
73, kelly
ve4xt
On 3/16/12 2:19 PM, "Kipton Moravec" <kip@kdream.com> wrote:
> I am supervising the installation of a 60 foot Rohn 25 tower. (This
> means finding the people with knowledge and muscle.)
>
> It will be placed next to a 50 foot building with concrete walls, a flat
> roof, and a 5 foot parapet (wall) around the roof. (Top of the parapet
> is 50 feet above the ground.)
>
> It will have one wall bracket for each section of Rohn 25 along the
> wall. I know this is probably overkill, but that is what they want, and
> they have the money for it.
>
> The proposed plan is to bolt a tilt-over base to the large 6" concrete
> driveway/parking lot by using butterfly expanders.
>
> Then they want to assemble it on the ground, and tie a couple of ropes
> to it at 50 ft and have 6-8 people pull it up from the flat roof. (With
> the same number on the ground to help get it started.)
>
> First question is this a good plan?
> Do we need to also pull from the middle (25 feet) so there is not a
> bow?
>
>
>
>
> Second part. The ground is all 6" concrete driveway. They are worried
> that we can not just drill a 5/8" or 3/4" hole through the concrete and
> put ground rods in because we have to have a certain amount of air gap
> between the ground rod and the concrete, or the concrete will explode
> when lightning hits.
>
> That does not sound right to me, because the even though concrete is
> somewhat conductive, the ground rod is going 10 feet into the earth. And
> if I have three ground rods the lightning will be spread into the ground
> and not as much through the concrete and the unknown places of rebar in
> the concrete. And we already have the tilt over plate bolted to the
> concrete driveway. So it is not like there is a point connection to the
> concrete.
>
> Do we really need an large air gap between the ground rods and the
> concrete driveway? If so how much?
>
> Kip
>
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> 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
|