Raising this tower, how much does it weigh?
January 15, 2019 4:45 PM Subscribe
I'm raising a 20 foot, homebrew ABS pipe tower with 10 feet of antenna mast, antenna and rotor at the end. Together, that part weighs about 6 pounds. The four, approximately five foot sections weight about 22 pounds each. The tower pipe is 3" in diameter.
The tower is four way stabilized at 5 foot intervals and two way stabilized at 5 foot intervals, so every 2 1/2 feet, it is stabilized to compensate for its flexibility. All joints are drilled and bolted. Me and one other person aren't enough to raise it into four notched ABS pipes set 2 1/2 feet into a concrete pad. These pipes are 4" in diameter. Once it's up, I will attach the steel guy wires to the three anchors in the ground at 120 degrees from each. The guys are attached to the tower at about the 15 foot level. I'll fill the gap between the pipes with sand.
The tower is next to a barn with a loft. I want to use a block and tackle connected to a beam in the barn loft to slowly raise the tower from above while below, helping lift and guide the legs into the pad set ABS pipe. I'm trying to figure out how much weight the block and tackle should be rated for so I now how big of one I should buy.
The tower is four way stabilized at 5 foot intervals and two way stabilized at 5 foot intervals, so every 2 1/2 feet, it is stabilized to compensate for its flexibility. All joints are drilled and bolted. Me and one other person aren't enough to raise it into four notched ABS pipes set 2 1/2 feet into a concrete pad. These pipes are 4" in diameter. Once it's up, I will attach the steel guy wires to the three anchors in the ground at 120 degrees from each. The guys are attached to the tower at about the 15 foot level. I'll fill the gap between the pipes with sand.
The tower is next to a barn with a loft. I want to use a block and tackle connected to a beam in the barn loft to slowly raise the tower from above while below, helping lift and guide the legs into the pad set ABS pipe. I'm trying to figure out how much weight the block and tackle should be rated for so I now how big of one I should buy.
I think the answer depends on how high your haul point is in the barn loft, assuming you've got the base of the tower under the haul point and the tower pointing away. (If you just hook onto the top of the tower and pull it straight up under the haul point, then you just need to be able to pull up ~100 pounds!)
Suppose you were standing at the base of the tower (at regular person height) and had a rope tied to the other end of the tower. You pull on the rope to try to raise the tower. Most of the tension is going into compressing the tower; very little goes into lifting it. (If the angle between the tower and the rope is 0º, it doesn't matter how hard you pull, the tower is not going up.)
If you were pulling from 20 feet above the base of the 20-foot tower, I think you'd start pulling at 1.414x tower weight, which would decrease as the tower got closer and closer to vertical. Eventually, you're not pulling at all when the tower is vertical and standing on its own.
So, my guess is, you need about 100 lbs (tower weight) divided by sin(θ), where θ=tan-1(h/l), where h is your barn height and l is your tower length.
You've provided all the info necessary except your barn height.
posted by spacewrench at 5:57 PM on January 15, 2019
Suppose you were standing at the base of the tower (at regular person height) and had a rope tied to the other end of the tower. You pull on the rope to try to raise the tower. Most of the tension is going into compressing the tower; very little goes into lifting it. (If the angle between the tower and the rope is 0º, it doesn't matter how hard you pull, the tower is not going up.)
If you were pulling from 20 feet above the base of the 20-foot tower, I think you'd start pulling at 1.414x tower weight, which would decrease as the tower got closer and closer to vertical. Eventually, you're not pulling at all when the tower is vertical and standing on its own.
So, my guess is, you need about 100 lbs (tower weight) divided by sin(θ), where θ=tan-1(h/l), where h is your barn height and l is your tower length.
You've provided all the info necessary except your barn height.
posted by spacewrench at 5:57 PM on January 15, 2019
Response by poster: The floor of the loft is about 15 feet off the ground.
posted by CollectiveMind at 7:46 PM on January 15, 2019
posted by CollectiveMind at 7:46 PM on January 15, 2019
My guess is 167 pounds. Add your 5x safety factor and you get 833 pounds. A 1,000 block & tackle ought to do it.
Show your work
posted by spacewrench at 9:24 PM on January 15, 2019
Show your work
posted by spacewrench at 9:24 PM on January 15, 2019
Interesting approach. I would do it quite differently, placing the tower so the 15’ point is directly below the beam, attach the rope at that point, and haul straight up. No need to deal with the additional forces mentioned by spacewrench. If dragging the base of the tower when raising is a concern, place the tower base on a dolly so it can roll freely as the tower is raised. That will actually reduce the total weight being lifted significantly since the dolly will always be supporting some of it. I’d still agree about a 1000lb rating on block, tackle, rope and attachment mechanisms (for beam and tower) just to have some extra margin.
posted by dttocs at 12:44 AM on January 16, 2019
posted by dttocs at 12:44 AM on January 16, 2019
Not any answer, but a concern: ABS has roughly the stiffness of a wet noodle. With 10' of directional antenna and rotator hanging off 5' of ABS above the guy ring, I'm not hopeful for its survival.
Don't forget to factor in the weight of your guy wires and stiffening when lifting.
posted by scruss at 9:22 AM on January 16, 2019 [1 favorite]
Don't forget to factor in the weight of your guy wires and stiffening when lifting.
posted by scruss at 9:22 AM on January 16, 2019 [1 favorite]
Response by poster: If the 15' point of the tower was directly below the beam attached to the block an tackle, the top of the tower would be in the barn. Altogether, it's about 30 feet high when the mast and antenna is included. And although I've tried to stiffen the pipe at regular intervals, I am not sure if it will raise as I hope. Each section is ramrod straight with little flexibility. But four of them do have a lot of bend. I hope it works and does what I want it to do, but if not, it was a good experiment.
posted by CollectiveMind at 1:42 PM on January 16, 2019
posted by CollectiveMind at 1:42 PM on January 16, 2019
This thread is closed to new comments.
I’m surprised that each of your 5’ sections weigh 22 lbs though - 3” ID schedule 40 ABS weighs just over 1 lb per foot
If you’re asking what the minimum capacity of your block and tackle should be, typical safety factor is 5, so rope, blocks and especially connection to the barn beam should be rated for at least 500 lbs.
posted by dttocs at 5:27 PM on January 15, 2019