Raising a 70' Tower: Calculate Cable Force

[Baluncore]

I really do not like using one 7' pole as the lever.

Without a crane, I would prefer to use two shear legs with a block and tackle, (B&T).
The shear legs could be 20' long steel pipe. The tower attachment would be at the 10' point where the lowest two sections meet. The shear legs would be seated 10' down range from the hinge line with the crotch about 6' up range of the tower. Raise the crotch of the shear legs to the tower using the B&T. Remove the remaining bolt from the free tower leg. Push the tower to tension the B&T. Then lower the tower by paying out the B&T. As the tower comes down the shear legs rise until they are vertical when the tower becomes horizontal. Fall the shear legs back to their starting position using the B&T or guy ropes. Raising the tower is exactly the opposite process.

The feet of the shear legs would be tied to the tower footing and to each other to prevent slip.

 

[aknisley]

Deign

This is what I have been looking to build.

This tower while only 23' weights around 620 pounds. View attachment TowerRaisingFixture.pdf

 

[Baluncore]

Where a fixed structure is being used to tilt a tower it is probably better to lift the hinge point as high as possible on the fixed structure. That often permits some counterbalance to be used in the tower base.

In many cases there can be little force needed to tilt the tower. That is especially true of wind-up telescopic towers that are only tilted for antenna access when at their shortest.

 

[aknisley]

I really do not like using one 7' pole as the lever.

Without a crane, I would prefer to use two shear legs with a block and tackle, (B&T).
The shear legs could be 20' long steel pipe. The tower attachment would be at the 10' point where the lowest two sections meet. The shear legs would be seated 10' down range from the hinge line with the crotch about 6' up range of the tower. Raise the crotch of the shear legs to the tower using the B&T. Remove the remaining bolt from the free tower leg. Push the tower to tension the B&T. Then lower the tower by paying out the B&T. As the tower comes down the shear legs rise until they are vertical when the tower becomes horizontal. Fall the shear legs back to their starting position using the B&T or guy ropes. Raising the tower is exactly the opposite process.

The feet of the shear legs would be tied to the tower footing and to each other to prevent slip.

I am starting to get what you are saying. I pretty dense so could you do a sketch? What size pipe?

 

[Baluncore]

Attached is a sketch showing shear legs and tower side elevation and plan.

The tower attachment would be at the 10' point where the lowest two sections meet. The shear legs would be seated 10' down range from the hinge line with the crotch about 6' up range of the tower.
The footings of the shear legs are about 16' apart.

The shear legs start in position 1.
They are then raised with the B&T to position 2.
The pin in the free leg of the tower is then removed.
The tower is then pulled gently down range, as it passes the balance point, weight is on B&T.
Then lower the tower by paying out the B&T.
As the tower descends, the shear legs rise until they are standing vertical in position 3.
The tower is then horizontal.
Fall the shear legs back to their starting position using the B&T or guy ropes.

Raising the tower is the opposite process.


Specification of the shear leg dimensions is a job for a real engineer.
Since they are quite long, the shear legs need to be designed with reference to column stability.
My first guess is that they would be a minimum of 4” diameter steel pipe with a 1/4” wall.
Alternatively, timber 6” to 8” diameter poles, maybe Douglas Fir to keep the weight down.
I use 6" diam x 1/4" wall Al tube. It comes with new felt spools for the paper industry. Scrap pipe or tube is also low cost. Once used you can keep it or sell it back into scrap.

The crotch where the shear legs meet and the block is attached needs to be designed to suit the shear leg material. A 30' rope attached to the crotch makes it easier to control the legs at the end of the lift, or to raise them into position prior to lifting the tower.

This system is applicable to raising or lowering a tower once or twice. For a more permanent solution a different structure should be used, probably with the hinge pin for the tower raised about 10' above the ground, at the top of the lowest section.

 

[aknisley]

This is what I had built

http://youtu.be/_ZlvBvIT1_k