Help with idea for tilting tower

[stryped]

First, I hate heights. I have 3 sections of triangle type tower at my house. So, total length is about 30 feet.

My idea is to make some sort of hinge so I could lower it over and
raise it. I know I mentioned it before but now seems to be the time I
need to do it. (My little boy is starting to find pieces of the
antenna in the yard.)

My thought was to dig a hole beside my current antenna a couple of
feet deep and in circumfrence. Place some 3 inch schedule 80 pipe (one
for each corner) into the holw with a 2x2 or so piece of 1/4 inch
steel on top. On the end of the plate would be welded a few pieces of
black pipe the diameter of a hitch pin. There would be another piece
of 2x2x1/4 piece of steel with more black iron pipe on it. The black
iron pipe would in effect be the "hinge" part of the mechanism. (sort
of the way I made the fold down gate for my trailer).


Here is where I am having trouble. On top of the "top" plate, I have
some 2 inch black iron pipe. My first thought is two weld three of
these as "legs" on top of the top plate, then put my cut down
exisiting tower into this pipe, drilling a hole through each leg. (The
new two inch pipe and the legs on the tower). Instering a grade 5 bolt
into this. I have also thought, I wonder if it would be easier to just
put the three legs up and use u bolts to attach the tv tower to the
outside of the legs.


I would place a 3x3x10 square foor piece of tubing in concrete behind the tower about a couple of feet back. On the bottom of this "pole" i would have a small hand crank winch. On top a pulley. The wire will go from the winch around the pulley and somehow on to the tower. This way I could raise and lower it.

One thing I am worried about is buckeling in the middle. Is there a way to attach the winch line where it would pull from several sections of the tower at the same time to eliminate buckeling?

I would still need to climb part way up it or have the capability to
to adjust my sat dish. I can't figure out a good way to do it with the
tower leaned over.


I appreciate it!

 

[Unrest]

I think you need to do some calculations, otherwise it's just guessing. I'd do some hand calcs for the overall structure and some obviously high-stress members, and an FEA model to get more accurate results and check all the individual member forces, stresses and buckling factors.

You can use pulleys to redistribute the load. However if you put more force on the 'lower' end of the tower, that could create a bending moment that it can't support and it crumples before it's even got off the ground!

It might turn out that you need a multi-stage lift. Like start by lifting from above, then when it's at a steep enough angle, change to pulling it from behind as you suggested.

 

[stryped]

Can you help me with that?

 

[Unrest]

Can you help me with that?

Maybe. But I there's a fair bit to it. Several things to check:

Lifting:
- Stress in the members
- Stress in the joints
- Buckling of the overall structure (like the whole thing bows)
- Buckling of individual members
- The different load conditions as the angle changes.
Modified connection to the ground:
- Fatigue
- Overload
- Maybe buckling
- If it's left unattended for long periods, corrosion.

For many of them you can make simplifications by considering only the worst cases.

I'd start with buckling in members near the base. That might immediately show that the whole approach is impractical. First you need to find the loads on the members. You might be able to do that with a free body diagram. Then use the Euler buckling formula to see if it's below the critical load.

If lifting sideways doesn't work, have you considered lifting section by section vertically, the way tower cranes do? Install the top first, then raise that and connect the next lower section, then raise them both and put in another section, etc.

This could be a half-term project for an engineering student. How much background do you have in this sort of thing?