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[N2MG]

I'm going to be assembling a Rohn 45 tower this summer on a pier pin base.  Since the tower will be unclimbable without guys, I'd like to know what other installers have done to stabilize it during the first part of assembly.

Do you use heavy rope or guy wire and come-alongs, or real guys with turnbuckles or???

How about the first few sections: how many can you bolt together and get up on the peir pin at the start?

Any other hints?

Thanks,
Mike N2MG

[N2NU]

We did the rope and come along thing and just put it on the bottom section on both of my towers.  Safer would be to use ehs, though.

[N4ZR]

Well, it's not on quite the same scale, but my R-25 tower is on a pin, and I began with 2 sections bolted together, rope guyed.  Felt a LOT better when the third section was on and the first set of permanent guys were installed, though.

73, Pete N4ZR

[N0RKX]

What's the advantage of a pier pin over a regular base?

Thanks, N0RKX

[N2MG]

For a fairly extensive, but easy-to-read study of the forces on towers in wind, go to K7NV's website:

http://www.freeyellow.com/members3/yagistress/

Hopefully I can explain this correctly...When wind blows on a tower/antenna it causes two major types of forces on the tower. One is a bending (leaning over) type of force. This force exists whether or not there are any antennas or other off-center loads.  The second force is a twisting force that tries to rotate the tower.  From what I can recall, the main contribution to this force is from off-center loads - these cause a twisting force on the tower whenever wind exists.  Almost any antenna, especially side-mounted antennas, will have some "off-center-ness".  If the tower's legs are rigidly connected to the concrete (sunken-base installation) then there is a huge force right at that junction where the legs enter the concrete.  If the tower can rotate on the base (on a pier pin) all the twisting forces are absorbed in the guy wires - where they should be.

If you have any doubts as to the engineering: notice tall, guyed commercial towers. They sit on something similar to but even better than, a pier pin.  These towers sit on a "point" so even the falling-over force contributes little to the forces on the base.

[N0RKX]

N2MG,

Thanks for the link. I wonder if "turning towers", where a section of tower is used as a mast and turns in bearings, would be subjected to the same forces as a monolithic tower. It seems that the main bearing below the turning section of tower would aleviate those forces on the concrete base. Of course there is the expense trade off.

N0RKX

[N2MG]

N0RKX,
The force I was concerned with was the force on the legs of the base section (probably should call it the bottom or first section) of tower, not the force on the concrete itself.

With a chunk of tower above a rotator, the brake system of the rotator will be required to handle the specific force (the twisting or turning of the tower above it) I was talking about.

Mike

[KR1G]

I don't necessarily suggest this method, but it worked here.

Put the first section of Rohn 45 on the Pier Pin, use a nut on the Pier Pin to hold it in place. Climb tower, pull up next section of tower, and place on top (using a gin pole or brute strength). Repeat.

Tower were put up to 30 feet (with no guy wires) using this method. Then the first set of guys were attached at the 30 foot level.

I wasn't climbing the unguyed tower If I was, I would have used temporary rope guys. But I can assure all that lots of Rohn 45 towers have been put up by this method.

73
Ted

[N9GXW]

Another advantage of the “pin” is that the foundation is allowed to move a bit during normal freeze and thaw of the seasons without throwing the tower out of plumb.

[N2MG]

Having reread it, I see that my post of May 10 is a bit incomplete in its wording.

I said "With a chunk of tower above a rotator, the brake system of the rotator will be required to handle the specific force (the twisting or turning of the tower above it) I was talking about."

What I left out, of course, is that the rotator, in turn, will pass the twisting force its brake holds to whatever the rotator is mounted to.