Design & Installation of 20m and 40m Instrument Masts

[nocturnal]

I am new to this site, and the navigation is a bit vague and awkward (I suppose for new users), so I hope I'm in the right place.

I am seeking some help in designing for the fabrication and erection of two instrument masts - the first @ 20m (66ft), and the second @ 40m (132ft).

This is my first attempt at something like this...

I understand that there are mainly two options.. (1) using a monopole design, adequately supported by guy wires and an anchored baseplate, and (2) using a lattice design.

For the 20m mast, I have concluded that a guy supported tubular monopole design should be adequate. I've used a 4" galvanized steel, and neglected tapering the mast on advice from a colleague experienced in this sort of work. He insists there's no real advantage, since this isn't a load bearing mast.

I am a little stumped however on how to handle the 40M mast. The mast will only be erected for 3 months. I am inclined to using a monopole design, but I am uncertain if this design is suitable to such a height. Using a monopole design, I would taper this mast based on the height. My initial consideration is to start with a 12" OD tubular base, and taper up ending with a 2" OD mast "tip". Is this feasible? Or is it recommended that I go with a lattice design?

Or are there any other suggestions? I would really apprecitate your responses.

 

[nocturnal]

Also.. any tips on erecting the masts? I find this to be equally as demanding technically as designing the structure.

 

[transmissiontowers]

Your 66' tube will probably require a splice or 2 which will probably be just base plates.

If you go tapered tube for the 132' pole and you use guy wires, you will have to be careful with the splices. Tapered tubes normally use a slip joint where the overlap is generally 1.5 times the OD of the upper section (for free standing transmission poles anyway). The problems occur when you guy a slip joint pole. If the pole is not jacked together and some bolts used to limit the slip, the sections can overslip when the guys get tight with a major wind load and the guys can then go slack.

The communication antenna people use these guyed masts and poles all the time. Since you are only going up 132', I'll assume you are going to erect it with a crane to hold it up while the guys are installed.

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