Guyed Towers

[k4kyv]

This will explain why the typical ham radio method of erecting guyed towers with the bottom section buried in the concrete base is not a good idea.

A study of what happens when we make changes to a tower configuration
 

                                             Preface

The following discussion is aimed at observing tower behavior subsequent to changes in configuration, and has selected the EIA/TIA RS-222-F spec as the standard for the comparisons. The information presented is just part of the work pursued here to understand how guyed towers work. I found the results interesting, and contrary to some amateur folklore, making it a shame not to share with others.

For many years I've seen hundreds of commercial installations with tapered bases. Until now, I always wondered why the commercial installations had tapered bases and the amateur ones did not.
After looking at my new Rohn commercial catalogue, the first thing I noticed is that all sections for guyed towers from 45G and up are offered with tapered bases. One of the rigid tube towers "J" offers a roof mounting base that actually has a ball and socket connection. This is exactly what was modeled in Configuration Variant #4.

This indicates that Rohn and their commercial users understand the problem, and agree that the base of the tower should not only be free to rotate about the vertical axis to reduce torsional load development, but also be free to lean over just as far as the guys will allow. The small tapered bases sit on bearing plates on a pier pin. It is obvious from the drawings that these connections will allow enough rotation, about the horizontal axes, to prevent development of significant bending loads.

Note: Rohn does (or at least did) make a tapered base for the 25G.  It is called a 25TG. I have one on my tower.

http://k7nv.com/notebook/towerstudy/towerstudy1.html

[Ed-VA3ES]

I  have a 56'  self-supporting tower, no guy wires.  The base is buried in concrete, 4.5' X 4.5' X 4.5' .

[k4kyv]

I  have a 56'  self-supporting tower, no guy wires.  The base is buried in concrete, 4.5' X 4.5' X 4.5' .

I stand corrected; the text should have read "This will explain why the typical ham radio method of erecting guyed towers with the bottom section buried in the concrete base is not a good idea.

I'll make the correction in the original post.

But from reading the article it is clear they are talking about guyed towers.

[AB2EZ]

Don

I found this article extremely interesting. I have never given any thought to the subject of how one does the engineering design tradeoffs for a structure like a tower. The combination of the numerical results from the simulations, the graphical results from the simulations, and the commentary from the author are a wonderful illustration of how modern engineering (using a combination of understanding of basic principles and computer design/modeling aids) is done. Furthermore, as someone who is considering putting up a tower for the first time... the conclusions and recommendations were of immediate interest to me. I will definitely take these computational results into account to get the maximum wind tolerance for a given amount of investment from any tower I decide to put up.

Best regards
Stu

[Todd, KA1KAQ]

Interesting stuff, Don.

My first tower was a HEIGHTS aluminum type, like Rohn 25 but much lighter. 60' or so, guyed top and center. I poured the base for it in early November of 1987. It was up for a few years before I sold it to a friend and we took it down.

A year or so after installing it I recall going up the hill one day to where it was located to find splits in at least 2 of the 3 legs. Just about eye level for me, so maybe 5.5' from the base. First thought was ice damage, but it wasn't cold enough and the bottom of the legs were open to prevent moisture from accumulating. Then I thought it might have taken a lightning strike, but there was no other related damage.

Now I wonder if the thing was torquing in the wind at some point and split the legs? The splits were just below the point where the 'zig zag' bracing was welded.

[K6IC]

Hi don,

Thanks for posting this,  very interesting.

As I recall,  you have stated a few years ago that you felt that a Pier Pin,  with ball/socket base was the way the pros did BC towers,  and that degree of freedon helped keep the tower aligned (in column).  Now it is easier to see how this works.

K7NV, Kurt is a very sharp guy on towers and things mechanical.
He builds some very nice bullet-proof prop pitch rotators for we Hams.

73  Thanks again,  Vic  K6IC

[WA1HZK]

For what it's worth before ROHN went to Canada with Radian and finally returned I posted the entire ROHN catalog on line and offer it to anyone that needs the drawings. They are in Adobe pdf format.
http://www.criticaltowers.com/ROHN%20Industries/Media/menu/main.html
Keith
WA1HZK