[TowerTalk] Heavy duty free-standing tower options?

[Howard Hoyt]

Hi Daniel!

As one who went down the Rohn SSV path, their method of sizing for wind 
loading is a bit different, and largely unpublished.  Their published 
loadings are all limited by the smallest top section and wind speed they 
specify.  Depending on the height and wind rating this top section could 
be the 1W/1WB, 2W or 3W/3WN.  For example, each section is 20', so an 
80' tower uses four sections.  Here are the relative ratings for 
different 80' configurations, 80mph rating no ice:

4N/3WN/2W/1W = 3.3 sq. ft.
5N/4N/3WN/2W = 8.0 sq.ft.
6N/5N/4N/3WN = 21 sq.ft.

These were sent to me by a Rohn engineer, but not on stamped plans, so 
they would not be considered certified, they were just to be used as 
guidelines.  Based on these guidelines I had planned a 120' tower using 
9N/8N/7N/6N/5N/4N which most likely would have been rated at 24 sq.ft. @ 
90mph no ice.  While I have obtained most of the steel, what has stopped 
me from executing this plan is the foundation requirements, which are stout.

Referring to the Rohn foundation plans, the options for my requirement 
vary between 7.8 and 9 cu. yds.  Between the concrete, rebar and 
drilling service, it would be many thousands of dollars for the 
foundations.  I am currently looking at a guyed 45...

Cheers & 73,

Howie - WA4PSC