[TowerTalk] 30 foot Rohn 25G calculations

[W2RU - Bud Hippisley]

> On Feb 12, 2015, at 9:58 10AM, bcarling at cfl.rr.com wrote:
> I am putting together a permit application with my city which requires certfication for 139 mph 
> for three second gusts as in TI-222 spec. Also steady 100 or 110 mph I think. 
> We are making a 30 foot Rohn 25G tower according to the Rohn specification with  4 foot 
> cube base of concrete with no guys.

I’m not sure I understand what you’re hoping to find.

My 4-year old Rohn catalog makes it VERY clear that 30 feet of Rohn 25 can hold only 1.7 sq. ft. of added antenna when the environment is 90 mph (ANSI/EIA-222 Rev. E) and NO ICE.  (For areas that experience icing, Rohn 25 is specified by the manufacturer at ZERO sq. ft. of additional antenna load!)  From your e-mail address and the wind speeds you mention, I’m going to guess you’re in Central Florida, and I daresay a 90-mph Rohn EIA-222 Rev. E specification is not going to be adequate for your city.

Nowhere in your posting do you mention what total antenna, rotator, feedline, etc. wind surface area or wind load you anticipate putting on this tower.  But my guess is that NO freestanding 30’ Rohn 25 tower is going to make the grade.

Also, you fail to mention which version of TIA/EIA-222 your city is using.  The latest I’m aware of is Rev. G — a substantial revision from previous methods of specifying wind loading.

Bud, W2RU