[TowerTalk] 30 foot Rohn 25G calculations
TexasRF--- via TowerTalk
towertalk at contesting.com
Fri Feb 13 10:11:01 EST 2015
Joe, the over tightened leg bolts you saw were very likely someone's
attempt to
In a message dated 2/13/2015 6:21:23 A.M. Pacific Standard Time,
w4tv at subich.com writes:
I saw plenty of Heights and Universal towers that were egged out
during my time on Ohio. Many of them had the bolts/nuts tightened
to the point that the legs were somewhat flattened but that did
not prevent "egging out". I know one old timer in the Columbus
area who replaced towers twice within 10 years - both times because
they were so badly egged out that nobody would climb them to repair
antennas.
Again after what I saw of those towers, I would not trust one here
in the higher/constant winds in Florida. If I had to use a free-
standing tower here, it would be the biggest sections available
from AN Wireless or a properly engineered commercial - Rohn SSV,
Pirod (if they're still around), etc. - tower with bolted flanges.
73,
... Joe, W4TV
On 2015-02-12 5:09 PM, n8de at thepoint.net wrote:
> Joe,
>
> The 'egging out' is usually caused by insufficient tightness in the
> original erection.
> Have had many (over eight) Universal towers since 1975, and only once
> did that factor into the situation ... my error is not retightening the
> bolts/nuts AFTER erection.
>
> Those 'light duty' towers are TV towers in my mind, and would never use
> one.
>
> 73
> Don
> N8DE
>
>
> Quoting "Joe Subich, W4TV" <lists at subich.com>:
>
>>
>> On 2015-02-12 2:00 PM, n8de at thepoint.net wrote:
>>>
>>> A free-standing Universal aluminum tower composed of 26" tapered,
>>> 22" tapered, and 18" topper will support ANY common
>>> tribander/vertical/VHF combo presently being used in ham radio.
>>
>> While that may be true in Michigan where the wind requirements are not
>> particularly high (70 MPH rev F, 90 MPH Rev G), that may not be true in
>> Seminole County, Florida where the building requirements are for 140
>> MPH (139) wind speed.
>>
>> Note the force due to wind is *2.5 times higher* at 140 MPH than at
>> 90 MPH. Directly comparing the allowable antenna in Rohn's example
>> designs for 90 and 130 MPH indicates the same tower will support
>> less than half as much antenna 1t 130 MPH as it will support at 90
>> MPH.
>>
>> Universal Towers does not even give windload data for 140 MPH on their
>> web site (they provide spec's at 80, 100 and 110 MPH for the light duty
>> towers but nothing for the heavy duty models) but given the nearly
>> constant winds in Seminole County, FL, I would *never* trust one of
>> their towers as I've seen how badly their bolted connections "egg
>> out" after only a few years in the much more calm areas of the Great
>> Lakes region.
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
>> On 2015-02-12 2:00 PM, n8de at thepoint.net wrote:
>>> Unless he is intending to put up a stack of huge monobanders and/or
>>> SteppIR yagis, he doesn't need the 30" sections.
>>>
>>> A free-standing Universal aluminum tower composed of 26" tapered, 22"
>>> tapered, and 18" topper will support ANY common tribander/vertical/VHF
>>> combo presently being used in ham radio.
>>>
>>> Do the research ... I have 3 Universal towers up now ... and plan to
put
>>> up 4 more soon.
>>>
>>> 73
>>> Don
>>> N8DE
>>>
>>>
>>> Quoting Gedas <w8bya at mchsi.com>:
>>>
>>>> Brian, I would not rule out a free standing tower esp since you need
to
>>>> stay under 30'.
>>>>
>>>> I have several self-supporting Universal towers here, each of which
>>>> uses as their first 3 sections, their 30" HD series sections. When
>>>> assembling the towers and after getting those first 3 sections up in
>>>> the air, you realize how strong that structure is.
>>>>
>>>> In your case, since you mentioned 24', I would use two 30" HD
sections.
>>>> See if you can get the top section modified either by Universal or by
>>>> a local welding/fab place to make it a topper with a collar where you
>>>> can then use a 2" or 2.5" mast. My gut tells me that two 30" HD
>>>> sections with a 4'-5' mast will still be standing long after your home
>>>> is leveled from some severe wind storm.
>>>>
>>>> Gedas, W8BYA
>>>>
>>>> Gallery at http://w8bya.com
>>>> Light travels faster than sound....
>>>> This is why some people appear bright until you hear them speak.
>>>>
>>>> On 2/12/2015 1:03 PM, Brian Carling wrote:
>>>>> Many thanks Bud.
>>>>>
>>>>> I will need to review which version they are using. Yes I had
>>>>> someone pointing me in the direction of a freestanding tower but I
>>>>> think I may go to using guys.
>>>>>
>>>>> It's either that or trade my tower sections in on a stronger better
>>>>> built freestanding tower designed for that purpose. I only need
>>>>> about 24 to 28 feet in height. Maximum.
>>>>>
>>>>> Best regards - Brian Carling
>>>>> AF4K Crystals Co.
>>>>> 117 Sterling Pine St.
>>>>> Sanford, FL 32773
>>>>>
>>>>> Tel: +USA 321-262-5471
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>> On Feb 12, 2015, at 12:27 PM, W2RU - Bud Hippisley
>>>>>> <W2RU at frontiernet.net> wrote:
>>>>>>
>>>>>>
>>>>>>> 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
>>>>>>
>>>>>>
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