[TowerTalk] Request for Advice - Rohn 25 vs TRI-EX HZN 471

[Bruce Ward]

Mark,

You make a very sane suggestion.

My reason for putting the tower on top of the building, if I do, is to 
get an extra 8' to 10' of height.  The building will be sufficient to 
handle the 1100 pound weight plus the horizontal wind loads.

The tower site is covered in 60' plus trees and there is a similar 
height hill with similar height trees between my tower and the far end.  
I need to get above the trees plus above the fresnel zone so I want to 
go as high as I can.

If I use the Rohn 25G we will add sections until we are high enough.  
This method could mean that I have to build sufficient structure to 
bracket even higher than 35'.  I would place the bottom section Rohn 25G 
on the ground (a concrete base) and bracket it to a pole embedded into 
the building.

If I use the the TRI-EX I am stuck with its 70' height plus a 10' mast.  
Since it is a one shot deal I would like to start as high as I can.

Thank you.

On 02/18/2012 06:19 PM, Mark Robinson wrote:
> I am not a mechanical engineer but why don't you put the tower in the ground
> and the building next to the tower.
>
>
> Mark N1UK
>
>
> ----- Original Message -----
> From: "Bruce Ward"<Bruce at IPIntel.com>
> To:<towertalk at contesting.com>
> Sent: Saturday, 18 February, 2012 6:53 PM
> Subject: [TowerTalk] Request for Advice - Rohn 25 vs TRI-EX HZN 471
>
>
>> I am setting up a tower (my first) to get internet service.  The
>> antennas will be less than 2 square feet of wind loading combined and
>> could be even less using 2 11x14" grid antennas.
>>
>> My plan is to build a 10'x10' 9' to 10' tall block building on a slab
>> that is larger in all directions.  This building will will have a
>> concrete roof with rebar and wire in all concrete.  The blocks will have
>> rebar and concrete in every cell.  The structure will use 12  to 15
>> yards of concrete plus 400 concrete blocks providing an over 45,000
>> pound base for the tower.  I have a civil engineer friend who will be
>> involved in the final design of the building.  The building is dual
>> purpose, it will provide a secure home for my servers and a stable base
>> for the tower.
>>
>> Now for the difficult part, I do not have room for guy wires.
>>
>> I am trying to decide between two options
>>
>> 1. I have 9 full and a top section of Rohn 25G in my yard waiting to be
>> be installed.  Currently Rohn rates the 25G for freestanding use up to
>> 40' with 1.4 square feet of wind loading.  From reading online it sounds
>> like Rohn 25s have been used for decades even higher without guy wires.
>> I do not want to risk stretching beyond Rohns specifications.  I have
>> access to 40' lengths of 8" pipe. If I go with the Rohn 25G my intention
>> would be to embed a  40' section of the 8" pipe into the building and
>> bracket to that pipe up to 35' or so then have the tower extend another
>> 35' to 40' above the pipe.  All the metal would be isolated from the
>> ground and properly guided with a ground rod to avoid corrosion issues.
>>
>> 2. There is a TRI-EX HZN 471 available locally.  I would have jumped on
>> this one earlier but it is worth more the the current owner than it is
>> to me.  This is a 70' (71'?)  crank up tower with a motorized winch. The
>> motor is broken and would need to be replaced.  The tower is free
>> standing with the exception of three diagonal pipe braces that connect
>> from the top of the bottom of the 4 sections to the ground around 10'
>> out.  I like that this tower is freestanding and I believe I could do
>> away with the braces if I bracketed the tower at the same location to a
>> sufficiently strong structure.  If I used this tower I would likely
>> build a 3'x3' column of solid concrete into my building and place the
>> tower on top.
>>
>> I would very much appreciate any suggestions and advice.
>>
>> Thank you.
>>
>>
>>
>>
>>
>>
>>
>>
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