Your friend is an engineer although a civil engineer that would be the first
place I would ask. 40' of basically free standing 25G sounds great until you
have to climb it or a big storm comes by. What are your minimum height
requirements? I am not an engineer so I really can't give you better advice
than to draw it and get the engineer to say OK. Yeah even engineers make
mistakes. Good luck. I will be interested in your final solution.
73 DE K4XZ Joe Patrick
God Made Man
Sam Colt Made Them Equal
From: Bruce Ward <Bruce@IPIntel.com>
Sent: Sat, February 18, 2012 6:53:08 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.
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