Wow, what a response. There were about 30 responses in less than one
day.
To summarize, I made a table, sorted by tower height, as to the
specifications that were used to construct the anchor.
Note how few of the concrete pours are >2 Cu.Yd., which
by the way, are the some of the ones designed by a PE.
Also, there was an excellent message by Arliss, W7XU, which has
some excellent data from Dick, K5IU, a ME who does the Rotating
Tower Systems thing. I attached the message in it's entirety
below.
Conclusions? There's a wide variety of installs, here. Some of
them I would probably bet money that they wouldn't survive 80MPH
winds. What I forgot to mention is that some of the below
examples have gotten pulled out of plumb. Using the same calculations
as for an antenna mast, a 4" x 0.25" wall pipe would snap off (bend)
at the concrete in my installation if it stuck out of the concrete
more than 3'!! (90' tower, 80MPH) And some are using it 6' or
even 10' out of the ground!
What am I going to do? Dunno. 6" pipe minimum, or W8x15 I-beam,
3-5 feet out of ground, and because of the large overturning/lever
action, probably a deep hole, 5-6' deep. Also, like the Rohn
standard anchors (4b and larger), I will probably make the concrete
wider being "broadside" to the tower and rebar the width of
the concrete.
Thanks for all the messages!
Chad
Twr Ant Elevated Guy Post Anchor Data
Hght Load Type Size Len In GndOut GndCu.Yds. Size Deep
---- ---- ---- ---- ---- ---- ---- ---- ---- ----
Pipe 6" 10 4 6 4
HDBX I-beam 4" 11 4 7
T/O Pipe 4"x0.25 12 6 6 bell 7
60 Pipe 8"x0.375 10 3 7 0.11 1x1' 3
73 L I-beam 8" 5.5 3 2.5 1 3
75 Pipe 4" Sc40 10.5 4.5 6 0.17 1x1' 4.5
80 M Pipe 4" 6 3 3 0.09 1'dia 3
80 S I-beam 6" web 7.5 4 3.5 1.3
90 S Pipe 6" 8 3 5 0.75 3
90 I-beam 8 4 4 0.11 1'dia 4
93 S I-beam 4W-15 8 4 4 0.16 14"dia 4
100 L Pipe 6"x0.25 9 3 6 1 3.5
100 L I-beam 10W-24 11 6 5 2 3x3' 6
100 Pipe 5"x0.25 10 4 6 1 4
105 M Pipe 6" 8 3 5 0.75 3
120 L Pipe 4" 7 4 3
120 L Pipe 6" 12 6 6 2 3x3' 6
120 L Pipe 4"x0.25 7 4 3 1+ 4.5x? 4
130 I-beam 4" std 10 5 5 0.33 18" dia 5
130 I-beam 6" wide 10 5 5 1.5 5
130 Pipe 3"x0.25 8 5 3 0.06 8"dia 5
130 Pipe 5"x0.25 10 4 6 1 4
140 L I-beam 12" 9 5 4 3 4x4' 5
150 Pipe 7"x0.5 9+ 4 5 4.5 3.5x7 6
160 Pipe 8"x0.375 10 5 5 1.3 3' dia 5
192 Pipe 4" 13 3 10
HDBX is Rohn HDBX self-supporting tower
T/O is a Tilt over tower
Ant Load: S=small, M=medium, L=large
Most measurements in feet.
------------------------
From: W7XU Arliss <w7xu@dtgnet.com>
Reply-To: w7xu@dtgnet.com
To: Chad Kurszewski WE9V <Chad_Kurszewski@csg.mot.com>
Subject: Re: [TowerTalk] Elevated Guy Anchors
Hi,
The following information was from a talk K5IU (a mechanical
engineer and owner of Rotating Tower Systems) gave at (I
believe) the New Orleans DX convention a few years back:
For posts 7-8 ft above ground:
Installation Width and Ht. Length
Small 2 ft 5 ft
Med 3 9
Big 4 10
The above dimensions are for the concrete bunker. The
post sits in the middle of the bunker. The top of the
bunker is 1 ft below ground level. (Yes, that's right,
almost 6 yards of concrete per anchor for a large
installation).
Post size:
Round post, with guys attaching at 7-8 ft above ground
Installation Post diameter Wall thickness
Small 5" or larger 0.25" or more
Med 7" or larger 0.38" or more
Big 9" or larger 0.50" or more
Wide flange I-beams, with guys at 7-8 ft above ground
Installation Wide flange I-beam size, A36 steel
Small W 6x12 (6" X 4" - 12 lbs/ft)
Med W 8x15 (8" X 4" - 15 lbs/ft)
Big W 10x33 (10" X 8" - 33 lbs/ft)
What is a medium or big installation? I have a rotating
Rohn 25 tower approximately 135 ft high. It has eight
17-el 2 meter antennas on it, stacked one above the
other from 30 to 135 ft. The windload of each antenna
is 2.7 sq. ft., plus phasing lines, etc. That qualifies
as a medium size installation (per K5IU).
I have another rotating tower, 140 ft high. Rohn 55.
It's designed to hold a 10 ft dia. dish, a 6 ft. dia.
dish, a 4 ft dia. dish, 8 long boom (~22 ft) yagis on 432,
4 long boom (~28 ft) yagis on 222, and a couple of
vetical beams for 2m FM and 440 FM. That is a big
installation.
I have elevated guy posts for both of the above
towers, and followed K5IU's guidelines for the
concrete bunkers. I also did some reading on my
own and discussed it with a friend who is a civil
engineer -- it takes a lot of concrete and steel to
make proper elevated guys. A friend of mine skimped
when he put up what is probably a small system (a
tribander and 2m beam on 70 ft of Rohn 25) and now
his posts are pulled out of plumb.
Hope that gives you some ideas.
73, Arliss
W7XU
---
Chad Kurszewski, WE9V e-mail: Chad_Kurszewski@csg.mot.com
The Official "Sultans of Shwing" Web Site: http://www.QTH.com/sos
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