Guy wire help
Wendell - W5FL
w5fl@flash.net
Wed, 19 Feb 1997 11:45:52 -0600
Paul,=20
I just finished installing my 64 foot Rohn 45 Foldover Tower and got my =
2 element quad setting at 66.5 feet one hour after the ARRL cw contest =
was over! Poor Timing. If you have EXCEL v 4.0 or later, I will send =
you a spreadsheet that calculates the loads for a Rohn Foldover Tower. =
I made it when I put up my tower. I designed mine for 110 mph winds and =
the loads in the guylines are quite high - about the same as a 120 foot =
tower with conventional guying at 80% of the height.
The main thing you really need to watch is that your anchors are really =
good and deep - and I would NOT use the screw in anchors that Rohn =
furnishes! The uplift forces are nearly 2400 # and the guy tension is =
over 1700 pounds which is about all I would want to put on 3/16 ehs =
(about 3000 pounds ultimate strength - not working load) but should be =
ok for 1/4 ehs (6600 pounds ultimate load). I used 1/4 ehs and it is =
pretty stiff if you follow their directions and serve the ends after the =
3 cable clamps. I did it, but had to wear gloves (Rohn's tool might =
work better.)
You will find that four way guying is really good, but only about 14% =
stronger than 3 way. That is why the economics favor 3 way guying, but =
it won't work for the foldover tower. Any stresses that work for 3 way =
guying will have an additional safety factor of 14% for 4 way guying.
I have included the point design that I used for my tower. Maybe it =
will show you the magnitude of forces on the tower: however, keep in =
mind that it is for a Rohn 45. I hope enough of it gets through the =
mailer to be readable.
Good Luck,
Wendell Wyly W5FL w5fl@flash.net
Rohn 45 Tilt Tower Calculations =09
=09
7/16 members 45G 22.09779 Height (H) 64 (Feet) =09
Bottom guy angle 49.24002 PSF (p) 50 #/sq-ft =09
Top guy angle 68.04445 Ant (A) 17.2 sq ft =09
5/16 members 25G 18.65643 Guy R (rad) 25 =09
Rohn 25 crossection=3D 2.540256 Guys (gy) 2 =09
Rohn 45 crossection=3D 2.796355 =09
20 psf at top of tower=3D 568 pounds or 28.4 sq ft Anchor Dist =
35.35534 =09
30 psf at top of tower+ 516 pounds or 17.2 sq ft =09
=09
Tower Load 13.98178 x height =09
Feedline Load (1 7/8 and 1 1/2 per leg) 3.819444 x height =09
Antenna Load 860 =09
Note: 30 psf =3D 86.6 mph windloading =09
F1 (This is resultant of all guy forces) 698.6392 40 psf =3D =
100 mph windloading =09
Tension top guys 1713.818 50 psf =3D 111.8 mph windloading =
=09
Tension bottom guys 1308.676 =09
Anchor uplift force 2347.428 =09
Base Down Force 9389.71 (Allowable vertical load on the bottom section =
is 18,960#) =09
=09
Note: Items in Bold can are variables and can be changed. =09
Note: This program primarily calculates guy wire forces, anchor uplift =
forces, and tower compression forces. =09
It is set up for two sets of guys, but will calculate more sets. You =
will have to modify the tension and guy angle outputs. =09
Note: This tower set in 30 in diameter hole 3 1/2 foot deep. Guy =
anchors are set in 16 in dia hole 5 1/2 ft deep. =09
Concrete is 3000psi 5 sack mix with 1 inch rock - not Sacrete or =
Peagravel. Guys are 1/4 inch EHS. =09
=09
This information provided for educational purposes only. It runs on =
EXCEL and you can look at the formulaes =09
used in the calculations and decide for yourself if the factors of =
safety fit your application. Do not under any =09
circumstances use a safety factor less than two. No liability of any =
kind is assumed by the author. =09
Use a Professional Engineer when you have arrived at a point design as =
this design does NOT consider torsion =09
of the antenna or a failure in bending of the tower if you don't assume =
the correct number of sets of guys. =09
=09
This analysis is for a fold over tower and requires four anchors. You =
can convert to 3 anchors, but the forces will =09
be higher because the worst case occurrs when the wind force is 30 =
degrees from a guy wire for 3 guys where the =09
worst case for four guys occurrs in line with a single guy. If there is =
sufficient interest, I will also produce this =09
spread sheet for 3 guy anchors. =09
=09
=09
* I removed a Rohn FK2548 tiltover tower from my old QTH and plan to=20
* install it at my new location as a FK2568. The code here is for a=20
* tower to withstand 100 mph. Rohn has sent me info for the 25G that is =
* for 110 mph. The FK25XX uses 4 way guying not 3 way.
* Here is the question: Can I / should I use 1/4 guys for the tower to=20
* help with the 100 mph windload or use the 3/16 that came with the=20
* tower? I have to order some new guy cable because the tower will=20
* taller. =20
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