Guy wire help

Wendell - W5FL
Wed, 19 Feb 1997 11:45:52 -0600


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

		Rohn 45 Tilt Tower Calculations							=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
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			=
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
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
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
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

* 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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