Tower Guy Anchors
Karl Beckman
guy on the downwind side of the tower is always in tension. This is
related to a mechanical phenomenon not usually explained in statics
class- You can't push a rope! Applied to this situation, a loose guy
provides absolutely no support to the structure. Warm temperatures will
cause the guys to slacken because the guys are longer than the tower is
tall, both have (almost) the same temperature coefficient of expansion.
This is one more case where tight is better than loose.
------------------------- Original Article -------------------------
Newsgroups: rec.radio.amateur.antenna
From: ja...@fc.hp.com (Jay Kesterson K0GU)
Subject: Re: Tower Guy Anchors
Date: Tue, 16 Nov 1993 16:19:45 GMT
Reply-To: ja...@fc.hp.com
References: <1993Nov4.1...@ccd.harris.com> <1993Nov5.061202.27862@ke4zv.
Nntp-Posting-Host: corona.fc.hp.com
Gary Coffman (ga...@ke4zv.atl.ga.us) wrote:
: If you can get access to a cable tension gauge, set the guy tension to
: 50-75 pounds depending on temperature, the tower will "grow" in warm
: weather so use the higher tension setting then. The guys will loosen in
: cold weather as the tower shrinks.
: Gary
The Rohn catalog says to tension the guys to 10 percent of their rated
value (when using the proper size guys they recommend for various towers).
I'm no expert on why, but thats what is says.
73, Jay K0GU ja...@fc.hp.com
Karl Beckman
reality here, but keep in mind that the third leg of the triangle is
the earth. When (other than CA earthquakes) was the last time you had
to adjust the length of your telephone drop wire or electric service
because the pole moved closer or further away from the house?? I've
heard that poles have jumped in front of cars, usually driven by well-
intoxicated drivers, but Ma Nature doesn't have to adjust its equatorial
belt by a notch or two as the seasons change.
------------------------- Original Article -------------------------
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From: rde...@casbah.acns.nwu.edu (Rajiv Dewan)
Newsgroups: rec.radio.amateur.antenna
Subject: Re: Tower Guy Anchors
Organization: Northwestern University, Evanston IL USA
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References: <1993Nov4.1...@ccd.harris.com> <1993Nov5.061202.27862@ke4zv.
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In article <1993Nov16.1...@stsci.edu>,
Phil Hodge <ho...@stsci.edu> wrote:
>
>Gary Coffman (ga...@ke4zv.atl.ga.us) wrote:
>: If you can get access to a cable tension gauge, set the guy tension to
>: 50-75 pounds depending on temperature, the tower will "grow" in warm
>: weather so use the higher tension setting then. The guys will loosen in
>: cold weather as the tower shrinks.
>: Gary
>
>Why don't the cables "grow" together with the tower in warm weather?
>Are they made of such different materials that their coefficients of
>expansion are significantly different? For long cables I guess a small
>difference could be significant.
>
> Phil, WD8PHO
You are neglecting to consider the third leg of the triangle: Ground.
Its expansion is not going to be that of steel. This causes all the
difference. If you take that into account and assume that the expansion
rate of ground is more than that of steel, then as I have shown below,
the tension will increase in warm weather and decrease in cold.
---- Now for some simple math to justify the above statement ------
To simplify, assume that the expansion rate of ground is zero.
Define `cold' and `high' to be some appropriate temperature
height of tower, cold h
distance from guy anchor to tower g
expansion rate of steel, from cold to warm a
expansion rate of ground, from cold to warm b
guy length needed (constant tension) sqrt[(1+a)^2*h^2 + (1+b)^2*g^2]
guy length after expansion (const tension)
(1+a)*sqrt[h^2 + g^2] = sqrt[(1+a)^2*h^2 + (1+a)^2*g^2]
So if a < b then tension will be higher in summer. So if there a minimum
tension that is to be maintained then summer installations should be at
a higher tension settings.
Question: Is the expansion rate of ground more than that of steel?
Rajiv
aa9ch
r-d...@nwu.edu
Phil Hodge
In article <1993Nov19....@schbbs.mot.com>, CSL...@maccvm.corp.mot.com
(Karl Beckman) writes:
|> I hate to have to interrupt your trains of thought to inject a bit of
|> reality here, but keep in mind that the third leg of the triangle is
|> the earth. When (other than CA earthquakes) was the last time you had
|> to adjust the length of your telephone drop wire or electric service
|> because the pole moved closer or further away from the house?? I've
|> heard that poles have jumped in front of cars, usually driven by well-
|> intoxicated drivers, but Ma Nature doesn't have to adjust its equatorial
|> belt by a notch or two as the seasons change.
I think you are correct that the ground does not expand or contract
with temperature changes, at least not in the horizontal direction.
The reason is that the temperature a few feet below the surface is
nearly constant throughout the year. If the ground warmed up throughout
the entire depth of the earth's crust during the summer, the horizontal
distance between objects fixed to the earth's surface would indeed
increase.
According to the CRC Handbook of Chemistry and Physics, the coefficient
of thermal expansion of steel is about 11 parts per million per degree
Celsius. I couldn't find dirt listed in their table (!).
So if the tower and cable are made of the same kind of steel, the cable
should be more slack in the summer, in contradiction with experience.
That suggests that the coefficient of expansion of the cable is smaller
than that of the tower.
Doug Braun
sunlight, and random changes in the shape of the ground
(caused by frost heaves, changes in the water table, the
tower base settling, etc.) would have a very significant
and unpredictable effect on the tension of the guy wires.
I would think in reality, that they keep getting loose and have
to be re-tightened regularly.
--
-------------------------------------------------------------------
Doug Braun Intel Israel, Ltd. M/S: IDC1-41
Tel: 011-972-4-655069 dbr...@inside.intel.com
Tom Bruhns
hard (or expensive if you are paying someone else to do it) to get a
significant amount of concrete. Does anyone have references or
experience anchoring guys in other ways? Two ways I can think of
that _seem_ reasonable:
-- A rod driven into the ground at a shallow angle so the guy
tends to pull toward the ground, with a second rod
driven a short distance further out and parallel to
the first, to "guy" the top of the first rod. Should
work well in compacted, undisturbed soil for fairly light
loads.
-- A "deadman" buried in the ground: perhaps an 8 foot length
of pressure treated 4x12, with the 12" face perpendicular
to the guy, and the 8 foot axis parallel to the surface of
the ground. This would depend more on the weight of the
soil put back over the top of it. Tough to put into
undisturbed ground, since you have to dig a trough for it,
but you can dig down at an angle, leaving the majority
of the gound in the direction of the guy undisturbed. What
do you use for the anchor bolt through the board, so it
doesn't rust out? Maybe something like 1" galvanized water
pipe? Maybe a loop of stainless steel cable around the
board?
Packing concrete through a wooded ravine 60 feet deep isn't very
appealing; any help to avoid that would be appreciated (unless
some strong backs wanna volunteer to pack the concrete for me ;-)
73, Tom -- K7ITM
Gary Coffman
>So if the tower and cable are made of the same kind of steel, the cable
>should be more slack in the summer, in contradiction with experience.
>That suggests that the coefficient of expansion of the cable is smaller
>than that of the tower.
Well let me reiterate my theory. Both the tower and the cable elongate
as they warm up, but the solid tower mostly expands upward while the
cable mostly twists. That's because the stranded cable has many many
twists per unit length. If my theory is true, then solid guys should
not increase in tension in the summer, but stranded ones should. Anybody
using clothesline wire for guys who can confirm this?
Gary
--
Gary Coffman KE4ZV | Where my job's going, | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems | I don't know. It might | uunet!rsiatl!ke4zv!gary
534 Shannon Way | wind up in Mexico. | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244 | -NAFTA Blues |
Gary Coffman
>Back to the guy anchors part of the thread: Some places it's mighty
>hard (or expensive if you are paying someone else to do it) to get a
>significant amount of concrete. Does anyone have references or
>experience anchoring guys in other ways? Two ways I can think of
>that _seem_ reasonable:
>
> -- A rod driven into the ground at a shallow angle so the guy
> tends to pull toward the ground, with a second rod
> driven a short distance further out and parallel to
> the first, to "guy" the top of the first rod. Should
> work well in compacted, undisturbed soil for fairly light
> loads.
This is not a good plan. You want the anchor rod in tension since
that's the way it's strongest. With this plan, it's the second
guy anchor that's bearing most of the load while the prime anchor
is just offering it's minimal bending resistance.
> -- A "deadman" buried in the ground: perhaps an 8 foot length
> of pressure treated 4x12, with the 12" face perpendicular
> to the guy, and the 8 foot axis parallel to the surface of
> the ground. This would depend more on the weight of the
> soil put back over the top of it. Tough to put into
> undisturbed ground, since you have to dig a trough for it,
> but you can dig down at an angle, leaving the majority
> of the gound in the direction of the guy undisturbed. What
> do you use for the anchor bolt through the board, so it
> doesn't rust out? Maybe something like 1" galvanized water
> pipe? Maybe a loop of stainless steel cable around the
> board?
A deadman is a good plan. Even pressure treated wood will rot
out fairly quickly in some soils though. A heavy walled galvanized
steel pipe makes a better deadman. Weld the emerging guy rod
to the deadman forming a 'T'. A couple of bags of ready mix
concrete will set the deadman in place in it's trench. Pour
a cylinder of concrete around the emerging rod to protect it
from corrosion as well. Then backfill and compact the soil.
>Packing concrete through a wooded ravine 60 feet deep isn't very
>appealing; any help to avoid that would be appreciated (unless
>some strong backs wanna volunteer to pack the concrete for me ;-)
Concrete is still your best tool. Using a deadman can minimize
the amount you have to use for a guy anchor, however, from a couple
of yards down to a couple of 50 lb bags of ready mix. You just need
enough to protect the metal from coming into direct contact with the
soil. You *can* coat the deadman and rod with roofing tar instead,
but concrete is usually cheaper, and easier to work with. Paint won't
cut it.
Gordon Couger
>A deadman is a good plan. Even pressure treated wood will rot
>out fairly quickly in some soils though. A heavy walled galvanized
>steel pipe makes a better deadman. Weld the emerging guy rod
>to the deadman forming a 'T'. A couple of bags of ready mix
>concrete will set the deadman in place in it's trench. Pour
>a cylinder of concrete around the emerging rod to protect it
>from corrosion as well. Then backfill and compact the soil.
>
Pressure treated wood creasote will out last unprotected steel by a
considerble margin. Several spieces of untreated wood will out last
steel. One in particular is Boi's deArc sp? I know of a corner post
that has been in place over 70 years. Only the heart wood is decay
resistant.
Concrete around steel is better than steel but in salt water enviorments
the Steel will rust out of the concrete in a few years and imersed wood
will out last reenforced concrete.
Some clay soils are very bad about moving as they cycle from wet to dry.
North of Dallas Texas to get a corner post to hold we set 3 10 inch
creasote post 10 feet long in 2 foot by 5 foot holes and back filled with
gravel we also placed a dead man between the corner and second post. Any
thing less would pull out of the ground in short order.
If you are going to use steel under ground make sure it is well protected
with concrete above the ground line and shaped so that water will not
stand on the steel also make sure the top is sealed so that water does not
run down the inside.
Sorry if this is a little disjointed I have been interupted several times.
Good Luck
Gordon AB5Dg
C
A conc
/* Gordon Couger */
/* Biosystems & Agricultural Engineering */
/* Oklahoma State University */
/* 114 Ag Hall, Stillwater, OK 74074 */
/* gco...@olesun.agen.okstate.edu 405-744-9763 day 624-2855 evenings */
/* I Speak only for myself and not for anyone else */
Tom Bruhns
: In article <CGwo5...@hpcvsnz.cv.hp.com> to...@lsid.hp.com (Tom Bruhns) writes:
: >Back to the guy anchors part of the thread: Some places it's mighty
: >hard (or expensive if you are paying someone else to do it) to get a
: >significant amount of concrete. Does anyone have references or
: >experience anchoring guys in other ways? Two ways I can think of
: >that _seem_ reasonable:
: >
: > -- A rod driven into the ground at a shallow angle so the guy
: > tends to pull toward the ground, with a second rod
: > driven a short distance further out and parallel to
: > the first, to "guy" the top of the first rod. Should
: > work well in compacted, undisturbed soil for fairly light
: > loads.
: This is not a good plan. You want the anchor rod in tension since
: that's the way it's strongest. With this plan, it's the second
: guy anchor that's bearing most of the load while the prime anchor
: is just offering it's minimal bending resistance.
??
Maybe I didn't explain it well in words.
Tilt this about 45 degrees:
Rod 2
|
Rod 1 | / . . . .
|-----------| . . . .
| /| . . . . .
| / >| . . . .
| / >| . . . . .
Air | / . . >| . . . .
| / . . >| . . . . .
|/ . . >| . . . .
Guy -----------------------+ . . >| . . .
/ | . . >| . . . ..
/. >| . . . . . . .
/ >| . . . . . .. .
/ . . >| . . . ... . . .
/ . >| . . . . . . . .
/ Ground >| .
/. . . >| . . . .. . .
">" indicates reaction from the ground into which the rods are driven.
It doesn't take too much ground reaction to insure that most of the
load is on first rod, not the second. The second simply stiffens
the first...it's a significant addition, but certainly less than
half the load is borne by it. Did I miss something in your
comments on this one? Certainly tension is better than bending,
but with something like a 2" or 3" pipe for Rod 1, it becomes a
lot like a deadman made with pipe except you don't have to dig a
hole for it and it doesn't have as much ground to pull against.
Gary Coffman
>
>Maybe I didn't explain it well in words.
>
>Tilt this about 45 degrees:
>
> Rod 2
> |
> Rod 1 | / . . . .
> |-----------| . . . .
> | /| . . . . .
> | / >| . . . .
> | / >| . . . . .
> Air | / . . >| . . . .
> | / . . >| . . . . .
> |/ . . >| . . . .
> Guy -----------------------+ . . >| . . .
> /. >| . . . . . . .
> / >| . . . . . .. .
> /. . . >| . . . .. . .
>
>">" indicates reaction from the ground into which the rods are driven.
>It doesn't take too much ground reaction to insure that most of the
>load is on first rod, not the second. The second simply stiffens
>the first...it's a significant addition, but certainly less than
>half the load is borne by it. Did I miss something in your
>comments on this one? Certainly tension is better than bending,
>but with something like a 2" or 3" pipe for Rod 1, it becomes a
>lot like a deadman made with pipe except you don't have to dig a
>hole for it and it doesn't have as much ground to pull against.
Ok, I see what you're doing, but you haven't analyzed the reaction
forces quite correctly. The top of prime rod is now a third class
lever dependent on the long moment arm from ground to the back stay.
It resists this force purely by it's bending resistance. The bottom
portion is restrained as you show primarily by the mass of the overburden.
The back anchor is a little more complex, the pivot will be somewhere
below ground level. The exact point will depend on soil characteristics.
So it will have overturning forces in both the fore and aft directions.
If the prime pipe is buried 50% in the ground, then the back anchor
bears half the load of the guy and the overburden of the prime anchor
bears the other half.
Using heavy wall 3 inch pipe should be sufficient to resist the bending
moments for a typical ham tower with maximum guy tensions under 3000 pounds.
But the overburden isn't as good as we'd like. We need at least 3000
pounds of overburden to resist the maximum guy tension. Whether we
have this much effective overburden or not is dependent on the cohesiveness
of the soil. It's probably good enough against steady pulls in heavy clay,
but wouldn't be sufficient in a sandy soil. The problem with this simple
analysis is that it disregards the impulse forces from gusting. In that
case, the anchors can be rocked sufficiently to break soil cohesion and
work their way loose. That's why a deadman buried perpendicular to the
guy is valuable. It's not subject to rocking forces. And it's why concrete
is valuable, it has known cohesion and spreads the loads to the overburden
in a predictable way.
Gary Coffman
>>[I wrote]
>>A deadman is a good plan. Even pressure treated wood will rot
>>out fairly quickly in some soils though. A heavy walled galvanized
>>steel pipe makes a better deadman. Weld the emerging guy rod
>>to the deadman forming a 'T'. A couple of bags of ready mix
>>concrete will set the deadman in place in it's trench. Pour
>>a cylinder of concrete around the emerging rod to protect it
>>from corrosion as well. Then backfill and compact the soil.
>
>Pressure treated wood creasote will out last unprotected steel by a
>considerble margin. Several spieces of untreated wood will out last
>steel. One in particular is Boi's deArc sp? I know of a corner post
>that has been in place over 70 years. Only the heart wood is decay
>resistant.
This is rather dependent on the particular soil chemistry of the site.
Unprotected steel corrodes rapidly in acid soils with high moisture
content. But creosote treatment is now EPA banned as a buriable wood
preservative, as are the copper sulphate pressure treatments still
allowed above ground. There are other treating agents, but long
term survivability hasn't been well established in various soils.
Concrete encased steel has a long established record of survival
in hostile soil environments. Osage Orange, ironwood, does survive
well in many soils, however, and is a potential wood substitute.
>Concrete around steel is better than steel but in salt water enviorments
>the Steel will rust out of the concrete in a few years and imersed wood
>will out last reenforced concrete.
There's a special concrete for marine environments that contains a
rubberlike substance that protects the steel.
>Some clay soils are very bad about moving as they cycle from wet to dry.
>North of Dallas Texas to get a corner post to hold we set 3 10 inch
>creasote post 10 feet long in 2 foot by 5 foot holes and back filled with
>gravel we also placed a dead man between the corner and second post. Any
>thing less would pull out of the ground in short order.
Yes. This is a problem for vertically set posts acting as second class
levers. Concrete stabilized perpendicular deadmen are much better under
these conditions. There's one condition where use of concrete coated
deadmen isn't a good idea. That's in extremely waterlogged soil, such as
is found in swamps. They can actually float out of the ground. In that
situation, you have to resort to a network of interlaced deep pilings.
>If you are going to use steel under ground make sure it is well protected
>with concrete above the ground line and shaped so that water will not
>stand on the steel also make sure the top is sealed so that water does not
>run down the inside.
Yes. If your soil conditions are unusual you should definitely consult
a civil engineer experienced in that soil's mechanics. It's not a bad
idea anyway if failure of your structure could possibly result in
harm to others, or cause extensive property damage.
Tom Bruhns
(lots deleted...)
: If the prime pipe is buried 50% in the ground, then the back anchor
: bears half the load of the guy and the overburden of the prime anchor
: bears the other half.
back anchor. It's quite possible for the prime anchor to bear all the
load in some circumstances, in which case the back anchor is not
required to bear any load.
: Using heavy wall 3 inch pipe should be sufficient to resist the bending
: moments for a typical ham tower with maximum guy tensions under 3000 pounds.
etc. ...
I'd like to thank all for their comments, but I feel a need to inject some
realism here. This isn't a "typical ham tower," but a "natural antenna
mast" which at the moment is self-supporting. If I really wanted to put
up a tower at that location, I'd pay for a concrete pumper to pump some
mud over there and be done with it. But this is supposed to be a cheap-
and-dirty installation to get as much life out of the mast as possible.
The tree grew to about 120 feet and then, rather suddenly a couple years
ago, died. It's sound, and I can keep the part above ground pretty sound
for some time, and the base isn't very likely to move, but it will fall
over within a few years if I don't give it some encouragement to stand.
When it falls, I'll move that end of the antennas (wires) to another
nearby tree. In the mean time, I'm looking for things that are
--cheap
--reasonably easy to install
--don't involve concrete
--maybe even use materials on hand at the location
(someone suggested using a boulder, and if I had an underground
boulder detector, that might work. But it did get me to thinking
about other things in the area that might be sturdy enough to
anchor a guy.)
The tree in question is (was?) a Hemlock, a bit over 2 feet diameter
at the base, and now completely devoid of foliage (so rather little
wind resistance, as such trees go). It probably weighs 5000 to 10000
pounds, but most of that is near the ground.
73, K7ITM
Doug Snowden
that I have learned a lot - but - I was sort of planning the following:
(blast me if you wish) 3 inch diameter (heavy wall) steel pipe of about 8 ft
long. I was planning on digging down about 3 feet with a shovel. Then in that
hole dig with a post hole digger another 3 feet. Put the pipe in and surround
all of it with concrete. Then use one of my screw anchors as a back stay tied
to the top of the steel post which should be a couple of feet or so out of the
ground. That takes care of two guys (if approved by the majority). My original
"problem guy" was one that is a bit close to the tower (probably 25% too close).One suggestion was similar to what I plan for the two guys I just mentioned.
What about using (just for the close guy) two guys that are 45 degrees off of
the center line of the tower leg? The problem I see is in getting them to pull
equally on the tower. I do have torque clamps to clamp around the tower at the
guying point.
Regarding the shrinking / expansion of guy wires. I always thought
that guy wires got tighter in the winter time. Seems to me that I have heard
of people up North putting towers up in the Summer time and when Winter came,
they actually had guys break because they got tighter.
Well Enough, Doug, N4IJ