Self Supporting Rohn 25G
B Nehl
I am interested in others experience in putting up a
Self Supporting Rohn 25G tower.
How high did you go?
How much antenna load do you have on it?
Are you using a rotor?
Problems?
How large a base did you pour?
Thanks & 73,
Bryan - k0emt
CAM
This life and death subject has no room for antidotal experiences.
Please obtain the necessary specifications and requirements directly
from Rohn, POBox 2000, Peoria, Il 61656 (309)697-4400. For example,
the allowable antenna area for a 30ft self-supporting 25G tower
exposed to ice and 90mph winds is ZERO.
--
http://www.mindspring.com/~w6rca
B Nehl
>Please obtain the necessary specifications and requirements directly
>from Rohn, POBox 2000, Peoria, Il 61656 (309)697-4400. For example,
>the allowable antenna area for a 30ft self-supporting 25G tower
>exposed to ice and 90mph winds is ZERO.
I agree that the Rohn specs & requirements should be followed.
I have been to the Rohn website (www.rohn.net) and have sent an email
to them detailing my plans and seeking their recommended base size.
However, I am still interested in knowing what others have done.
Problems, etc that others have run into. The group I run with tends
to "over-engineer." Can a base ever be "too-big?"
73,
Bryan - k0emt
'Doc
If I remember correctly, Rohn 25g can be un-guyed up to
50 feet. I also think that encludes an 'eave' brace on a
house. It just depends on what you 'hang' on the tower.
As to how large the base/pier should be, going slightly
larger than what Rohn recommends won't hurt a bit. doing
it 'right' the first time is always better than re-doing it.
'Doc
Peter Bertini
> Problems, etc that others have run into. The group I run with tends
> to "over-engineer." Can a base ever be "too-big?"
>
> 73,
>
> Bryan - k0emt
Over-engineering in this case is good. Get the Rohn data and follow it.
Wind loading changes with geographical area as well, what works in
central Maine may not last in the Texas Gulf.
Pete
CAM
> However, I am still interested in knowing what others have done.
The guy who says, "I just stuck it in the ground with no concrete and
it has worked fine for six months", may experience a catastrophic
failure at any time, including death. Best to trust the Rohm engineers.
--
http://www.mindspring.com/~w6rca
Peter Bertini
"'Doc" <w5...@oio.net> wrote in message news:3A07266A...@oio.net...
Rohn 25 will not self-support at 50 feet--the only time this is done is
when a Hazer system is raising or lowering the antennas on hopefully
a very, very calm day. If a house bracket is used, it is no longer a
self supporting tower, and Rohn has published guidelines for these
installations as well.
Also, the base requirements differ for different style bases. For example,
a foldover base requires a minimal base, but it can only be used on guyed
towers regardless of the number of square yards of concrete used below
ground. It is very risky to accept anedoctal advice from newsgroup
participants, especially when the specifics for your tower aren't specified.
The Rohn engineering plans are a must, IMHO; since there are insurance
and safety issues, as well as zoning regulations, that come into play as
well.
Pete
Crazy George
insurance and safety. Years ago, someone might get away with a tower
falling on a neighbor's property with little lasting ill effect. Now,
however, as they say, in today's litigious society, I sure would want to be
able to say: "It was installed to the manufacturer's specifications plus a
50% safety factor." if something untoward happened. And, it seems like the
weather is getting wilder. We had a couple dozen power poles snapped in the
middle in a thunderstorm yesterday, and that used to never happen. When I
was a kid, back when dirt was new, I put up a tower with minimal guying, and
sure enough, it blew down. Put a couple of holes in the roof, and broke
most of the elements on one side of the tribander, and bent one of the tower
sections. I made it a point that would never happen again. So I have a
whole file of Rohn, Andrew, and Hy-Gain commercial tower specs. It sure
makes the cement companies happy when I install a new tower now.
--
Crazy George
Peter Bertini <comm...@erols.com> wrote in message
news:8u7f0u$q44$1...@bob.news.rcn.net...
>
> "'Doc" <w5...@oio.net> wrote in message news:3A07266A...@oio.net...
> > Bryan,
> > If I remember correctly, Rohn 25g
<snip>
>
>
> Rohn 25 will not self-support at 50 feet--
<snip>
Joe Schlatter
follow it to the letter, if you have questions, contact Rohn. Do not rely
on the experiences of folks on the newsgroup, some of whom may tell you "Dig
a hole until it looks big enough and fill it with concrete." When the whole
thing crashes down, taking a big piece of your roof, your wife's car, and
your neighbor's brand new SUV, the insurance company will deny your claim
based on Rohn's figures, not on what Good Ol' Boy Engineering told you.
You can work the world on any old piece of wire fed with any old piece of
cable. You can work DX with a one-transistor rig. It's fine to experiment
with wires and flea power but when it comes to a tower, everything must be
strictly professional or someone will get killed.
--
Regards,
Joe Schlatter
joeN...@schlatter.org
http://www.schlatter.org/
http://www.miafacts.org/
Amateur Radio Extra Class call sign W4HH
B Nehl <k0...@dbbear.com> wrote in message
news:1a2e0t0fambivicl6...@4ax.com...
> >This life and death subject has no room for antidotal experiences.
> >Please obtain the necessary specifications and requirements directly
> >from Rohn, POBox 2000, Peoria, Il 61656 (309)697-4400. For example,
> >the allowable antenna area for a 30ft self-supporting 25G tower
> >exposed to ice and 90mph winds is ZERO.
>
> I agree that the Rohn specs & requirements should be followed.
> I have been to the Rohn website (www.rohn.net) and have sent an email
> to them detailing my plans and seeking their recommended base size.
>
> However, I am still interested in knowing what others have done.
'Doc
Peter Bertini,
I dug out the Rohn spec book. The eave braced tower
is considered a 'non-guyed' tower. I'll admit the spec-
book is a bit old, but I doubt if they would change their
minds...
'Doc
Peter Bertini
"'Doc" <w5...@oio.net> wrote in message news:3A08080B...@oio.net...
Hello 'Doc...
I think the original wording was "Self Supporting", not 'non-guyed'.
73
Pete
Jerry Oxendine
This thread brings up a question for me. My 25G is 60', non-guyed, 5
feet in the ground, concrete, corner braced at 2 points to the house.
It sits in a "L" shaped part of the house and braced on 2 sides. At
50', before I extended it, it stood thru Hurricane Hugo in '89. Do I
have safety issues here? (Winds in that Hurricane were 96+ gusts).
TNX,
Jerry
K4KWH
Peter Bertini
"Joe Schlatter" <j...@schlatter.org> wrote in message > I'll dig out my Rohn
>
> I had a 40' 25G with NO concrete -- it was on a base staked into the
> ground -- eave bracket at 30' and it was rated at a lot of MPH with the
> 10 sq ft of antennas I had on it.
>
> --
> Regards,
> Joe Schlatter
>
> Respond to: j...@schlatter.org
I can believe that. With a 40' tower firmly attached to the house at the
30' mark, there would be very little leverage applied against the tower
base.
Pete
Joe Schlatter
jox...@bellsouth.net wrote:
> Doc,
>
> This thread brings up a question for me. My 25G is 60', non-guyed, 5
> feet in the ground, concrete, corner braced at 2 points to the house.
> It sits in a "L" shaped part of the house and braced on 2 sides. At
> 50', before I extended it, it stood thru Hurricane Hugo in '89. Do I
> have safety issues here? (Winds in that Hurricane were 96+ gusts).
>
> TNX,
>
> Jerry
> K4KWH
>
I'll dig out my Rohn spec book but I'll bet that a 60' tower in 5' of
concrete (how many yards?), with house brackets at two points is rated
for very high winds.
I had a 40' 25G with NO concrete -- it was on a base staked into the
ground -- eave bracket at 30' and it was rated at a lot of MPH with the
10 sq ft of antennas I had on it.
--
Regards,
Joe Schlatter
Respond to: j...@schlatter.org
Sent via Deja.com http://www.deja.com/
Before you buy.
Roger Halstead
properly installed self supporting 25 G are: 70 MPH wind survival and *NO*
ice...At a 40 foot maximum for a 25 G the maximum allowable wind load is 1.5
sq. ft of antennas consisting of "round" tubing.
--
Roger Halstead (K8RI) www.RogerHalstead.com
N833R World's Oldest Debonair? s# CD-2
"B Nehl" <k0...@dbbear.com> wrote in message
news:o1nd0toa0v6rqtmfc...@4ax.com...
> This seemed like the best newsgroup for this.
> I am interested in others experience in putting up a
> Self Supporting Rohn 25G tower.
>
> How high did you go?
> How much antenna load do you have on it?
> Are you using a rotor?
> Problems?
> How large a base did you pour?
>
kl7ifp
of 90 plus winds .... 120 knots so far been the greatest gust that it has
with stood. only reason I didn't do the 3x3x5 that was manufacture recommend
was hit bed rock 3 feet down.
Dick Carroll
>
> I got a 4X4 X3 under my tower that is self supported and it has survive many
> of 90 plus winds .... 120 knots so far been the greatest gust that it has
> with stood. only reason I didn't do the 3x3x5 that was manufacture recommend
> was hit bed rock 3 feet down.
I once had a 50 ft Rohn 25 set in a cubic yard of concrete, unguyed,
with a tribander and stacked Cushcraft 11 el 2 meter yagis on top. It
stayed up FB for about 6 years, through some pretty daunting winds, and
would probably still be there if not for one late winter day when Mother
Nature played one of her tricks...
Feb 28, '82 began sunny and warm, a really nice late winter day
portending an early spring. But in late afternoon, a Blue Norther blew
in, rain changed to freezing rain, the Rohn 25 became a huge 14 inch
icicle, and the heavily gusting winds from the north really whipped it
around. I wondered if it would stay up, and late that evening as a
virtual blizzard howled away, it came down, falling south, kinked over
at the base just above the concrete. It fell across a storage shed and
the end of tribander boom just nicked the roof of the house, taking down
the rain gutter.
One of the Cushcraft 11's was history, but the other and the tribander
were in pretty good shape for the ride they had gone through. They now
reside atop the replacement 60ft unit, also set in a cu yard of
concrete, which has a single set of stainless steel guy cables at the
50 ft level, and over the past 15 years has withstood everything Mother
could toss at it, so far.
Brian Kelley can explain it in Mechanical Engineerese, but I know
that what happened is that the buffeting winds caused the tower to whip
back and forth, and with the heavy ice load, a strong wind gust caught
it leaning the wrong way, and with the added ice load it overpowered the
lower part of the tower's mechanical strength to withstand it all, and
over it came. Note that the 4x4x4ft concrete base didn't budge.
While such weather events are rare in this part of the world, I am
lucky that it wasn't situated where it could come through the middle of
the roof - mine or someone else's. No more freestanding rigs for me.
And none situated where it could possibly come down on property
belonging to others. The present version is located alone in the middle
of a 150x150ft lot. If it should succumb to one of Mom's whims at least
it misses everything but the earth.
Dick
Louis Bybee
wish I had such material available where I lived. If oversized holes
were drilled into the rock at an angle, and Epoxy used to retain the
Rebar, which was bent vertical after leaving the rock, the result could
be unequaled support, unavailable without great expense!
Louis
kl7ifp wrote:
>
> I got a 4X4 X3 under my tower that is self supported and it has survive many
> of 90 plus winds .... 120 knots so far been the greatest gust that it has
> with stood. only reason I didn't do the 3x3x5 that was manufacture recommend
> was hit bed rock 3 feet down.
Brian Kelly
Dick Carroll wrote:
>
>
> Brian Kelley can explain it in Mechanical Engineerese,
>
Thanks a whole bunch Richard, I intentionally stayed away from this thread because
I knew half the denizens of this NG would quite properly and predictably point
the guy toward the Rohn tower installation specifications and requirements so I
didn't add to the din. But since you mentioned it . .
>
> but I know
> that what happened is that the buffeting winds caused the tower to whip
> back and forth, and with the heavy ice load, a strong wind gust caught
> it leaning the wrong way, and with the added ice load it overpowered the
> lower part of the tower's mechanical strength to withstand it all, and
> over it came.
>
Cometh another short-form lecture on applied mechanics, the basic field spanning
several engineering disciplines which deals with the behavior of structures under
load.
>
The deal goes something like this: An unguyed tower sticking up out of the ground
is a simple "cantilever beam" as are are the wings of an F-16. All beams will fail
when loaded to a point which exceeds the material strength. In the case of low
carbon steel which is what Rohn uses the failure stress ("yield stress") is around
30,000 Lbs. per square inch. A one inch square steel bar pulled like a length of
rope is on the edge of failure when the load goes up to 30,000 Lbs. Failures can
occur due to either compression (column collapse) or tension (break rope). Tower
legs usually fail first as columns vs. tension failures. Which is why when you
examine a failed tower you usually see one leg really crumpled and the other two
legs just bent over. The crumpled leg should be on the downwind side of the tower
which was in compression when it crapped out.
>
For simplification visualize a 10 ft. length of pipe poking up out of a concrete
base rather than a complex structure like a tower. Pull horizontally (wind load on
the antennas) on the top of the pipe with a force of 200 Lbs. If you multiply the
wind load by the length of pipe you get a quantity called the "bending moment", in
this case 200 x 10 = a 2,000 ft-lb bending moment. The bending moment in a simple
cantiliver beam varies from zero at the top to it's maximum value at the point
where it enters the concrete.
>
Whether or not a 2,000 ft-lb bending moment is enough to fail the pipe obviously
depends on the geometry of the pipe. Common sense indicates that a 10" diameter
pipe with a 1" thick wall will not fail but a 1/2" diameter pipe with a 1/16" wall
will be history. Thus all beams have what is called the "cross section moment of
inertia" ("I"), the number which defines the effect of the physical geometry of
the beam. For common structural shapes like standard pipe "I'" can be looked up in
published tables which makes checking pipe antenna masts a fairly simple process.
For more complex structures like tower sections with three legs and cross bracing
ya got a real rat's nest of calculations to deal with.
>
The third factor which enters into the analysis is the orientation of the load
with repect to the orientation of the geometry of the beam. A 2x4 for instance
will take a much higher load if pulled in one direction than in the other. The
number which defines this effect is "c", the distance from the "neutral axis" of
the geometry to the "extreme fiber" in inches. In the case of a 3" diameter pipe
the neutral axis is simply the axial centerline of the pipe and c=1.50 inches.
Once again, determining "c" is another rat's nest when dealing with more complex
structures.
>
Roll all these factors together and plug the numbers into a very simple equation
s=Mc/I and bingo you'll have the maximum stress in the tower or mast or whatever.
Which in the case of a tower sticking up out of a concrete base always occurs at
the surface of the concrete. If the result is anywhere near 30,000 Lb. per square
inch for a steel structure you better go back to the drawing board and either get
rid of some load or beef up the cross section geometry.
>
Reality is much more complex than my simplistic rant on the subject but the basic
relationships are there. There's a whole stack of additional factors which also
need to be cranked into a realistic analysis. A secondary load called the "shear
stress", the non-uniform but distributed wind load on the tower itself in addition
to the point loads created by the antennas and mast, stress concentration factors,
corrosion allowances, the design safety factor, determination of the failure mode,
tension or compression buckling of one of the legs, etc.
>
Which in a nutshell is why you put towers up by the book and don't get stupid and
try to outguess the pros who designed the tower by pushing their published loading
and installation envelopes.
>
>
> Note that the 4x4x4ft concrete base didn't budge.
>
There are two kinds of bases. The base for a guyed tower is there simply to keep
the tower from sinking into the ground because the guys take the horizontal loads,
the base of the tower is loaded in compression, not in bending except in specific
odd circumstances like not enough guying. It might be noted that the guys only
take out the horizontal load on the tower. They *add* vertical load to the tower.
Trig 101. Therefore the vertical load on the base and the tower legs is the dead
weight of the whole shebang *plus* the downward component of the wind load on the
guys. Given enough wind you can collapse a guyed tower and/or the base straight
into the ground. Which is why once again you pay attention to the book and don't
anchor the guys too close to the tower.
>
In the case of a freestander the primary function of the (much larger) base is to
act as a sort of counterweight which balances out the wind load at the tipover
pivot point. Gets into soil mechanics, etc. In all cases more concrete deeper is
always better.
>
>
> While such weather events are rare in this part of the world, I am
> lucky that it wasn't situated where it could come through the middle of
> the roof - mine or someone else's. No more freestanding rigs for me.
>
You got bit too hard. Lotsa freestanders out there which can take the loads.
Lookit all the freestanding cell phone poles. Ya just don't push the numbers.
>
>
> And none situated where it could possibly come down on property
> belonging to others. The present version is located alone in the middle
> of a 150x150ft lot. If it should succumb to one of Mom's whims at least
> it misses everything but the earth.
>
AMEN.
>
Hey, Dick - Put another set of guys on that tower willya?
>
>
> Dick
>
w3rv
Dick Carroll
> Which in a nutshell is why you put towers up by the book and don't get stupid and
> try to outguess the pros who designed the tower by pushing their published loading
> and installation envelopes.
Nutshell/thumbnail, the weight of all that ice, probably a lot more
than the tower itself, moving in the same direction as the wind gust
that broke it, just proved too much load, and at the fulcrum, at the
base, it gave way. No way I could have forseen that, but I DID plan it
to be far enough away from the house to miss it if it did come down.
Except for the raingutter, I was right on that score.
> In the case of a freestander the primary function of the (much larger) base is to
> act as a sort of counterweight which balances out the wind load at the tipover
> pivot point. Gets into soil mechanics, etc. In all cases more concrete deeper is
> always better.
Outfit I used to work for had a 350 footer, wide base freestanding,
that was hit by a tornado on the other end of the state. For a long time
I kept a photo of the hunk of concrete that one leg pulled out of the
ground. Helluva a chunk it was, too. MANY cubic yards. Then it laid the
tower across US36.
> >
> > While such weather events are rare in this part of the world, I am
> > lucky that it wasn't situated where it could come through the middle of
> > the roof - mine or someone else's. No more freestanding rigs for me.
>
> >
> You got bit too hard. Lotsa freestanders out there which can take the loads.
> Lookit all the freestanding cell phone poles. Ya just don't push the numbers.
> >
After all my towering experiences, it just seems natural to ask- just
how much are these installations professionally overengineered? I think
its a given that any vendor or engineer would make absolutely,
positively sure that no one ever could, for any concievable reason, be
able to point the finger backward after any tower came down, so that
naturally means "overdone". By how much?
> Hey, Dick - Put another set of guys on that tower willya?
>
I would've bet that was coming <BSEG>. Point is, the darn thing has
stood there 15 years, through some hellacious Midwestern winds, without
flinching. And after previously closely watching the freestander that
the iceload took down, I really believe *it* would still be there
without the ice storm. So really, What's the deal?
In fact, if I read your detailed info right, another set of guys would
add more vertical compression. I know that they would also stabilize the
middle and forestall twisting - but thats why I put them at 50 ft
instead of the top (60), and I haven't detected anything that looks like
a deficiency or any hint of problem. A middle set wouldn't keep it up if
one of the top guys failed. Explain for us all, pse. Us backyard
injuneers want to know.
BTW I did a bit of reading back when working about how towers fail in
earthquakes, since I had New Madrid in my area of responsibility. Turns
out that the freestanders fare better than guyed types, which suffer
slackening in one set of guys as the first earthquake wave arrives, and
the opposite guys, still tight, pull the beast down. The freestander
just sways and stays put....some of the time, anyway.
tnx, Brian
Dick
> >
> >
> > Dick
>
> >
> w3rv
Roger Halstead
--
Roger Halstead (K8RI) www.RogerHalstead.com
N833R World's Oldest Debonair? s# CD-2
"Louis Bybee" <lou...@datacomm.com> wrote in message
news:3A0F4764...@datacomm.com...
> How about a number of stout Rebar pieces drilled into the Bed Rock? I
> wish I had such material available where I lived. If oversized holes
> were drilled into the rock at an angle, and Epoxy used to retain the
> Rebar, which was bent vertical after leaving the rock, the result could
> be unequaled support, unavailable without great expense!
Cost of "one" 5/8" X 12" long drill bit for hammer drill is over $50
You'd probably want to go at least 18" if not 24. Depends on the rock. If
it's granite you'd need a diamond drill and they make the hammerdrill bits
look cheap.
Good hammer drill is $200 give or take.
I had one of the good industrial ones (5/8ths inch, not 1/2 inch, with 8 amp
motor) and it caught fire on the second day. (totaled it, but they replaced
it no questions asked)
You might be able to find one at a rental agency, but the drill bits could
get realy expensive.
It takes a really good set of shoulder and arm muscles to keep from getting
hurt when the thing hangs up. <:-))
I had an electrician friend get one hung up and the power cord pulled his
thumb out by the roots. Completely tore it off.
Roger (K8RI)
B Nehl
FWIW, when I contacted Rohn, they told me I needed a 4x4x4' base.
A bit bigger than I had expected, but I'm over half there now.
I would still like to hear about pitfalls to avoid, etc.
This is my first go around with a tower, so I'm
trying to "learn from others mistakes."
I'll be making my base slightly deeper than 4' so I can line the
bottom with gravel - for drainage. I've heard some people also
put a first layer of sand down. However, an army engineer
that I talked with reccommended skipping the sand. We have
a mostly clay & rock soil here and he thought it would just
hold the moisture.
The base of the tower will be wider at the bottom than the top.
The sides are "scalloped." The corners are square.
I will have at least 4" of concrete above ground so that water
won't run over and into the base where the bottom section
protrudes.
I will be making a "basket" of 1/2" re-bar around and through
the bottom section. (Neither the re-bar nor the section will
be in contact with soil. Avoid rust.)
My ground rod will go into the earth beneath the base,
attaching to re-bar/tower section and protrude through top
of concrete.
The Army engineer also suggested I coat the bottom section with
oil to help with rust prevention.
I guess one of the fun parts will be trying to get the bottom section
aligned correctly. (I'll be using a standard 10' section.)
I'm thinking 4' level and/or maybe a plum-bob.
I'll be using 4500psi concrete as it's only $4 more a yard then
3000psi. (Oh yeah, make sure ground is damp before pouring so
that the ground doesn't suck the moisture out of the concrete.)
I'll let the concrete cure for 30+ days before going to the tower
erection phase.
Am I missing anything?
73,
Peter Bertini
> Thanks for all the comments guys.
> oil to help with rust prevention.
>
>
> 73,
>
> Bryan
>
tar
{roofing cement?) where it will be in contact with the cement. It should
also be
mentioned in the spec sheets.
Pete
WE0H
base? I would think that if the ground stake was under the base and attached
to the rebar in the concrete, that if lightning hit the tower the current
would be flowing through the rebar, heating the concrete till it exploded.
Dick Carroll
several 2ft steel rods into the sides of the empty hole, so that the
earth was effectively tied to the concrete after it was poured. This
effectively gives you the ground surrounding the base as a part of it.
73, Dick W0EX
B Nehl wrote:
>
> Thanks for all the comments guys.
> FWIW, when I contacted Rohn, they told me I needed a 4x4x4' base.
> A bit bigger than I had expected, but I'm over half there now.
>
> I would still like to hear about pitfalls to avoid, etc.
> This is my first go around with a tower, so I'm
> trying to "learn from others mistakes."
>
> I'll be making my base slightly deeper than 4' so I can line the
> bottom with gravel - for drainage. I've heard some people also
> put a first layer of sand down. However, an army engineer
> that I talked with reccommended skipping the sand. We have
> a mostly clay & rock soil here and he thought it would just
> hold the moisture.
>
> The base of the tower will be wider at the bottom than the top.
> The sides are "scalloped." The corners are square.
>
> I will have at least 4" of concrete above ground so that water
> won't run over and into the base where the bottom section
> protrudes.
>
> I will be making a "basket" of 1/2" re-bar around and through
> the bottom section. (Neither the re-bar nor the section will
> be in contact with soil. Avoid rust.)
>
> My ground rod will go into the earth beneath the base,
> attaching to re-bar/tower section and protrude through top
> of concrete.
>
> The Army engineer also suggested I coat the bottom section with
> oil to help with rust prevention.
>
> I guess one of the fun parts will be trying to get the bottom section
> aligned correctly. (I'll be using a standard 10' section.)
> I'm thinking 4' level and/or maybe a plum-bob.
>
> I'll be using 4500psi concrete as it's only $4 more a yard then
> 3000psi. (Oh yeah, make sure ground is damp before pouring so
> that the ground doesn't suck the moisture out of the concrete.)
>
> I'll let the concrete cure for 30+ days before going to the tower
> erection phase.
>
> Am I missing anything?
>
> 73,
>
> Bryan
Dick Carroll
>
> When I installed my base (3x3x3ft)I first dug the hole then drove
> several 2ft steel rods into the sides of the empty hole, so that the
> earth was effectively tied to the concrete after it was poured. This
> effectively gives you the ground surrounding the base as a part of it.
>
I should have said "drove several 2ft steel rods a about halfway into
the sides of the empty hole..."
Rebar pieces will work.
Dick
Brian Kelly
Dick Carroll wrote:
> Brian Kelly wrote:
>
>
> Nutshell/thumbnail, the weight of all that ice, probably a lot more
> than the tower itself, moving in the same direction as the wind gust
> that broke it, just proved too much load, and at the fulcrum, at the
> base, it gave way. No way I could have forseen that, but I DID plan it
> to be far enough away from the house to miss it if it did come down.
> Except for the raingutter, I was right on that score.
>
Might have been some additional nasties at work. You indicated in an earlier post that
the tower was swaying before it flopped over. Might be that with all that ice there
could have been a big inertial "flywheel effect" in play in addition to the straight-in
wind load. Basically the tower was fighting the swaying but the weight of the ice simply
overstressed a leg at the base during the terminal rotation. These sorts of
considerations move the matter into the realm of dynamic mechanics, vibrations and
material fatigue which becomes a whole new rat's nest. In the end you probably had a
combination of sources of stresses at work. The weight of the tower itself, the weight
of the ice, the static wind load and a cyclic rotational dynamic load. They all added
together at a critical moment and over she went.
>
>
> > In the case of a freestander the primary function of the (much larger) base is to
> > act as a sort of counterweight which balances out the wind load at the tipover
> > pivot point. Gets into soil mechanics, etc. In all cases more concrete deeper is
> > always better.
>
> Outfit I used to work for had a 350 footer, wide base freestanding,
> that was hit by a tornado on the other end of the state. For a long time
> I kept a photo of the hunk of concrete that one leg pulled out of the
> ground. Helluva a chunk it was, too. MANY cubic yards. Then it laid the
> tower across US36.
>
When you get into tornados all bets are off, you forget the book, run like hell and
pray. Some time when you get to downtown St. Louis check out what's left of their
ancient monster radio tower. A tornado blew most of the thing over I think sometime in
the 30s or 40s and dropped it thru an apartment building and killed something like 14
people.
>
>
> > >
> > You got bit too hard. Lotsa freestanders out there which can take the loads.
> > Lookit all the freestanding cell phone poles. Ya just don't push the numbers.
> > >
>
> After all my towering experiences, it just seems natural to ask- just
> how much are these installations professionally overengineered?
>
All of them. "Depending".
>
> I think
> its a given that any vendor or engineer would make absolutely,
> positively sure that no one ever could, for any concievable reason, be
> able to point the finger backward after any tower came down, so that
> naturally means "overdone". By how much?
>
The grunt engineer can run the numbers and via straight up physics design a tower which
has a specific failure load and expected life. From there it gets "overdesigned" by it's
chosen design safety factor which is some number like 2X, 4X, 10X etc. It basically gets
down to management decisions on risk vs. cost, tower industry design standards, building
codes and lawyers and fear thereof. None of which have much if anything to do with the
physics. I'm not in that biz but I'll guess they get overdesigned by somewhere around
500%.
>
>
>
> > Hey, Dick - Put another set of guys on that tower willya?
> >
>
> I would've bet that was coming <BSEG>. Point is, the darn thing has
> stood there 15 years, through some hellacious Midwestern winds, without
> flinching. And after previously closely watching the freestander that
> the iceload took down, I really believe *it* would still be there
> without the ice storm. So really, What's the deal?
> In fact, if I read your detailed info right, another set of guys would
> add more vertical compression. I know that they would also stabilize the
> middle and forestall twisting - but thats why I put them at 50 ft
> instead of the top (60), and I haven't detected anything that looks like
> a deficiency or any hint of problem. A middle set wouldn't keep it up if
> one of the top guys failed. Explain for us all, pse. Us backyard
> injuneers want to know.
>
It depends on how big your antennas are and I have no clue. But for discussion puposes
I'll assume a healthy stack of HF beams on a longish mast which is to say a decent wind
load. Visualize how the tower will bend in a heavy wind. The base ain't going anywhere.
The point at which the tower is guyed ain't going nowhere, either. But given enough wind
on the antennas the tower will rotate with the guy point acting as the upper pivot
point. It'll bend outward into the wind in an arc with the point of maximum lateral
deflection being around the midpoint between the guy bracket and the base. This could
set up a really nasty potential column failure scenario. The guys will impose their
compression load on a long skinny bent column. It's a double-whammy because the more you
bend a column the weaker it becomes at a huge rate, it gets many times weaker per pound
of compression load the more the tower gets bent and you can get into a runaway
situation.
>
The fact that your guys are ten feet down from the top is not necessarily in the right
direction. That configuration definitely increases the "leverage" the wind has for
bending your tower. There's an optimum guy bracket location which could be determined by
a lot of numerical engineery pushups and it could just be that the 50ft level ain't even
close to where it should be guyed.
>
The purpose of the center set of guys is to prevent the tower from bending in the first
place thus completely eliminating the prospect of a column bending failure. A straight
tower can take many time more times downward guy-induced compression load than it can
when it's a bent tower. In your particular case your tower might be plenty stiff enough
for it's loading conditions and won't bend enough to be concerned about not having the
second set of guys. Ya hafta get really specific about the numbers before any real-world
conclusions can be drawn.
>
Gets back to the Rohn specs: If Rohn sez guys every 30 ft just do guys every 30 ft.
Y'know?
>
>
> BTW I did a bit of reading back when working about how towers fail in
> earthquakes, since I had New Madrid in my area of responsibility. Turns
> out that the freestanders fare better than guyed types, which suffer
> slackening in one set of guys as the first earthquake wave arrives, and
> the opposite guys, still tight, pull the beast down. The freestander
> just sways and stays put....some of the time, anyway.
>
Yupper! Tornados = 'quakes = BOOGIE outta there right now!
>
>
> tnx, Brian
>
> Dick
>
Brian dit dit.
Dick Carroll
Yep, now -thanks to you- I know. I've already got the guy cable, and if
I can still climb that thing next spring your advice will be followed.
Now I understand the dynamic forces that come to play on the
installation.
Fact is I have only a medium size tribander just above the tower top,
with a single 2meter 11-eleven element and a 5/8 wave 2m GP, all on an
8ft mast. I've been thinking about replacing all that anyway, so next
spring looks like the time.
Tnx, Brian.
73, Dick
Brian Kelly
Dick Carroll wrote:
>
> Yep, now -thanks to you- I know. I've already got the guy cable, and if
> I can still climb that thing next spring your advice will be followed.
>
Climbing "issues" are one of the big reasons I'll be putting up some small crankup next time
around. Heh.
>
>
> Now I understand the dynamic forces that come to play on the
> installation.
>
> Fact is I have only a medium size tribander just above the tower top,
> with a single 2meter 11-eleven element and a 5/8 wave 2m GP, all on an
> 8ft mast. I've been thinking about replacing all that anyway, so next
> spring looks like the time.
> Tnx, Brian.
>
Go for it, you'll sleep better.
>
>
> 73, Dick
>
Brian
Roger Halstead
N833R World's Oldest Debonair? s# CD-2
"Peter Bertini" <comm...@erols.com> wrote in message
news:8v4m8l$jbn$1...@bob.news.rcn.net...
>
> "B Nehl" <k0...@dbbear.com> wrote in message
> news:5ncb1tomtk7lm517p...@4ax.com...
> > Thanks for all the comments guys.
> > > The Army engineer also suggested I coat the bottom section with
> > oil to help with rust prevention.
The towers (ROHN) are double hot dipped galvanized. There is nothing (that
I've ever seen) in their engineering and parts catelog about coating with
oil, or tar.
What they do have is a detailed section on prepareing the bottom of the hole
to get proper drainage for the tower base legs.
I'd be a bit concerned about using oil to coat the bottom as it would
migrate down and probably contaminate the material at the bottom and hinder
drainage.
It would depend on how much were used, but oil is not a permanent cure.
If I felt the need to coat the bottom of a tower (non galvanized like the
old American Standard, or American Steel ?), I'd use a material that would
not flow after application. Tar would be one that comes to mind.
Roger (K8RI)
> >
> > Am I missing anything?
> >
> > 73,
> >
> > Bryan
> >
Roger Halstead
N833R World's Oldest Debonair? s# CD-2
"Brian Kelly" <ke...@dvol.com> wrote in message
news:3A171F7E...@dvol.com...
>
>
> Dick Carroll wrote:
>
> >
> > Yep, now -thanks to you- I know. I've already got the guy cable, and if
> > I can still climb that thing next spring your advice will be followed.
>
> >
> Climbing "issues" are one of the big reasons I'll be putting up some small
crankup next time
I'm past 60 and still do all my own climbing. (97 foot ROHN 45G and a 90
foot American Standard) My wife put her foot down though and I had to quit
climbing towers for the young guys.<:-))
The past few weeks I've been climbing that 45G up to 6 times a day. I seem
to be getting in pretty good shape <G>Antenna installation and working on
the multiple rotor system.
The system uses concentric masts and will eventually have a rotor for each
once I get my machine shop set up.
Roger (K8RI)
Jim Fuller
>
....
> The system uses concentric masts and will eventually have a rotor for each
> once I get my machine shop set up.
Could you elaborate a bit? It has occurred to me that concentric
masts, with the big multi-band yagi on the outer mast and the vhf/uhf
beams on the inner (taller) mast, would be nice, but I have not seen
any commercial rotors that would work with the outer mast, allowing
the inner to pass through. And everyone else that I mention it to
seems to think that I'm daffy.
--
Jim Fuller
Peter Bertini
"Roger Halstead" <rdha...@tm.net> wrote in message
news:v8TR5.502$El3....@newshog.newsread.com...
> news:8v4m8l$jbn$1...@bob.news.rcn.net...
> >
> > "B Nehl" <k0...@dbbear.com> wrote in message
> > news:5ncb1tomtk7lm517p...@4ax.com...
> > > Thanks for all the comments guys.
> > > > The Army engineer also suggested I coat the bottom section with
> > > oil to help with rust prevention.
>
> The towers (ROHN) are double hot dipped galvanized. There is nothing
(that
> I've ever seen) in their engineering and parts catelog about coating with
> oil, or tar.
>
>
> > >
> > > >
> > Check with Rohn on this, but I believe they recommend coating the tower
> with
> > tar
> > {roofing cement?) where it will be in contact with the cement. It
should
> > also be
> > mentioned in the spec sheets.
> >
> > Pete
> >
The following is quoted in part from the Rohn Engineering Data and
Specifications Handbook;
copyright 1970 by Rohn Mfg. Co.
From the page titled INSTALLATION INSTRUCTIONS FOR #25 FOLD-OVER TOWER
dated Sept. 15, 1969...
"..... Before pouring the concrete, coat the base section in an area about
3" above and 3" below
the space where the top of the concrete base will be, using a waterproof
asphalt type material..."
Regards
Pete, K1ZJH
Roger Halstead
N833R World's Oldest Debonair? s# CD-2
"Jim Fuller" <jefu...@netscape.net> wrote in message
news:3A183780...@netscape.net...
> Roger Halstead wrote:
> >
> ....
> > The system uses concentric masts and will eventually have a rotor for
each
> > once I get my machine shop set up.
>
> Could you elaborate a bit? It has occurred to me that concentric
> masts, with the big multi-band yagi on the outer mast and the vhf/uhf
> beams on the inner (taller) mast, would be nice,
That's the way I'm setting it up.
The innermost mast ( 1 1/2" steel pipe) sets into a conventional
rotor...Hy-gain 300.
The outer mast is driven via a heavy duty chain drive with the rotor mounted
external to the tower, or it will when I get that far.
There are several ways which this could be accomplished. Gears, or chains
being the easiest.
With gears, the thing to remember is to either use a third gear so the mast
turns the same direction as the rotor,*or*, reverse the direction unit
readout. (lots easier)
The outer mast (2" ID steel pipe) extends on up to the bottom VHF antenna
so it adds lots of support.
The machine work involves making the adapters for either the sprockets, or
gears. It also takes a bit of metal fabrication and a little welding to make
the offset rotor mount.
Right now the only thing on the tower is a quadature array of TV antennas,
which kinda, sorta work. They work better than a single antenna, but they
are extremely sharp and have three very strong side lobes (indicating to me)
that the spacing is not wide enough.
As far as I know, no one is currently manufacturing systems like this, but
there were similar systems a few years back.
BTW, extending more than a few feet above the tower top adds greatly to the
wind load as well as adding a bending moment.
Roger (K8RI)
Roger Halstead
N833R World's Oldest Debonair? s# CD-2
"Peter Bertini" <comm...@erols.com> wrote in message
news:8va383$mf$1...@bob.news.rcn.net...
>
> "Roger Halstead" <rdha...@tm.net> wrote in message
> news:v8TR5.502$El3....@newshog.newsread.com...
> > Roger Halstead (K8RI) www.RogerHalstead.com
> > N833R World's Oldest Debonair? s# CD-2
> >
> > "Peter Bertini" <comm...@erols.com> wrote in message
> > news:8v4m8l$jbn$1...@bob.news.rcn.net...
> > >
> > > "B Nehl" <k0...@dbbear.com> wrote in message
> > > news:5ncb1tomtk7lm517p...@4ax.com...
<bunch snipped>
> The following is quoted in part from the Rohn Engineering Data and
> Specifications Handbook;
> copyright 1970 by Rohn Mfg. Co.
>
> From the page titled INSTALLATION INSTRUCTIONS FOR #25 FOLD-OVER TOWER
> dated Sept. 15, 1969...
>
> "..... Before pouring the concrete, coat the base section in an area about
> 3" above and 3" below
> the space where the top of the concrete base will be, using a waterproof
> asphalt type material..."
I haven't been able to find it in my copy, but it certainly makes sense as
that is the area where moisture can penetrate. The expansion and
contraction of the metal differes from that of the concrete and the
moisture as well as the air can penetrate about that far.
Roger (K8RI)
I'd not expect rust/corrosion any lower than that.
>
> Regards
>
> Pete, K1ZJH
>
>
Jim Fuller
>
....
> The innermost mast ( 1 1/2" steel pipe) sets into a conventional
> rotor...Hy-gain 300.
>
> The outer mast is driven via a heavy duty chain drive with the rotor mounted
> external to the tower, or it will when I get that far.
>
> There are several ways which this could be accomplished. Gears, or chains
> being the easiest.
That's sort of what I had concluded.-- that there is no off-the-shelf
equipment available to do it, so it would have to be custom. There
is also the matter of the thrust bearing(s) to take the weight of the
outer mast, and how to lock the rotor and boom(s) to the mast. Both
items seem to suggest welding plates onto the mast, since
throughbolts are not possible.
> As far as I know, no one is currently manufacturing systems like this, but
> there were similar systems a few years back.
I just got relicensed after a 20-year hiatus, and I am finding that
lots of things have changed. Lots of things haven't....
> BTW, extending more than a few feet above the tower top adds greatly to the
> wind load as well as adding a bending moment.
Few people consider that bending moment of a beam on a tall mast
until it's too late. Removing and lowering a hairpin-shaped mast and
the antenna(s) on it can be interesting.
Thanks, and good luck on the installation. Put pictures of it
somewehre for us to see....
--
Jim Fuller
Roger Halstead
N833R World's Oldest Debonair? s# CD-2
"Jim Fuller" <jefu...@netscape.net> wrote in message
news:3A19DA11...@netscape.net...
> Roger Halstead wrote:
> >
> ....
> > The innermost mast ( 1 1/2" steel pipe) sets into a conventional
> > rotor...Hy-gain 300.
> >
> > The outer mast is driven via a heavy duty chain drive with the rotor
mounted
> > external to the tower, or it will when I get that far.
> >
> > There are several ways which this could be accomplished. Gears, or
chains
> > being the easiest.
>
> That's sort of what I had concluded.-- that there is no off-the-shelf
> equipment available to do it, so it would have to be custom. There
> is also the matter of the thrust bearing(s) to take the weight of the
> outer mast, and how to lock the rotor and boom(s) to the mast. Both
> items seem to suggest welding plates onto the mast, since
> throughbolts are not possible.
Rohn makes some really heavy duty thrust bearings which I'm using to support
both the inner and outer masts. They feel a bit rough when unloaded, but
with load from the masts they are as smooth as silk.
The outer mast is supported at the top of the tower and again about 11 feet
down for alignment. The inner mast is supported about 3 feet below the
bottom of the outer mast and again at the rotor (alignment only). The
bottom rotor does not support any weight.
I have a ways to go to get this finished and probably won't be driving the
masts seperately until some time later this winter, or even next spring.
As for connecting the adapters to the masts, the easierst way I've found, is
to use a "keyed" setscrew arrangement.
My adapters are long enough that I can use either a 3 or 4 screw arrangement
on top and bottome of the adapter.. The mast is drilled just deep enough to
allow the end of the set screw to fit into it This makes for an arragement
where none of the screws have to be super tight. That makes 8 of them Just
good and snug.
>
> > As far as I know, no one is currently manufacturing systems like this,
but
> > there were similar systems a few years back.
>
> I just got relicensed after a 20-year hiatus, and I am finding that
> lots of things have changed. Lots of things haven't....
>
> > BTW, extending more than a few feet above the tower top adds greatly to
the
> > wind load as well as adding a bending moment.
>
> Few people consider that bending moment of a beam on a tall mast
> until it's too late. Removing and lowering a hairpin-shaped mast and
> the antenna(s) on it can be interesting.
>
It takes two things: Good insurrance and a hacksaw<:-))
There are two pictures of the old installation and one of the partially
completed new at http://www.rogerhalstead.com/kim.htm There are a couple of
the old Debonair on that page as well.
They are pretty high resolution so if you don't have a fast connection ....
It takes a while.
I hope to have a history up on a page "tower.htm" shortly. Those will be
thumbnails linked to high resolution JPGs which will make the page much
faster to load.
Roger (K8RI)
Brian Kelly
Roger Halstead wrote:
> > >
> > Climbing "issues" are one of the big reasons I'll be putting up some small
> crankup next time
>
> I'm past 60 and still do all my own climbing. (97 foot ROHN 45G and a 90
> foot American Standard) My wife put her foot down though and I had to quit
> climbing towers for the young guys.<:-))
>
I gave up the wife crap and climbing stupid towers, climbing broads is bunches
more fun.
>
>
> The past few weeks I've been climbing that 45G up to 6 times a day. I seem
> to be getting in pretty good shape <G>Antenna installation and working on
> the multiple rotor system.
>
Not here, knee got bashed in an auto accident ten years ago, my climbing daze is
over and good riddance. Worked one summer for a painting contractor, did the
stripes on one of the 1,300 foot TV transmitter ants. It's nice and cool up
there.
>
> The system uses concentric masts and will eventually have a rotor for each
> once I get my machine shop set up.
>
I have a machine shop but fuhgeddit, sounds like a major violation of the KISS
theory.
>
w3rv
Jim Fuller
>
....
> There are two pictures of the old installation and one of the partially
> completed new at http://www.rogerhalstead.com/kim.htm
Thanks for the ideas and explanations. Good pictures. Thanks.
> There are a couple of
> the old Debonair on that page as well.
Nice plane. I don't remember seeing very many with tip tanks.
--
Jim Fuller
'Doc
Jerry,
I'm sure you know that any/all manufacturers build-in a
safety factor. By exceeding those specifications, you are
'eating away' at that safety factor. That decision is yours
to make, and without going through a site survey, I or you
have no way of knowing for 'sure' if you have a safety problem
or not. The thing is, it never hurts to be safe, but the
opposite can cause problems.
Everyone 'fudges' to some extent. What I would consider a
reasonable risk, may not fit your way of thinking, and the
same the other way around. I can't tell you if your safe, or
not...
'Doc
Roger Halstead
--
Roger Halstead (K8RI) www.RogerHalstead.com
N833R World's Oldest Debonair? s# CD-2
"Jim Fuller" <jefu...@netscape.net> wrote in message
news:3A1BD020...@netscape.net...
> Roger Halstead wrote:
> >
> ....
> > There are two pictures of the old installation and one of the partially
> > completed new at http://www.rogerhalstead.com/kim.htm
>
> Thanks for the ideas and explanations. Good pictures. Thanks.
>
I started the story on tower.htm which is linked from the top of my home
page.
It has a log way to go, but there are a number of pics. A couple have to be
replaced with thumbnails and the large versions linked to are unformatted.
Meaning that on a smaller screen, or with anything less than 1200 X whatever
they are huge. Get to se a bit of detail though <:-))
If the weather turns crappy, which it is in general this time of year, I may
get the thing finished up in about a week. I really have had to dig for
some of the pictures.
I currently have over 12,000 digitized and cateloged (kinda, sorta). My
filing system needs a bit of work. I currently run the negative strips
through a scanner and do them at 300, 600, 1200, and 2400 dpi. (No, I don't
put the 2400 ones on the web <G>)
Roger (K8RI)