Securing a Mast in a storm

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neighbor whose wifi I share has a 20 foot mast, looks to be fairly thin
in diameter with 3 guidewires at 19feet and 3 more at 10 feet. Last
typhoon storm with winds about 150km/hour bent the mast over in half and
we are without internet for a month while local crews tried to catchup
with their backlogs. The diameter of this mast appears to be fairly
small, maybe 1 inch-guessing cuz it's on the room of his house. Is there
any way to prevent such winds from destroying the mast again? More
quidewires? What?  

Re: Securing a Mast in a storm
wrote:

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I can calculate the wind loading if I knew the actual dimensions and
what manner of antennas were attached.  If the antenna is small, I
suspect what I'll find is that the 1.25" OD standard size mast, may
have been adequately guyed for 150 km/hr (93 mph) winds if the guy
wires were sufficiently thick, and the endpoint anchors sufficiently
strong.

If the antenna bent in half, it is obvious that one of the guy wires
came loose or broke.  When that happens, a buckling type failure is
probably inevitable.  You can do better with a proper tower (Rohn 25
or bigger), but 1.25" OD should be sufficient for a small panel
antenna.

Before you can re-engineer the structure, you will need to analyze
what caused the past failure.  Did the guy wire(s) break?  Did the
saddle clamps slip?  Did the guy wire anchors rip out of the ground or
roof?  Was there a corrosion problem?  Were the guy wires too tight or
too loose?

I've seen a few mast and tower failures caused by the wind.  Most
common is installing the saddle clamps the wrong way.  See Pg 15:
<http://www.criticaltowers.com/ROHN%20Tilt%20Up%20Wind%20Power%20Poles/Files/ARE_Short_Twr_Install_Manual_080106_with_DWGs.pdf
<http://www.billavista.com/atv/Articles/Recovery_Bible/images/use%20of%20wire%20rope%20clips.jpg
and badly designed anchors:
<http://www.w8ji.com/screw_in_guy_anchors.htm
Wind load from a 20 ft mast with an antenna on top is trivial compared
to the wind load from a wind turbine generator.

If you need help with antenna towers and masts, I suggest you ask on
the TowerTalk mailing list for ham radio operators.
<http://lists.contesting.com/mailman/listinfo/Towertalk

--  
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: Securing a Mast in a storm
What exactly is a backwards clamp?
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Re: Securing a Mast in a storm

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It's a saddle clamp (or wire rope clamp) installed backwards.  They
should be installed like this:
<http://www.billavista.com/atv/Articles/Recovery_Bible/images/use%20of%20wire%20rope%20clips.jpg

There are two sides to the cable loop.  The live side is the one under
tension.  The dead side is the one that is NOT under tension.  When
you tighten down on the saddle clamp, you'll see that the U-bolt makes
a dent in the cable, while the cast part of the saddle clamp does not.
You do NOT want a dent in the live side of the cable as it might
weaken the cable.

If something is going to slip, it will be the cast part of the clamp,
and not the U-bolt part.  With the cast side on the live side of the
loop, if the cast part slips, then the assembly just tightens up
against the thimble.  No problem.

However, if you assemble it backwards, and put the U-bolt on the live
side, the dead side will slip and cause the whole mess to fall apart.
Usually, what happens is that it slips partially in a high wind
because of the increased cable tension.  Then the mast or tower starts
to bang around because of all the slack in the guy wires.  Towers are
designed for static loads, not dynamic inertial pounding, which will
finish the job of disassembling the saddle clamps.

Loose guy wires can be a bigger danger than having the saddle clamps
fall apart.  I know of an 80ft tower that came down in high winds
because of slack guy wires.  The owner was worried that his guy
anchors weren't strong enough, so he left the guys slack.  When the
wind caused the tower to bang around, the anchors and saddle clamps
stayed in place, but the guy wires snapped.  Sorry, but the owner
doesn't want me posting photos.

Hint:  I use preforms, thimbles, and only a few wire rope clamps.
<
http://www.youtube.com/watch?v=gSRMDOGj0iQ



Sigh... I washed my car and now it's raining.  It NEVER rains in
California in summer.

--  
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558


Re: Securing a Mast in a storm
wrote:
(...)
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If you're into this kind of stuff, I suggest you download and read
through the Rohn and Valmont/Microflect catalogs:
<http://www.rohnnet.com/resourcesmodule/download_resource/id/731/src/@random4d91e05320426/
<http://www.sitepro1.com/resources/pdf/13catalog.pdf
Lots of goodies and clues on how things should be done in both
including TIA-222 "Structural Standards for Antenna Supporting
Structures and Antennas".
<http://www.rohnnet.com/resourcesmodule/download_resource/id/610/
While this is probably massive overkill for a 20ft pole, it does offer
a clue as to the calculations and saftey factors involved.



--  
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: Securing a Mast in a storm
On 9/2/2013 8:30 PM, Jeff Liebermann wrote:
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Yep. I drove to the park to do a hike and it started to rain.

I understand the backwards clamp now. Not the best description. Very  
obvious once someone points it out. I have only wired up trees, but will  
review my handy work. Nothing has failed thus far.

I don't get the video. The guy is twisting the wire so there is no  
"correct" side.

Next time I'm at a transmitting site, I'll take a look at the guy wire,  
but I'll you, the powers that be don't seem to like guy wire supported  
towers very much these days. I see mostly free standing towers. I have  
hiked the hill where those asses cut the guy wires and crashed the  
tower. Now I was thinking, well if it had a VHF pager this could be  
justified...but nah, even then, it is still a terrible idea. There must  
have been a dozen wires on it. How he/they knew what to cut and not kill  
themselves is a good question. [I left out "she" because I can't  
envision any woman doing something that stupid. To knock down a 200ft  
tower, you need a good dose of the hormone of assholes: testosterone.]

I've seen my share of Microflects. They make sense in the boonies, but I  
was surprised to see one on Volmer Peak. Well the FCC website is down,  
but I will look up to see who uses the Microflect on Volmer. They show  
up as PR (passive radiator) in the database.

BTW, the comment about backfill being weak is interesting .Having run a  
Ditchwitch in native soil and engineered fill, fill can be mighty hard  
if watered and compacted.



Re: Securing a Mast in a storm

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I can see you've never used a preform.  The idea is to eliminate the
wire clamps.  The preform has a rough surface, that cuts into the guy
wire, holding it in place by friction.  It's also slightly tapered to
provide some level of self tightening.  The guy wire will break before
it will let go.  It's kinda like a Chinese finger puzzle.

The problem with guy wires is that you need lots of real estate for
the wires.  That's available in some areas, but not in urban installs,
rooftops, or crowded mountain tops.  Monopoles are easier (and
cheaper).  

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I recall that he did something crude, like bury foundation blocks for
guy wire anchors.  That's not strong enough for an 80 ft tower with
lots of wind load.  See the Rohn catalog for how to do it right.


--  
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: Securing a Mast in a storm
On 9/3/2013 12:07 AM, Jeff Liebermann wrote:
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I've learned long ago that if you are doing a "one off", just pay a  
professional. So if I find myself in need of installing a tower, I would  
just pay somebody. But it doesn't hurt to know the foo such as the right  
way to put on the clamps.


Re: Securing a Mast in a storm

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How do you get fires like that at the top of a cell tower? Other than
those fake palm fronds sometimes used as (somewhat pathetic) camouflage,
what combustible material is up there to sustain a fire like that?  


Re: Securing a Mast in a storm
(Neill Massello) wrote:  

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Just a guess, but it would make sense to have the actual radio
transmitters and receivers up top immediately adjacent to the antennas
to avoid having to run a lot of expensive low-loss RF cables from ground
level.  

--  
bert@iphouse.com    St. Paul, MN

Re: Securing a Mast in a storm
wrote:

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That's being done.  They're called "tower mounted amplifiers".
<https://www.google.com/search?q=tower+mounted+amplifier&tbm=isch
<http://en.wikipedia.org/wiki/Tower_Mounted_Amplifier
The problem is stocking expensive spares and swapping boxes when the
weather is not very cooperative.

More monopole fire photos:
<http://www.wirelessestimator.com/wifi/images/uploads/Monopole-Fire-PA.jpg
<http://www.wirelessestimator.com/wifi/images/uploads/Monopole_Fire.jpg
<http://www.wirelessestimator.com/wifi/images/uploads/Monopole%20Fire3.jpg

--  
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: Securing a Mast in a storm
On Wed, 4 Sep 2013 01:58:10 -0600, nmassello@yahoo.com (Neill
Massello) wrote:

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The poly and vinyl plastics used in coaxial cables is highly flamable.
A monopole fire works by convection, exactly the same as with a
charcoal barbeque fire starter.  It's usually started when someone
wants to weld reinforcements, brackets, or mounts to the pipe with a
torch.  It doesn't take much to get it the cables to burn.  Once the
fire starts, convection insures that all the cables are suitably
torched.  Incidentally, depending on the size of the pole and air
flow, it can burn for several days.

More:
<http://www.wirelessestimator.com/t_content.cfm?pagename=Monopole%20Fire%20NV
  "A Clark County Fire Department spokeswoman said that Alan  
  Bunker said he was welding approximately six-feet up on  
  the east side of the monopole when he heard a popping sound  
  and then noticed smoke coming from the tower."

It's kinda difficult to extract individual articles from this site, so
just type in "tower fire" into the search box.  Lots of horror
stories, examples, and interesting reading:
<http://www.wirelessestimator.com

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All the coax and control cables in the pipe are flamable.  Take a
length of CAT5 cable.  If possible, make it plenum rated cable (not
riser cable).  Hold it vertically and ignite the lower end with a
propane torch.  Be prepared to drop the cable.  If you're somewhat
insane, do the same thing inside a length of thin pipe.  A bundle of
CAT5 cables inside about 6ft of old 1" EMT sounded like a rocket
engine for a few seconds.

--  
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: Securing a Mast in a storm
Any fires causes other than welding? In electronics, you can account for  
internal problems, even surges if you are willing to throw money at the  
problem, but if the welder torches it, I think you are doomed.

This seems like a situation where (gasp) standards need to be set. I can  
hear Rand Paul screaming at that statement, but fire is a community  
problem. It spreads. We are all in this together, and thus government is  
the solution.

Back to the cables, my recollection in fire standards is there are  
materials that burn, and materials that are destroyed in fire but  
doesn't support the fire. [I'd have to dig up the technical terms.]  
Material science gurus surely can solve this problem.

Speaking of palm tree fires, one scenario is tree squirrels and  
smoldering cigarettes. Squirrels like the filters for building material.  
They can be ripped up and there is quite a bit of material in one. But  
if they pick up a lit one, woosh! Every once in a while I see the  
remains of a grass fire by the highway and it is blantantly obvious it  
started by the road at a point source, spread in a V, and then set the  
hill on fire. OK, I didn't get out of the car to investigate, but doh!.

But back to the burning palms, I was in the socal dessert, maybe 20  
miles west of Victorville and spotted a palm tree on fire. Just the top  
was burning. Took a while for fire to show up since it was one of those  
odd places in the desert where you wonder why people live there, well  
other than to make meth.




Re: Securing a Mast in a storm

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Lightning!



--  
_____________________________________________________
Knowledge may be power, but communications is the key
             dannyb@panix.com  
[to foil spammers, my address has been double rot-13 encoded]

Re: Securing a Mast in a storm

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Very cool.  The original burning bush.  My ancestors took 40 years of
wandering around the desert to figure out how it works.  Maybe you can
do it in less.

Maybe they were practicing?
<http://www.chron.com/news/houston-texas/article/Arsonist-burning-palm-trees-in-Galveston-2227004.php

Incidentally, tonight is the first evening of Rosh Hashanah, the
Jewish new year.  
--  
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: Securing a Mast in a storm


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I'm getting an unable-to-make-connection/timout when trying
to access the site, so this is a WAG. Could there be an
emergency power supply up there with a generator and
100 gallons of fuel?


--  
_____________________________________________________
Knowledge may be power, but communications is the key
             dannyb@panix.com  
[to foil spammers, my address has been double rot-13 encoded]

Re: Securing a Mast in a storm

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Jeff almost ALWAYS has the good answers. Thanks Jeff for your time and  
good contribution to this group.

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