Interesting threads out there on the guy rod angles...
First of all one should DO what the Rohn book says to do; that's most
important. But I'm guessing here that most tower installations
of the amateur variety don't **exactly** follow all the specs
listed in their respective installation instructions. As far
as the +-1 degree specs as concerned, I'll bet most amateurs
would simply measure (or guess....D'Oh!) the angle to the best of their
ability with the equipment they have and let it go at that.
73,
Charlie, N0TT
On Fri, 07 Sep 2001 11:40:17 -0500 "J. Kincade" <w5kp@swbell.net> writes:
>Hmmm. Charlie, my new 45G has about 700 lb on the top guys and about
>400 on
>the bottom guys, according to my trusty Loos Tension Gauge, which is
>about
>what Rohn specifies, and is the reason for the equalizer plates. So I
>can't
>buy into the equal tension thing from a practical viewpoint. If you
>stretch
>a cable between two points and put say 1000 pounds on it, and tie a
>separate
>cable near one end of it at an angle, you can put about any amount of
>strain
>on the second cable you want to. It will simply deflect the first
>cable more
>or less, depending on the pull on the second cable. Not math, but
>makes
>practical sense to me and is borne out by Rohn's guy wire
>specification
>tables. :-)
>73, Jerry W5KP
>
>
>----- Original Message -----
>From: N0TT@ juno.com <n0tt1@juno.com>
>To: <towertalk@contesting.com>
>Sent: Friday, September 07, 2001 9:16 AM
>Subject: Re: [TowerTalk] guy rod angle
>
>
>>
>> Hi gents,
>>
>> My barbershop comments... :)
>>
>> I would think that if there were say, 3 guys running to the same
>> anchor, that one would want to line up the anchor with
>> the "middle" guy wire. If there are two guys then I
>> would think the anchor would line up between the two
>> guys. This is because all the guy wires should be
>> tensioned the same, no one guy wire pulling more than
>> the others during low wind conditions, thus averaging
>> out the load.
>>
>> It would be nearly impossible to predict dynamic wind
>> load on any one guy wire because wind speed is
>> not always the same at all levels of elevation. Thus, there
>> is a logical reason (other than mechanical "neatness") why
>> here are equalizer plates installed at the anchors.
>>
>> BTW, quite a few years ago there was a QST article named
>> "Guys for Guys that have to Guy"...or something to that
>> effect...might be of interest to some of you.
>>
>> 73,
>> Charlie, N0TT
>>
>> On Wed, 05 Sep 2001 22:25:30 -0400 "Michael Rauh"
>> <michaelrauh@hotmail.com> writes:
>> >
>> >Jerry, Stan, Dave, Tom,
>> >
>> >I agree with Jerry and Stan - the angle is probably not critical.
>> >Rohn
>> >presents the angle to 0.1 degree in their guyed tower drawings.
>This
>> >seems
>> >impossibly precise to me - there is probably way more sag or bow in
>> >the guy
>> >anchor than that.
>> >
>> >I also suspect that Dave is correct when he suggests taking the
>vector
>> >sum
>> >of the loads on the guys when the tower is at its rated wind load
>to
>> >find
>> >the guy rod angle.
>> >
>> >In thinking about this problem I realized I don't know how to
>> >calculate the
>> >individual loads on each guy wire. I use a rigid body model for
>the
>> >tower
>> >that will give the total load on the guys, but won't tell me how
>the
>> >guys
>> >share the load, at least as far as I can see. To figure out the
>load
>> >on
>> >each individual guy, I think I will need to consider how the tower
>> >deflects
>> >under load.
>> >
>> >Consider a tower with two sets of guys and an antenna on top. I
>could
>> >start
>> >by assuming the tower is fixed at the top and the base. I
>calculate
>> >the
>> >wind load and how the tower will deflect under that load. Draw a
>> >curve,
>> >deflection vs. load. Then assume the lower guy is attached at
>> >mid-point,
>> >draw a curve of elongation vs. load. The load on the second guy is
>> >where
>> >the curves meet. The reminder of the load on the tower, including
>the
>> >
>> >antenna load, is absorbed by the top guy.
>> >
>> >But wait! The top guy elongates under load too, relieving the load
>on
>> >the
>> >bottom guy. So I will have to set up a system of simultaneous
>> >equations in
>> >order to get the loads on each guy. I will need equations for the
>> >elongation of the top guy, the bottom guy, the deflection (bowing)
>and
>> >the
>> >pivoting of the tower. If the tower has a pivot base that is all I
>> >need,
>> >but if the base is cast in concrete I might need an equation to
>> >account for
>> >the force needed to tilt the tower as the guys elongate.
>> >
>> >Does that sound right? Do you know of any references where this
>kind
>> >of
>> >problem has been worked out? I know Kurt Andress has found guy
>loads
>> >using
>> >a finite element program. I need to understand the principles
>> >involved
>> >before I resort to a program!
>> >
>> >I think it would be very cool to know how to find the loads on the
>> >individual guy wires in a tower system.
>> >
>> >Best Regards,
>> >
>> >Mike Rauh, NV7X
>> >
>> >Reply to mikerauh@ic.org
>> >
>> >
>> >
>> >
>> >_________________________________________________________________
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>>
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>> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
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>>
>>
>
>
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Join Juno today! For your FREE software, visit:
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