[TowerTalk] AB-105 Safety Question

[Bill Hider]

Dave Hawes wrote:
> 
> When I installed my government surplus AB-105 tower 20 years ago, I
> had a machine shop fabricate the guy wire attachment plates, since
> the tower sections that I acquired did not come with them.  They were
> made of carbon steel, and although I primed and painted them well,
> they have become quite rusty over the years.  In addition, the
> Preformed Dead End Guy Grips pass through countersunk holes in the
> plates, with no thimbles.  Although inspections reveal no evidence of
> failure of the grip at the stress point at the plate's hole, I plan
> to replace the grips with new ones, this time using a clevis and
> thimble for attachment.  Unfortunately, the holes in the plates are
> not large enough to pass the bolt from the clevis, so merely
> repainting the existing plates is not an option.
> 
> Recently, I acquired a complete new set of plates from Norm's Rotor
> Service (301-874-5885) in Frederick, MD, and am faced with the task
> of replacing the old with the new.  To complete the description of
> the current installation, the tower is standard duty AB-105, 117
> feet total height, with three-way 5/16" galvanized steel guys
> attached at 47, 77, and 107 feet, with a 4 element 20 and 2 element
> Cushcraft 40.
> 
> The issue of safety in this project is two-fold:
> 
> 1.  Detaching the existing guy wires, one a at a time, to do the
> work on the attachment plates, and
> 2.  Unbolting the plates and replacing them.
> 
> As to Issue #1, I believe that the AB-105 tower is robust enough to
> withstand this kind of maneuver.  In fact, I have detached one top
> guy wire many times to allow my large yagis to pivot down to the
> tower using a "PVRC (tm) Yagi Mount."  I see no reason why removal
> of intermediate guy wires, one at a time, should present any
> significant danger, but am interested in opinions.  Of course, the
> work would be done in calm wind conditions to minimize the potential
> for buckling forces.
> 
> Regarding Issue #2, it is important to note that guy attachment
> plates mount on top of the splice plates at each tower juntion.
> Replacement of the plate requires unbolting half of the bolts at the
> splice!
> 
> Concern:  Structural stability of the tower.  Probably not a worry,
> since the splice plate has six more bolts holding the joint stable.
> 
> Concern:  Settling of the tower section.  This is my real fear.  I'm
> not so sure that the tower sections are actually butting.  I think
> that the bolts at the splice plate are in shear and taking most or
> all of the dead weight load of the tower.  If I take the bolts out,
> even of just half of the splice plate, especially at the 47 foot
> level, and the tower settles, I might not be able to get the holes
> lined up again.  In that event, I can visualize (in my nightmares)
> having to jury rig some kind of jack to separate the tower sections
> far enough to get the bolt holes lined up.  (I'm pretty sure a drift
> pin would not have the mechanical advantage needed for the job, but
> then again it might.) This would not be able to be done right away,
> and the tower could be left in a dangerous condition for some period
> of time while a workaround is developed.  Not a happy thought.
> 
> I would appreciate any insights other owners of or maintainers of
> AB-105 tower might be able to provide on this subject.  I'm hoping
> my fears as described above are merely overreaction, but better safe
> than sorry.  I fully realize that this is a very, very narrowly
> focused question, and apologize for the bandwidth.  However, this
> reflector is a great resource, and I figured it was worth a shot,
> especially since this is essentially a safety related issue.
> 
> TIA.
> 
> 73 - Dave N3RD
> n3rd@ix.netcom.com
> http://www.QTH.com/topten
> 
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Hi Dave,

I have a heavy duty AB-105 tower, not the regular duty one you have, but
am familiar with it.

First of all, I agree with your approach to issue #1.  Although, an
alternative would be to build new guy sets (to replace your 20 year-old
ones) and attach them at:
37, 77, 117.  The 77 would be done last, replacing them one at a time.
(Abandon, in place, the existing guy attachment plates at 47 and 107.)

If you consider the alternative described above, or not, you might think
of replacement with fiberglass guys. I can elaborate further if you
like, but, K3MM, W3LPL, W3EA, N3RR (I) and others have used these
successfully. In fact, K3MM recently posted some fiberglass guy rod for
sale.

As far as issue #2, if you can remove one-half of the dual guy
attachment plate at a splice, I do not believe that the leg will move. 
To be certain, tighten the other guy attachment/splice plate combination
fully before loosening the opposite side bolt/nuts.  Loosen them and
remove the bolts one at a time and try to swivel the guy attachment
plate away from the leg before you have removed the last of the three
bolts holding the guy/splice plates together (while the opposite side
guy/splice plate still has its bolts/nuts tight).  That way, once it's
swiveled away, re-insert one bolt/nut to keep the leg in place while you
remove the last of the three bolts, remove the old guy attachment plate,
install the new guy attachment plate, re-insert one bolt, swivel, etc,
etc....  Similarly, install the new guy attachment plates at 117 and 37.

Before you do any of the above, verify that the shackle (you called this
"clevis") that will pass through the guy attachment plate will actually
pass through the combination of the two attachment plates while in the
same angle in which they will be installed on the tower!!!  I had to
ream the holes out of mine WHILE ON THE TOWER when the shackle bolt
would not fit!!! (Even though I tested this on the ground before trying
it on the tower.)

Speaking of that, if you have enough "meat" left on the existing guy
attachment plates, why not consider reaming them out on the tower once
the existing guy is removed??  Then strip and paint and install the new
guy...this would eliminate issue#2.

I would also recommend having the new plates galvanized if they are not
already.

Also, referring to my suggestion of repositioning the guys to 117 ft. 
The closer you have the guys to the top of the tower, the less moment
you will have above the guys.  Frank, W3LPL, recently described his
situation with the tops of the towers above his top guy set.

That's all I can think of for now.  Good luck with it.

73!

Bill, N3RR


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