TowerTalkians,
I need your expert advice. I climb for a friend who has a 100' Rohn 45
tower. When the big Nor'easter tore through New England recently, a large
tree fell on one of his top guys. Luckily, the tower did not collapse.
Off the top of my head, I think the tree was at least 40 feet tall and the
trunk was 8-12 inches in diameter. Maybe bigger. Way too heavy to move by
hand. It was a deciduous hardwood, perhaps beech or birch, I can't remember.
The main trunk didn't hit the guy wire, but at least one of the large upper
branches did. When I got there, the branch in question (at least 5-6 inches
in diameter), was resting on the lowest part of the guy wire, just a few
feet above the big grip connecting to the equalizer plate. Further up the
guy, about 15 feet off the ground, there was a noticeable dip in the wire.
Not exactly a kink, but a deformity that strongly suggests the tree
initially hit the guy there and either bounced or rolled down to the bottom.
Even so, the weight of the tree had caused the wire to sink at least 1/4"
into the branch that was resting on the lower portion of the guy.
Using my chainsaw, I separated the upper portion of the tree from the trunk,
and cut apart the mass of branches until the weight was reduced enough for
the two of us to wrestle the big branch off the guy wire. We had to yank
back and forth on the branch pretty hard to disengage it from the guy.
We noticed right away that the top guy was much looser than it should be. In
fact, all nine guys have considerably more slack than they did when tension
was last set with a Loos gauge last fall. My friend doesn't tension his guys
particularly tight, probably somewhat less than the recommended 10%, but I
climbed the tower last fall and felt the tension was at an acceptable level.
The catenary was pretty shallow. After the tree hit, the catenary was much
deeper and you could grasp one of the top guys and kind of whip it up and
down. I'm not real experienced at this, but would guess anywhere from 6"-12"
of slack will have to be taken out to retension the guys, with the top guys
needing the most.
We inspected the guys and anchors for damage. Aside from the mild dip in the
top guy at the point of impact, there does not appear to be any damage to
the wire, even where it cut into the branch. The anchors appear solid and
there is no sign they have deformed or the anchor blocks have moved (this
tower uses 3'x3'x1.5' concrete footings four feet down, per Rohn spec.)
However, I was able to grasp an anchor rod and move it up and down a few
inches. This was partly due to the guys being slack, but I think the soil is
relatively loose near the surface, too. It's an area of forest that was
cleared about 20 years ago and has that soft forest floor consistency. BTW,
this is why the tree (and many others) fell -- the root balls disengaged
from the loose, super-saturated soil and the heavy winds blew them over.
Anyway, if I had to bet on it, I'd say the anchor blocks didn't move. My
friend doesn't think so, either, and he's intimately familiar with them,
having done the digging and pouring himself.
The guys are broken up with insulators. I visually inspected the grips and
could see the little stub of EHS sticking into the thimble area, as it
should be. I don't think any of the grips slipped. I was not able to closely
inspect the grips right at the guy brackets, but will do that through
binoculars before climbing the tower. I think it's unlikely the grips
slipped at the tower end.
The tower appears to be perfectly plumb and there's no obvious damage to the
legs or lattice. I plan to inspect the legs and welds through binoculars
before climbing.
It was a very windy day, and we were impressed with the fact that the tower
wasn't swaying at all, despite the loose guys. It was rock solid (though I'm
sure I would have felt some sway if I was riding the top.) This tower has a
40-2CD, 6m beam and TH-7 on a 12'+ mast and a TH-7 on a TIC ring at 60'.
That's 25-30 sq feet of wind load. The 3/16" guys are at about 95'/60'/30'.
Torque arms are used on the brackets. The tower sits on a pier pin. The
tower and guys were installed about 20 years ago.
Questions: What caused the slack in the guys? Is it possible for EHS to
stretch that much? If so, is it OK to simply retension the guys, or is there
a compelling reason to replace them? Is it likely that the impact point is
weakened enough to require that section of the guy to be replaced? Should I
look elsewhere for the source of the slack?
Before I climb the tower, I want to be confident that it's in good order.
Please, no speculation. This is a serious safety issue and I would
appreciate answers from people with lots of experience, preferably with
similar damage.
Thanks & 73,
Dick WC1M
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