Basejumper.com - archive

I am curious, those of you who have designed, worked on, or know about wire guyed towers? specifically the massive ones, 500+meters.

specifically the frailness of the towers wires, as in what forces can be put on the individual wire without the tower coming down? As in a jumper impacting a wire mid-span, halfway from top to bottom, or say an airplane impact. I know of a few cases where a plane impacting wires brought the tower down, but no jumpers right?

thoughts?

a tower fell on 19 march 1969 in emley moor, uk. ice built up to the point that it simply put the tower off keel and it went down. the picture of the building is a church; the guy wires cut right through it.

another tower fell on 12 jan 2008 just 20 miles south of my house. a crew was attempting to restring guy wires and it went down. apparently there was a guy on it as it tumbled to the ground.

i realize this isn't exactly what you were asking but it does show that a tall antenna can be brought down without intending to.

My reply doesnt specifically answer your question but here is some information on recorded aircraft collisions.

50m in San Antonio-1958
628m in N Dakota-1966
161m in NYork-1967
610m in S Dakota-1968
530m in Wisconsin-1968
352m in Germany-1978
66m in Ontario-1978
285m Dudelange Radio Tower-1981
198m in Florida-2000
258m in Russia-2001
195m in California-2004
325m in Nebraska-2005

These were listed online under catastophic failures for radio masts and towers

looking at the picture of the little rock incident it is always quite amazing to me to look at what the force of impact has on things. I know its a little morbid, but look what the ground (looks like a grass meadow) did to that steel structure. all contorted, twisted and very gnarly. puts some things in perspective for me at least.

the '05 Nebraska collision was my friend a her boyfriend and his daughter

I understand all the aircraft collisions, thats a massive dunamic impact to the mast or a guy. what does help is any info (and I have found most of the stuff i could just google searching) on the guy wire replacement tower failures, such as what is the assymetric load required to drop a tower (ballpark). does on wire have to be missing? or simply loaded slightly assymtric?

it makes sense that re-'stringing' a tower is insanely dangerous, they are 100% relying on their guys not only to stay standing up, but for overall strength as far as internal strength goes, ALL wires are VITAL.


right?

About a decade ago there was a gnarly ice storm that brought down a big tower in this area. The ice built up over about two or three days to the point where it was about an inch thick on alot of the trees on the ground. It cleared overnight and when the sun came up in the morning it melted all of the ice on the east guys & the asymmetry led to a catastrophic collapse.

There was a aircraft collision on a 1000ft tower in Quebec about 5 yrs ago and the tower stayed up. If I remember right it was a cessna. They decided to bring it down but, it survived the impact, unlike the pilot

We had a mast go down here in the UK a few years ago....

http://www.arar93.dsl.pipex.com/mds975/txmaps/peterboroughmast.html

They suspected fireworks fired at the mast got lodged 80ft up and caused a fire on cable insulation which caused the collapse.

How could this be, you ask? Well, these masts are built so that all the weight of hundreds of tons of steelwork is positioned perfectly vertically over a central point, generally not much larger than a dinner plate. This works as long as the guys are equally taut and there is no slack anywhere. as soon as the mast is allowed (or caused) to move just slightly off then it's likely to collapse. Stack up the beer cans after a heavy night with your buddies and you'll find the tallest beer can tower is the most vertical. Just a little bit off, and down it comes.
In this case it's believed the fire softened the metal just enough to bend a small section (not difficult with hundreds of tons sitting above it) and as soon as there was just a little bit of slack in the guys, it collapsed.

On the plus side, I'm pretty certain that a wire strike by a BASE jumper wouldn't cause enough stress in the system to collapse anything, but try to steer clear anyway, just in case, eh?

Max

Impact with the guy wires in freefall. Wouldn't that be like a knife through butter? In my opinion it wouldn't damage the guy wires or their integrity whatsoever.

~J

I wouldn't sweat it. Those things are plenty strong. If the wind is down the wire, just cut the damn thing off. I would have tonight but I can't find my ladder and hacksaw.

not sure about body impact at terminal... but it'll certainly cut the riser(s).

BFL #92 Vadim

of course then there's a rumored incident of certain individual wrapping his canopy in a guy wire and sliding all the way down to find just a bit of grease damage and no rips in his canopy.

Still, I'd stay on the safe side and avoid the wires :)

Agreed

sadly, underdelaying as badly as you often do might make avoiding the wires a tad more difficult than it should be