> Hi all,
> As being the lucky person to clean up the mess left by Owen's tower failures,
> I can tell you first hand that all antenna weights, wind load specs, lengths,
> etc. were passed on to Heights before Owen put them up, anyone who knows Owen
> knows he goes by the book and documents!! He was told that his loading was
> within spec.
I hope I can properly phrase this and although experienced I'm certainly
no expert either and it has been a while.
> I am no expert on aluminum welding but I do a fair amount about steel welding
> and what I have seen is a failure of welds on his towers.
There are some differences, but the appearance of a good weld and
failure is pretty much the same except for granularity in the weld and
the depth of the "melt in" at the edges. Impurities including air.
cover gas, cover gas flow, and technique can cause granularity in the
weld and at the junction where the weld "penetrates" into the base metal.
Another problem with welding Aluminum is the alloy of the base metal
and welding rod. Now that TIG welding is available welding aluminum is
far easier than in the past. From what I've seen and done, Aluminum
welds differ slightly in appearance as we are working with a fairly weak
base metal that depends more on shape to maintain its strength than does
steel although shape is important with both. Aluminum welds do tend to
be thicker than steel with less of the "melt in" or recess showing than
with steel. You need to see that melt in to know you are getting the
penetration, but on a thin, Aluminum tower leg it has to be tiny.
However the overall weld appearance is about the same as a good steel
weld with a slightly concave surface consisting of a series of half moon
shaped ")". IOW the weld should look like ))))))))))). Welds showing
granularity and particularly when the granularity is pronounced tend to
be much weaker than a normal weld or even the base metal. these welds
are brittle and they tend to break at the weld to base metal interface.
Making the weld thicker to cover more base metal in that case does
little to increase the strength as the critical area ends up being about
equal to the the base metal thickness at either edge of the weld.
> Normally, a weld is stronger than the surrounding material. If there is a
> failure, the weld is intact but metal is ripped away around the weld.
From what I remember is Aluminum is a little more subtle in this area,
and may pull, or rip apart at the junction, but the idea is still the same.
> A sign of a good weld is a slight cutting away of material right at the weld.
> This is the point where the material starts to melt and becomes one with the
> welding rod material. Some of the failed welds on his HF tower that came over
> first look like they just poped off, like a cold solder joint.
Which is a sign of insufficient penetration, and/or granularity.
> His second failure, just a couple of weeks ago, occured at 36 mph as measured
> by his Davis wx station and verified by the local airport which reported only
> a 31 mph gust. The top section failed right where it went inside the next
> section. A leg buckeled in and it was all down hill from there. Once again,
> as the leg that was receiving all the downward pressure (opposite the legs in
> the wind) pushed inward and the Z bracing which is supposed to keep it from
> collasping, didn't. I did not see the Z bracing buckle, the welds just broke.
I've never seen one break there, but I've only seen one Aluminum tower
with a hefty load. On that one the welds broke at the hinge with a
mixture of granularity and insufficient penetration. The 20 meter beam
went through their living room roof.
I've seen the welds break on the Z bracing for many different makes of
Aluminum towers as well as a wide range of alloys used in their
> All the discussions thus far seems to be centered around just self supporting
> foldovers, not crank ups as Owen's was. I'm sure there is a difference
> between the way the load is distributed down the tower.
> At K8GP, we use a lot of Univeral self-supporting towers that pivot up from
> atop our school buses. Our towers take a lot of abuse from being overloaded
> (it's only 5 days twice a year!) and riding around on bumpy roads on top of
> school buses. Our towers have survived 80+ mph winds and when we have a
> break, it's usually a fatigued Z brace and NOT at a weld and we only go up 30
> to 40 feet.
I've never had a Z-brace break, but I've had them bend from climbing and
I've had the Z-brace welds break. Another problem with some aluminum
towers is the way they are constructed at the top with the legs just
flattened against the top tube. These allow water down into the legs
where spiders tend to build nests. The water collects, freezes, gets
more water and eventually swells the leg to the breaking point. It's
rate to see this in even cheap steel TV towers, but not at all uncommon
in Aluminum. However with those it's easy to weld up the breaks and use
the towers for 40 meter antennas. <:-))
> I'm not passing judgement on Heights towers or aluminum towers in general,
> just adding to the discussion of what I saw. For most of us, a tower is a
> pretty good size investment in time and money, and since my tired, old, fat
> butt is climbing up, I want nice heavy, thick, galvanized STEEL under me!
I've climbed them but not very high and only after a through inspection.
Since installing a 45G I don't even like climbing 25G <:-)) I don't
climb self supporting towers unless they are substantial and don't move
in the wind. <:-)) As I mentioned earlier, the alloys used in Aluminum
towers varies over a wide range as does the quality and price of the towers.
Roger (K8RI - ARRL Life Member) (At least I can climb again<G>)
N833R (World's oldest Debonair)
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