380 kV Tower Collapse

The second picture shows (3) bolt holes. Can you find out if the original stress analysis took into account this reduction of area? It looks as though the remaining cross-sectional area of the steel angle is greater than the doubled shear area of the bolts, but this is only an eyeball guess.

Good thing it wasn't energized yet!

It looks as though this is in a desert location. Over a long time, sandstorm abrasion might be an issue, but this seems unlikely in a new installation.

Can you obtain samples of the structure near to the break and submit them for testing?

I'm seeing oxidation at the fracture points, as though there was a separation before the wind storm that caused the catastrophic failure. A dry desert environment should not cause that amount of oxidation so soon, and I would expect to see shiny metal for some time.

Good eye, but it's a little too uniformly brown along all of the fracture points for me to say that it's oxidation. I'm wondering if these are counterfeit painted parts? If they are, how many more counterfeits are there in the rest of this tower system?

Another idea popped into my addled brain, how does the mechanical design handle thermal expansion and contraction?

I can't understand the color. Could it be that this piece has been broken for some time? And rusted?

It almost looks like it's not steel, but that couldn't be right (surely).

It looks like the foot could have been cast. Perhaps it's sand filled flaw in the casting.

Thanks for everybody joint for this discussion

Actually this accident unknown when it happen? due to the line not yet energized and in remote area.

But we think this discovered, almost one week after the high wind attacked that area according to forecast whether…

I will submit more pictures

I know you can't get a whole lot of detail from a picture; but, the steel looks a little light to me. You say you are running a double circuit of 4 wire bundled conductor.That is a heck of a lot of weight. What size is your conductor? I'm guessing about 477MCM or smaller from the picture. How long are the spans? Those bolts look like 5/8th inch bolts on your attachment plate to the cement. What size are they? From looking at the sand I'm guessing you're in the Middle East. Your temperature is going to swing 50 degrees in a day. What kind of tension are you pulling at the DEs? Did you use a local contractor? I agree with redfred on the counterfeit parts. If you are where I suspect you are I'd just about bet on it. I think your answers are going to be interesting. Thank you.

I used to work in the transmission pole industry--note pole, not lattice towers. The company quit making those poles I think in 1984 so my info is thus dated.

At 380 kv, these things would be huge; the only scale I see is the 15 meter bar.

At that time we used ASCE specs--the safety factors were put on the loads rather than on the steel strength (per AISC.) I think we used 2.54 on wind loads. As I remember we had two wind criteria: wind on bare conductors, and wind on ice covered conductors. (Doesn't look like you have ice concerns though! Many of our customers also required Charpy steel at -20 degrees, but you don't appear to be cold.) We also used the resultant of the angle change and tension with a different safety factor that I forget (1.4???)

I mention this and safety factors to say that unless there was a gross computation error, the problem was likely due to poor material or a construction fault.

I too am concerned about that rusty broken angle. Has it been broken for some time and the normal loads were carried through redundant load paths? But why did it break? (Hopefully the designers didn't forget to reduce the load area due to the bolt holes.)

Where was the collapse arrested? Was it at dead-end towers? I'm guessing that one tower failed, and the others were a domino effect.

Take a good look at that broken angle. I'm guessing it was loaded in tension by the wind you had. A busted angle doesn't hold tension very well at all!!

Looking at the first photograph, the fracture surfaces have all the appearance of the tower having failed due to brittle fracture of the material. There does not appear to be any sign of the metal having yielded, but, instead appears to have literally snapped.

Suggest you get samples of the fractured members to a competent metallurgist for analysis.

Regards.

Is it possible that the towers were overstressed during assembly because the fit of the parts was poor? Possibly they had were forced into alignment causing built stressing. Note, I am not a tower man, but I have seen badly built and mis-aligned antenna towers where parts had been force fitted.

Looks like material failure to me based on the base angle pic.......rust appears to happen over a period of time in that fracture at the bolt line.

I would suggest that material analysis be done on several sample coupons taken at high stress areas. As stated before this looks like a counterfeit material problem, BUT may also be an engineering design failure as well.

Strongly suggest that you obtain copies of all design calcs for these towers as well as the Shop Drawings to determine where and when errors creeped into the process.

I foresee a long road of litigation ahead for all concerned, so immediately hire a Forensic Engineering firm before anything is disturbed or removed!

Adding my 2 Cents (not worth much anymore...)

The fracture in the steel at the base may be the result of a different mechanical failure that had this eventual affect. A broken guy wire or one that slipped because it was not properly clamped and tightened is something else that needs to be investigated. A bracing/guy wire issue could cause the joint to fail outright or cause creep and fracture growth over time.

Please have a qualified failure analysis performed based on all the information that may not be apparent in only these pictures.

The steel in your structure came from China and there was an excess of sulfur causing the brittle failure shown in your photgraphs.

This type of sulfur induced failure is called "red short" or "hot short".

Structures typically fail because of inferior materials or the presence of MBAs in the project team.

Next time buy real steel from Japan, Korea or the USA....

or the presence of MBAs in the project team.

Love it!

Can you share with us how you obtained your apparent definitive information? You are obviously 'in the know', certainly relative to myself! Interestingly, your conclusion supports the content of my earlier input to this discussion.

There seems to be no sign of a ductile failure in the joint.

Even with an undersized bolted joint, there shoud be some sign of bolt hole elongation, member elongation, bolt shear etc.

It costs money to remove sulfur during the production of carbon steel.....under many circumstances, because of the overdesign of many structure, supplying inferior steel is never "caught".

This is a highly competitive marketplace.

Only in a few types of extreme structures (like the joints in your towers) is the material put to an extreme test.

Plus.........in the 1980s and 1990s I have had repeated experience with "hot shorted" steel supplied from the east.

My opinion only

I noticed the lack of hole elongation myself. That led to my earlier suggestion of counterfeit material.

PS Every Friday the 13th I think fondly of Churchy la Femme.

The answer is in the top left picture. Rather than the bolts shear, which are of lower cross-section, the metal between the bolt-holes has sheared instead. So the bolts are stronger than the metal they pass through.

The presence of the rust on the parted surfaces is of interest. An estimate of the time-to-rust would indicate whether the metal was flawed before the tower was assembled, or whether the flaw developed since the fracture opened.

It's interesting that the piece broke before bending rather than bent first. It would suggest that the piece was either constructed of the wrong material, or that it had a catastrophic flaw in it either before it was assembled or that happened during the assembly.

In any case, the tower wasn't sufficiently strong to survive the wind-loading.

Any update on latest findings regarding tower failures!

I am very curious to know about the probable reasons.

Thanks

AKM