Silo Demolition in Denmark Goes Wrong 3

[bimr]

Silo demolition in Denmark goes wrong and crushes cultural centre. No one injured when 53-metre high silo fell the wrong way, but library and music school were crushed.

https://www.theguardian.com/world/2...enmark-goes-wrong-and-crushes-cultural-centre

 

[3DDave]

I liked the video that article linked to where two out of six apartment buildings refused to go down for the count. Just standing there as if to say - a wounded apartment building is a dangerous apartment building. Or a character from Monty Python and the Holy Grail.

 

[LittleInch]

I saw that one. Looks as if the tower had a substantial section at the base which wasn't being destroyed. The hole in the tower was presumably being propped up with something which is then removed by explosives and the tower should then fall sideways.

What seems to happen is that the structure actually moves slightly to the left as we see it and the outer shell moves and falls to the ground. However the hole in the cylinder then hits the solid lower structure and the lean becomes reversed.

Maybe just too much explosives on the retaining device or not enough of the wall removed to start with.



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[dik]

LittleInch:
With explosive demolition, it's sometimes difficult to determine the stiff elements of a structure.

Dik

 

[LittleInch]

This is a better video - scroll through to about 2:09 for the explosion, but shows how they removed a large section and also seem to have weakened the right hand side by the line in the concrete.

https://thenewdaily.com.au/news/world/2018/04/09/silo-demolition-goes-wrong/

True, demolition seems more art than science.


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Also: If you get a response it's polite to respond to it.

 

[JohnRBaker]

I suspect that if they had cut that notch further back another foot or so, that would have done it. If you look carefully, it does not appear that the notch that was cut was far enough past the center axis of the silo.

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[IRstuff]

Looks pretty clear from the 2nd video that the silo essentially rebounded off the base section that should have collapsed, but didn't...

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[JAE]

Yes - the back side slipped outward and that side "nested" with the lower back side wall. The rubble from the initial explosion created a fulcrum on the "fall side" and reversed the fall direction.

I think John is correct that a deeper notch may have been needed here.

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[IRstuff]

I don't think the notch mattered. There's expectation that the silo would rotate into the direction of the cut, but Newton's Law says that things will go in the direction they started, which is down. It's likely that a deeper notch wouldn't have mattered, since the issue is they purposely weakened the un-notched side with a horizontal cut, so blowing the temporary supports caused the horizontal cut to give way almost immediately, thereby eliminating the expected rotation. Had they not made that horizontal cut, the un-notched side might have stayed intact long enough for the imbalance to develop the rotation needed to tilt the building in the direction desired.

Obviously, in hindsight, and in view of other, similar, YouTube demos gone awry, they should have demo'd the base side under the notch instead of demoing the supports in the notch.

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[Latexman]

I think the back side slipped outwards when the mid-silo, steel-framed(?) access door approached the right steel-framed(?) base access door. The concrete below the mid-silo, access door and above the right base access door went into compression and halted the collapse of that side.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[IRstuff]

But, you can clearly see the cuts they made on the side away from the notch, and that part of the silo failed exactly along that cut.

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[Spartan5]

Looks like they cut the notch on the wrong side *shrug*

 

Speaking as a metallologist, it appears they cut a large notch on one side and then expected it to fold over like metal would. The initial phase of collapse was approximately straight downward; from there it went its own way.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[3DDave]

There was a big notch on one side and a thin slot on the back; the silo started to rotate the correct direction but the rear cut allowed the tube to fall farther than height of the notch; since the opening of the notch was smaller than the height it fell from, the notch hung up and halted the rotation and reversed it. Unlike a tree, there's no hinge material to prevent hopping off the stump so it allows for random behavior. I suspect there was a structure inside the tube that was the fulcrum; the 'ground floor; seemed unaffected by the fall of the tube and must be substantial preventing them from blowing it out at the base. The initial rotation pushed the far side off the internal structure which is where the amount of drop became a problem.

 

[dik]

Hindsight is good... the stiff wall and the right should have been blown away... it acted as a fulcrum and caused the silo to fall to the left...

Dik

 

[JohnRBaker]

I know this is hindsight, but if they had reversed the orientation of that cut, that is if it had it been angled DOWNWARD instead of upward, the base of the silo would not have acted as a fulcrum, at least not one that would reversed the intended trajectory of the collapse. Granted, there may have been too much structural material in the lower section to make that sort of cut practical, but as has been stated before, if more attention had been taken to removing as much of the base on the side toward the direction they intended the silo to fall, that would have certainly helped.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

More 20-20 hindsight: they should have waited for a more favourable wind direction.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[ornerynorsk]

A buddy of mine that is a retired Navy construction diver has a favorite saying - "There are few problems which are not solved by the application of an excess of explosives".

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[VEBill]

Somewhat unrelated comedy story:
A lumberjack claimed that he can make a tree fall, "...in any direction I want."
So I pointed to a tree that was leaning 60° straight South and challenged him to make it fall North.
His reply was, "Well, in this case, I want it to fall South."

 

[jrs87]

Hmm, 53 meters, same as FIU bridge.

Tall structures have more resistance to rotation during fall than intuition suggests. What ever happened to just using a wrecking ball?

This video

https://youtu.be/vCPRBwp1TLM

is very clear and is valuable even if silo collapsed in desired direction. I would encourage engineers to rewatch it several times, not just trying to determine why silo fell wrong way, but to note dust puffs, structural flexing, etc.