Strong River bridge collapse in Mississippi 1

[Sym P. le]

3 killed, 4 injured in Strong River bridge collapse in Mississippi - UPI article

It looks like an excavator went down with the structure during the demolition phase of reconstruction. Sad.

WJTV 12 News

Google Maps location link

 

[LittleInch]

Demolition is a high risk game. Especially with something that is in poor condition.

Without any video or details though not much to say really other than sadness for needless loss of lives. Probably with no comeback for anyone who should have known better.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

I don't know much about bridges. Probably why I will never figure out what an excavator, or is it a backhoe, or is it both, was/were doing on a condemed bridge. Can't you stand off and away while the C4, or cruise missile does its thing?

 

[DirteJoe]

1503, exavators are often run back and forth on old bridges as some of the main demo tools, be it for moving mats, other equipment, busting concrete, etc.

A few years back a company I was working for had an issue with a collapse during a demo job. Someone forgot to weld some braces to the span to hold it in place until it was ready to torch it in half and lift the sections it of there. The excavator operator didnt watch his swing, hit the span with the counterweight and sent the span and a crane into the water. No injuries thankfully. All sites started getting inspected and on ours we found similar issues with our temporary platforms only being tacked and no cantilever braces. Thankfully we caught that just before we took delivery of new counterweights that were due to be stored near the edges. The welder's excuse for why he initially claimed it was all done was he didn't want to overhead weld on rusty steel between tide changes.

 

[1503-44]

Nobody likes overhead welding. Must be especially true when you're thinking about tides. Just one good smart bomb ...

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[DirteJoe]

I was the unlucky one who got to go weld the braces, and smart call on the first guy. One rust explosion sent a hot bb somewhere no one wants red hot metal and it took me a few minutes just to wiggle my way on out of there.
But it was weld that stuff down or let an accident happen. Our geotech guy was doing welding elsewhere and nearly the same thing happened to him.


Seeng how the span here managed to find itself upside down with the road surface below it, I'm suspecting something similar happened that caused it to twist and flip off it's footing. At least that is how it looks to my eyes.

 

[1503-44]

I'm terrible at analyzing pictures. All I see is twisted metal.

Bet that felt like an anti-infrared flare launch!

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[3DDave]

I think safe demolition that doesn't use explosives is riskier than any construction but doesn't always get the engineering review it should get because, why spend money on that if it's just getting torn down?

There was a case of a multi-arch bridge over a railway that was also no big deal. The plan was to block the tracks for one arch section at a time and let the others remain in use. Everyone in the decision path forgot how arches work and as soon as the first was cut through the thrust loads were no longer resisted for the others and all the tracks were blocked.

In this case, not using explosives probably was to prevent material landing in the stream and to save having a crane come to haul the debris out.

It's a lot better when no one is killed or even injured. Making dumb mistakes is one thing, but this is terrible.

 

[1503-44]

I think some debrie is in the stream.

This makes sense to me.
The 62 m-long, 46 m-wide, 6400 t module was the seventh of eight modules required to complete the CPF topsides. Maybe cranes large enough to do a lift can't get to all the places they need to.

https://www.energytodaymag.com.au/ichthys-successfully-lifts-6400-t-topsides-module/

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Lomarandil]

I think safe demolition that doesn't use explosives is riskier than any construction but doesn't always get the engineering review it should get because, why spend money on that if it's just getting torn down?

You're right, it often doesn't get the attention it deserves. And cases like this are tragic.

When done properly, it needn't be risky. Shameless plug here for the best practices guide we published last year

https://ascelibrary.org/doi/10.1061/9780784485361

Maybe cranes large enough to do a lift can't get to all the places they need to.

Absolutely. Planning demolition work is driven by 1) access and 2) material removal. If a crane can accomplish 1, 2 is easy. But most of the time that's either impossible or cost/schedule prohibitive. So you end up finding a balance of what equipment can get there and reach, and how much that will make the material difficult to handle afterward. Explosives are great for #1 but they can make a real mess out of #2.

 

[Sym P. le]

I think I see what happened now. The bridge deck was stripped off the far end of the structure leaving the skeleton frame work. This removed the counterbalance to the cantilevered center span. With the mini excavator on the center span, the centre span dropped, landing in the river intact while flipping the far skeleton frame on its end. This would be a case of poor planning.

 

[LittleInch]

NOt so sure. The digger is sitting right on top of the upper road deck and side supports which have fallen directly down some how.

but agree it lost some counterbalance and the beams have fallen off their supports.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Sym P. le]

The road deck had not been removed from the center span. That was the primary imbalance with the digger being the final straw. The frame sticking up in the air is from the far end of the structure flipped over the support. It's not from underneath the center span. It's a truly bizarre spectacle.

The center span was supported by cantilevers at both ends. The section of the far road deck that was atop the cantilever fell over onto the center span in the river. It is seen upside down.

 

[DirteJoe]

The road deck had not been removed from the center span. That was the primary imbalance with the digger being the final straw. The frame sticking up in the air is from the far end of the structure flipped over the support. It's not from underneath the center span. It's a truly bizarre spectacle.

The center span was supported by cantilevers at both ends. The section of the far road deck that was atop the cantilever fell over onto the center span in the river. It is seen upside down.

This is exactly what it looks like.

 

[3DDave]

I wonder if material removal in reverse of the original material placement schedule would have worked - and - is the original material placement schedule part of filed plans?

 

[Lomarandil]

3DDave -- that's usually the easiest approach, but construction sequences and methods rarely survive 50 years of county records offices.

 

[DirteJoe]

State of deterioration, available equipment, and real world experience of the superintendent also play a major factor in demolition schedules. Things often go wrong in demo, it's a matter of mitigating the severity of it.

The course they were going would have worked just fine had they secured the cantilevered spans from moving during demo and left torching attachment points for last once the beams were being carried by equipment.