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OT: Minneapolis Bridge
IlPadrino:
--- Quote from: KingSparta on August 04, 2007, 07:39:08 am ---So lets say you have metal fatigue, cement that was taken off and was being put back on, you could see in the images more than one cement truck on the bridge (they are very heavy), We know the water is swift and 60% of bridge failures happen at the footings, as we know the bridge shifted 50 feet, that could have been because one side of the bridge was heaver that the other, maybe a bad footing, metal over stressed due to the traffic on the bridge, added with the new construction could have created a structure failure, and caused the bridge to shift 50 feet.
"Seconds From Disaster" It is a very good show and here is a link.
http://channel.nationalgeographic.com/channel/seconds/
--- End quote ---
I'll notify the NTSB they can call off their investigation... :-)
That looks like a good show... I'm hoping I can find an air time.
KingSparta:
--- Quote from: JimH on August 03, 2007, 08:09:36 pm ---Yes, it's too early, but I think they had removed the surface, and the surface could act as a compression layer on the top of the deck.
--- End quote ---
I saw a show on Roman Arches a few weeks back, They also went into modern construction and arches, and most bridges are made from arches. Normally when a Arch Fails It Fails Due To Stress Being Too High For The Material That Is Used, Be It Brick, Rock Or In This Case Metal.
Since Arches Transfer There Loads Evenly Thru The Arch, Then Transfer There Loads To the Footing thru the spandrel wall. If The Footings Move And Can Not Transfer The Loads From The Arch Correctly The Arch Will Fail.
There Was No Other Reason Given Why A Arch Would Fail
KingSparta:
--- Quote from: IlPadrino on August 04, 2007, 08:04:10 am ---I'll notify the NTSB they can call off their investigation... :-)
That looks like a good show... I'm hoping I can find an air time.
--- End quote ---
next shows on my Tivo are at
8/6 10am est, 8/8 3 am, 4 am & 5 am, 8/14 3 am
They take data from the NTSB and other sources to recreate the event, and explain both visual and verbal the key steps\events in the Disaster.
my wife hates it, but I am always thinking about how things break or failed and what could be done to make it better. I have made suggestions to companies I normally work with on how to make this work better or safer.
I have seen some disasters closeup, and when someone dies you know it makes you think about many things at many levels.
PeterS:
There was more talk in the local news today about the possible causes of the collapse, and one possibility is a design flaw in the steel (gusset) plates that connected beams. On top of this there more speculation about contributing factors from the construction that was taking place. The constuction company are adamant that their repairs did not cause the failure.
Here are some extreme close up photos taken shortly after the bridge went down:
http://drugoi.livejournal.com/2280005.html
scthom:
Those are some pretty amazing photos.
I'm not a forensic structural engineer, but...
I've heard about the gusset plate too. I believe that most of these events are connection failures as opposed to gross failures of the members, so the gusset plate makes sense, though it might be possible that the reduced concrete thickness where the construction was taking place might have made the bridge more flexible (I understand they were removing & replacing 2" of the 10" concrete deck). Which might have contributed to extra movement and loading on any reportedly fatigued members.
I also heard this particular bridge was only really supported in one direction (longitudinally -- along the roadway) and there wasn't much support in the lateral (across the roadway) direction. Given the dead weight of the bridge itself, it's not usually possible that the vehicles could unbalance it. But between the lighter concrete deck(20% removed), rush hour (all the traffic on one side?) and the construction vehicles, they may have been able to do it. It's not clear to me which direction it moved in relation to those factors.
In any case, it's still a miracle there weren't more casualties.
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