Posted on 08/01/2007 4:28:27 PM PDT by ButThreeLeftsDo
Just turned on the news. 35W bridge collapsed in the Mississippi River. Cars, trucks, semis.....
Fires burning, tanker trucks, at least one school bus, more than ten cars......
Just now breaking.......
More great stuff, Holly.
I need to call it a night, since I’ve been here since the git-go....and the alarm will go off at 05:00.
Thanks to you and all FReepers that made this an important evening. Your help was well received.
Bill Oh Really........This ain’t a right wing hate site!!
So there....
blu wrote:
So, to sum up, can we surmise that the bridge collapsed because of the following:
overload (too many construction vehicles, poorly placed, too much traffic)
freight train vibrations/displacement (oh, please say this had something to do with it! It makes such a
simple visual for me!)
You have given some great explanations, pictures even. Thanks for all your work!
********************
We don’t know why the bridge collapsed, but we are getting a better idea of how it collapsed, the progression of the failure.
In a cantilever bridge like that one, the live load, cars and trucks, construction vehicles, etc., is a pretty small fraction of the dead load, the weight of the bridge structure itself. Sure, extra vehicles will increase the chance of failure, just as one extra straw will break the camel’s back. But it’s not the one straw that does it, it’s the total load, of which heavy traffic probably wasn’t the largest fraction.
I could see vibration from trains disturbing old concrete, but that’s why they inspect bridges periodically. Significant subsidence, or cracks from vibration, even in a sidespan pier, are unlikely to remain unnoticed.
Best guess right now, heavy live loads, train vibration, construction mistakes, and metal fatigue look good, with metal fatigue being a critical element. Something brought down the supports for the bridge deck, either at the north main span pier, the next sidespan pier north of that, or both.
I’m less likely to look for footing or concrete issues because concrete usually shows visible problems before they are fatal.
Metal fatigue shows problems too, but it can be very difficult to judge precisely how severe they are. Fatigue occurs when metal is stressed beyond it’s elastic limit. Bend or stress metal, let go, and it returns to it’s original shape, fine. Bend or stress it too far, deform it permanently, and internal issues start to cascade. Internal means “hard to see”.
Vibration from a train or construction work puts much or all of the dead load in motion. Energy calculations involving motion include a velocity squared parameter, a force magnifier which can quickly become signnifcant, either at the time of a failure, or leading to metal fatigue before a failure.
The devil’s going to be in the details on this one, either in the steel over the north mainspan pier, or the next sidespan pier and/or steel above that. Looks to me like the area around the 1st sidespan pier north of the main is hard to access right now.
But then I looked very closely at the lock and dam. Before a lock can be opened, the water must be drained. Where are the water currents located, when this lock is being emptied?
I have enjoyed a boat trip with my wife at this location, where we sat in that lock and waited for the water to be emptied.
TOKYO (AP) - Japan’s Meteorological Agency says strong quake has hit southern Sakhalin, issues tsunami warning for northern Japan.
#1659, top pic: due east of the maroon car: all those bolts missing from their holes: probably what made the ‘jackhammer’ sounds as they stripped and shot out and reverbed around the structure.
Prayers for all those involved..
We found out about this listening to Jason Lewis on the radio late on the way home. Unbelievable!
First reports are always wrong, and Shep Smith is about as far from being an experienced civil engineer or expert of any kind as it is possible to be.
I’d LOVE to have Sheppie on one of my crews for a week or two. He’d be whimpering before the first coffee break.
Also a 6.9 in Alaska!
After the Andreanof Islands quake?
Mine too. I still can’t believe how horrible this is.
I’m inferring direction here. I’m trying to allow for ambiguity on bridge orientation, but you’d probably have to follow the posts from the beginning to stay on track.
I’m pulling up some maps now, should alleviate that issue soon.
That doesn't make sense. All the bridge pilings were on dry land. The bridge had no structural elements in the river.
They also mentioned that there was significant rain and potentially some flooding a couple of weeks ago.
Jeffers, I am intrigued by your theory on this.
It disturbs me that that the pier on the south(?) side is so out of plumb, post collapse. The north side pier has both towers intact, except for a violent reaction at the top of the piers, where the rocker plates have been ripped off the top of the piers.
The other pier has both rocker plates intact, and the span appears to have snapped cleanly off at the pins.
If something happened at the north side, with a lateral deflection sideways of the span(not the piers), I could see the center span pulling at the south pier, pulling it toward the center of the river. The half arch span to the south broke cleanly off once the southern pier went out of plumb, and leans, almost intact to the south.
But what if there was scour at the south pier, which is at the waterline and has no lateral support similar to the support enjoyed at the northern pier. What if that pier went out of plumb and twisted toward the river, making both spans it supported rip off their rocker pins, and the center span falling into river, tore the northern part of the span and twisted it off of the northern pier, which is not out of plumb post collapse.
The fact that the southern pier is now out of plumb is disturbing, because it shows that, in either case, it was the weaker of the two piers.
The slide show posted by Norms Revenge earlier shows some more shots of the southern pier.
The local news reported that a 2006 inspection noted stress cracks and metal fatigue problems in both the main girders and the diaphragms, but there was no indication of the (now apparent) severity. I would hate to be the engineer who authored that report.
Prayers for all involved in this tragedy.
PERFECT!
The builders allowed for the rapid flow of the river on the North side, but below the lock, that is normally calm water. However, when they drain the lock, the bridge pier would be subjected to scouring.
If this happened, the East side of the bridge pier (down on the first image on 1674, would be on the down flow side and would be the first to drop.
If the down-flow side dropped, it would cause the twisting movement of the bridge towards the East, and cause the North side of the bridge to move West. This is what we see in the images.
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