Posted on 08/04/2007 11:49:45 AM PDT by kathsua
I've been looking at some of the video showing the collapse of the I-35W bridge over the Mississippi River in Minneapolis and it looks like the collapse could have resulted from a major mistake by the company working on the bridge's surface. The bridge carries eight lanes of traffic, four each direction. To maintain an even load on the bridge supports during construction the contractor should have either worked on the two inside lanes of both sides of the bridge or the two outside lanes. Instead the contractor worked on the inside two lanes of one side and the outside two lanes on the other.
The result was the support on the side in which the outside lanes were carrying traffic had to support a greater load than the side on which the inside lanes carried traffic. I'm oversimplifing, but essentially the support on this particular side would have been carrying the load of the traffic directly above it as well as a portion of the traffic on the other side. The support on the other side would only have been carrying a portion of the load on its side.
If you've watched videos from the scene you know there is a school bus and semi truck next to each other in those outside lanes. There is another semi just behind them. These heavy vehicles went across the supports just before the collapse. The supports on this side of the river shifted toward this side with the roadway shifting toward the other side as if the weight of the heavy vehicles may have been too much for it to carry in a weakened state
My background is in math and physics rather than engineering so I'm not familiar the precise distribution of weight and how the supports carried it, but the basic math would indicate more stress on one side of the bridge than the other.
A computer analysis of the remains of the bridge and its design will be necessary to determine the precise amount of stress on the different pieces of the bridge and their physical condition. This analysis will show exactly which part(s) failed. Fortunately investigators have a computer program using Finite Element Analysis developed at the University of Minnesota.
Read my post above.
The higher the concentration of libs, the bigger the tragedy that follows.
It’s not the vertical force from sodiers feet. It’s vibration caused by them. The natural frequency of a structure is the one that creates standing waves. If an army marching in step happens to be marching at the natural frequency of a bridge when crossing it...standing waves result and the bridge falls.
The tacoma narrows bridge fell from standing waves created by wind.
The fine was $50 million dollars, I don’t think that made cheating worth it, do you?
That is a low, sleazy slam. How do you think ythe thing stood 40 years if it was a bad construction job. Do you think all of us contractors are just scumbags who only rip people of? That's a really ignorant view. If it were true, wouldn't more of us be in jail?
How about wising up instead of making spurious, ignorant accusations.
Oh, and WTF is rake-off? I’ve been in construction my whole life and never once heard that term.
That’s a lovely bunch of Brits shagging us with bad concrete.
I put about 30,000 cy of their concrete in the ground, and every single bit of it I poured passed inspection by BPB (Central Artery prject management) inspectors.
Nice to see the guy who hecks on us contractors agrees we aren't the sleazes the ignorant folks try to mak us out to be. Yes, there are sleazes, but they don't last long, and very rarely are they in heavy construction.
Very unlikely, IMHO. If weight distribution could cause it, then bridges would be falling down with every traffic jam when one side is lined bumper to bumper all the way across and the other is virtually empty. A bridge cross twice every day is always backed all the way across on one or the other lane at rush hour.
Isn’t the contractor ultimately responsible for all the material bought and people they hire? If not who is?
Someone has to provide the material specs to the suppliers, qualify the supplier, order the materials, then do on-site tests for things like at-pour concrete cylinders and steel samples for the lab tests. Who else would be responsible for that? Who hired the resident engineer and tesing lab?
I couldn’t have said it better than myself! I’ve seen way too many mistakes made, in fact I rarely watch anymore because I find too many flaws to list...
That follows in everything, construction, law, medicine, defense ...
I've been involved in construction nearly all my life, and I would have to say, if someone approached the guys who do these big projects with an offer of a cheaper-non-approved materials,(Insert Eddie Murphy doing ambulance noises here)
And it probably does happen, but the consequences are too pricey. There is a number of checks and balances, including the most important thing of all, simple pride in doing a world class project, sounds corny, but these guys will drag their grandkids clear across the country to show off something they built.
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