Which could of easily been caused by heat these cracks. The road cracks all the time from heat. I am not sure if we will ever know the true cause.
Which could of easily been caused by heat these cracks. The road cracks all the time from heat. I am not sure if we will ever know the true cause.
I'm a structural engineer, but I work on railroad bridges, old (100 years +) and new.
It's not a secret that our country is in severe need of funding for thousands of bridge repairs and replacements, large and small, across the country, both railroad and traffic. I'm sad to say that a tragedy like this may be what's needed to get our citizens' and lawmakers' eyes to open up.
It's very shocking to see something like this. From what I read it sounds like fatigue cracks were present that ma have been a main factor. But it's too early to tell....there appear to be different types of structures and multiple spans collapsed.
It's not a secret that our country is in severe need of funding for thousands of bridge repairs and replacements, large and small, across the country, both railroad and traffic. I'm sad to say that a tragedy like this may be what's needed to get our citizens' and lawmakers' eyes to open up.
It's very shocking to see something like this. From what I read it sounds like fatigue cracks were present that ma have been a main factor. But it's too early to tell....there appear to be different types of structures and multiple spans collapsed.
daniel1113
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Seriously, leave the engineering discussion to the engineers, because you don't have a clue what you are talking about.
Cracks in the road will not cause a bridge to collapse. The roadway isn't even a structural member.
Well, luckily Minnesota is gearing up to spend 1 billion + on a new light-rail road line which will do nothing to alleviate traffic while our road system continues to deteriorate...
The general public should not have to worry about structural failures of a bridge on a major interstate without some sort of Act of God or major accident. It's not like a small overpass (like the one in Quebec) built by some possibly shaky contractors. A lot of people (contractors, engineers) are going to be in deep sh!t over this.
daniel1113
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Sure, but back in the real world, nothing is perfect, even engineering. Even structures that would be considered "standard" designs can have flaws.
Of course, it is important to keep in mind that these types of collapses are extremely rare.
Depending on how a bridge is built, if it is composite concrete/steel, the "roadway" is considered to be structural. If you every see brudge beams with steel shear studs welded onto the top flanges, they are engaging the concrete to work (in compression) compositely with the steel (which is partially in tension). I am not talking about the concrete/asphalt overlay, but the concrete bridge deck.
you have absolutely no clue how engineered concrete works, so shut the fuck up.
any type of structural concrete will crack. in fact, if it doesnt crack, its been grossly overdesigned and will have costed x10 more than an efficient member would have. engineered concrete (reinforced/prestressed) will crack because it relies on the reinforced/prestressing steel to pick up the tension loads. the concrete that is under tensile forces will have to crack in order for the steel to pick up the tensile loads.
My brother uses this bridge everyday during work and I can't reach him. I tried text messaging but it doesn't work.
daniel1113
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One comment was made early on in this on going story that made some sense.
The Northern end of the Mississippi flows very fast during the Spring and possibly under-mined the footings of this bridge. It was only mentioned once, seems like it was hushed for some reason. (law suits for sure)
The Northern end of the Mississippi flows very fast during the Spring and possibly under-mined the footings of this bridge. It was only mentioned once, seems like it was hushed for some reason. (law suits for sure)
13Gigatons
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- Apr 19, 2005
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The coefficient for thermal expansion for steel is 0.00000645in/in/deg F. Unless you are exposed to extreme temperatures, normally you design bearings to move for temp fluctuations of +/-70F from an air temp of 50F. I doubt heat had anything to do with this.
I also doubt scour (undermining of the footings due to washout) is a factor. That would have been too slow and would probably have been noticeable prior to collapse.
I also doubt scour (undermining of the footings due to washout) is a factor. That would have been too slow and would probably have been noticeable prior to collapse.
I don't know how the environment is in MN, probably a lot of cyclic loading and thermal induced loading. I just can't imagine a major interstate that allows tanks to run over isn't engineered with a very high FS (They don't do LRFD back then).
depending on the bridge, the deck may or may not be a structural element. from the pictures i see on CNN.com, it does not look as if the deck is a structural element. you can see the structural beams spaced out under the deck
I live in the TC metro area. I grew up about a mile from that bridge.
I've never seen anything like this.
I've often wondered whether that bridge was under-structured compared to most of the dozens of other bridges spanning the Mississippi in the area. It only lasted 40 years before it fell on its own. Many bridges in the area are much older.
I've never seen anything like this.
I've often wondered whether that bridge was under-structured compared to most of the dozens of other bridges spanning the Mississippi in the area. It only lasted 40 years before it fell on its own. Many bridges in the area are much older.
In a simply supported span, yeah, it'll all be in compression. In some sections of a continuous span there will be negative moment (aka concrete will be in tension).
I just graduated with a BS from Civil Engineering so I don't know too much.
daniel1113
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One important item that has been mentioned multiple times is that only half of the lanes on the bridge were in use. This is why it seems unlikely that the original bridge design was overloaded/under-engineering, and there must be another external factor (construction, etc.).
One year from being a Civil Engineer, and I won't even bother talking out of my as* what happened. Can't tell from pictures since every span seemed to collapse, and even though it looks like a truss system (article says it is), don't know exactly which member carries what to where. The best thing from this is that it wasn't an overpass. A few months ago, an overpass made hamburgers out of a few cars below with multiple passengers around here.
daniel1113
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Non-reinforced concrete will crack on its own due to shrinkage. However, reinforced pre-stressed or post-stressed concrete will crack as the tensile members (the steel) absorb the load.
daniel1113
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Speaking of which, there have been a few shots on TV showing a train that was passing under the bridge during the collapse, and the train cars are absolutely demolished.
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