Solve bridge collapse ~ win prize

[Iamme]

The prize is (drum roll)......your own personal pride and satistfaction that you figured it out.

I have several theories. But would LOVE to have the blueprints of the bridge or close up photos of the underside of the bride (when it was intact, of course).

I do NOT believe the collapse was caused by an aged weak bridge, per se. Listening to tv reports, it said this bridge, along with thousands across the nation, are not up to snuff. Yet, they were still deemed worthy to allow to be open to traffic.

No. The collapse was sudden. It was not as if the concrete were weak and crumbly. If it were, the girders still should have remained, like a human skeleton remains after something happens to your skin.

Did years of salt eat away at critical rebar? Sounds plausible. But why woudn't then the deck crumble and fall in and leave the girders standing?

Did the construction workers jack hammers trigger it? Doubt it. As said, even if they scored through the concrete like someone scoring tiles, where then they can snap...how do yo explain the whole bridge, skeleton and all, come down. Did guys operating heavy machinery go flying their vehicles laterally and come to a sudden stop creating a scenario undesigned for lateral shift? Hmmmm. Only the construction workers would know what they were doing up there.

And it came down in such fashion as if...well, here:

As if the pier, outside the video they show, of the collapse, took a shift.

Or some dopey construction workers filled in the expansion joints because vehicle tires were banjhginginto them too much.

Expansion joints are very critical to such spans. VERY critical. The weather had been very hot there. Around Eau Claire our 8-10 inch thick roadbeds suddenly explode in areas, every year it is hot, due to the heat, and have to be sectioned out and replaced.

Perhaps heat expansion triggered the whole thing.

Perhaps construction or other debris fell down into the finger-jointed? expansion seams.

No reports I have heard give any witness accounts of hearing a bomb explosion before the collpse, so I doubt terrorism. How else could a terrorist cause a bridge to collapse? Think there was someone hiding under the bridge with oxygen-acetylene torches cutting the steel?: I doubt it.

I doubt structural 'fatigue' also. I can't see those heavy duty H-beam? girders just suddenlky 'sheering'. I think they shifted off the pier. Notice how the segments of the concrete sections are not torn. Note that they are likely the expansion seams, in a perfectly straight line. It is as if someone pulled the bridge off the supports. And*I* believe this is what collapsed it. Now it is really a matter of figuring out exactly why.

But I doubt they will find the answer in the twisted rubble. I think the answer will come from theory from the bridge design, and known facts about the piers ...possible water eddies eroding the base or some sudden collapse of the river bank that kicked out a pier just enough to create a shock wave, or the other stuff I said.

The "structural engineer" who was interviewed on the news the night of the collapse offered no explanations, like I am doing here now. I thought to myself when listening to him that a 5th grader knows more.

You can watch the collapse on YouTube by typing in bridge collapse. Several links on there my friend tells me. When I get time, I'm going to keep watching these.

[webfusion]

I say that there was a localized sudden increase in the earth's gravitational force, which was directly focused on that section of the Mississippi, causing the flimsy man-made structure across the river to to buckle under these extra g-forces.


On second thought, I'll go along with James E Amrhein ----
""Structural Engineering is the art of molding materials we do not wholly understand into shapes we cannot precisely analyze so as to understand forces we cannot really assess in such a way that the community at large has no reason to suspect the extent of our own ignorance."

(Newtons Bit sig line)

[Iamme]

That is a pretty neat quote. Almost sounds like something a politician would come up with if they knew lawsuits woud be involved. :)

[MWare]

Boy I'm glad we don't have any old bridges here in Brooklyn :)

[Iamme]

Boy I'm glad we don't have any old bridges here in Brooklyn :)

Ah...ya. They said on tv that the I-35 bridge was relatively young (40-some years?) compared to the likes of the Brooklyn Bridge (like a hundred?).

Oh. And that is why I think something catastophic happened as opposed to the bridge getting weak and/or wearing out.

[MWare]

Ah...ya. They said on tv that the I-35 bridge was relatively young (40-some years?) compared to the likes of the Brooklyn Bridge (like a hundred?).

Oh. And that is why I think something catastophic happened as opposed to the bridge getting weak and/or wearing out.

Ok. Then would you accept "They don't make 'em like they used to?" as a valid entry to the contest?

BTW -
Brooklyn Bridge - completed 1883
Williamsburg Bridge (my bridge) - completed 1904
Manhattan Bridge - completed 1909

But of course, you already know which one is for sale...

[Iamme]

No. I believe the engineering was flawed. Not the materials. Or someone did something dumb or accidental like the expansion joints got filled up. Something like that. But on the I-35 bridge massive steel beams were used (from what I can tell) and reinforced concrete. See nothing wrong with that.

[Newtons Bit]

The reason why most older bridges don't have fatigue problems is because how they were designed.

Fatigue is a function of cyclic loadings that are close to the yield stress of a material. The cyclic loading for the bridges is all approximately the same, though same bridges see more heavy traffic than others. The difference between new bridges and bridges such as the Brooklyn bridge is how close to failure they were designed. The brooklyn bridge designer basically licked his finger and stuck it out into the wind to figure out what the load and stress in the bridge would be. And then applied a really large factor of safety or as I like to call it, a fudge factor. Fudge factor being that his methods of analysis and the knowledge of mechanics of materials at the time were very very poor.

Newer bridges are designed to be as economical as possible, which means designing for exactly what the bridge will see in it's lifetime and not spending millions of dollars for more steel and concrete than is needed. This bridge, being built in the 60's, had designers who were almost as proficient as today in terms of analysis and mechanics of materials. They just had to do everything by hand while today we do it with computers.

Being designed to be economical, this bridge does have problems with fatigue. The size of the beam doesn't matter as much as how close to yield the material is and how large the cycles are.

[alfaniner]

My theory is already posted elsewhere.

[roger]

Gravity.

[Dan O.]

I think you will not find a single cause but a set of circumstances that add up to the catastrophe. There was undoubtedly corrosion of the steel and crumbling of the concrete caused by the harsh winters and deicers. The construction changed the load balance on the bridge by stripping part of the roadway and confining traffic to 1/2 the lanes.

Part of the strength of the bridge comes from the structure as a whole so when 1 section fails it is easier for the rest of the bridge to topple in a domino effect.

[Snide]

The reason why most older bridges don't have fatigue problems is because how they were designed.

Fatigue is a function of cyclic loadings that are close to the yield stress of a material. The cyclic loading for the bridges is all approximately the same, though same bridges see more heavy traffic than others. The difference between new bridges and bridges such as the Brooklyn bridge is how close to failure they were designed. The brooklyn bridge designer basically licked his finger and stuck it out into the wind to figure out what the load and stress in the bridge would be. And then applied a really large factor of safety or as I like to call it, a fudge factor. Fudge factor being that his methods of analysis and the knowledge of mechanics of materials at the time were very very poor.

Newer bridges are designed to be as economical as possible, which means designing for exactly what the bridge will see in it's lifetime and not spending millions of dollars for more steel and concrete than is needed. This bridge, being built in the 60's, had designers who were almost as proficient as today in terms of analysis and mechanics of materials. They just had to do everything by hand while today we do it with computers.

Being designed to be economical, this bridge does have problems with fatigue. The size of the beam doesn't matter as much as how close to yield the material is and how large the cycles are.That's pretty much what I heard an expert say on TV. The old bridges...he's not so worried about. They were built with lots of redundancies (I assume that's the same as reinforcements, or like 3 beams where 1 should be strong enough). He personally had a bridge of his lose four beams over time, and the bridge had no problem withstanding it. A bridge as "sleek" as the I-35W bridge can't withstand such breakage.

In other words, MWare was right!

[Iamme]

I forgot something important. Could be wrong about terrorists. Maybe they painted acid on the girders undernheath. Like in a James Bond movie where someone falls, screaming to their death, into a vat of acid.

[Iamme]

I think you will not find a single cause but a set of circumstances that add up to the catastrophe. There was undoubtedly corrosion of the steel and crumbling of the concrete caused by the harsh winters and deicers. The construction changed the load balance on the bridge by stripping part of the roadway and confining traffic to 1/2 the lanes.

Part of the strength of the bridge comes from the structure as a whole so when 1 section fails it is easier for the rest of the bridge to topple in a domino effect.

So you think bumper to bumper traffic in only 2 lanes would have been worse than a bridge that should have been designed for a convoy of tanks, bumper to bumper, in all 8 lanes at once?

Which two lanes I wonder were closed?, or open?

I wonder if the designer of the bridge is still alive ? and swallowed his false teeth when this happened. If this was MY bridge, I think my heart would have skipped some beats at the very least.

[Iamme]

My theory is already posted elsewhere.

Well? Where?!

[Iamme]

The reason why most older bridges don't have fatigue problems is because how they were designed.

Fatigue is a function of cyclic loadings that are close to the yield stress of a material. The cyclic loading for the bridges is all approximately the same, though same bridges see more heavy traffic than others. The difference between new bridges and bridges such as the Brooklyn bridge is how close to failure they were designed. The brooklyn bridge designer basically licked his finger and stuck it out into the wind to figure out what the load and stress in the bridge would be. And then applied a really large factor of safety or as I like to call it, a fudge factor. Fudge factor being that his methods of analysis and the knowledge of mechanics of materials at the time were very very poor.

Newer bridges are designed to be as economical as possible, which means designing for exactly what the bridge will see in it's lifetime and not spending millions of dollars for more steel and concrete than is needed. This bridge, being built in the 60's, had designers who were almost as proficient as today in terms of analysis and mechanics of materials. They just had to do everything by hand while today we do it with computers.

Being designed to be economical, this bridge does have problems with fatigue. The size of the beam doesn't matter as much as how close to yield the material is and how large the cycles are.

I can tell a structure famework by looking at it if it should work. Take that bridge that looks like a Roman aquaduct, that stands next to the collapsed bridge: THAT bridge could see a convoy of tanks. I can tell.

Remember when the crane Big Blue collapsed over the being-constructed Miller Park in Milwaukee some years back? Well any idiot could see that that crane was too tall and lanky. Just because the thing was 'bridged' by all sorts of angular metal means nothing. You KNOW that something has to give! Idiots!!! And they go to design school for this? Idiots!

Designing a bridge as some borderline case would be stupid. What if they had a parade over it and everyone were to jump up and down in synchrous harmony, while floats were going over it? The designer, unless weighing in every possible factor, would have to be an incompetent moron and worthy of being sued if he did not account for realistic scenarios that could happen at any time in the lifespan of the bridge. (Having it withstand a full impact by a jet, I would not consider required.)

[fuelair]

I can tell a structure famework by looking at it if it should work. Take that bridge that looks like a Roman aquaduct, that stands next to the collapsed bridge: THAT bridge could see a convoy of tanks. I can tell.

Remember when the crane Big Blue collapsed over the being-constructed Miller Park in Milwaukee some years back? Well any idiot could see that that crane was too tall and lanky. Just because the thing was 'bridged' by all sorts of angular metal means nothing. You KNOW that something has to give! Idiots!!! And they go to design school for this? Idiots!

Designing a bridge as some borderline case would be stupid. What if they had a parade over it and everyone were to jump up and down in synchrous harmony, while floats were going over it? The designer, unless weighing in every possible factor, would have to be an incompetent moron and worthy of being sued if he did not account for realistic scenarios that could happen at any time in the lifespan of the bridge. (Having it withstand a full impact by a jet, I would not consider required.)
And your degree in structural engineering is from which accredited school of engineering again?

[NotJesus]

And your degree in structural engineering is from which accredited school of engineering again?

Iamme doesn't need education. He just knows stuff.

[strathmeyer]

Why start with this bridge collapse, Iamme? There are plenty of older bridge collapses that we know much more about, why not start there?

[rtalman]

http://www.cnn.com/2007/US/08/02/bridge.collapse/index.html

Two years ago, the U.S. Department of Transportation (http://topics.cnn.com/topics/u_s_department_of_transportation/)'s National Bridge Inventory database said the bridge was "structurally deficient."



The bridge received a rating of 4 on a scale of 0 to 9. A bridge receives a rating of 4 when there is "advanced section loss, deterioration."Sounds like the bridge was plain old worn out.

I think there should be a new law enacted that all bridges should have their DoT rating posted on a big sign on both sides. Then you can decide if you are going to take your chances driving across a structurally deficient bridge or not.

[Newtons Bit]

http://www.cnn.com/2007/US/08/02/bridge.collapse/index.html

Sounds like the bridge was plain old worn out.

I think there should be a new law enacted that all bridges should have their DoT rating posted on a big sign on both sides. Then you can decide if you are going to take your chances driving across a structurally deficient bridge or not.


The current cost to replace all of the detoriating bridges around the nation is about 1.2 trillion dollars. Yee-haw. That's the money for things that should already be retired.

[rtalman]

The current cost to replace all of the detoriating bridges around the nation is about 1.2 trillion dollars. Yee-haw. That's the money for things that should already be retired.That's politics for you.

Here in WA, we have a heavily traveled viaduct that the DoT has determined will collapse in an earthquake of magnitude 6.9 (rare, but not unheard of in this area). Tax money is being collected that is earmarked to repair/replace this piece of road. The determination of the danger of collapse was made soon after it was damaged in an earthquake in 2001. More than 6 years later, and have they started work on fixing the problem? No, the pols are embroiled in a state vs. city *********** contest.

[Iamme]

And your degree in structural engineering is from which accredited school of engineering again?

The accredited school of working with tools for 36 years in nuclear power plant construction, high rise beach condo construction, house and apartment building...and common sense that develops after even building decks.

[Iamme]

Iamme doesn't need education. He just knows stuff.

That too. Must come from God as a blessing for being a good boy.

I make a career hobby out of finding out and trying to do what I otherwise haven't done before, and take pride in being able to figure things out without being formally schooled in the 'how-to's' of it, as THAT wouldn't be any fun... as then it be exPECTed of you.

If you were driving along and saw this building and the walls were bulging outward so that the top of the wall where the rafters sit had a curve, from the perspective of you sighting down the length of the building...would you be at all curious as to what caused that on THAT building and not on others? You have to be that type of person. I am.

[Iamme]

Why start with this bridge collapse, Iamme? There are plenty of older bridge collapses that we know much more about, why not start there?

The only other bridge collapse that was of great significance that I can recall was that of the Tacoma Narrows Bridge. I don't specifically seek out these things and can't recall them being in the news. But I heard the other day that they said there is like one bridge a week that collapses in the U.S.. Really?

That said, with these other bridge collapses, have they learned from other steel truss/deck bridges that have collapsed?

[Iamme]

(See post 20)

rtalman,

That particular bridge was given a rating of 4 out of 10?

I wonder what the interpretation of a 4 is, since they allowed traffic on it?

I wonder exactly what the repair work consisted of?

[rtalman]

(See post 20)

rtalman,

That particular bridge was given a rating of 4 out of 10?

I wonder what the interpretation of a 4 is, since they allowed traffic on it?

I wonder exactly what the repair work consisted of?I don't know, but I would give a bridge with a 4 of 9 rating the same title as Nader's book on the Chevy Corsair: Unsafe At Any Speed.

[Iamme]

Corvair

[fuelair]

The accredited school of working with tools for 36 years in nuclear power plant construction, high rise beach condo construction, house and apartment building...and common sense that develops after even building decks.
No offense, but working on and knowing structural requirements are minimally associated. Also, you were not working (unless you left out something) on things that use the same structural standards, methods, load calculations as the bridge in question.

[fuelair]

4 of 9 means the bridge needs work - soon - but is ok for use by the public. Apparently (no hard reports) soon means around 4 - to -10 years.
For real thing read the part on bridges: http://www.fhwa.dot.gov/policy/2006cpr/chap3.htm - it is a way down but gives the details on the 0-9 thing.

[Iamme]

I just got on the board and have not looked at the posts yet. Something I want to say. I was wrong in some of my assessments. After last nights news reports on the bridge I now know more about the bridge.

It was a piece of junk. Not at all like I imagined it being designed. It was one of those like 1920's-1930's relics that have all the metal joints and tons of rivot-type bolts hoding it together. I have heard now that here was severe rusting, even a 4 foot long fatigue crack..and missing bolts!

Come on! And they let cars across that thing? Especially being that it is what is called a redundant bridge where if one link breaks the whole thing goes?

Lawsuit time.

Regarding the expansion joint theory I had. Well, the winter salts could have leached down in these gaps, as an expert stated, and contributed to the deterioration.

[Iamme]

No offense, but working on and knowing structural requirements are minimally associated. Also, you were not working (unless you left out something) on things that use the same structural standards, methods, load calculations as the bridge in question.

No offense? That's all right. I am a sporting chap. If you guys don't let me have it on this thread, I know you will when I talk about God, so what's the difference? :)

[Carnegiea]

No reports I have heard give any witness accounts of hearing a bomb explosion before the collpse, so I doubt terrorism. How else could a terrorist cause a bridge to collapse? Think there was someone hiding under the bridge with oxygen-acetylene torches cutting the steel?: I doubt it.


There's also intense heat. I'm a little unclear on the particulars, but an East Bay bridge partially collapsed in late April due to fire. The heat from a burning gasoline tanker melted the steel underbelly of the overpass, causing it to collapse onto the road below.

I'm not an engineer, but it seems likely that increased traffic caused by more people living in urban areas (as well as in increase in population in general) increases wear and tear on roads. This would probably apply to bridges and overpasses as well. The bridge that collapsed was on the low end of the bridge strength acceptability scale, or whatever it was they use to rate the structural integrity of bridges.

[Iamme]

There's also intense heat. I'm a little unclear on the particulars, but an East Bay bridge partially collapsed in late April due to fire. The heat from a burning gasoline tanker melted the steel underbelly of the overpass, causing it to collapse onto the road below.

I'm not an engineer, but it seems likely that increased traffic caused by more people living in urban areas (as well as in increase in population in general) increases wear and tear on roads. This would probably apply to bridges and overpasses as well. The bridge that collapsed was on the low end of the bridge strength acceptability scale, or whatever it was they use to rate the structural integrity of bridges.

Sure heat can do it. But none was applied I don't think. A burning tanker...or no jet that crashed into this, for that matter...was involved in THIS collapse.

Your second paragraph states things that are already known now by the general population. They discussed more about all this in greater detail last night on the cable news shows, with engineers.

[Carnegiea]

I'm just mentioning intense heat as a cause of bridge collapse. I'm not saying that it caused this bridge collapse, as obviously someone would've noticed a huge fire.

[Newtons Bit]

I was talking to some of the other engineers in the office. The problem with bridges of this type is that the welds on the splices are concealed and can't be inspected. If any fatigue cracks developed they'd never be detected.

[Iamme]

I was talking to some of the other engineers in the office. The problem with bridges of this type is that the welds on the splices are concealed and can't be inspected. If any fatigue cracks developed they'd never be detected.

Or what about workers heavily painting over stuff?

[Iamme]

Well I'll be.

Read this from the same forum, different thread on same subject:


Not a structural engineer, and I didn't read the report, but I am a civil engineer.

My take on it is that the vehicle load during rush hour, combined with some aspects of the renovation construction (and presumably, removal of some features of the bridge that provided a measure of strength in one axis or another....I'm thinking of removal of roadway compromizing the strength of the box structure of the bridge, myself) exceeded the design load of the bridge.

I know this sounds like a lot of supposition, but typically the most stress a structure undergoes is during construction, as all the pieces that act together to provide operational strength that includes a good margin of safety are not there. The pieces in place are under far greater stress than they'd ever be once the structure is complete and fully loaded.

I hope my wild speculation doesn't derail this thread.


It just dawned on me! Just like I'm the first one who saw the big W in the Mad, Mad World movie, after reading the above.

Of course! If they removed let's say heavy roadbed or other weight off the bridge in ONE section... the weight of the forces downward on the trusses where the weight still WAS would then try to shove UP on the section that was being stripped of some of it's decking! Of course. That's IT!!!

I hope someone from CNN, Fox, or the NTSB, Minnesotas DOT or ? reads this!

............

This is so important, I have to add to what I said. IF...the bridge had some of it's weight removed, in certain sections...do any of you understand the principles of cross bracing? Well, if you no longer have the same downward forces acting on all the braccing, uniformally, some of the adjacent bracing then wil try to thrust upwards! Picture this in your head:

Imagine for simplicity, a heavy flat line ontop of a big U line. Underneath the U-line is another long heavy duty horizontal line. Draw that out on paper. Now picture adding cars, and trucks, evenly across the top line. This exerts tremendous but even forces on the u-line. Now picture removing some of the top line, let's say on the right, above the U-line. Now what will happen is there wil be more weight on the left side of the U than the right. The left member of the U will go downward and after hitting the botom line, will try to push up on the right side of the U.

[Newtons Bit]

Well I'll be.

Read this from the same forum, different thread on same subject:




It just dawned on me! Just like I'm the first one who saw the big W in the Mad, Mad World movie, after reading the above.

Of course! If they removed let's say heavy roadbed or other weight off the bridge in ONE section... the weight of the forces downward on the trusses where the weight still WAS would then try to shove UP on the section that was being stripped of some of it's decking! Of course. That's IT!!!

I hope someone from CNN, Fox, or the NTSB, Minnesotas DOT or ? reads this!

Are your postings supposed to be dense and sarcastic? I can't tell.

[Iamme]

Are your postings supposed to be dense and sarcastic? I can't tell.

Neither. Why do you say that as a response?

OH. And my title is "illuminator", so I guess you can't take anything I say with as much merit as you could is if I were given rank of "scholar". So that gets me off the hook some, I guess. :) (I'll smile even though you are now coming across as trying to fuel something here.)

[Newtons Bit]

Neither. Why do you say that as a response?

OH. And my title is "illuminator", so I guess you can't take anything I say with as much merit as you could is if I were given rank of "scholar". So that gets me off the hook some, I guess. :) (I'll smile even though you are now coming across as trying to fuel something here.)

Some people like to make silly posts to be funny.

Of course! If they removed let's say heavy roadbed or other weight off the bridge in ONE section... the weight of the forces downward on the trusses where the weight still WAS would then try to shove UP on the section that was being stripped of some of it's decking! Of course. That's IT!!!

This would be funny, if you weren't serious.

[Iamme]

Some people like to make silly posts to be funny.



This would be funny, if you weren't serious.

Because of the Big W part? Well, sometimes I use the Wizard fo Oz movie so I thought I'd change this time.

Now if I stated facts that are ovbvious to all..to all the engineers AND all the people here reading these posts, then I guess I could seem like I'm an idiot savant I suppose. But so far I have not heard one remark from anyone that wieght shifts or added loads or load removals on the deck could have caused the bridge to actually create UPward stresses on some other nearby support, have you? The presumption is that the constuction work and the weight of the machinery and all the banging, etc. could have caused it.

[Dan O.]

But so far I have not heard one remark from anyone that wieght shifts or added loads or load removals on the deck could have caused the bridge to actually create UPward stresses on some other nearby support, have you?

Was it actually necessary to spell out what unbalanced means? I figured anyone reading this thread would have some engineering skills.

...The construction changed the load balance on the bridge by stripping part of the roadway and confining traffic to 1/2 the lanes.

So you think bumper to bumper traffic in only 2 lanes would have been worse than a bridge that should have been designed for a convoy of tanks, bumper to bumper, in all 8 lanes at once?

[slingblade]

He made up his mind before he wrote the OP. He doesn't want anything to change his mind, and I'm reasonably certain that nothing will.

A closed mind gathers no thoughts.

[Newtons Bit]

Because of the Big W part? Well, sometimes I use the Wizard fo Oz movie so I thought I'd change this time.

Now if I stated facts that are ovbvious to all..to all the engineers AND all the people here reading these posts, then I guess I could seem like I'm an idiot savant I suppose. But so far I have not heard one remark from anyone that wieght shifts or added loads or load removals on the deck could have caused the bridge to actually create UPward stresses on some other nearby support, have you? The presumption is that the constuction work and the weight of the machinery and all the banging, etc. could have caused it.

Are you saying that there was UPLIFT on the concrete piers?

[NotJesus]

Because of the Big W part? Well, sometimes I use the Wizard fo Oz movie so I thought I'd change this time.

You mean you were the first one to notice that the Land of Oz was in color?

[Iamme]

Originally Posted by Iamme
Neither. Why do you say that as a response?

OH. And my title is "illuminator", so I guess you can't take anything I say with as much merit as you could is if I were given rank of "scholar". So that gets me off the hook some, I guess. (I'll smile even though you are now coming across as trying to fuel something here.)

Some people like to make silly posts to be funny.



Of course! If they removed let's say heavy roadbed or other weight off the bridge in ONE section... the weight of the forces downward on the trusses where the weight still WAS would then try to shove UP on the section that was being stripped of some of it's decking! Of course. That's IT!!!

This would be funny, if you weren't serious.

__________________
"Structural Engineering is the art of molding materials we do not wholly understand into shapes we cannot precisely analyze so as to understand forces we cannot really assess in such a way that the community at large has no reason to suspect the extent of our own ignorance." James E Amrhein
---------...........---------------...........--------------.....

Iamme's response:

What happens if a person gets on a teeder todder who is heavier than the other person? The light end goes up? Both sections do not go down at the same time!

What happens on cantelevered sections if more weight is placed out on the cantelever? The main section will bulge... upward! The transfer of directional forces through truss 'bridging' will behave the same way.

[Iamme]

You mean you were the first one to notice that the Land of Oz was in color?

No. But I did notice how the good witch of the North's voice sounds a little like Norma Zimmer on the Lawrence Welk show.

[Iamme]

Are you saying that there was UPLIFT on the concrete piers?

No. Within the criss-cross truss bracing that was already fatigued. One or more of the W shaped angle braces would have broke at one of the rivot-like bolted gussets and could have forced it's way upward before it all came down.

Do you know I was able to bring down a chimney in an attic by jacking it up first?

[Newtons Bit]

No. Within the criss-cross truss bracing that was already fatigued. One or more of the W shaped angle braces would have broke at one of the rivot-like bolted gussets and could have forced it's way upward before it all came down.

Do you know I was able to bring down a chimney in an attic by jacking it up first?

That would not be a problem, if it even happened at all. The braces on the underside of the bridge are designed for two purposes: reduce the length of the chord at the bottom (obvious) and provide bracing for out-of-plane loading (wind/earthquake). The wind and earthquake loads are reversible, the brace connections would be designed for both tensile and compressive loads.

I am assuming that you are referring to the braces underneath the deck and not the truss itself:
http://en.wikipedia.org/wiki/Image:I-35W_Bridge_-_April%2C_2006.jpg

I can't believe wiki already has an article on this.

If you check out http://www.cnn.com/2007/US/08/02/bridge.collapse/index.html picture number 7 you can see a pretty good picture of the bracing.

[Newtons Bit]

What happens if a person gets on a teeder todder who is heavier than the other person? The light end goes up? Both sections do not go down at the same time!

What happens on cantelevered sections if more weight is placed out on the cantelever? The main section will bulge... upward! The transfer of directional forces through truss 'bridging' will behave the same way.

This makes more sense, but still not accurate. Two lanes on either side would be loaded. The truss itself should minimize any negative bending moment on the interior beams. Notice the diagonals on inside and outside of the main-truss. This is what reduces the negative bending.

A heavily loaded cantilever would almost certainly be a design consideration. I say almost because it was built in the 60's and things were pretty barbaric back then.

[Iamme]

This makes more sense, but still not accurate. Two lanes on either side would be loaded. The truss itself should minimize any negative bending moment on the interior beams. Notice the diagonals on inside and outside of the main-truss. This is what reduces the negative bending.

A heavily loaded cantilever would almost certainly be a design consideration. I say almost because it was built in the 60's and things were pretty barbaric back then.

My theory does not rest with the two lanes being loaded. It has to do with what the construction workers were doing, and where their equipment was at the time, and how much surface was stripped off, reducing the weight at that area, while the weight was at it's heaviest somewhere else in the interconnected criss-cross bracing.

But let's stop the presses!

I visited a truss deck bridge moments ago. I am a scientist at heart and just had to know. This bridge was in our news as it is about 70 years old and was inspected yesterday by mandate due to the collapse of W35. I visited the bridge outside of Augusta, Wisconsin (about 15 miles from Eau Claire) and I went under the bridge and just stared. It too rises many, many feet above the Eau Claire river; 60...80 feet whatever. WAYYY up there.

This is how it is built: Like a brick **** house. I was actually surprised. Not flimsy as I thought. From outward appearances in design, it appears at any one given spot it could withstand a load of a million pounds! I'm not kidding. I was there, right under it, feeling the metal, even when vehicles past over. ... looking across, looking up. The W's are more vertical than I thought due to the fact they rest on absolutely gigantically huge and thick concrete piers. From the piers, the trusses rise maybe 20 feet high. The first thing that came to my miond, due to this height off the pier, was "lateral shift". Obviously, that would be catastrophic. However, based on my observance of the bridge's truss construction, I could not see how this likely could happen even if one or several of the criss-crossing metal was even removed. To have any sort of sudden collapse like W35, I'd suspect that you'd have to remove or destroy so many supports completely that this theory of failure within the truss networking seems like a ludicrous theory, especially in light of the fact the bridge did not slowly bend and sink into the river.

But this is what I saw and what stood out in my mind:

Remember how I mentioned about the expansion joints? I did not realize this about this type of bridge construction until seeing it, is that we are dealing with WAY more than some channel cut out of the road bed, for expansion. It is incorporated into the design and support of the bridge itself!

Get ready. The entire weight of the bridge sits on about 3 inch round steel pins that support the ENTIRE weiught of the bridge and loads placed upon it! These pins raise the bridge trussses about 3 inches above a huge thick curved plate (like the rails on a rocking chair) that in TURN rest on top a flat super thick plate of steel, which that inturn sits on the concrete pier. When the expansion, and subsequent contraction (due to the fact our weather here and the Cities can range from 100, maybe 130F on the roadbed, to a possible minus 40 in the winter!) occurs, the entire structure will rock forward or backward, and all stresses go thru that pin which must be continously be grinding away, ungreased! And if that metal say crystalizes over time?.......

This was only a 2 lane bridge. Obviously there would have been one support pin on each side of the bridge ontop the pier, and going down the length of the bridge, you'd have one of these every 100 feet about. Uptop, the expansion joints are steel edged, built into the concrete, with a curved piece of rubbe down in there. In the rubbe cradle was gravel filling it up. Not ideal you'd think. But then again, maybe they want some junk in there, as why do they have that rubber cradle in there for?

If one of those pivot pins sheered due to fatigue, the bridge would take a sudden drop of 3 inches down onto the pier,... and because the bottom of the steel under the pin is curved, perhaps this would cause a sudden forward or rearward thrust in the bridge. A sudden thrust of the bridge of say only 2-3 inches forward or backward would be creating an extreme inertial momentum of mass.

So, that was my "weak-link" theory. That indeed would be the weak link in the bridge. As stated,the entire weight of the bridge transfers through those pins suspended there 3 inches above the rounded steel bottoms.

Another theory that maybe could have caused the SUDDEN collapse, as opposed to slow bending of the bridge, is if one of the approach piers kicked out some, suddenly, due to some ground settling behind the approach pier, or the eddying out of the pier in the water. And that could have been caused over times previous by some kind of shock waves sent through the structure by having heavy vehicles come off solid land and then onto the bridge, if there was a slight unevenness, and the transition was not smooth. Or the rumblings of the feight trains for years. It could have been like a vibrator action on the land behind the pier or shaking of the pier under the water, for years.

I propose we make a real sporting game of this and try to bring up design pictures of this very bridge. It has to be this bridge. An 8-lane bridge, so we can gusess as to what brought it down, suddenly. They must have photos of that bridge's underside somewhere.

[alfaniner]

...I propose we make a real sporting game of this and try to bring up design pictures of this very bridge. It has to be this bridge. An 8-lane bridge, so we can gusess as to what brought it down, suddenly. They must have photos of that bridge's underside somewhere.

Your analysis is very interesting but please don't refer to this as a "game".

[Iamme]

Okay.

[Iamme]

Update!

Not seen on tv. (At least *I* didn't.)

Interviewed construction workers claim bridge was wobbling days before the collapse! What?!

And they said that as they removed more and more concrete decking, the wobble got worse! What?!

And that these bridges 'move' with traffic. Hmmmmm.

And that in Wiscoinsin, all similar bridges are going to be equiped with in essence, 24/7 inspectors; a device called an "accelerometer", which acts like a seismic detecting device. The person being interviewed about these said that if the bridge is moving 1/2 inch...then 1/2 inch...then 1/2 inch...but then suddenly moves 2 inches...they are going to have someone on sight mach schnell.

Why wasn't this bridge inspected just prior to major reconstruction I wonder? Didn't they know that disturbance of the existing structure may compromise it's design by the designer? That perhaps the decking itself plays more of a roll than what they think in locking the bridge together?

I can't get enough of this bridge story just like I can't get enough of how the universe happened. [I thrive on mysteries and love to see if I can solve them. Otherwise you just die as any other dopey person who lives, eats, craps, procreates, and is forgotten by everyone especially after your next of kin dies also. That is why perpetual motion inventors are driven also, like Joe Newman.]

[alfaniner]

Is there a picture/diagram of the immediate before/after scenario somewhere? I would like to see the positions of the cars and the construction crew, in relation to the supports on the bridge.

[Iamme]

Is there a picture/diagram of the immediate before/after scenario somewhere? I would like to see the positions of the cars and the construction crew, in relation to the supports on the bridge.

Me too! I'm just thirsty to try to figure this whole thing out. Somebody was a total moron about this whole change of events! If *I* had been crossing that bridge on a daily basis and noticed these changes in the way the bridge felt, I would have been on my cell phone to the DOT immediately demanding they send someone down to see what is going on, since I'd tell them that it didn't used to do that. Duh.

Didn't a lot of people call up? Duh! The fools!

Around where I live I am forever calling the highway dept (like about potholes and debris in the road, like potholes and tire carcasses from semis) and police about stuff and they claim, "Huh...nobody else has told us about that."...they say. People are complete oblivious morons to what is going on with their surrounding. I even reported a tornado once that nobody else saw up in the sky! I just asked my friend if HE would have kept crossing that bridge if he felt it wobbling worse and worse by the day. He said absolutely not, and would have went miles out of his way. Me too. Especially with it being 64 feet up in the air.

I am dying to see drawings on what the underside structure of the bridge design was. I want to know if the concrete deck is an integral part of locking the bridge together to help control sway. Even though I saw a 2-lane one first hand underneath, there could be a world of difference in how they did the criss cross bracing of the 8 lane wide bridge.

[Iamme]

News flash!

Heard this on the radio about 1/2 hour ago.

A spokesperson for the NTSB said that they have found what they believe is a design flaw in how the bridge was made!

[rtalman]

What caused the bridge to collapse? Pigeon poo. (Or at least that is cited as a possible factor)


Inspectors began documenting the buildup of pigeon dung on the span near downtown Minneapolis two decades ago.
Experts say the corrosive guano deposited all over the span's framework helped the steel beams rust faster.http://www.iht.com/articles/ap/2007/08/22/america/NA-GEN-US-Bridge-Collapse-Pigeons.php

[baron]

It was Mothman. Again.