Tons of Repaving Material Was on Bridge at Collapse

[RamboLiberal]

Source: NY Times

Trucks carrying tens of thousands of pounds of crushed stone were parked on the Interstate 35W bridge, and more stone was sitting on the deck when the bridge collapsed, investigators said Sunday, raising suspicions that the added weight of materials intended for repairs may have played a role in the bridge failure.

The chairman of the National Transportation Safety Board, Mark V. Rosenker, said investigators had questioned employees of Progressive Contractors Inc., which was doing work on the bridge deck, regarding quantities of various materials, specific equipment they had put on the bridge, and where the materials and equipment were on the bridge. The weight and location will be entered into a computer program, Mr. Rosenker said, to calculate the stresses generated on each girder and other bridge components.

So far, investigators say they have ruled out nothing and will consider everything from the expansion and contraction of the bridge in the extreme weather conditions of Minneapolis to the possible corrosive role of bird droppings.

The stone was being used to add a two-inch layer to the bridge deck. Its weight, and the weight of the trucks carrying it, would most likely not be a threat to a bridge in good condition, engineers said, but could play a role in causing the failure of a structure that was already weakened.



Read more: http://www.nytimes.com/2007/08/06/us/06collapse.html

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That's been one of my personal suspicions. I've wondered if heavy construction equipment parked on the bridge helped overload it - I really wonder if that is factored in when repairing bridges. In my area of Pittsburgh they are just about done repairing the Homestead Greys Bridge which is much older and of a similar design to I35W - I'm sure glad it has had an extensive renovation done - but they still have quite a number of heavy equipment trailers parked on it while painting.

Another bridge upriver is due to be next - the Rankin bridge which is also of same design - and I've decided to try to avoid it completely till it's done.

[MadMaddie]

1. I was thinking the same thing....the added construction material

probably wasn't weighed and monitored.....

I think when the investigations is completed Americans will be shocked at the carelessness that occurred.

[villager]

2. The Homestead Grays have a bridge!?

[RamboLiberal]

6. Yep - it was renamed recently to honor the team

and during renovation repainted in gray. Used to be the Homestead High-Level Bridge. Other famous thing that happened here was the crash of a B-25 in the 50's into the Mon River near the bridge. The plane was never found. Speculation was it was carrying something secret - a nuke? And was lifted in secret out of the river by the government.



Since DU'ers love :tinfoilhat: How does a whole aircraft disappear and never be found in a river that is not that wide nor that deep?

In the middle of the afternoon on January 31, 1956 a B-25 bomber crash-landed into the Monongahela river near Homestead, Pennsylvania. All six aboard survived the impact, though two of them died before they were saved from the cold water. It was an unfortunate accident, and in the following weeks a search for the sunken plane was conducted.

The odds of finding the plane seemed pretty good - at the crash location the river was only 500 to 1,000 feet in width and 25 to 35 feet in depth. In comparison, a B-25 bomber is 52 feet long, 17 feet tall and has a wingspan of 67 feet. It took 15 minutes to sink underwater, and there were plenty of witnesses, so its last location above water was well known. It did not seem that finding the bomber would be a difficult task; yet after two weeks of hard searching, the plane was still missing and the operation was abandoned. So where did the B-25 really go?

The conspiracy theories flew fast and loose on this mystery. The most popular story was that the plane secretly carried some important, confidential cargo and was recovered incognito by the government. Anything from nuclear bombs to aliens were said to be inside the plane. As such, in the middle of the night a squad of elite government cover-up men retrieved the plane from the river, and had it shipped away. There were, of course, eyewitnesses who saw this secret operation. And the public search? Nothing but a hoax to cover for the real rescue. Oh, there was also an undercover seventh member of the crew who was pulled from the river. And Glenn Miller was aboard, they flew into the Bermuda Triangle, and…

Courtesy Pittsburgh Post-GazetteLike most conspiracy theories, it's rather preposterous. The government's side of the story is both less ridiculous and less intriguing. According to military representatives, the plane was carrying no secret cargo - instead, it was to deliver two people to Harrisburg, as well as pick up airplane parts. Due to a malfunction the plane ran out of fuel on the way to its destination. The crew tried to turn around and get to a nearby airport, but by the time they realized they were under-fueled they were just too far away. The engines sputtered to a halt over the Mon, and the pilot crashed it there.

http://www.damninteresting.com/?p=579#more-579

Major Dotson advised the crew that the aircraft would be ditched in the river. Captain Jamieson transmitted a "Mayday" which was overheard at the Allegheny County Tower at 1609E on either 126.18Mc or 257.8Mc. Major Dotson lowered wing flaps and completed a wheels-up touchdown, heading downstream in a generally south, southwest direction at approximately 1610E to 1611E. The ditching was successful and all occupants evacuated the aircraft with no apparent injuries. all six persons were able to climb aboard the upper surfaces of the aircraft as it floated down the stream. The Monongahela river at this point varies from 500 to 1000 feet in width; the river depth varies from 25 to 35 feet. The current was estimated to be approximately 8 to 10 knots; the recorded water temperature was 35 degrees F; the recorded air temperature was 27 degrees F; the recorded wind velocity was 8 to 10 knots, from the northwest. The aircraft remained afloat for an estimated 10 to 15 minutes.

...that the aircraft was sinking, the crew and passengers to remove their shoes and swim to a log observed floating nearby. ...all six persons could swim. Sergeant Alleman, Airman Smith and Major Dotson reached the nearby log successfully, Major Dotson and Airman Smith remained with the log until recovered by a commercial river boat, approximately 15 minutes later. Master Sergeant Alleman reached the log but struck out for the left bank of the river. He was able to swim ashore with great difficulty and was assisted from the water by civilians and local police officers. Captain jamieson was able to remain afloat until recovered by a police launch.

Captain Ingrahm disappeared beneath the water. Sergeant Soocey was on some unidentified debris when last seen. The aircraft drifted for an estimated 1 mile from the point of impact prior to sinking. Major Dotson and Airman Smith, the last personnel to be recovered were recovered approximately 1 1/2 to 2 miles from the scene of impact. At the time of this report neither the aircraft nor missing personnel have been located.

http://www.caterpillarclub.org/b25/b25.htm

[villager]

13. Must be where Pennsylvania native-son George Romero got the idea

..for the military plane crash that opens his film "The Crazies..."

[valerief]

3. The extra 40,000 vehicles per day the bridge was designed to hold could

have made a difference, too. Also, the extra weight of Murka's beloved SUVs could have made a difference.

One thing we know for sure. The politicians holding the pursestrings DEFINITELY FAILED Minneapolis. And many more are failing the rest of the country in concert with BushCo.

(edited for typo)

[burrowowl]

4. If it were ll concentrated at one

place, then maybe. But wouldn't have engineers said how much could be concentrated in one place!?

[Gregorian]

9. They probably did, but it wouldn't be as meaningful on a faulty structure.

And as someone who used to be a roofing contractor, I can tell you nightmare stories. Even if someone were to check on the dead load specs of a structure, they may not know the actual accumulated weigh they are applying. I've seen all kinds of materials piled on roofs that could have been disasterous failures. And I've heard of some that were. A friend in San Francisco. Old old buildings. Who knows how they were built. Pile up tear-off materials, and suddenly you have things going down through the building three or four stories. Same with a bridge. They could have easily put an extra load of 50,000 pounds (as an example), because it was ten minutes to getting off of work. The boss knows the load limits, but his back is turned, and some trucker just dumps. And in the right critical location...

I still have to marvel at how the bridge put up no resistance, and just fell without any rotation. A possible sign that the structure failed well below expectation. I would have expected one end to get hung up, and the structure to swing down.

[burrowowl]

16. Plus the fact that all a little too much dead load

with a bit of movement can become a hell of a live load!

[sutz12]

5. This could be big...

especially considering that the weight was probably concentrated in one area, rather than being spread out like it would be after it is laid down as paving. Several heavy trucks parked next to each other and/or large piles of materials concentrates the weight a lot.

[Zensea]

7. I don't like saying this -- but duh!

or should I say d'oh!

Kind of what I suspected also.

[okoboji]

8. "......the possible corrosive role of bird droppings"

Someone, please round up Big Bird and bring him in for questioning. Just what has that bird been eating?

[RamboLiberal]

10. You get a bunch of pigeons who roost under a bridge

for a number of years, you'd be suprised how corrosive those droppings are, especially when combined with corrosive road deicers and salt.

Though there are some other thoughts as to what happened in Minnesota, a British engineer is blaming birds.

"A truss bridge like this is a lot of steel work, a lot of girders all interconnected. This unfortunately provided a very useful home for a lot of pigeons and pigeon droppings. Guano is very corrosive and might have caused some deterioration locally of some of the steel work," said Keith Eaton the Institute of Structural Engineers.

Henry Scarton at RPI says a jackhammer and its vibrations should also not be overlooked.

"Those loadings are not just restricted to the deck they were trying to break up. It will propagate down into the structure and it may be severe," Scarton said.

http://wnyt.com/article/stories/S157374.shtml?cat=10114

[Gregorian]

12. Now that would be weird if the jackhammer set up a resonant frequency failure.

A small forcing function can, at the resonant frequency of the structure in a specific mode, amplify it's movement into a very large motion. But I would really doubt that it would occur in the vertical mode. From side to side, maybe. But not up and down. That's the same direction the automobiles are forcing the bridge, and those resonant frequencies are carefully avoided.

It's going to be a long study, I'm afraid. Unless there are more video cam recordings. A combination of poor design, poor manufacture, poor maintenance, and even overloading during resurfacing.

I think the bottom line is, we are doing the same things to bridges all over the world every day without failure.

[Occulus]

18. Can girders be sprayed with something (safe) that will prevent the corrosion? n/t

[TankLV]

19. Yes - I believe it's called "paint".

BTW - paint only lasts so long before it has to be REpainted...

That's why they're supposed to repaint it at regular intervals to avoid the corrosion...

But thanks for playing...

Sorry - I couldn't resist being snarky...

There is currently NO coating that lasts FOREVER without reapplication at regular time intervals...

A while back they had developed a steel that develops a coating of rust that was supposed to stop the additional rusting - like a protective layer - but all of those have proved to be not exactly true and the "rusting steel" has to be maintained just like all the other steel...

And the Japanese Steel that is being used now is entirely different that the US made steel that used to be manufactured...

[Tesha]

21. CorTen steel is pretty effective at resisting all corrosion.

> There is currently NO coating that lasts FOREVER without
reapplication at regular time intervals...

CorTen steel is pretty effective at resisting all corrosion
with very little maintenance. Of course, you have to like
your bridge styled in brown.

Meanwhile, yes, paint is the answer, but as you pointed
out, that requires a maintenance budget. And that requires
taxes. So forget that; our strategy since about the 80s is
that all taxes are bad and all tax money is wasted.

So we've been living off the infrastructure "capital"
that was built up after the second world war, and the
bank balance is just now starting to go strongly
negative; expect a lot more catastrophies in the
near future.

Tesha

[bleedingheart]

24. the US Steel Building in Pittsburgh was built with CorTen

the funny part was that as the CorTen was "curing" to it's brown/rust color...it would cause the streets to run with rusty water when it rained...that didn't last long though and it is an impressive structure...

[Occulus]

17. 10,000 sparrows = BIG bird. n/t

[Myrina]

22. ... western civilization's engineering and technology ...

... brought to its knees by bird shit.

:rofl:

[ben_meyers]

11. Bird droppings?

That bridge was the most heavily salted structure in the state! In 1999 they even installed an automated deicing system that sprayed salt solution on the bridge before it snowed.

That bridge was deemed to be "structurally deficient" in 1990 and there is an inspection report from 1994 warning of a problem with the hinge joint on the north span. Guess where the construction materials were? Yep, the north span! PCI, the resurfacing contractor, has lawyered up and the state better too.

[defendandprotect]

14. And, evidently, this construction job somehow got ahead of the bridge maintenance check --

which was to be carried out with some urgency -- !!!!

[ben_meyers]

15. Not really, here is a report from 2006

It details years of inspection reports and recommendations. MDOT was well aware of the problems and had been for years. My old Mn. attorney (and friend) says that the lawyers are all over the place, one is even advertising on TV already looking for clients.
Careful, PDF format..
http://www.dot.state.mn.us/i35wbridge/pdfs/bridge_inspection_report_06-15-06.pdf

[liberal N proud]

20. No mention of all the jack hammers that would have been present

During deck repairs there would have been jack hammers causing vibrations on the bridge as well.
Vibration can lead to structure failure, couple that with the weight of the materials, the age of the bridge, traffic vibrations.
Who knows, I hope they can determine what brought it down so as to prevent another from falling. There are so many bridges with similar construction.

[Love Bug]

23. That's very interesting

The extra weight may or may not have been a factor. Let's remember, that 4 of the 8 lanes were closed for weeks, so there were half as many cars on this bridge as usual. Also, today's cars, even SUVs, are much lighter than the cars that were on the road 40 years ago when the bridge was designed. Also, this bridge was designed to handle the extra weight of semis.

They can't discount anything but I have to wonder.

[RamboLiberal]

25. More Early Tuesday report

The parts of the Interstate 35W bridge in Minneapolis considered most susceptible to fatigue cracking were located in the toughest places for inspectors to see, according to a consultant's report to the Minnesota Department of Transportation.

The consultant told the department in June 2006 that it couldn't discount the possibility of a critical part of the steel superstructure cracking and failing because inspection access was very limited. The report also warned that "a timely discovery is unlikely to happen should a crack occur from some unusual causes."

The consultant made two recommendations -- reinforce the bridge or monitor fatigue cracks through yearly inspections. The state chose to inspect rather than undertake repairs.

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"It's nuts," said a second MnDOT expert who has inspected the bridge. "The first thing you notice is that the traffic is not giving you a break. And in MnDOT there is a real reluctance to close a lane of traffic because then you're impeding flow. Then there's the height over the water, the pigeons, bats and spiders. If you're a little squirrelly about those things, you shouldn't be in the business. It's nasty business down there."

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Heaps of corrosive pigeon droppings obscuring parts of the bridge's steel supports have been a bane to inspectors at least since 1994, documents show. The birds were nesting in welded steel box sections of the superstructure, gaining access through the same holes used by inspectors to peer inside to look for cracks. In 1999, MnDOT covered the inspection holes with plastic screens, but the problem persisted.

http://www.startribune.com/10204/story/1347900.html