New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse

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• Minnesota
• bridges
• engineering
• infrastructure

Sixteen fractured gusset plates in the center span on Interstate 35W were a main cause of the deadly bridge collapse in Minneapolis last August, the National Transportation Safety Board (NTSB) said on Tuesday. The plates, which connected steel beams in the truss bridge, were roughly half the thickness they should have been because of a design error. How that flaw made it into the bridge is unclear; according to NTSB chairman Mark Rosenker, investigators couldn’t find the original design calculations. Extra weight from construction was also a factor in the tragedy, which killed 13 people and injured 100. The findings confirmed forecasts by investigators from three months after the collapse—and by engineering experts in the immediate aftermath—and underscored the dire state of America’s crumbling infrastructure.

Meanwhile, construction marches on at the new St. Anthony Falls Bridge—it commenced Oct. 29. Billed as “smart” by its designers at the Figg Engineering Group, the concrete box girder bridge will have redundant systems, monitoring technology and high-strength concrete that will increase its service life to 100 years or more—and make it one of the safest bridges in the country. “The design offered many benefits,” says Linda Figg, the architectural firm’s president and CEO. “It has long-term durability with low maintenance, and it allows Flatiron Manson, our joint partner on the project, to build the bridge concurrently from multiple directions.”

Crews are currently digging and laying the foundations for piers, which will be cast in place as other structural members are precast on site to speed up construction in hopes of completing the pier system sometime in March. The St. Anthony Falls Bridge will have five lanes of traffic in each direction—two lanes wider than its predecessor—and will come ready for a potential commuter rail line in the future. A collection system for storm water has also been added.

In addition to its design, St. Anthony’s state-of-the-art construction materials will ensure a high level of safety. The bridge will be built entirely with high-performance concrete (6000 psi or more), which, in addition to strength, offers low permeability and corrosion inhibitors, Figg says. The 15.8 million pounds of reinforcing steel rebar in the bridge will be coated with epoxy to thwart corrosion, which can lead to structural weakness. The segments of the bridge will be linked together with threaded post-tension steel cables; the cables can easily be replaced with fiber reinforced polymers strands when they become available.

The bridge will also come rigged with monitoring technology created in collaboration with researchers at the University of Minnesota, according to Figg—just one of several new solutions in engineering circles that will see early implementation in Minneapolis. Though officials haven’t decided on an exact system (wired and wireless options are both available), Figg says sensors in the bridge will continually share information on structural behavior as well as provide the Minnesota Department of Transportation with information on construction status, weather, traffic and security. An automatic anti-icing system will monitor the temperature of the bridge deck, ambient air and humidity levels; recessed anti-icing sprayers will be engaged when certain thresholds are reached to prevent the formation of ice.

Most important, however, are the multiple levels of protection and redundancy present in the design. “There are no fracture-critical elements,” Figg says. “Multiple components of the bridge share similar loading paths in the design, so there are backups to the primary load-carrying member.”

Crews are working around the clock seven days a week to complete the bridge, which is slated to open on Dec. 24.

29. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
Making the plans public would just allow the terrorists to analyze bridges and figure out where to place their explosives. Everyday engineers don't have time to pour over all the bridges in the U.S.

28. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
I'm so glad you're all experts. By the way...the new bridge is going to be beautiful.

27. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
but its......so ugly...i like the dubai's new bridge design WAY better

26. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
Really there was nothing 'wrong' with the bridge - it's just that new, heavier road systems and increased traffic were piled on top of it over the years and 'somebody' didn't do a proper re-evaluation. It's structure was never designed/meant to take on all those extras. Plus factor in the vibrations from construction and weight of rush hour traffic. No one part or one factor makes a bridge collapse - it takes many to fail in order to get a collapse like that.

25. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
there are a lot of things that contribute to failures of structures. indeed if events such as these happens, it's usually the designers who are the first to be investigated. but there is also a thing as liability for a period of time, in this case, 50years is a long time. you also have to consider wear and tear. nowadays, allowance for extra loads and factor of safety were being consider in the design analysis.

24. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
Really there was nothing 'wrong' with the bridge - it's just that new, heavier road systems and increased traffic were piled on top of it over the years and 'somebody' didn't do a proper re-evaluation. It's structure was never designed/meant to take on all those extras. Plus factor in the vibrations from construction and weight of rush hour traffic. No one part or one factor makes a bridge collapse - it takes many to fail in order to get a collapse like that.

23. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
everyone seems to forget that the standards to which the old bridge was built became outdated as congress allowed heavier and heavier vehicles on the roads of America. the original standards were adequate for the time when the bridge was built. meaning that no one anticipated these much heavier vehicles were coming down the road, so to speak.

22. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
All of the redundant systems in the new bridge give me the impression that MN DOT is saying "forget about the past loss of life, you can trustus now, pretty please."

21. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
Just curious if there is a way to find out how many other bridges built around this time had similar designs and may have had similar gussets which may have been undersized? Na, don't think we should give it a rest, or maybe we just wait for the next tragedy. Most engineers like to learn from their mistakes. We should too.

20. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
Website: Minnesota bridge collapse
I was project engineer for 10 years on bridge building and rehabilitation.The best quality bridge was from 1936. The two worst bridges were build 1942,WW2, and early 1950th, Korean war. Both were poorly designed and badly build( defective and vibrating excessively). Might I guess on a Vietnam era bridge?

19. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
MN Department of Transportation did a "lipstick" maintenance job on the 35W bridge. I drove across it two weeks before the collapse and the crews were drilling holes in the deck. Leave it to MN DOT to work on a bridge during rush hour and NOT shut the bridge down! That bridge stood for years with no problem. MN DOT's own meeting recording had them stating the bridge had a potential to collapse! Too bad they did not tell the MN driving public!! What about the Lt. Governor who was in China touting MN transportation?? Nice junket!! Who here thinks you can tear up a road deck and allow traffic on a metal frame bridge???

18. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
Another example of the media trying to steer Americans to a politically prescribed way of thinking. Thank God we aren't a flock of sheep and can think for ourselves. You notice how activists don't blame as much on George Bush as they used to? They got tired of egg on their faces, as usual.

17. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
really i am wonderful of this a nice issue and it's a very good anidea i hope you go on

16. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
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15. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
Instead of spending all these millions in a super bridge just build a safer bridge and spend the extra millions to upgrade other bridges around the nation. Dont put all the eggs in one bag

14. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
What I cannot believe is that a major rework of the road deck was even started with out a complete inspection of the entire structure. If this bridge had 16 cracked gussets why was this not picked up in previous inspections? They did not happen over night unless it was the roadwork that caused it. There was more failure here then a design error.

13. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
I bet corrosion was the main cause of the failure. A note in "Industrial Finishng, June 1985, regarding "Oliver W. Siebrt's belief that every enineering candiate should take at least six crdit hours ...on corrosion... I have seen at least two cases of catastrophic failure that were a result of perfect calculation but with no allowance for corrosion. The engineers did not know that rebars in concrete eventually rust.

12. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
I don't doubt the gusset plate as an issue, and I can see how extra weight factors in, but can anyone tell me why the North piers are tilted toward the river without so much as a dent to their tops?! If the bridge collapse pulled them they should be upright and cracked; if they were shoved by the delayed north span collapse, again shear forces should have damaged them. Look closely at the photos, there were reports of lifting first then drop.Is anyone looking at the piers?

11. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
It isn't practical to keep the working file with all the design calculations for more than 10 to 20 years, depending on how much archival space your company has. Granted now, much can be archived electronically and stored indefinitely. However, back then the working file could have taken up a whole filing cabinet. Sooner or later your archive space is going to run out and you have to throw out the old stuff. Making the design calcs available to the public would probably be stepping over the line on intellectual property grounds. However, even if it was done, who in their right mind would spend their free time crunching numbers, when the results of such 90% of the time would show the calculations were correct. Not to mention all the extra cost associated with making the data shareable. Someone has to pay for that you know.

10. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
If it was a design error, it was just politicized vs. "underscored the dire state of America’s crumbling infrastructure.".

9. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
I have a cousin who worked on the original design for the bridge. He said that President Johnson and SecDef McNamara demanded that the steel plates be made thinner in order to allow more steel be redirected towards the manufacture of 500lb bombs then being used in Viet Nam.

8. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
According to the NTSB preliminary report, available at ntsb.gov, the NTSB has no reason to believe (at this time) that this design or construction error exists on other bridges. The reporter is engaged in advocacy regarding an alleged "crumbling infrastructure" having succumbed to the construction industry lobbyists who are trying to capitalize on their own horrific mistake to extract more money from taxpayers (a proposed 40 cent per gallon federal gas tax to take effect almost immediately) to launch new construction projects nationwide.

7. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
Why not publish the design calculations for existing and proposed public structures online. Once the designs have been purchased by the State, don't they become public property? If they were posted, there are plenty of practicing MEs and SEs who could review them and point out any flaws. They should be posted in electronic form, like Autocad files, so that it would be easy to check them.

6. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
While there are no doubt many similar bridges, each bridge's design calculations would have been done independently of the others. *Some* critical design flaw may (or not) be present in the other bridges, but not likely the *same* design flaw. Crumbling infrastructure has been a problem since long before Bush took office. It can just as easily be argued that prioritizing social spending was responsible. Give it a rest.

5. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
Bridge projects of this size are individually designed and detailed. The same engineering firm may have repeated the error on the next "similar" bridge design it was responsible for, and the detailer for the steel supplier on that project may also have failed to notice the error and call the designer on it, but it is not all that likely.

4. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
I'm astounded that the original design drawings and calculations are not still around! It's a normal requirement that such information be archived for future reference and kept as long as the original structure exists. How can anyone assess the importance of cracks or other deficiencies without design information and calculations like these? What were the "bridge inspectors" actually doing?

3. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
Exactly how does the fact that the 60's era design had critical components that failed because the were half as thick as they should have been "underscore the dire state of America's crumbling infrstructure"?! Are you sure it wasn't because Bush spent so much money in Iraq? Positive?

2. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
You note that the Minnesota bridge collapse underscores the "dire state of America's crumbling infrastructure" yet your article notes that its actually engineering errors that caused its fall. Which leads one to believe that your writer is writing from a position of political advocacy or alternately has trouble with associating cause and effect. A more useful track might be to examine our processes for assessing engineering and design.

1. RE: New Minn. Bridge Plans Arise as Bad Plates Fingered in Collapse
I recall (possibly incorrectly) from the original stories on this collapse that there are many other similar bridges. Is there any information on whether such bridges have been checked for this flaw ?

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