Minneapolis Bridge Collapse: How should the investigation proceed?

My husband worked for a company a couple years ago that built bridges. My husband says that so many different things could have happened including that someone could have hit the pier at some point even days before the bridge fell. If something hit the pier that the support sits on, it could have shifted something. He also says that a bolt could have been loose and with the cars driving on the bridge, it loosened and sheared.

It is a law that bridges have to be inspected thoroughly every 5 years and every bolt and screw etc is checked. They even have dive teams that go under the water during every inspection to check the ground that holds the bridge underwater. My husband was going to be certified to be a diver for inspections but they just didn't get around to his training before he changed jobs.

Some people are saying that the salt from winter caused it but that is most likely not what happened because that would only affect the surface not the underside of the bridge.

I heard this on the news as soon as it happend. I also saw the slide show online of it occuring as captured by camera. It is so sad. One would think that bridges would be checked out frequently for damage or problems. I am off to read the articles that you have links for. Thanks for the information. Have a wonderful day.

I realize they have to start investigating, but my main concern is in hoping they find a way to get the bridge rubble off the remaining cars in the river.

Tracey E., does your husband know how the investigators would identify that sort of impact damage? I don't know enough about how that works and I'm interested in what he has to say.

Hope you check back in, Connie, and let us know what you'd like to see from the investigation.

You have a point, Mary H. Since the investigation is pending/in the planning stages, I'm just looking for feedback. I'll have to check coverage to see what the status is on that.

The root cause is even more important that finding the immediate, physical cause. Let's face it, the bridge failed because of some deterioration of some portion of its support structure. While identifying the exact nature of this may help to indentify other, similar problems before they claim lives and cause enormous property damage.

But the real reason for the failure, and for many other potential failures waiting for us in Minnesota, the other 49 states, all the provinces and territories of Canada is that we have been on a three decade binge of tax reductions. We want to have more take home pay. We haven't worried about what cuts have to be made in order to get that tax break.

Reduce bridge insprectors? Do it, I want a tax cut.

Reduce maintenance budgets? Do it, I want a tax cut.

Prolong the usable life of public assets, regardless of the physical viability of the structure? Do it, I want a tax cut.

Taxes are the price of civilization and, just as with everything else, you get what you pay for.

I like the idea of having and independant firm also look at it. Once the finger pointing begins there will be internal bias from city, state, and national agencies that have been responsible for inspections and reporting of the status of the bridge.

Neither politcal party advocated for the bridge to be repaired. Neither.

The big question is ..................

Can we alocate money just to this bridge project or do we have to give 40% of it to light rail because of that stupid amendment that passed last year?

Latest out is that one end shifted about 50 feet right before the rest fell in place. But they still don't know why it shifted yet.

What happens when an inspection report is written? Where does it go when leaving the author's desk? We have to ensure that the right people are making the safest decisions based on safety alone. I fear that economics and politics may determine more than we know.

Rory wrote, "...identifying the exact nature of this may help to indentify other, similar problems before they claim lives and cause enormous property damage."

I'm very interested in who would lead that sort of process, and if it would actually be adopted by other states and agencies. Anyone have thoughts on that?

Gary I believe that firm has done work the State of Minnesota before but I'd need more coffee and some time to check notes and coverage on that. Have you contacted your local reps with your question about the fund allocation? I'd love to hear what you find out.

Thanks for checking in Charles M and providing updates.

Jane something tells me that inspection report will receive an immense amount of coverage, notice, and review by multiple parties and the public. But you raise a great point: what. then?

I realize that when people die everyone wants a quick explanation and punishment of the blameworthy, but on the other hand the media frenzy surrounding this bridge collaspe may do more harm then good by sensationalizing what is essentially an engineering problem.

As an engineer I know this, buildings collaspe, aircraft fall out of the sky and bridges fail. Of course engineers take all possible steps to avoid this and to avoid loss of life when failures occur. And when failures occur there is always an investigation to determine the cause. And, if necessary, design codes are revised to prevent future failures. This failure falls under the authority of the National Transportation Safety Board and they are known for thorough work.

That being said, as I understand it, the bridge was last inspected in 2005 and found to be structurally deficient due to cracking. Now, bridges are known to crack and cracks are known to cause bridge failures. Not every crack will cause failure, but crack growth can be highly unpredictable and finding the line between an "acceptable crack" and a potentially dangerous one is a nerve wracking decision and the engineer charged with this decision often comes under external pressure to do what is expedient.

If I had my way all bridges with the same structural deficiency rating, or worse than the I-35 bridge would be shut down and repaired. However, even if the money was available for this, the result would be traffic gridlock from Manhatten to San Francisco. So there you have it. Yet, another national problem that I have no answer for. Be safe folks.

Jack, thank you for weighing in and speaking your view on the NTSB's work. I'm wondering: Can you tell us about how forensic engineers determine what went wrong?

One note about some of the cracks that has been brought up were some that were there from the original welds from 40 years ago but at the last inspection of them a few years ago did not show any significant growth.
But that doesn't mean that there hasn't been a problem since.
One thing that is I think becoming apparent is how much worse this could have been. The surface repair might have been a small blessing by reducing the number of cars on the bridge and the speed at which the approaching traffic was traveling. I think the speed limit in that area is normally 65 but I could be wrong. I do know that state laws is 55 through road construction areas.
Lets all pray that the death toll stays put.

Charles,

If the bridge did shift sideways at one end of the main span that may indicate that the failure began on the main truss on that side of the bridge. After viewing the video of the main span collapse it is obvious that the main 390 foot span failed first, and apparently the first failure occured closest to the end of the bridge in the video. Unfortunately, the video did not show the main support pier on that end. I'm sure that in the end they will conclude that either a main tension member failed due to fatigue, cracking, or corrosion of a main member or joint in the main support truss.

This type of bridge ( a truss type) has no redundancy built into it. In other words, if only one joint or member fails, then there will be a collapse, and most likely a full collapse.

Also, you are correct in stating that the construction could have easilly been responsible for saving a large number of lives. If this bridge carried four lanes of slow moving traffic in each direction during normal rush hour traffic, then it is amazing it did not collapse prior to the construction project to resurface it. I also want to know if they added more paving over old or removed it and replaced it.

The problem with cracks is that even if there is no propogation from stress, there is now a pathway for water entry, and corrosion that can hide defects within welds. There also needs to be a review of the original design to see what the factor of safety was in the original design. I am a structural engineer, but do not design highway bridges. Cyclical loading is a very important factor in the design of bridges, and could also play a role in this collapse. Codes are much more stringent for cyclical loading now, than they were 40 years ago.

Thanks for your expertise Dave.

Seconding that thank you, Dave H.

If all the bridges in the US collasped today that the News Media has falling down in the near future, it would be off and running to something else in a couple of days. Maybe a bear turning over an outhouse or something. We would be History folks, nothing more.