More than a year after the I-35W bridge collapse, questions still loom about the state of Minnesota’s bridges.
There are 11 “major” Minnesota bridges that will be replaced or repaired by 2018. Click on the dots to get information for each bridge.
Map by Denise Rath.
The incident also raises questions about bridge inspections — how they are conducted, what inspectors look for, how records are kept and how inspection policies have changed since the I-35W bridge fell on Aug. 1, 2007.
The Minnesota Department of Transportation (MnDOT) oversees the safety of more than 19,000 bridges in the state with about 275 bridge inspectors, and two key experts in the agency — bridge engineer Dan Dorgan and Todd Niemann, the structural metals and bridge inspection engineer — offered answers to those questions and others in an interview.
(Dorgan and Niemann would not comment on the bridge collapse because at the time of the interview, a federal investigation on the case of the incident was still underway.)
Here are excerpts of the interview:
MinnPost: How often do bridges get inspected?
Dan Dorgan: Requirements for inspections start nationally and then we also have state statute, but we have to follow what the federal guidelines are, so the federal guideline is every bridge has to be inspected at least once every 24 months. But, in Minnesota, and for a number of years now, we’ve got a group of bridges, that we also — when they hit a certain condition level, we inspect at least once a year. So, we always meet the federal requirements, and for a number of our bridges, we inspect on a shorter cycle.
MinnPost: I know you guys rate your bridges on a 0 to 9 scale; at what number do they go to that more frequent …
Dorgan: That would be at a 4. That’s the condition rating that triggers the annual inspection. There’s also a small subset of bridges called “fracture critical” bridges that get an additional inspection once every 24 months, which is an in-depth, very detailed inspection. You’re specifically, generally looking for fatigue issues, like cracks in steel. And plus, there’s underwater inspections, and that’s another federal requirement. Once every 60 months, we have to have a diver go out and go down in the river and look at the foundation, and if they can’t see it in the Mississippi since it’s so muddy, it’s really more feeling down there, but the divers go down there, and the inspection reports are generated from that.
MinnPost: With so many bridges to inspect, do you ever get behind? Like if there’s a bridge you haven’t inspected it in 25 months, instead of 24?
Todd Niemann: There are always a small percentage of inspections that may be late, and data that can be entered late [into the database]. In the state of Minnesota, we have a lot of different bridge owners. Every county is their own bridge owner, every city is their own bridge owner, and the state is bridge owner, and there’s Met Council, Airport Commission, Department of Natural Resources, there’s federal owners, federal and state parks, Indian reservations, so there’s lots of different owners. There’s always issues with some owners, that they’re dealing with a flood in a year, so there’s always some instances where there are some owners that are a little bit behind.
Dorgan: I think about 90 percent were getting done, and then within about another month or two, all of them were getting done. So, if they’re behind they are probably no more than a month or so. There’s about 19,000 bridges get inspected in Minnesota, and of those, MNDOT owns about 4,600. So, 15,000, the greater number, are out there amongst the 87 counties, cities, and all those other owners.
MinnPost: If one bridge was maybe just overlooked a little bit and they didn’t get around to it for another six months, is there any consequence with the federal administration?
Niemann: There can be. The federal highway administration can withhold federal funds to a certain agency and withhold distribution of federal funds, but to my knowledge, that’s never happened in the state of Minnesota.
MinnPost: How detailed do inspectors get with their reports?
Niemann: They’re generally pretty detailed. We do have these numerical grading systems that we use, as you referred to before, but beyond that, there’s room for inspectors to put notes in, to elaborate on a specific condition in certain portions of the bridge, so they can be fairly detailed. We encourage them to. If I can speak from MNDOT’s perspective, yes, they do. There are some owners, local owners, counties, cities, that aren’t always as detailed, and we encourage them to be more detailed.
Dorgan: An inspector will note something they’ve seen, and at times they carry over those notes from past years. They’ll note something in 2004, and they’ll say, keep reviewing in future inspections, and there’s often quite a few notes on there. The newer the bridge, the less notes, the more it’ll just be numerical because there’s really nothing to say. But as a bridge ages — you know, a 67-year-old bridge — you’ll probably start seeing a lot more notes on there.
MinnPost: So, once the inspections are done, once the inspectors come back, have filled out their report, they come back and you said it gets entered in a database? What happens to it after that?
Niemann: Well, all inspection reports are reviewed by a registered engineer within a given agency, so that review is done to ensure whether or not there’s any maintenance that needs to happen on the bridge, routine maintenance, they would identify maintenance needs at that time, or potentially any repair or rehabilitation that they would want to consider for the structure.
MinnPost: And then it goes into the database, and then it would be revisited again in the next 24 months when an inspection is done again?
Niemann: Yeah, whenever it’s scheduled for inspection again, very routine for the inspector to collect the past report and take it out there to compare any change of condition from the previous inspection.
Dorgan: And those files are maintained. If one needs, we can give you the inspection reports back for 15-20 years, and at times, inspectors do go back to their old reports to look for something.
Niemann: The database is mostly used for statewide analysis of what’s the overall condition of our system — that’s kind of the basis of the database is to make reports to the federal highway administration at the end of the year.
MinnPost: Can you give me an idea of who the inspectors are and what kind of training they’ve had?
Niemann: Most of the inspectors are from the maintenance forces within the agency, so they are maintenance workers that have been specially trained for bridge inspection, and have also been certified by the bridge office here.
MinnPost: Can you give me an idea of what kind of training they get, though? Is it like a year-long program that they have to take, or a few days?
Niemann: There are two different classes. There’s a one week training class, and then there’s a two-week training class. And those have to be taken in successive years; those can’t be taken back to back. And then beyond that, there’s an experience requirement, and if you’re a non-engineer, and you’re a technical person that’s working on a maintenance crew, you have to work five years kind of as an apprenticeship under the oversight of someone that is certified. So, there’s not only classroom training, but there’s five years of practical, in-the-field, on-the-job training like experience. Now, if you are a registered engineer, you don’t have to have worked with someone for five years.
Dorgan: Additionally, we require them in Minnesota to take a proficiency exam, meaning, after they’re done with the classes and they’re ready to be a certified inspector, they go out and inspect a bridge, and then a certified inspector will be with them, and will compare their inspection and what their ratings were to a test bridge — so it’s kind of a final exam type of thing. And then, ongoing, they need to go to what we call refresher training. So, your training doesn’t end there; it’s sort of like continuing education.
MinnPost: How long does a typical bridge take to inspect?
Niemann: Anywhere from several hours to a couple weeks. It can range that much.
Dorgan: When we’ve got busy bridges, we need to shut down a lane so we can do the inspections, so we’ll often get several pieces of equipment out there and different teams of inspectors, since you’ve got traffic shut down, you get as many, as much inspection staff on there with equipment as you can to try to get the bridge done.
Dorgan: Yeah, but of course, we want to be thorough, but if you just give it to one team, they’d be out there forever, and you don’t want them to be hard pressed, you want them to do their job, so that way, you give them a sizeable piece to inspect and then the next team is doing the next span.
MinnPost: When you have a lot of people working on one bridge, inspecting one bridge, do you think there’s ever a miscommunication as far as, who’s looked at what and who’s covered each part of the bridge?
Niemann: Well, we have a pretty detailed system when we’re in the field. The bridge is broke down into pieces and elements, and we’re taking notes all along, so everybody knows what pieces they’ve looked at.
Dorgan: Plus, particularly for these busy ones, you’ve done a lot of pre-planning, because you’ve had to get out there, shut down lanes with traffic control, you have a certain window you were going to work, so you’ve had to study how much crew and how many people do we need to cover this.
MinnPost: Are there any tell-tale signs they should be looking for, or things that get to the point on the scale where you’d need to close the bridge?
Niemann: Well, you’re looking for any type of change in conditions, from how the bridge was originally constructed. Generally, deterioration shows up in the form of concrete cracks or squalls, or steel corrodes; timber rots. So, depending on what your material is, whether or not you’re looking at concrete or steel or timber, those are your classic forms of deterioration for those materials. There are always cases of advanced deterioration, and when you get into a situation of advanced deterioration and the bridge is starting to show additional signs of distress in certain ways, then you enter into communication with engineers that are trained for analysis. And the inspectors forward that information to those engineers. Right away, though, that happens, immediately those communications are done.
MinnPost: So, if they see something that’s advanced deterioration, they would immediately call somebody at the office?
Niemann: The person in the field makes all the documentations that they need, they measure whatever they need to measure, they’ll take photographs of everything they need to photograph, so that analysis is done from here in the office.
Dorgan: I think a lot of that depends on the level of severity of what the inspectors see. Just to give you an example, there was one probably about a year ago, it was the Highway 11 one, where up in the northwest corner of the state, along the North Dakota border, an inspector calls in one afternoon on his cell phone from the bucket and explained, “Here’s what I’m seeing,” and he had a concern, and properly so. There was a crack in the steel and we were concerned about it. I think within about half an hour a decision was made. I think he was even able to text us a photo, so, he’s out there on site and talking to staff back in our office, and a decision is made to shut the bridge down. In that case, we had to call North Dakota, too, and have them shut off traffic on their side of the roadway.
So, if it’s that kind of level of severity where they’re really concerned, it’s all done in real time as quickly as you can to get to that decision.
MinnPost: So, from the time that you make that call, maybe, and say, “I think this bridge maybe should be shut down,” how soon did they shut that bridge down? Within the next day?
Dorgan: Oh, no, within about an hour. Once the decision [is made], you call for maintenance to come out and start blockading the road as soon as you can. So that was all done quite rapidly. Again, though, that was unusual, that doesn’t happen too often. But, most of the time, it’s more — changes are more subtle.
As you mentioned, there’s a nine-point condition rating, starting from “excellent” on down. So, when something moves from a 6 to a 5, that’s very routine that something moves down one grade, but that’s not alarming unless you’re further down the scale than that.
MinnPost: Are there factors other than design, or general wear and tear, that can affect the safety of a bridge?
Dorgan: In Minnesota, probably the most important factors are to keep roads open in the winter, we put down chemicals and salt, I mean, that’s a necessity, and a lot of that is corrosive, and it’s hard on steel, and it’s hard on the reinforcements that’s in concrete. So that’s probably one of the things that ages bridges more rapidly. And just the fact that we go through the seasons and the freezing and the thawing is hard on the materials out in the field, too, so that shortens the life as opposed to a bridge sitting in Arizona, which may see very little deterioration.
MinnPost: There was a report put out by GrayPlant Mooty, saying that MNDOT has quite an oral culture. Do you guys still do that, or can you explain to me what that means?
Dorgan: Well, we talk to each other all the time. Yes, within the agency, a lot of communication is required. Without going back to their report, I think, you know, one of the areas that has probably changed over the last six months is the documentation following inspections. Our maintenance people were always looking within our districts after inspection reports and determining what kind of maintenance needed to be done, scheduling it, and going out and doing it. But, often, they just did that, with some … minimal records, which would be kind of understandable because they controlled the whole thing; owned the structure, inspected it, maintained it.
So, if I was part of the inspection-type staff, I might have called an employee and said, “Can you send the bridge crew out in the next two weeks and fix this?” And that employee went out and fixed it and was done. But we didn’t always keep a record of all those transactions, so we’re — and I think that’s probably mainly what they were citing there. Since then, we’ve got follow up reports that we’ve required now on inspections that document, what are — and maybe there’s nothing, you know, on a fairly new bridge, you decide “no action needed” on anything, but others you might identify two things that should be done over the next year in terms of repair. So, we’re keeping records now of what those were, when it got assigned to maintenance, and when it got completed.
MinnPost: So it’s just more documentation now?
Dorgan: Really, and it’s probably more to satisfy those outside of MnDOT that want to know answers to those questions, more than just ourselves, but, you know, I think we agree, it probably helps you get more regimented to make sure you get it all done, too, in that kind of way I just described.
MinnPost: I know you guys don’t want to talk about 35W bridge, and that’s fine, but my only question in relation to that is, since August 1, 2007, has the process of inspections or any of that protocol changed at all, or will it?
Dorgan: Will it? Um, I would say probably nationally. Nothing has changed on the national level because they’re waiting for the NTSB investigation to be completed so they have a definitive cause and see what actions are needed.
[The NTSB released its report Nov. 17 and cited design errors and excessive construction loads as factors in the I-35W bridge collapse.]
In January, the National Transportation Safety Board released information regarding gusset plates, and recommended that states review bridges with gusset plates, so based on that, we did a lot of inspections through the early part of this year, of our 25 trusses, so I think the procedures we were using now, and a lot of the folks working for Todd, we were checking probably more intensely corrosion at gusset plates using ultrasonic equipment to test in areas that one cannot see.
So, I would say our inspectional procedures have changed particularly with trusses in that respect. And I think most of the changes are probably more process, field inspections are fairly the same, it’s more the process of things, of following up on inspections, which I mentioned on the documentation, and probably some more of formal quality control processes, on quality assurances processes, on our fracture critical inspections. So, yeah, we are making some changes. Not necessarily triggered by I-35, though, but more, we’ve taken a hard look at everything, from maintenance and inspections to design and construction.
MinnPost: Do you think that in the future, you’ll get better at knowing when things need to be replaced?
Dorgan: I think there could be improvements there. Generally, we, from our inspection trends, we pretty well know when they should be replaced. But there are gradual improvements in all that forecasting, too, but I think most often, our people do a pretty good job forecasting when those are needed.
Courtney Sinner is a journalism and English literature honors student at the University of Minnesota. She has written for the Pioneer Press, Detroit Lakes Newspapers and the Minnesota Daily.