Bridge Collapse in MN Part 2 8

[JAE]

The other thread was getting quite long so I thought I'd start a new one.

Here's a snippet from a news report today about some of the engineering thinking about dealing with the bridge in the months preceeding the collapse:

[blue]Documents obtained by the Star Tribune of Minneapolis for a story published Sunday reveal details of how officials decided to conduct periodic inspections of the bridge rather than repair it in the months before it crumbled.

According to the internal state Department of Transportation documents, officials were ready Dec. 6 to go ahead with a plan to install steel plates at several areas on the bridge as a patchwork fix amid reports that it was structurally deficient, as recommended by an outside consulting firm. The project was shelved after the state determined the process could actually weaken the bridge.

Instead, officials decided in January to go with periodic safety inspections that would look for any cracks in the beams that would warrant emergency repair. Senior engineer Gary Peterson said contractor URS Inc. assured them that any cracks could be detected before they posed a serious safety risk.

Inspections of 52 steel beams began in May but were suspended when concrete repairs began earlier this summer.

The inspection strategy was also deemed to be more cost effective, but Peterson and state bridge engineer Dan Dorgan denied that money played a role.

Engineers were to have met Aug. 20 to discuss whether the inspections were effective or if they had to go back to the plating idea.[/blue]

 

[graybeach]

What does everyone think should have been done? Of course, 20/20 hindsight says that the bridge should have been closed and repaired back in December. And maybe the lesson learned here is not to mess around with deficient nonredundant structures.

But put yourself in the MNDOT's shoes. It must have seemed out of the question to just shut down a high volume bridge like that. That would be a polical nightmare. Better to go out and find an expert to do a study. If the expert tells us everything will be OK, we can all breath easy.

What would you do if you were a rank and file DOT or other government engineer faced with a similar situation?

I do not know about MNDOT but, at my agency, there are fewer and fewer high level people who care to discuss our very real and serious engineering problems. All they seem to be concerned about is monitoring performance based on meeting schedule milestones. What needs to happen in government agencies to avoid these types of catastrophes?

 

[jike]

You can bet the pressure to keep that bridge open was enormous! There is also a tendency to hire the consultant that will give you the answer that you want.

I have already been in situations where the Architect has told me not to use the words "structurally deficient" in a report because the Owner would not be happy and it would cause too much concern. How many others have been put into this position?

 

[csd72]

Accountability is required,

In the UK they brought in corporate manslaughter laws which held the directors accountable for such incidences.

The problem is that those that hold the power are too far removed from the consequences.

They had report that it was structurally deficient but they chose not to rectify the problem. Monitoring is pointless if they are not going to do anything about it when problems are found - they had already found a problem which they chose to do nothing about.

I am sure there is more to it, but (in my opinion) this senior engineer should never have recommended inspections when it was already shown that the bridge was inadequate.

I love how they claim that money was not a factor, on what basis did they make these decisions then?

It will be interesting to see how this plays out when we have all the facts.

csd

 

[rb1957]

aren't the politicans there to make the hard choices ?

personally i think it's stupid (and insulting) to be told "money wasn't the issue".

i think it's possible that the repair might have weakened the bridge (but then it would be a pretty lousy repair wouldn't it !). i'm willing to bet it was an expert's opinion, and possibly only 1/2 the message was received "as is it might weaken the bridge; if you did this as well it'd be ok".

it sounds like the discussion at NASA before Challenger's reentry ... it's like they say, if you want to know the price of safety, have an accident.

 

[prost]

How many other bridges could you compile a similar audit trail of inspections, engineering recommendations, political pressure to change recommendations, etc.?

One wonders who the gov't really works for? In my industry, aviation, the FAA is supposed to promote flying and promote safety--these two goals have a conflict; almost inevitably, the FAA goes with the commercial airlines, especially when it relates to accidents. Accidents are ALMOST ALWAYS "pilot error." I just got an FAA publication that talked about 'wake turbulence' with the rather astonishing statement that there has never been a loss of life due to wake turbulence. If you are thinking of that Airbus that crashed in November 2001, you might recall one of the pilots pushed the rudder over one way then the opposite, trying to maintain control of the aircraft that was flying into severe turbulence caused by a much larger aircraft that took off right before it. Because the pilot overcorrected, causing the tail to break off from the severe aero loads, the accident's cause was 'pilot error.' The wake turbulence was a 'contributing factor.' This seems ludicrous to me--if the plane had not flown into heavy turbulence, would all those people on that plane survived the take off of that Airbus? I believe the answer to that question has to be "Yes." Or the opposite, would anyone have died if their had not been heavy turbulence? I'd say that one was "No." Sounds to me like 'wake turbulence' was the accident's cause, not pilot error. But I am just a lowly engineer and a member of the flying public, what could I know?

Months afterward, there was a debate in Aviation Week over whether the pilot made a mistake. Two letters in particular stand out--each claimed to be a pilot of this particular aircraft; one pilot claimed it was easy to control your inputs into the rudder control, another pilot claimed exactly the opposite. Two alleged experts, claiming exactly the opposite--which do you believe?

The point of all this is that it appears that some of these gov't officials who should be looking out for us are in fact, not looking out for our safety (don't take this for an anti Bush rant; this kind of thing has always occurred, it usually takes a few deaths or injuries to really focus the public's gaze).

 

[HgTX]

"I am sure there is more to it, but (in my opinion) this senior engineer should never have recommended inspections when it was already shown that the bridge was inadequate."

Not practical. A staggering percentage of the bridges in this country are "inadequate".

Hg

Eng-Tips policies: faq731-376

 

[cvg]

In my opinion it is not up to the engineers doing inspections to determine what is or isn't practical, only to offer clear, unambiguous opinions of the adequacy of the structures and recommended course of action if repairs are needed. Recommending inspections vs repairs could be argued till the cows come home, but deferring maintenance in my opinion is rarely a cost effective method of managing our infrastructure. It only increases the cost and risk to the public. Management should be making the hard decisions of setting priorities for the repair work. The politicians can then decide which departments need increased funding...

 

[graybeach]

It is an old story, isn't it? But what should a lowly engineer do when he is in the thick of it, after a—es have been covered by “documenting the recommendations?” Stand on his desk and scream?

 

[prost]

This is certainly a dilemma for the engineer. Aerospace is just full of similar examples--the engineer at Morton Thiokol who screamed and jumped up and down about the seals on the Shuttle boosters; the engineer at Douglas who had a similar reaction with the design of the DC-10 doors. Each is considered a seminal example of management overriding engineering recommendations. On the other hand, I'll bet there are many counterexamples in which engineers 'cried wolf' so to speak, management ignored calls for change, nothing happened anyway.

 

[HgTX]

cvg, what is or isn't practical is by all means a necessary consideration for any engineer. Pie in the sky is pointless. In an ideal world, a state DOT would have all the funding it needed to fix the bridges that should be fixed; replace all those that would cost more to fix than replace; repave all the roads that need repaving (dangerous surface conditions, doncha know); upgrade the guardrail that needs upgrading; replace the signage that has been stolen (for the aluminum), defaced, or weathered away; provide at least slightly competetive salaries for employees so that there can be engineers to make the kind of decisions you want them to make; upgrade to only two versions ago (instead of five) of AutoCAD, Office, Windows, and other software and get computers that will run said software; and so on. (Note that things like cost-of-living raises or keeping up with healthcare costs aren't even on the list.)

This isn't an ideal world. Ultimately a DOT reports to a politician. An executive director who sticks their neck out too far gets replaced with one who won't. Their funding priorities are not always theirs to set, and even if they are, it's not as black-and-white as you seem to imagine. So they look at the cost of, say, replacing this bridge this year vs. replacing it next year, on engineering advice that it doesn't seem to have anything wrong with it that is of such immediate concern that it can't wait another year, and spending that money on other efforts to make other roads safer. Or on such wasteful notions as the first cost-of-living wage increase in many years for the state employees. I could go on and on, but I've said enough.

What happened in Minneapolis is awful, but I doubt it will be able to be pinned down to any specific act of negligence.

Hg

Eng-Tips policies: faq731-376

 

[cvg]

HGTX I'm sorry, I will have to disagree with you on this one. I truly believe that all engineers, including the "senior engineer" who supposedly recommended the inspections on the bridge in Minneapolis do have a sense of what may be practical, but still have a duty to provide technically sound recommendations (in this case, to repair the bridge) even if it may not be "feasible". At least for Civil Engineers, our code of ethics requires this since most if not all of our work affects the public - we have a duty to the public, not to the budget.

http://www.asce.org/inside/codeofethics.cfm

(see canon 1 in particular)

I agree with most of your post, however most (all) engineers, inspectors do not get paid to make feasibility / budget decisions, and are not given the responsibility for them. If that were the case, then we wouldn't need the chief bridge engineer. His is the final decision on which recommendation to put forward. It then is up to the director of the transportation department to fight for the money to support his bridge department. However, even he may be trumped by other department heads who are fighting for a piece of the same budget pie. Unfortunately, these department heads and directors are not always engineers - often are more political positions and simply do not understand the risk that they are placing on the public.

 

[csd72]

HgTx,

You make some excellent points, but.

Engineers are experts at engineering, not accounting, not politics. We should leave the politics to the politicians and the accounts to the accountants.

If something isnt adequate we should recommend that it be fixed even if it is 50th in the list of priorities.

I wasnt trying to imply that the relevant engineer was negligent, only that it was pretty poor risk management making a recommendation like that.

csd

 

[JAE]

One thing to consider.

Despite all the warnings by consultants, reports of fatigue cracking, etc. it COULD BE that the cause of failure had nothing at all to do with any of the reported deficiencies.

What if the true cause of the collapse wasn't anything that was seen, inspected, observed or even understood by the bridge design industry for that bridge?

It could be that, yes, this was a bridge in need of fixes and maintenance but the collapse just happened from an "other" cause totally unrelated to anything that could have been forseen. They could have initiated all the recommended repairs and it still would have fallen down.

Until we KNOW what caused it, suggesting that MNDOT wasn't funded enough, didn't prioritize enough, etc. might be moot.

 

[apsix]

Does anyone really know the definition of "structurally inadequate" as reportedly used for this bridge? You can be sure that it doesn't mean that it was about to fail. Without further evidence I would say that frequent inspection was probably a valid option. Whether the inspections which actually occurred were adequate should be assessed.

Of course, with hindsight, we know that either; the original condition report underestimated the problem(s), the inspections were not adequate or collapse was caused some unrelated incident.

 

[BSE05]

Quote from CBS news......"There are 75,621 bridges in the United States that have been slapped with the same label of "structurally deficient."

What does that term mean? Not much in my opinion. If I were to use such a term applied to a building structure it would mean evacuation of all occupants until repair could be made.

The real crime here could be in the sloppy use of the term structurally deficient. Any bridge engineers out there to explain this?

 

[bridgebuster]

SteelyLee - the term "structurally deficient" can be confusing because it can be deficient based upon inspection or analysis. I'll give you my $0.02, which will probably muddy the waters even more.

The rating scores assigned to bridges that you see being broadcast in the media are based on inspection. The components are rated (I'll use the NYSDOT system for this example)on a scale of 1 to 7.

1 = potentially hazardous
3 = serious deterioration or not functioning as originally designed
5 = minor deterioration or functioning as originally designed
7 = new condition
2,4, and 6 are used to shade between 1,3,5, and 7.

The components have a weight and the weight is multiplied by the component rating. The total of the component ratings is divided by the total component weight and the result is a rating score.

A score less than 5 is the realm of structurally deficient. However, the when the public sees rating scores they don't see the whole picture. Suppose two similar bridges have the same rating, say 3.111, but for different reasons.

One is becuase the framing is in poor condition and the other because of the deck and overlay. Bridges don't collapse becasue the deck and overlay are in poor condition but they can collapse because the framing is in poor condition. Both would be deficient but a distinction needs to be made.

A bridge could also be deficient based upon analysis. All DOT's have a design live load policy - AASHTO HL-93 or HS-25. AASHTO uses the terms Inventory and Operating Rating. Inventory is the maximum truck load that can be used for an indefinite period (the minimum design live load); Operating is the maximum permissible overload.

If a bridge is overstressed for the Inventory condition it could be considered deficient. The policy varies between agencies. Some have alternate methods to determine the IR if the initial rating comes up low.

 

[miecz]

Article 3.8.1.4 of AASHTO's Manual for Condition Evaluation of Bridges reads:

[blue]Critical structural and safety-related deficiencies found during the field inspection and/or evaluation of a bridge should be brought to the attention of the Bridge Owner immediately, if a safety hazard is present. Bridge Owners should implement standard procedures for addressing such deficiencies, including:

Immediate critical deficiency reporting steps;
Emergency notification to the police and the public;
Rapid evaluation of the deficiencies found;
Rapid implementation of corrective or protective actions;
A tracking system to ensure adequate follow up actions;
Provisions for identifying other bridges with similar structural details with follow-up inspections.[/blue]

I don't see the term "critical deficiency" defined.

bridgebuster-

Is there a provision in the NYSDOT to highlight "critical deficiencies?" Is any structural element given a rating below 5 considered critical?

 

[rb1957]

maybe somebody was trying to make points by labelling 75000+ bridges as "deficient"

 

[bridgebuster]

jmiec,

during an inspection if a strucutral problem is found, it's categorized as either a "red flag" or "yellow flag". In both cases, the inspecting engineer calls the regional DOT office ASAP.

Red flag requires immediate action, close the bridge, or have a maintenance crew come out, etc. Yellow flags have a little more time; off the top of my head I don't recall.

It's a very stringent procedure with NYSDOT. There has to be documentation each step of the way from the time the flag is issued until it's repaired.

Inspection reports also have to have all the flag documentation; the cover of the report also has in big, bold print: RED FLAG or YELLOW FLAG.