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Bridge Collapse in MN Part 2
8

Bridge Collapse in MN Part 2

Bridge Collapse in MN Part 2

(OP)
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:

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.

RE: Bridge Collapse in MN Part 2

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?


 

RE: Bridge Collapse in MN Part 2

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?

RE: Bridge Collapse in MN Part 2

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



RE: Bridge Collapse in MN Part 2

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.

RE: Bridge Collapse in MN Part 2

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).

RE: Bridge Collapse in MN Part 2

"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

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RE: Bridge Collapse in MN Part 2

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...

RE: Bridge Collapse in MN Part 2

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?

RE: Bridge Collapse in MN Part 2

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.

RE: Bridge Collapse in MN Part 2

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

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RE: Bridge Collapse in MN Part 2

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.

RE: Bridge Collapse in MN Part 2

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





RE: Bridge Collapse in MN Part 2

(OP)
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.

RE: Bridge Collapse in MN Part 2

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.

RE: Bridge Collapse in MN Part 2

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?

RE: Bridge Collapse in MN Part 2

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.

RE: Bridge Collapse in MN Part 2

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

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.


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?

RE: Bridge Collapse in MN Part 2

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

RE: Bridge Collapse in MN Part 2

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.

RE: Bridge Collapse in MN Part 2

csd72,

You said that "In the UK they brought in corporate manslaughter laws which held the directors accountable for such incidences." Well if it worked then I'd agree with you. No one has yet been charged with corporate manslaughter although many should have been. Herald of Free Enterprise sinking, Hatfield train crash and now Stockline Plastics explosion all show the worse cases of corporations ignoring safety.

In my company apparently "safely is the highest priority" but in practice its the bottom line that's most important. Until someone (in the UK or US) gets put away for killing people then this problem of technical specialists being ignored will continue.

I also think JAE is correct in saying that they're may be other causes other than the known deficiencies that caused the collapse. The good news is that its the engineers who do the collapse inspections and write the reports.
 

RE: Bridge Collapse in MN Part 2

(OP)
The problem I have with prosecuting engineers for manslaughter, or even corporate executives, is that it is very difficult, in structural collapses, to pin the blame solely on one person.  

If someone is prosecuted it's one person who perhaps shared a small percentage of the blame, but was the one who got punished.  
  
Some collapses certainly can be identified as ONE PERSON's negligence, but not many.  Usually a collapse is a comedy of errors and circumstances.  Some do deserve punishment so I'm not advocating limiting all liability all the time.  

In addition, for cases like the MN bridge, there is always some level of risk inherent in any structure.  Thus, owners, DOT's, engineers, etc. must ALWAYS weight relative risks and cost/benefits.  

There is no such thing as a completely RISK FREE structure, but unfortunately our societies today want the world to be perfect, without risk, and anyone in authority who allows more than zero risk to occur is somehow guilty of a nefarious crime?  I just don't see it that way.

RE: Bridge Collapse in MN Part 2

I feel that if someone has been informed of a potential problem and they choose not to act due to cost or what ever the issue then they are the one caught holding the bag and should be punished accordingly. If its negligence on the part of the professional engineer there are already thing in place to deal with this although I don’t feel that this is the same issue as someone that is making a conscious choice to allow a hazard to human life without that person knowing. They put safety labels on cigarettes why can’t we do something of the same for structures? At a minimum I think any structure that has been deemed unsafe or inadequate should be conveyed to the public so they can make a conscious decision on whether or not to use the structure.

RE: Bridge Collapse in MN Part 2

i quite agree JAE, management (who make the decisions) will squirm and weasle "I'm not an expert, I acted on the experts recommendations"; the engineer will say "if the bridge was inspected properly it wouldn't have failed"; the inspector's lawyer would ask "what never?"; and the negineer will be forced to say "well, hardly ever.  the probability of failure is 1E-6 if the loading is accurate" lawyer "so how accurate is the loading ?"
engineer "i used data from manuals, measurements from the site, traffic forecasts from DOT" ...
and so it goes !

negligence could be proven if the inspector falsified the record, or if the engineer fulphed the calcs, but could the decision maker get dragged into this (probably not?)

RE: Bridge Collapse in MN Part 2

fasboater,
IMHO, and presumably JAE's as well, that's a bit of a perfect world viewpoint.  risk is everywhere, 99% of decisions increase the risk to someone.  and what about the 95000+ similar bridges (ie similar declared "deficient") ?

RE: Bridge Collapse in MN Part 2

Thanks to bridgebuster, that was a good explaination of the structural investigation process. It certainly is more rational than its label. The term "structurally deficient" certainly needs some modification. As we see the media has gone into "chicken little syndrom" with that label.

Unfortunatley the general public has very little understanding of what engineers do. The little publicity we get is usually linked to a major disasters. The engineering profession typiclly doesn't get very good coverage due to the media's general lack of engineering knowledge.

RE: Bridge Collapse in MN Part 2

Thanks SteelyLee. You're on-target about the public's lack of understanding.

JAE - I agree with your last post.

As engineers we're often caught between the proverbial rock and a hard place. I don't know about anyone else, but, I don't have a crystal ball that's going to tell me when a structure will collapse. From experience, we can tell when a structure is in imminent danger of collapse but there are many circumstances where we cannot predict the time to failure.

There are probabilistic methods to determine like fatigue crack growth and tests to detrmine concrete durability but can anybody truly say "this bridge (or wall, or building) is going to collapse in 24-hours"? Unfortunately, we're sometimes forced into that situation.

Here's an example of how the media and the public twist things:

In June, two engineers in my group inspected a publicly-owned retaining wall; they reported the condition as poor. The wall is next to a condo; during the inspection someone on the condo board brought out an architect, who also lives there. Anyway, the architect thought he was a self-proclaimed expert on walls and he told my guys it's about to collapse. Granted, it's in poor condition - because of certain elements that are driving the rating score - and something needs to be done but I don't think it's about to collapse. Last week, a neighborhood paper had a story about the wall (the local politicians are involved), they got a copy of our report and wrote "according to the inspection report it's a disaster waiting to happen."

We never said that; we only said it's in poor condition.

Gotta go now, but I have another story - about a concrete bridge but sort of a reverse scenario from the wall.




RE: Bridge Collapse in MN Part 2

Hard pill to swallow guys, but there are outdated inadequate structures on every street corner of the US, not just bridges.  It's just the normal fiscal balance of life. From the little info I have, I think said engineers made professional judgments that are in line with the constraints of the system.  The normal system takes risks, it has to or else we'd be taxed to bankruptcy.  

It's the lawyers and uneducated public who need to point fingers just to get some resolution and live in their naive world that everything is 100% safe.

RE: Bridge Collapse in MN Part 2

Everyone is blaming the politicians about not spending the money to fix the bridge but have any of you ever said yes to paying more taxes??? I'm sure there are a few but, truly if MN had posted a tax increase for the reason of updating bridges that were deemed structurally deficient, I bet the proposition would have been slammed and almost no one would have voted for it.

RE: Bridge Collapse in MN Part 2

"At a minimum I think any structure that has been deemed unsafe or inadequate should be conveyed to the public so they can make a conscious decision on whether or not to use the structure."

How do you do that without scaring the travelling public un-necessarily and cause them to lose confidence in the processes and steps that have aready been put in place? The majority of the "structurally deficient" bridges have problems that will not cause catastrophic failure .This must be true because the majortiy of these bridges have NOT fallen down.

There are inspection and rating programs that were put in place by FHWA as a result of the Silver Bridge Collapse and for the most part these programs DO work. Warnings are posted at problem bridges as a result of this by the DOT. Bridges are posted for maximum un-permitted loads (I have not heard if the I-35 bridge was posted) based on the results of the rating program and inspections.

We have to trust the system that is in place. That being said we should also look for ways to improve upon it.

RE: Bridge Collapse in MN Part 2

People in this thread are making absolute statements like "I feel that if someone has been informed of a potential problem and they choose not to act due to cost or what ever the issue then they are the one caught holding the bag and should be punished accordingly," but there is simply NO WAY to address all "potential problems".  For some large percentage of "potential problems", the choice MUST be made to do nothing; the question is which problems are addressed and which are not.

We have no idea where the money that was not used to fix the MN bridge was spent (and since the money wasn't marked as "$$ not spent on bridge repair", no one knows this).  Perhaps, as a random and completely invented example, there was a program to add rumble strips along the edges of the state's highways that would not have been funded if the choice had been made to repair the bridge.  And perhaps choosing to repair the bridge instead of adding the rumble strips might have meant more than 12 traffic fatalities over the next several years from people falling asleep and driving off the road.

There are finite (and seeminly ever-decreasing) resources, and increasing demand.  Part of managing a state highway system involved deciding how to allocate the resources.  And yes, allocating them here means not allocating them there.  Always.  Problems are documented, problems are noted, and not all problems are solved.  That's reality.  And not everyone within the organization will agree with all the decisions.  That is also reality.  If you go looking for someone who can say, "I told you so," you'll probably find them.  That is not an automatic indicator of negligence on the part of the agency.

I'm not saying that it's impossible that there is some blame and liability to be assigned in the MN case, but people should get off their high horses and stop assuming that there surely must be.

Hg

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RE: Bridge Collapse in MN Part 2


I never agreed to allow my taxes to fund junkets to China either.

"If you are going to walk on thin ice, you might as well dance!"

RE: Bridge Collapse in MN Part 2

(OP)

Quote:

Everyone is blaming the politicians about not spending the money to fix the bridge but have any of you ever said yes to paying more taxes???

heh.

The economic record shows that when you LOWER taxes, government revenue goes UP due to better economic conditions.  This isn't an opinion, it's a proven fact.

So what you are saying doesn't make sense.  Raising taxes deters the economy and REDUCES revenue over the long haul.



I'm in agreement with many above that you can identify risk (which is always everywhere) but it does not follow that you can identify collapses.

 

RE: Bridge Collapse in MN Part 2

Actually, we pay alot in taxes for roads and bridges. about 15 cents a gallon for the highway trust funds. However, Much of it was "borrowed" by the general fund and reduced the levels of available funding until TEA1. However, under the current administration, continuous funding for roads and bridges came to halt for many states due to opposition to the required levels of dedicated funding for roads and bridges. As a result many states were unable to do much for those years. Now even though SafetyLu is in place, at much lower funding levels than needed to address the problems, Money for projects flows slowly.
When asked about the condition of the roads and bridges, the engineering community as a whole has said "Yeah its low, but they are still okay." We need to scream "Hell yeah they need work. We can't fix them all at once, but we can do as much as we can"
I don't know if criminal charges as dicussed in earlier posts should be brought, but the engineering board should look at the company that wwrote the report and decide if they exercised competent engineering judgement in recommending inspection over repairs.

RE: Bridge Collapse in MN Part 2

I do not think we should be so quick to pass judgement on the engineer or the DOT in this instance. The engineer and DOT people involved will be questioned I am sure and if they were negligent it will come to light, but as engineers, particularly bridge and structures we have make decisions based on our engineering judgement. In this case (From what I have read) the bridge was inspected, the problems were thought to have been identified, and the plans and alternate plans were presented to the owner. Hopefully The owner made a decision that they believed was in the best interest of the public based first on safety then on fiscal responsibilty. Apparently none of the posters on this forum were involved with the decision so all the rest of us can do is speculate on why the bridge collapsed and what the smoking gun looks like.

RE: Bridge Collapse in MN Part 2

Quote:

At a minimum I think any structure that has been deemed unsafe or inadequate should be conveyed to the public so they can make a conscious decision on whether or not to use the structure

Yea right, who the heck is going to do that? Cities like St. Louis and Nashville would have a major panic.  Do you know what would happen if the a average sized New Madrid seismic event occurred?? We're talking about entire portions of downtowns leveled.



RE: Bridge Collapse in MN Part 2

My wife grew up in a 3rd world country and when they came to a bridge, they would unload everyone from the bus and then the bus would drive across the bridge empty and then the passengers would walk across.

RE: Bridge Collapse in MN Part 2

(OP)
....and I would hope the passengers walking across would use a stutter step to avoid resonance in the bridge!!

RE: Bridge Collapse in MN Part 2

Quote:

Quote:
Everyone is blaming the politicians about not spending the money to fix the bridge but have any of you ever said yes to paying more taxes???

heh.

The economic record shows that when you LOWER taxes, government revenue goes UP due to better economic conditions.  This isn't an opinion, it's a proven fact.

So what you are saying doesn't make sense.  Raising taxes deters the economy and REDUCES revenue over the long haul.

Well, in Coloraod Springs, it was voted to increase the sales tax, with the funds to marked for transportation projects.  I was at an ASCE meeting where one of the City Engineers siad that it was an exciting time to be in his position, because they finally had the money to do projects.

These projects have ranged from radius changes at intersections with restriping to a few single point urban interchanges.

I am sure our city engineering would not agree that we should have lowered taxes so that we can wait for the economy to pick up to the point that there are millions flowing in. Maybe at thatpoint, they could repair the failing bridges here?  Or  perhaps that money would be better suited for something else.

RE: Bridge Collapse in MN Part 2

(OP)
TDAA - your dripping with sarcasm.  I can feel it!! smile

My statement is based on federal taxation patterns over the last 20 to 30 years and do not reflect short term effects of local/state taxes.

I also wonder how long those taxes continued to go to that City Engineer's projects.  Eventually they all get mushed up into myriad other programs and bureaucracy.

RE: Bridge Collapse in MN Part 2

Lowering taxes will only work (sometimes) if you are currently in an over-taxed situation. There are also a few other factors which affect the well being of the economy!

RE: Bridge Collapse in MN Part 2

(OP)
Well, in the last 30 years, every time there's been a federal tax decrease the economy has improved drastically and revenues have gone up.

But you're right, there's a lot of factors and economics is quite a fog.

RE: Bridge Collapse in MN Part 2

Let's take a break from the vodoo science of economics and get back to the cause of the collapse: The pigeons did it.

http://www.foxnews.com/story/0,2933,294153,00.html

Someone sent me the following quote; taken from an Eng-Tips posting in 2004 (pretty much sums things up):

"Structural engineering is the art of molding materials we don't wholly understand, into shapes we can't fully analyze, so as to withstand forces we can't really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance."

RE: Bridge Collapse in MN Part 2

In 1980, a stay cable on the Brooklyn Bridge snapped (the BB is a hybrid - suspension & cable-stayed); the cable hit a tourist on the walkway killing him.

NYCDOT's Chief Engineer for bridge maintenance cited pigeon droppings as the cause. The media raked him over the coals; there were editorial cartoons in the local papers calling him a fool. At that time, no one really thought about pigeons.

RE: Bridge Collapse in MN Part 2

Why not consider pigeons? There is an instance long ago in which a security guard severely damaged an airplane on the ground by urinating on the landing gear. He was relieving himself on the gear, the surface pitted because of the acid in the urine, crack formed and propagated unexpectedly after many landings, gear collapsed and the aircraft was damaged.

Aren't the chemicals in pigeon droppings are as nasty as road salt? Uric acid, etc.?

RE: Bridge Collapse in MN Part 2

Bridgebuster - that headline in the foxnews article on pigeon guano is the problem with media today or ever really.

Pigeon Droppings Contributed to Mn Bridge Collapse.....


I have seen the effects of 2' high mounds of pigeon guano on bridges, but I don't recall anyone from NTSB or MnDOT or any of it's hired consultants reporting that Pigeon Droppings specifically contributed to this very collapse.  The media is really stupid.  If they only knew how stupid this was.

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Bridge Collapse in MN Part 2

Qshake - we can't too much from the media; anything for a headline and higher ratings.

About two weeks ago Fox News, which is usually reliable, interviewed a forensic structural engineer. He praised railroads for the longevity of their strucutres and rambled on about our inability to build highway bridges to last 100 years. I looked out the office windows a few minutes ago and the Brooklyn Bridge is still standing. I e-mailed Fox tto explain that this engineer wasn't giving a fair and balanced report.

Anyway, back to pigeons. I've seen more than my share of 2' piles as well. When I started doing inspections in the early 80's there were warnings about the health hazards posed by breathing in pigeon droppings. In the early 90's NYSDOT issued warnings about histosplasmosis. Then again, I had an uncle who raised pigeons for 50+ years, it never affected him; go figure.

RE: Bridge Collapse in MN Part 2

My anonymous source has informed me that the pidgeons in the Twin City area have ties to Al Qaeda.  Actions are being taken to investigate if there are any "sleeper flocks" in the NYC and DC areas.

RE: Bridge Collapse in MN Part 2

While doing bridge painting inspections on bridges in northern Massachusetts I remember a bascule bridge over the Merrimack River that had the lift machinery removed  30 years previous. As part of the bridge cleaning contract the old machine pit had to be cleaned of several feet of pigeon guano... and I thought bridge painters had a dirty job.

RE: Bridge Collapse in MN Part 2

"They put safety labels on cigarettes why can’t we do something of the same for structures? At a minimum I think any structure that has been deemed unsafe or inadequate should be conveyed to the public so they can make a conscious decision on whether or not to use the structure."

I remember driving along the LA-TX border once, and came to a sign that said "Substandard Road- Next 19 Miles".  So yes, it's been done.

The thing is, in most cases, you don't have a real choice about how to go.  You could slap a warning sign on every bridge across the Mississippi, and then what are people going to do?  Just stay on their side the rest of their life?

RE: Bridge Collapse in MN Part 2

I worked on the design of a truss over the Mississippi; hopefully it doesn't need a warning sign.

I didn't design the gusset plates; it was the guy in front of me.  

RE: Bridge Collapse in MN Part 2

From Publication No. FHWA NHI 03-001, Bridge Inspector's Reference Manual

functionally obsolete – a bridge that has deck geometry, load carrying capacity, clearance or approach
roadway alignment that no longer meets the criteria for the system of which the bridge is a part

structurally deficient – bridges where 1) significant load carrying elements are found to be in poor or worse
condition due to deterioration and/or damage or, 2) the adequacy of the waterway opening provided by the
bridge is determined to be extremely insufficient to the point of causing intolerable traffic interruptions

Jeff

RE: Bridge Collapse in MN Part 2

I think we should post a warning on all bridges.

"Proceed at your own riskxDOT"

This might help with future litigation.

RE: Bridge Collapse in MN Part 2

(OP)
Fine print on all future structure's cornerstones:


All individuals entering this structure acknowledge, by the mere act of entering, that they understand and accept the potential exposure to danger by placing their carcass within or upon this structure, that any and all possible deleterious events can and may occur while within.  These events include, but are not limited to full or partial collapses from:
a.    Seismic Events
b.    Deterioration
c.    Pigeon Guapa
d.    Lack of maintenance
e.    Poor design
f.    Construction errors
g.    Union or non-union labor
h.    Bird dung from other than pigeons
i.    Sink-holes
j.    Human resonance
k.    Collisions with airplanes, ships, submarines,
          hovercraft, monster trucks, wheel barrows, or
          other vessels
l.    Just about any other kind of dung
m.    Earth Wind and Fire (good music huh!)
n.    High winds from visiting politicians or other low
          pressure zones
o.    Sudden increases in gravity

The individual releases and holds harmless the building owners, shareholders, officers, employees, building designers, constructors, and anyone else, directly or indirectly connected with planet earth.  

In the event of injury or damage of any nature (or perhaps even death) to the individual or anyone else caused by or incidental to the election of entering said premises, the individual acknowledges that it is totally his or her fault.  Risk exists.  Deal with it.

RE: Bridge Collapse in MN Part 2

oh now jae, you've gone to far...expecting the general public to be reasonable...pretty funny though...i guess it's about like people being appauled that our volunteer soldiers die in war; all while they sit on the couch in their cozy home complaining about soldiers dieing in war.

RE: Bridge Collapse in MN Part 2

JAE - you forgot to include global warming on your list.

The Connecticut DOT does post a warning sign on highway & bridge construction projects. It says something to the effect that road use and State liability is limited.

RE: Bridge Collapse in MN Part 2

We have traffic overload, media overload, stretched resources, and by the way, reliable news is an oxymoron.  

I think we would all agree that to engineer is human, and stressful.  Don't you love it?

RE: Bridge Collapse in MN Part 2

to continue JAE's list:

p. (a word that is homophone with the letter designation)

RE: Bridge Collapse in MN Part 2

Have you read the fine print on the software used to design our structures?  I can tell you from experience, that some bridge software companies limit their liability to essentially - zero.  

We designed an interstate bridge using a well known software package, and got burned when the software failed to check a critical code provision.  After much legal maneuvering, we had to pick up the cost of reinforcing the bridge.

RE: Bridge Collapse in MN Part 2

Sticking up for the software people, as much as I sometimes hate them, how can the software people take any liability? They can't control the bumbling of the user. We as engineers are still completely responsible (as we should be, IMO) for making sure the answers out the computer make sense, or that the answer takes the code into account.

RE: Bridge Collapse in MN Part 2

d2y:  Stressful?... not to an existentialist <G>

Dik

RE: Bridge Collapse in MN Part 2

Prost,

If the software doesnt do what it claims to do then there should be some penalty to the software company. Otherwise what is the motiivation for them to improve their software?

As engineers we shoud always check the computer output though.

csd

RE: Bridge Collapse in MN Part 2

prost-

In our case, the bumbling was by the software writer.  They admitted the error.  The underdesign was small enough that the design seemed reasonable.  There was no way to pick up the error without a detailed hand calculation.  (Even then, the code provision was so subtle that the first hand calc missed it.)

I agree, for the reasons you state, that the software vendors cannot take any liability.  This is why I no longer design with software, or spreadsheets written by others.  There is simply no way to verify correctness in each case without a hand calc. I write my own MathCAD sheets.  

RE: Bridge Collapse in MN Part 2

I like JStephen's idea about ever one staying on their side of the Mississippi River.  Unfortunately I live in the Minneapolis area and cross the river on a daily basis.  

Just on Tuesday of this week I crossed the river four times on three different bridges.  Here it is pretty hard to go almost anywhere with out crossing over the river several times on different bridges.

RE: Bridge Collapse in MN Part 2

During my stint as a combat engineer we were taught how to classify bridges and post load ratings etc.

One classification and sign posting was called "risk crossing".

That would be an interesting sign to come across in your travels. Yesterday I crossed a box girder bridge in Fall River , MA. Box girders, rivets, and lots of rust, 100's of feet in the air.

I felt like it might of been a risk crossing. Nothing like a rusty rivet.

RE: Bridge Collapse in MN Part 2

I decided to look up this bridge in the NBI. It starts with a big red tag "This bridge is structurally deficient"

Built in 1965 with rivets, I didn't think they used them that late. They were gone when I came into the profession in 1970's.

Functional Classification: Urban Minor Arterial
Service On Bridge: Highway
Service Under Bridge: Highway-waterway
Lanes On Structure: 6
Lanes Under Structure: 2


Structure Length: 1761.7 m
Bridge Roadway Width: 28 m
Operating Rating: 44.1 Metric Tons
Navigation Vertical Clearance: 41.1 m
Minimum Vertical Underclearance: 4.42 m over Highway
Number of Spans in Main Unit: 3 Spans
Material Design: Steel
Design Construction: Truss - Thru


Number of Approach Spans: 23
Approach Material Design: Steel
Approach Design Construction: Girder and Floorbeam System


Deck Condition: Good Condition
Superstructure Condition: Poor Condition
Substructure Condition: Satisfactory Condition
Scour: Foundations determined to be stable for calculated scour conditions
Bridge Railing: Meets currently acceptable standards.


Structural Evaluation: Meets minimum tolerable limits to be left in place as is
Water Adequacy Evaluation: Equal to present desirable criteria
Estimated Total Improvement Project Cost: $145780000
Year of Project Cost Estimate: 2006


Average Daily Traffic: 89000
Year of Average Daily Traffic: 2005
Sufficiency Rating: 47 %

47% ?? what does that mean? Its probably 500 or more feet above the river---- along way down.

RE: Bridge Collapse in MN Part 2

SteelyLee, as you probably can surmise a sufficieny rating is a culmination of multiple factors some of which are structural, other geometrical and yet others are needs and purpose.  However you look at it, closer to 100 is better than closer to 0.

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: Bridge Collapse in MN Part 2

A highway sufficiency rating is similar to a bridge rating; it works on a scale of 0 to 100%;  50% is considered  "tolerable."

The rating is based in part on type of road - urban or rural; pavement condition; and traffic volumes.

RE: Bridge Collapse in MN Part 2

2
Giving a bridge an overall rating based on a weighted average of the components is silly.  A bridge with a perfect deck and a badly corroded superstructure should be give a rating based on the superstructure.

RE: Bridge Collapse in MN Part 2

hokie66 hit it on the head.  a chain is only as strong as it's weakest link.  same for bridges...

RE: Bridge Collapse in MN Part 2

Having spent most of my working life with steel railway bridges, I have seen a number of "ratings" of the types above and all seem to be trying to link a risk of failure to a cost of restoring the bridge to a near-new condition - it can't be done with consistency.  The reality is that SOME well maintained bridges are operating at high stress levels or develop serious local faults (eg active cracks in stringers) whilst SOME bridges with poor paint, rust and minor cracks are safer due to more structural redundancy and generally lower stresses.  

RE: Bridge Collapse in MN Part 2

I wholeheartedly agree with hokie66. Structures usually fail because of one poor or deteriorated detail or a series of events but not because of their "overall condition."

RE: Bridge Collapse in MN Part 2

I agree with hokie66.  It's hard to believe rehabilitation decisions are made based on a weighted average.  

SteelyLee

Could you explain how to look up a bridge in the NBI?

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