Bridge Failure Comments 3

[Robertmet]

Here are some interesting comments about bridges as a result of the Minnesota bridge failure.Interesting that you can design but can't inspect bridges !

 

[hokie66]

LobstaEata,

For an old buildings structural engineer, I would appreciate it if you could elaborate on how you do a load rating analysis prior to inspecting or examining the plans. Or am I confused about the sequence?

rmifl,

Your file downloaded, but I can only access the overall picture. Can you (or someone else) help me?

 

[JLNJ]

My question about the inspectors catching it was a bit rhetorical.

I have only been in on a couple of bridge inspections (one was I-75 over a major river - while still in school) and I know that the "lead" on our team wouldn't know an undersided connx plate or anything else if he saw it. We were looking for wear and tear, not design flaws. If a rocker bearing had bottomed out or the concrete was spalling we noted it, but we couldn't be expected to see a serious design flaw unless it was REALLY obviously deformed. Don't ask me to define "REALLY".

I know of a company doing plant "inspections" for a nation-wide manufacturer. The inspections were seen as a "safety" crackdown. The engineers were charged with looking for obvious deficiencies. One day a pre-engineered girder buckled in a building which had been previously "inspected". Some of the bottom flange bracing was either mis-designed or was flat out missing. Should the "inspector", a guy with a PE and years and years of experience as a structural engineer, have predicted this? When is obvious, obvious? Short of a complete survey and running through a zillion calcs, what can be done? These are the tough questions.

 

[Qshake]

Hokie66 -

Knowing that bridges are to be inspected and rated frequently it is even expected of inspectors (at least consultants) to review the older ratings and know where the defects lie. This also includes reviewing the bridge inspection history and special inspection history such as fracture critical.

Doesn't a prudent Doctor always want a bit of background before jumping off into a new patient?!

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[hokie66]

Qshake,

I certainly agree with that. But was there a comment of mine that led to yours?

 

[Qshake]

Hokie66 - You inquired how one does a load rating prior to inspecting a bridge or looking at the plans. My comment is in reference to that inquiry. Generally, the history of the bridge is investigated prior to setting foot on the bridge.

Did I misunderstand?

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[hokie66]

Well, maybe I phrased my question inappropriately. What I was asking LobstaEata was to give me a sense of how he downrated the bridge from H15 to H6 before discovering the error. But perhaps I misunderstood his chronology, or else the bridge had already been rated H6 before he was involved.

 

[LobstaEata]

OK...obviously we had the design plans prior to conducting the load rating. Let give the old guy (me) with mad cow the benefit of the doubt. Our research confirmed a not so obvious mistake in the design plans by reviewing shop drawings and finally confirming by inspection.

 

[hokie66]

Yes, from one old guy to another, I did give you the benefit of the doubt. But I have never done a bridge inspection or load rating, and just wanted to make sure I wasn't confused, as I frequently am. Thanks for the clarification.

 

[concretemasonry]

All I seem to hear is opinions on contributing factors without access to all the real factors/conditions. The "proof of the pudding is in the result". There were many factors ranging from the hindsite of the original design, the level of construction, the amount of inspection, the inspection methods, the inspection analysis as a beginning.

Add to that, the normal deterioration with time (hidden and overt) and the effect of modifications/improvements and the effects on modifications to other portions of the structure.

The process of construction/improvements multiplied the engineering confusion and may have been a factor because no engineer is willing to sign off on the effects of a project without being able to control the scheduling and sequence of moving materials and equipment. Imbalance and vibration are also factors, especially with that type of structure.

All this points to a conclusion that will not be able to nail down the ONE specific cause of the failure, but only contributing factors on ONE SPECIFIC OLDER STRUCTURE AT A SPECIFIC TIME. This is just like all engineering where personal perspectives and assumptions are used to reach a conclusion within the framework not controlled by the engineer.

My first design project, a reinforced CMU control structure designed for seismic, projectiles, external dynamic loads and blast pressures failed two days after it was first used, but a explosion that pushed the roof to the floor. No one ever conceived of a large "bubble" of hydrogen gas that would drift over the structure and be ignited by static electricity, causing the roof system to collapse from the explosion from "ground zero, which was 50' above the building. That was determined to be the cause of the failure, but I still wonder if that was the only cause. This is still after walking into an invisable hydrogen flame caused by a leak and the friction/escape velocity.

There is no ONE answer, but only opinions when it comes to engineering and its limits to control.

Dick

 

[unclesyd]

I have two acquaintances that use to work for me that are now inspecting bridges for large metropolitan areas. Both tell me that it has become a joke with some inspections as they are now told to look at specific spots and nothing else. One told me that he thinks he has become a sacrificial lamb in case something goes amiss. Both said that the inspection procedure is never a formal one, mostly verbal and maybe a few notes.


concretemasonary,
Off topic from the OP but I been there and done same with H2 leaks. Our process had H2 at 6700 psig and it has taken the hair off my arm several times. If one heard a leak it would be located and if not burning strike the area of the leak so the night crew could fix or tag the leak.

 

[youngstructural]

Wow Unclesyd; That's horrific, and the complete opposite of my Canadian experience... The reviews we proformed on our bridges were loosely scheduled and permitted additional time upon need. Engineers discussed various possible areas of focus, but reviewed the entire bridge. It was drilled into me time and time again to never assumed you know what will need consideration or what will require review, but to approach each time as if virgin.

I am appauled by the "standard of practice" your post makes me infer... And I had thought just the qualifications of people involved bad enough. Pressing them to inspect nothing more than a few paultry locations is quite literally criminal in my mind.

Regards,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[Qshake]

I have always maintained that this is a bridge collapse with many factors, not just one and that is way I try to stop those, with no knowledge of the matter, from simplying making a comment that the public may use to become further uninformed.

That's the reporters job not the engineers! Engineers work with facts, reporters use shock and awe.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[unclesyd]

It is bothering both of the people as when they worked for me at a large synthetic fiber plant it was their job to check everything inside or outside and report same. Both were hired originally due to their ability to notice things and get nosey.

Another practice that is pervasive on new construction is where there used to one inspector they are using several so called specialized inspectors like one for materials, one for welding, one for paper work and so one. One said that they are trying to reduce the number of inspectors with credentials. This may work on an assembly line making the same thing day in and day out, but to me on inspection of equipment being fabricated whether it is a tank or bridge component needs to have one pair of eyes covering the job.

 

[hokie66]

I understand where you are coming from, Qshake, and you are probably correct that there are multiple factors involved. Hopefully we will find out in due course. But the issue with the gusset plates is not speculation, and the NTSB considered it important enough to publish an interim report. What we have been mostly discussing here is bridge inspections, and whether better inspections or required reanalysis would have saved this bridge or others. Admittedly, some of us, including myself, are not bridge engineers, but I don't think that precludes experienced structural engineers from commenting.

 

[jt12]

Interesting conversations. I still can't get over in the article that a state is actually hiding tokens on bridges at obscure places to make sure the inspectors are doing an in-depth inspection job?? That's either sad or hilarious, and I can't make up my mind.