Partial Bridge Collapse in St. Louis 2

[prost]

Looks like weak bridges and (IMO) inadequate inspection procedures are as common in the US as they are in Canada.

http://www.stltoday.com/stltoday/ne...5FDA36F6B06430F88625729200247233?OpenDocument

There was a good picture in the newspaper, but not on the online source. Sorry.

Here's one with an 'at night' photo

http://www.stltoday.com/stltoday/ne...14F213BEB4A63DA3862572920010EEA7?OpenDocument

Fortunately this didn't happen during rush hour. Unfortunately, looks like inspection procedures in the highway dept. need some work. This would be expensive of course, but why isn't the same standard applied to bridges as airplanes, namely, any damage that is 'detected' by whatever inspection procedure you use must not cause failure of the structure within two (or 3 or 4, depending on design safety factor) inspection intervals. If you can't guarantee with reasonable uncertainty that this is the case with the inspection procedure you use (that is, eyeballs!), then don't you have to use better inspection procedures? Using such a philosophy in the aircraft industry almost guarantees no structure will fail before it is inspected again.

In a perhaps related development, was it Structural Engineering mag. where I saw this? A small study of visual inspection techniques and inspector abilities was not too favorable towards visual inspection. Even the same inspector had difficulty with detecting damage he/she should have detected with reasonable certainty, so the problem wasn't the inspector, IMO, it was the technique.

 

[MichSt]

Not much detail in the newspaper writeup. Any one in the stl area have more details?

 

[prost]

This just happened last night, so not so much online as yet.

I meant no disrespect to bridge builders or inspectors for that matter. If a bridge doesn't get inspected, and fails, then obviously the inspectors aren't at fault. But when a bridge is inspected, and still fails, then doesn't that call into question the reliability of the inspection procedure? If your inspection doesn't detect all potentially catastrophic damage _before_ it happens, doesn't that call into question the inspection procedure itself?

 

[kelowna]

Quote:

I meant no disrespect to bridge builders or inspectors for that matter. If a bridge doesn't get inspected, and fails, then obviously the inspectors aren't at fault. But when a bridge is inspected, and still fails, then doesn't that call into question the reliability of the inspection procedure? If your inspection doesn't detect all potentially catastrophic damage _before_ it happens, doesn't that call into question the inspection procedure itself?

None taken, but it might help putting things in perspective.
There are literally over 600,000 bridges in the USA alone. Every day they get used and abused withouth anybody giving a second though. Only when one of them has a problem, then ...

Bridge inspection is difficult at best, specially if you are not going to start taking Xrays or coring concrete or stopping traffic.

I would immagine that many proffesionals would love to have a failure rate of 1 in 500,000. Obviously we always go for 0, and there are checks and checks on the checks and safety factors and inspection on the inspectors,but funny how that happens, most of us are just humans!

 

[JStephen]

Your inspection is going to be limited by what can reasonably be done, regardless of whether that is entirely adequate. Otherwise, owning a bridge would be like running a nuclear power plant.

 

[MiketheEngineer]

I am in St. Louis and supposedly it was inspected in the last 6 months!! Some minor concerns were noted - but NOT THIS.

Speculation is that salt ate through all the rebar and the high winds (less than 40 mph) finally blew it off the bridge. I presume the concrete had cracked long ago... AMAZINGLY - no one seriously hurt.

Makes you feel better - right???

 

[Qshake]

Based on the one picture I saw of the problem on the St. Louis paper website, there appeared to be a overlayed sidewalk on the concrete bridge. It looked like this overlay from one bent to the other bent is what fell off taking the parapet with it.

For other bridge engineer's you'll know what I'm talking about. It looked like the bridge proper was overlayed on each side with sidewalk and parapet and that those were not originally integral with the actual bridge slab.

At any rate, the bridge itself did not fail from the photo I could see.



Regards,
Qshake

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

 

[prost]

Sure, the cantilevered sidewalk/pedestrian walkway was the thing that fell. Small consolation to the guy it fell on.

What seems reasonable to me as an automobile driver is that a bridge inspected annually would NEVER experience this kind of catastrophic failure. That's why you are doing the inspections, right, to avoid failures in which people are injured and/or killed? Shouldn't the question be: what inspection can we accomplish that ensures that this has a 1 in (pick a number, 10 million) probability of occurrence? So no, 1 catastrophic occurrence in 500,000 bridges doesn't seem reasonable to me as a member of the driving public.

 

[Qshake]

prost - no one is saying that it's better the sidewalk and not the bridge but rather we're trying to (from our limited perspective and available data) determine the design and construction characteristics of the bridge so that we can make sense of the failure.

Regards,
Qshake

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

 

[MiketheEngineer]

Per the local StL paper - the bridge was built about 42 years ago and inspected 18 months ago. The main deck was poured with rebar sticking out at the edges to hold a somewhat cantilevered sidewalk slab that was poured later.

So - now you have this "cold" joint which would eventually allow water and salt (and we use a lot of salt) in.

I have little inspection experience - but I am not sure how you would inspect for this??

Regardless - the Mayor, Governor and MODOT are all over it --- because we apparently have dozens of similiar bridges!!!

 

[prost]

The 'fix' they are going to do is replace all steel bolts in all bridges with similar design. Would some kind of coating on the steel bolts give you better structural integrity?

 

[Qshake]

Hopefully, they'll use stainless steel which will be expensive but far less expensive than the alternate!



Regards,
Qshake

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

 

[plasgears]

I place the blame on inspection. This should be a regular function of bridge maintenance.

Many years ago in the Chicago area, a rapid transit overpass beam exhibited a lower flange break with the crack extending deeply into the web. It took a passenger car driver to identify the damage. The picture in the Chgo Trib was shocking.

 

[swall]

Actually the CTA bridge crack was found by a structural engineer riding to work on an I.C. (ow Metra) electric commuter train.

 

[Qshake]

This detail is a period dependent detail and not common for bridges in this age. As a result, today's inspectors probably don't understand all that they should about the many different details and what to look for.

I'm not trying to excuse anyone's lack of effort but rather noting that industry wide we don't educate our inspectors enough and most are not engineers with design knowledge.

Regards,
Qshake

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