But looking at photographs of the bridge before it collapsed causes me to suspect something will be found with the substructure (the piers and columns that make up the foundation). Why? This bridge carried 8 lanes of traffic. Look at how narrowly built the substructure is. Further, my guess is that when this bridge was built it only carried 6 lanes of traffic. The combination of the extra weight for the added lanes, aging, its narrow base and traffic flow while under constuction became more than the bridge could tolerate.

Like I said, however, I am not an engineer. Only an observer.

heh

i dint git my ENGI cert either, but lack o handrails don knock down bridges, an them things are overbuilt anyways.

my theory on thet thar bridge is depletion of th oil fields messes up tectonic adjustment, so when th river shimmied a bit, th expansion joint thet warnt put in caused th tensioners in th frame ta yank th frame over.

note: by your theory, th bridge would more likely fall ta one side or t'other, while in th video it jus dropped like a puppet with th strings cut - which supports my theory.

;- {

Nomo

Check this CNN photo. It shows one end of the bridge jutting one way and the other end jutting the other way. Torquing could have caused a pulling apart that would have dropped the bridge straight down rather than a topple sideways.

http://www.cnn.com/

There is a couple of photos actually showing one of the two piers/pylons/pilings is tilted toward the river. It could have happened during the collapse--but could it have caused it? The information I've read it that there was a train going under one side at the time, too. Could one of these two piers have been undercut by the river, and/or vibrated off its caisson by the train, or both. Seems like either or both would cause the collapse., which sounded like a domino effect.

If you're not an engineer, then you probably shouldn't be publicly making uninformed conjectures. I am a licensed structural (bridge) engineer and I will tell you, that with the possible exception of a bearing connection at the top of a pier, this was not a substructure failure. All new bridge plans, including rehabilitation of existing ones, must be stamped and signed by licensed engineers following rigorous design and review processes. Additionally, USDOT (FHWA) requires that all bridges be load-rated. There is no way that two additional lanes would have been added to the bridge without consideration of the load capacity of the piers and supporting footings, piles, or shafts.

The failure was, in all likelihood, associated with one of two things: 1) fatigue of non-redundant structural elements (I believe that MNDOT has acknowledged the presence, and previous repair, of fatigue-related defects) or 2) a structural instability related to or directly caused by the construction that was going on at the bridge. Because I am not familiar with that particular bridge or the work going on, I am unqualified to suggest anything more specific. I will say, however, that when you start removing portions of structures (such as concrete deck slabs that provide restraint against buckling to beam and truss elements in compression) you have to be really careful. Likewise, when pouring concrete slabs, you have to provide buckling restraint to the supporting superstructure elements; wet concrete does not provide the same restraint as a fully cured slab. Construction history is rife with examples of structural failures caused by the inability of falsework or previously erected structural elements (especially uncured concrete) to support wet concrete slabs.

The public's implicit refusal to accept roadway closures for major bridge repairs only exacerbates the construction issues and loading - not that anyone has much of a choice these days given the congestion resulting from under capacity highways. Add onto that the fact that you have construction workers (lowest bidder, I might add) conducting repair operations in the absence, in all likelihood, of a structural engineer (a consequence of limited transportation agency budgets) and voila, you have a recipe for potential disaster.

Ultimately, investigators will find the specific cause. Hopefully, there will be additional implementable findings beyond the fact that we should not be taking the safety of our bridges for granted. Beyond that, we really need some serious dialogue on our nation's priorities as they relate to maintaining and further developing our infrastructure to meet today's burgeoning traffic needs.

Todd Patina:

Beyond that, we really need some serious dialogue on our nation's priorities . . . .

Now there is an understatement. I completely agree with you, but it is not going to happen.

I don't think any rational person can look at how we spend our money and conclude that we are a rational socieity.

It seems every year I hear how fire, police, and infrastructure budgets are being cut while there is always money for some campaign contributor's pet project.

There will be much hand wringing and blame throwing, and promises that things will change. Yet it seems like there is a similar catastrophe every 20 years or so.

Spending money on safety is just not that exciting.

The following concerning the rail cars-some crushed by the bridge segment-and the train operation on the tracks near the site was part of a news item on the Trains magazine web site.

"In an email to Trains News Wire this morning, Minnesota Commercial President John Gohmann said that no trains had been in the area for a couple of days. The bridge collapsed on top of three cars of plastic pellets on a team/reload/lease track. A fourth car may also be damaged, but the three cars of plastic pellets actually stopped the bridge section from falling further directly to the ground. Gohmann said Minnesota Commercial personnel were at the scene last night, and the railroad had a standby locomotive on call in case it needed to move any cars to help access and recovery."

I understand a casual observer might think that something about the rail operation could be a proximate cause of the collapse. It doesn't appear to be the case here. If train cars had derailed and struck any part of the bridge it would first have been readily appearant to the people assigned to determine cause and second, would certainly have been reported by the railroad as required by Federal law. Movement of rail cars on the tracks under the bridge was infrequent and at low speeds and probably caused little or no vibration of the bridge.