Here’s a new theory for the I-35W bridge collapse–blame the pigeons. Apparently “piles of pigeon guano” may have impeded inspectors from discovering the true state of the bridge:

Heaps of corrosive pigeon droppings obscuring parts of the bridge’s steel supports have been a bane to inspectors at least since 1994, documents show. The birds were nesting in welded steel box sections of the superstructure, gaining access through the same holes used by inspectors to peer inside to look for cracks. In 1999, MnDOT covered the inspection holes with plastic screens, but the problem persisted.

“The interiors of the box members have severe pigeon debris,” MnDOT workers wrote in their 2006 inspection report. (Star Tribune

The armchair failure analysis that’s happening in the wake of the I-35W bridge collapse kind of makes me laugh.

• We’ve had good stretch of 90+ heat in the Twin Cities, therefore the bridge couldn’t handle the expansion and collapsed. Please. In July 2006 we had more days above 90 than we did this year, never mind the stretches that were much hotter. I would expect any bridge would be designed to handle expansion in temperatures well above 90.
• With the construction on the bridge and the lanes narrowed from eight in each direction to four the imbalance caused the failure. What?!
• With bumper to bumper traffic on the bridge it had to carry the weight of traffic at a standstill as opposed to traffic at full speed. Weight is weight, no matter the speed. (poorly paraphrased from several different online forums)

I’ll be the first one to tell you I’m no physicist and can’t explain what happened or how it happened but some of these theories are so bizarre, as if the bridge had certain tolerances that we just happened to push too far on August 1. I suppose in a sense that’s what happened, but it’s most likely in conjunction with a major failure. The way people are talking it’s as if any bridge could fall over if we get too many days over 90 degrees or if too many fat people walk across a bridge at the same time. You don’t blame the heat or the fat people, you blame the structural failure.

For all the talk of “structural deficiencies” and the what not, this is most likely a bridge that had some issues but they didn’t appear to be catastrophic. Turns out we were wrong and it was catastrophic. But I don’t think there’s going to be any smoking gun of Joe Blow didn’t tighten a bolt or overlooked this massive hole in the steel truss. And while improving infrastructure is important, it’s not like this bridge would have been first in line for replacement if we had millions or even billions to spend on infrastructure. They talked about replacing it by 2020. We had systems in place and those systems were followed. Obviously those systems will now be closely inspected and hopefully some improvements made if possible

But bottom line: I think this was a simple accident. I doubt many changes in procedure or funding would have changed that. There are no conspiracies here or scapegoats we can easily blame.

Of course we’ll know for sure in about a year when the report comes out and we can all stop doing armchair failure analysis.