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