Wednesday, August 01, 2007
How Safe Are Our Bridges?
Here's a photo of the I-35W Bridge over the Mississippi River in Minneapolis which collapsed this evening, leaving several dead and many others injured. The bridge, as it appeared in the photo above prior to the collapse was built in 1967. Its claim to fame is a single 458 foot long steel arch to avoid putting any piers in the water to impede river navigation, which might help explain its failure today. I discovered there was an in-depth inspection of the bridge in 2003, which gave it a "med-low" criticality rating. The comments indicate the need to "monitor fatigue cracking from out of plane bending at the approach girders and diaphragm connections." I'm not an engineer, but that couldn't have been a very good sign. Indeed, a transportation report last year said the "bridge would need to be reconstructed or replaced in the coming years." Early reports indicate the bridge was under construction at the time of the collapse, but that work simply involved surface repairs to the bridge. The Department of Homeland Security has already issued a statement indicating terrorism is not suspected. It looks like the case of an old bridge somebody failed to properly maintain. It's a major artery in Minneapolis so its loss creates a bit of transportation nightmare for the city. If a 4-year-old report alerted transportation officials to these problems, why was the bridge not closed to make the needed repairs? How many other bridges like this exist around the country?
UPDATE: The AP reports: "Gov. Tim Pawlenty said the bridge was inspected by the Minnesota Department of Transportation in 2005 and 2006 and that no structural problems were noted." "There were some minor things that needed attention," he said. How do you square that with the 2003 report I link to from the state's own Department of Transportation? And why has nobody else in the media picked up on this 2003 report? Hint: A simple Google search is all it took to find the 2003 report.
CNN has a spectacular security camera footage of the bridge's actual collapse. You can see the center span giving way and falling straight down into the water.