By Jesse Marx
By Chris Parker
By Jake Rossen
By Jesse Marx
By Michelle LeBow
By Alleen Brown
By Maggie LaMaack
By CP Staff
Are such bridges safe to drive on? So they say. "We view that term as a programmatic classification rather than an indication of level of safety," says Tom Everett, of the National Bridge Inspection Program. "It is not a classification that indicates a bridge is dangerous, nor that that bridge must be replaced."
How many bridges in Minnesota have been labeled "structurally deficient?" According to MNDOT, there are currently 1,160 in the state that carry this designation. That's roughly 8 percent.
How does this compare to other states? Nationwide, 13 percent of the country's bridges, or approximately 75,000, are labeled "structurally deficient."
How long had the I-35W bridge been deemed "structurally deficient?" Since 1990.
Why was it deemed "structurally deficient?" The I-35W bridge initially earned that designation because some of its bearings were corroded, according to Dan Gorgan, MNDOT's bridge engineer. Subsequent inspections revealed additional corrosion in its joints. Finally, there were "fatigue cracks" on the approach spans of the bridge.
How often was the bridge inspected? It's been inspected annually since 1993. Prior to that it was inspected every two years. "During recent inspections in 2005 and 2006, we found no evidence of additional cracking in the bridge or growth in the preexisting cracks," says Gorgan. The 2007 inspection had been interrupted by construction on the bridge and was to be completed in the fall. In addition, the University of Minnesota's Department of Civil Engineering conducted a study of the bridge's fitness in 2001. The conclusion? It did not need to be replaced in the near future.
Who built this thing? Industrial Construction, a company that is no longer in business. Construction began in 1964 and the bridge was opened to traffic in 1967.
How many cars drove over this bridge? Approximately 141,000 daily. That makes it the third busiest bridge in the state, next to I-94 (157,000) and I-694 (150,000).
What kind of bridge was it? It was a steel arch truss bridge. "It's an underdeck truss, meaning it's supported from below," says Gorgan. "There were two arches that supported this bridge."
Are there any other bridges of this kind in the state? Yes, five others: Inspections on three of them were completed last week and no problems were found. The remaining two are slated to be examined ASAP.
When will the bridge be rebuilt? Nobody knows for sure yet. The city and state have put together a team to study the issue, according to MNDOT engineer Khani Sahebjan. But any rebuilding will obviously have to be put on hold until the collapse of the bridge has been thoroughly investigated, says Sahebjan. "When we get permission to remove the structure, that's when we can start construction." MNDOT hopes the bridge will be rebuilt by the end of 2008. —Paul DemkoSETTING THE RECORD STRAIGHT
John Weeks is what some people might call an obsessive. Over the past two years, he has spent weeks at a time traveling alongside the Mississippi River, photographing more than 300 of the bridges that span that mighty body of water, from Itasca to New Orleans.
His downtime between trips is largely devoted to cataloging information on each bridge, such as its age, construction material, daily traffic count, river elevation, and other factoids that, until last week, might have seemed somewhat superfluous to anyone but himself.
So Weeks is perhaps uniquely equipped to tackle some of the conspiracies that cropped up about the I-35W bridge collapse. And that is what he has done over at his website, www.johnweeks.com. Among the more entertaining new urban myths that Weeks has debunked: