If I’m going to have a series on infrastructure fails, it has to include one that was in the news for weeks or months. Lessons learned from the 35W bridge collapse. In case you were sleeping in the summer of 2007, this happened in Minneapolis.
Why did the bridge collapse? The short answer comes in 2 parts.
- Parts of the bridge were under-designed. (But it had stood for 50 years as built.)
- Construction crews getting ready to do work on the bridge placed some of their equipment and supplies on the bridge, exceeding the design-load by a factor of 4
And the only reason they could overload the bridge like that, was because there was no communication with anyone about known problems. So let’s review…
On August 1, 2007, at 6:01 PM, right during rush hour, a span of I-35 through Minneapolis collapsed. 13 people died, and 145 were injured.
I remember reading at the time that bridge inspectors in Minneapolis were constantly harassed by the driving public. Because “Why are you blocking lanes of traffic to inspect the bridge? There is obviously nothing wrong with it.” I wonder if any of the people who died, harassed any of the inspectors. Probably not. (There isn’t that much Justice in the universe.)
“We knew early on that this was a design error,” said Dorgan. “One of our people put it best — in the days after I-35 with the terrible event that happened, that something good has to come out of this. And I think people proceeded on that basis with, let’s take a look at everything we do and see where we can improve.”
The National Transportation Safety Board ruled that the 35W bridge collapsed because of under-designed gusset plates. But it also pointed to contributing factors, like too much weight from construction materials on the bridge.
Tyler Ley is a professor at Oklahoma State University, and he has a video on the collapse, which is short, at just over 8 minutes, and to the point.
The gusset plates were undersized by about a factor of 2. The gusset plate that failed was showing signs of deformation, or bending, which is an early indication of failure. And a construction crew parked a bunch of weight on the bridge. How much construction materials and vehicles? Estimates are that 580,000 pounds were placed in a 12ft by 115ft section of the bridge. That is 4 times the design load of the bridge. Of course it failed.
Everything needs repair. Everything needs maintenance.
This bridge failed at a place that was KNOWN to be a problem. When a structure starts to bend it is LITERALLY starting to fail. The construction crew overloaded the bridge in that exact spot, because no one reviewed what they were going to do, or at least no one with knowledge of the identified problems. (The bridge had been listed as “structurally deficient” for a long time.)
Breakdowns in communication have a long history, though you usually study them with respect to military defeats. But they are a breakdown of management, and we are refusing to manage our infrastructure. It needs to be repaired. Eventually, it will all need to be replaced.