On December 13th, 2000, a section of the Daniel Hoan Memorial Bridge through downtown Milwaukee buckled and sagged about 4 feet. No one one was injured.
For details on the initial incident… Wisconsin Winter Wages War on Hoan Bridge. Cold weather was a factor. Outdated construction methods were a factor.
At approximately 7 a.m. on the morning of Wednesday, Dec. 13, 2000, northbound commuters got a rude surprise when a 217-ft. long by 55-ft. wide (66 by 17 m) portion of Milwaukee, WI’s, Hoan Bridge buckled and sagged.
The bridge had been inspected a few weeks earlier, but nothing to indicate it would be unsafe was detected.
Weight-bearing steel beams on bridges are usually flexible and behave much like a rubber band, bending and moving with the wind and traffic. In the case of the Hoan’s two failed beams, the girders probably experienced what is known as a brittle failure.
Two weeks after the deformation the offending section was removed with explosive demolition and repairs begun. It took just under a year to complete repairs.
Initial thoughts were that all the salt trucks which had left the Port of Milwaukee, fully loaded to combat the weather, were at fault. But the forensic analysis points to a failed weld and related design issues, with the cold weather contributing.
FHWA Structures Lab Investigates Milwaukee Bridge Collapse.
The primary cause was found to be related to the design details used for a welded joint assembly. Wright reports that although the bridge is not old-it was built in 1974-the details of the joint design used for the Hoan structure are no longer used in the construction of new bridges.
The details of that joint design, coupled with the cold weather caused the bridge to be susceptible to brittle fractures, which is apparently what happened on that day. The forensic analysis was detailed, right down to testing of the steel.
The results showed that the steel would have met today’s material specification requirements set by the American Association of State Highway and Transportation Officials (AASHTO) for use in bridges down to temperatures as low as -34° C (-30° F).
So here’s a question: If they knew there were problems with that joint design, to the point that they don’t use it anymore, shouldn’t every bridge built using that design be retrofitted or reinforced? And temperatures in Milwaukee are frequently -20°F, so shouldn’t the steel be able to handle even much colder weather? (There was one day when I was in college where the mercury in Chicago showed -30°F. I doubt Milwaukee was warmer.)
The complete forensic report is at this link: HOAN BRIDGE FORENSIC INVESTIGATION FAILURE ANALYSIS FINAL REPORT. It is long and written by engineers who work for the government.
357 Magnum Archive 
So here’s a question: If they knew there were problems with that joint design, to the point that they don’t use it anymore, shouldn’t every bridge built using that design be retrofitted or reinforced?
Interesting question – and a huge question. That could mean regularly rebuilding every bridge. Not that it’s a bad idea, but it would be an expensive idea. We know how flush with cash cities and states are, and the complications down that well-worn path (e.g. – money for rebuilding the bridge could take money from “welfare” distributions).
I have an example with my troubleshooting a ground fault circuit interrupter in the addition on my house. The GFCI typically just pops once every few weeks, but sometimes more often. My addition was built in ’14 and the National Electric Code was revised later that year. Which means my addition is built to the ’08 code. They don’t typically mandate that the room be re-wired, but it’s the same basic question as rebuilding those bridges. Someone has to pay for it, and there should be a sort of cost/benefit analysis involved. Those are notoriously hard to evaluate. If the bridge fails, is it a “gentle” failure like this, or do dozens of cars fall into a frozen river killing dozens of people? How do you evaluate that cost/benefit?
In my case, the 2014 NEC revision has imposed requirements on GFCIs that make them pop easier when used in certain types of circuits. Like when driving motors. That’s what mine does, it just doesn’t always pop when a motor is running. My gut feeling is that rebuilding the shop to the current NEC would make my annoyance failure worse.
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It was only by shear luck that this wasn’t a full-on collapse like the Silver Bridge or the I-35W bridge in Minneapolis.
In the wake of the Minneapolis failure, Minnesota (and a few other Midwestern states) suddenly found money to reinforce/repair all under-slung truss-bridges that had a rating of “structurally deficient” even though a couple of them were then replaced (or slated to be) less than 10 years later.
Here’s another question. How many bridges in the US have that design of weld joint, that makes those style of bridges subject to brittle failure when the temperatures are above the magic number of -34 degrees C? Every interstate bridge and overpass built in that era? Half of them? How many people drive over those bridges in January?
Now that particular defect is mostly an issue for the north, but I doubt that this is the only known defect in every bridge built since the 1960s. Why did they abandon the joint design used in Milwaukee? Was it an engineering study, or the result of other failures? I have a guess, but I haven’t looked. (Government never changes what they are doing unless forced to do so.)
And what the hell is/was the State of Minnesota and/or the State of Wisconsin spending money on that was so much more important than safe bridges? Art in the park? Monuments to the vanity of some politician? (Like a new community center or museum?) Those things are important, but in the cost/benefit analysis I choose safe-bridges.
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And I do understand about cost/benefit. And not just because I worked in manufacturing and the cost accounts would come by and explain to you just how much you cost the company every time you made a mistake. (They did at some places.)
I passed on the purchase of a house that still had a whole lot of knob-and-tube wiring. I thought the price was way to high, given the amount of work required to rewire a house with real plaster walls. It was too bad really, that was a beautiful, 3-story brick house in a somewhat-historical area. From an era of craftsmanship in construction. And really bad electrical wiring.
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