Insights Into the Minneapolis Bridge Collapse

The incredible collapse of the Minneapolis bridge will send a message to the nation that has been repeatedly sent for decades, but that our political system has refused to effectively respond to. America’s physical, engineered infrastructure has been in desperate need for massive spending to repair and replace, but the multi-trillion-dollar cost has been rejected by local, state and federal politicians.

We have had bipartisan government neglect. The bridge fell down because our politicians have let us down.

First, understand that I have a professional background in this area. My career started as a metallurgist, than I obtained a Ph.D. in Materials Engineering and became a full professor of metallurgical engineering at the University of Wisconsin, Madison where I taught about mechanical metallurgy and failure analysis, and in my consulting practice regularly worked on explaining actual failures of products and systems.

Many academic and professional groups have for many years produced countless reports on mounting unpaid public costs for updating our crucial physical infrastructure, including bridges, but going way beyond those to, for example, roads, water and sewer systems, tunnels and much more. Make no mistake: The deeply researched and totally supported case for a massive national infrastructure spending program could not have been clearer. For example, in an excellent essay It’s Time to Rebuild America, Felix G. Rohatyn and Warren Rudman wrote about the national crisis.

But spending on infrastructure is not sexy and politicians at ALL levels of government have found countless excuses for not facing the totality of the problem. Instead, public spending is dribbled out, dealing with the most urgent problems or, worse yet, the ones that are the most visible to the public. But unaddressed are massive numbers of problems, such as the Minneapolis bridge and thousands more bridges, that our bureaucratic system has learned to game, postpone, rationalize and, therefore, put the public safety at considerable risk.

As a metallurgist I can pretty much assure you that if there is a technically honest and complete investigation, the ultimate explanation of the Minneapolis bridge failure will be related to fatigue cracking in the metal structure. Already, news reports have revealed some prior observation of a fatigue problem with the bridge and that the bridge had a relatively low rating of four out of a possible nine, showing that it was structurally deficient. The game played by virtually all government agencies is to find excuses for delaying the most costly repair or replacement of bridges and other parts of our physical infrastructure. As just another example, in most older urban areas there are constant repairs of busted underground water pipes. What is really needed, but avoided, is a total replacement of very old underground pipe systems – in many places 100 or more years old!

Government inspection programs have been terribly compromised over many years. The incredible political pressures to minimize spending on infrastructure have filtered down to the people, procedures and technologies used to examine bridges and other things. When it comes to bridges it is also important to admit that many aspects of our automobile addiction have raised risks, including enormously greater numbers of vehicles creating heavy traffic during much of the day in urban regions. Add to this the massive increase in vehicle weight resulting from the incredible increase in monster SUVs, as well as huge increases in large truck traffic.

The Minneapolis bridge collapse happened during evening rush hour because that was a period of maximum stress, and that would be the trigger for expanding existing fatigue cracks. Once fatigue cracks get to critical sizes they grow and propagate very rapidly, producing powerful loads and stresses on remaining steel components and creating what appears to be a virtually instantaneous bridge collapse.

What should be the focus of government and public attention is the various inadequacies of bridge inspections. Were the very best metal analysis technologies used, rather than reliance on visual observations? Were the inspectors the very best educated and trained? Were inspections constrained by federal or state regulations and guidelines so that best available methods and technologies were not (justifiably) used? Here is the big point: The fact that this bridge fell down is proof positive that the entire inspection and maintenance program was a FAILURE! The central goal and responsibility of engineering practices is to protect the public and PREVENT deaths.

Can responsibility also be assigned to the design of the bridge? Yes, to some extent. The design was the opposite of “fail-safe.” If any key bridge structure component failed, then the entire bridge was doomed to fail. And perhaps it can be reasonably argued that at the time of the original design, that this feature was accepted practice. However, we must understand that if cost constraints had not been imposed, designers could probably have built in various redundancies so that only portions of the bridge would have failed under the most catastrophic scenarios.

Here is yet another big issue that I have not seen mentioned or discussed by anyone yet. I can absolutely guarantee that there were countless discussions over the years by engineers, bureaucrats and politicians that combined risk assessment and cost-benefit types of thinking. It comes down to this: To bite the bullet and conclude that to provide maximum protection of public safety the bridge should be replaced would inevitably face debates about the incredibly high costs and the enormous difficulties of obtaining the funding, and also how obtaining such funding would imperil other government projects.

So the decision moves in the direction of higher levels of inspection to postpone the inevitable high cost/low risk scenario. On the other hand, all people connected to these kinds of discussions know one big reality: If the crap hits the fan and there really is a catastrophic bridge failure, then the money WILL be readily available to replace it! This is the way the system works. Of course, to replace the bridge and deal with all the many horrific impacts of the bridge failure AFTER the fact will cost much, much more money than if a planned replacement strategy had been adopted!. But that is exactly what the Minneapolis story ultimately is all about. It is what virtually all of our national infrastructure thinking is about. The New Orleans disaster was totally preventable, as every technically sound and objective analysis showed.

As time goes on and our national physical infrastructure continues to degrade from many causes, including corrosion, fatigue and inevitable wear and tear, we will continue to see deaths, injuries and incredible economic harm. And, yes, global warming and all of its anticipated climatic changes will just increase the risks of catastrophic infrastructure failures. As just one example, sea level rise is known in some quarters to put in jeopardy virtually every major American city that sits on or close to a major water body. Ultimately, our biggest infrastructure investment will be for constructing massive, complicated dikes and walls, as the Dutch have done, to protect our major coastal cities.

The remaining public policy question is clear: Will the nation spend what is necessary? Seven other major bridge collapses in the last 40 years have not done the trick. Inadequate bridge inspection has been a frequent documented problem, as well as some design defects. Many people have already died from bridge failures. But still the nation’s elected officials have not bitten the bullet and agreed to spend trillions of dollars over several decades to bring America’s physical infrastructure up to the most modern standards. Waiting for politicians to make physical infrastructure a priority is like waiting for Godot.

Think about all this the next time you go over a bridge.