The Bridge Collapse in Miami

It goes without saying that this is a disaster:

At least four people have been killed and 10 others hurt after a footbridge collapsed near Florida International University in Miami, officials say.

The 862-tonne, 174ft (53m) bridge fell over an eight-lane motorway on Thursday afternoon, crushing at least eight vehicles, police said.

They told local media that vehicles were stopped at a traffic light when the structure collapsed at about 13:30 local time (17:30 GMT).

It is still unclear how many people were under the bridge at the time.

For a standard, single-span footbridge to suddenly collapse in this manner in the United States in 2018 is incredible. Reinforced concrete footbridges have been built worldwide for decades, and ought to be the sort of thing a highways department can design and build on their own. Perhaps one 53m long over an 8-lane highway requires some specialist assistance, but still. This was not the Millau Viaduct.

These days engineering firms use finite element modelling (FEM) programs which can predict how a structure will perform under load, identify any weak points, and calculate the stresses induced in every location. The bridge which collapsed looks to be of an unusual design, no doubt approved by an architect somewhere, but that is precisely what the FEM models are for. Using them you can depart from a traditional design, incorporate architectural features, and still be sure your structure is sound. A newly installed footbridge suddenly collapsing onto traffic in the US is the equivalent of a batch of canned goods killing people, the contents having reacted to the metal. There is enough knowledge and experience by now to ensure these sort of accidents no longer occur.

Yet it did, so why? The BBC tells us this:

The bridge was erected on Saturday in just six hours.

It was built using a method called “accelerated bridge construction” to avoid traffic disruption. A major section of the bridge was assembled on the side of the road and then raised into place.

I’ve written before about bridge collapses, and how they tend to happen during construction, but I don’t think the installation method described above had anything to do with it. There’s a video here of the bridge being installed, and it looks to me like a pretty common technique which doesn’t in itself explain why it collapsed a few days later.

So here’s my guess: somebody screwed up the calculations or the finite element model, and nobody picked up the error. If this was in the developing world I’d be more inclined to believe it was shoddy construction or poor materials rather than a design error, but this being the US I can’t see that happening. The company that carried out the engineering was Munilla Construction company, a family-owned firm whose website is here. They’re based in Miama and have been around since 1983 and they claim:

WE BUILD YOUR PROJECT ON TIME, ON BUDGET, AS DESIGNED AND WITHOUT ANY SURPRISES.

They might want to update that at some point.

What follows is pure speculation on my part but it’s based on what I’ve observed of engineering companies and corporations over the past 15-20 years or so. Back in 1983 the firm would have employed serious engineers who held themselves accountable, and the brothers who founded it probably did a lot of the work themselves. There is no doubt this company was able to successfully deliver engineering projects for a couple of decades, so they’re not some fly-by-night outfit owned by the wife of the local mayor.

But I suspect things changed sometime in the past 5-10 years. There is nothing on the company website to suggest they succumbed to the relentless pressure placed upon firms to hire people based on their appearance and sex rather than competence and ability, but I’d be surprised if they were wholly unaffected by demands for greater workforce “diversity”. After all, this was a firm which did several projects for the public sector, and installed the bridge on behalf of a university. It’s unlikely they weren’t required to demonstrate they were fully on-board with the latest progressive directives. At a guess, I would say this is a company which has seen several experienced engineers retire over the past decade, replaced with people whose abilities are questionable.

Secondly, as I have complained about in the past, there has been a major shift in modern companies from delivering something useful – such as a bridge which doesn’t collapse – to managing processes. A lot of companies have subcontracted out the actual work – designing, building, manufacturing, operating, maintaining – and instead busy themselves with “managing” the whole process. This involves lots of well-educated people in nice clothes sitting in glass-fronted office buildings sharing spreadsheets, reports, and PowerPoint presentations by email and holding lengthy meetings during which they convince one another of how essential they are. I’m sure this is pretty much what Carillion was doing when they went bust: anything useful was done by subcontractors. The distance between those doing the actual work and those supposedly responsible for the outcome has, in far too many companies, grown into a yawning chasm. Survival in a modern company is all about compliance and obedience, and accountability is non-existent because it is no longer required.

In such an environment, it is inevitable that the quality of work suffers, errors go unnoticed, and – occasionally – catastrophes occur. Now I don’t know if that was the case at the Munilla Construction company, but somehow they’ve gone from an outfit who could deliver a project with their eyes closed to one that has just dropped a simple footbridge on eight lanes of highway. If I were investigating, I’d want to know who did the actual design and where it was done. I’d be willing to bet a hundred quid the calculations and finite element modelling were done outside the US to save money, or subcontracted to another company, and supervision – which involves expensive Americans – was at nowhere near the levels it should have been. Regardless of where they were done, I’d also be willing to bet the company spent more manhours on progress meetings and overly-detailed weekly reports to let the management know what was going on than they did checking the engineering calculations.

I might be wrong, and maybe I’m being unfair to the Munilla Construction company. But I’m not wrong in describing how modern companies work. I have a hunch we’re going to see more disasters like this in the coming years as successive generations of managers and engineers fail to deliver what were, until recently, pretty ordinary projects.

UPDATE

David Moore posts a link to this video which reckons the bridge was supposed to be supported from above using cables in the final design. If they’re right, then this is a classic case of a poorly-supported bridge span collapsing during construction, and we can all go and read my previous post. It doesn’t make the cock-up any less severe though, just slightly more understandable.

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61 thoughts on “The Bridge Collapse in Miami

  1. That was a pretty good punt as to what caused that failure. I have experience in pre and post tensioning and I gotta say that what he indicated might have happened should never have happened. Post tensioning is a special process that is closely measured and monitored, the parameters would be known and there would be a number of methods to ensure that the steel rods never got anywhere near their yield strength, but they did and worse still the jacking didn’t get shut down and the steel got into the plastic range and failed, there would have been a moment of time where they could have stopped this once the yield point was reached. Gross failure here on many aspects this is not a single point failure either.

    On the final cable stayed arrangement it looks like they were adjusting the post-tensioning in the truss to keep the concrete in tension and that would explain that there was a staging plan to take this off when they eventually hung the deck from the cable stayed final support. There is no way that post tensioning would have been permitted above live traffic, high pressure jacking and post tensioning requires exclusion zones, to be done above live traffic would never be permitted. I have worked on many bridges and nothing like this would ever be contemplated above live traffic. I still want to know about and am genuinely interested in the staging and as to when the final overhead cable support would be in place, it’s not even as if the column for the cables takes up a big footprint and it was going to have to be permanently erected anyhow, so I still don’t get it why they were going to all this bother in the first place. Either way I don’t think we will ever see this type of staging ever been allowed again. Regretfully they will probably hang the Mexican stressing jack operator out to dry on this one.

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  3. As a retired civil/sanitary engineer, I have some ongoing interest in civil engineering projects. Now my steel and concrete design courses happened over 50 years ago, and I have forgotten nearly everything, but I should have thought that the cable-stayed pier would have been erected first, and afterwards the bridge deck would have been hung from it. Is the sequence used at FIU standard?

    Post-tensioning I am award of, but was there enough concrete thickness in the deck to make this possible?

  4. When Mrs SE regailled the details to me earlier in the week, my concern was why a bridge due to be opened late next year needed to be put up so quickly. Now I just boggle.

  5. It looks like they did outsource some stuff, as suspected.

    The Guardian (when it’s not being woke, it really does do proper reporting. Much better than the Beeb) has this:

    State officials revealed on Thursday night that the university’s bridge-build team, which included MCM and the Tallahassee-based Figg Bridge Group, had hired a third-party company to conduct an independent, secondary design review of the project, and that that contractor was not pre-qualified by the Florida transport department to do the work.

  6. @bob

    “‘Post-tensioning I am award of, but was there enough concrete thickness in the deck to make this possible?”

    Yes definitely don’t forget that concrete has a very high compressive strength so you don’t need a big cross section to resist any compressive load that would be introduced by post tensioning.

    There have been some comments made about the quality of the concrete, they are very speculative at this stage and yes if the concrete had quality defects then it may not have been able to resist the induced compressive forces from post tensioning. Personally I doubt it that inferior quality concrete played a part in this failure.

    “steel and concrete design courses happened over 50 years ago, and I have forgotten nearly everything

    The basis of concretes performance in structures like this hasn’t changed in the last fifty years and it is the same with steel as well.

    There has been plenty of innovations with respect to concrete material improvements, superplasticizers, early setting, very high strength concrete, fibre reinforced concrete, placement methods and sulphide resistant concrete for marine applications but at the end of the day concrete in its plastic state performs the same as it has always done.

    There has been massive improvements in the alloying of steel, corrosion resistant duplex and super duplex applications and manufacture but like concrete in its end state it still performs exactly as it always has done.

  7. The distance between those doing the actual work and those supposedly responsible for the outcome has, in far too many companies, grown into a yawning chasm. Survival in a modern company is all about compliance and obedience, and accountability is non-existent because it is no longer required.

    I cannot stress enough how correct the above two sentences are. For many years, I did outside work for various Fortune 500 companies. When I started, it was me (the pointy end of the spear) and one supervisor from the client who gave me general guidelines and then trusted me to get the job done. In the last ten years or so, we’ve moved into the situation you describe above. I’m still the pointy end of the spear, but above me their are layers upon layers of nominal “supervision,” which supervision consists of micro-management and myriads of meaningless forms and reports repeating prior forms and reports. Yet, despite the additional layers of “management,” there is no one who wants to make a decision. No one wishes to be accountable or to take responsibility for anything, should the result be less than optimal.

    On one hand, I should be grateful because my income has gone up because I have to deal with the incessant interference from all the corporate worthies. Still, it’s frustrating because it’s more difficult for me to actually do my job.

  8. In a world where no one has to accept responsibility for their actions, ever, this sort of thing will be happening more and more often.

    On the contrary, everyone these days “takes full responsibility”, and then nothing at all happens. It started with Blair’s vile crowd. Blair realised that in the modern arena all that matters is that you say the “right thing”; actions are irrelevant.

    Yet, despite the additional layers of “management,” there is no one who wants to make a decision.

    More opportunities to pass the buck to someone else. In an organisation like that your salary and benefits aren’t going to be linked to being a dynamic and visionary leader. Take responsibility, make the wrong decision and you’re buggered; even make the right decision and everyone else fucks it up and you’re buggered; evade responsibility, things work out, you benefit with everyone else.

  9. “On the contrary, everyone these days “takes full responsibility”, and then nothing at all happens. It started with Blair’s vile crowd. Blair realised that in the modern arena all that matters is that you say the “right thing”; actions are irrelevant.”

    Which is exactly my point – no one has to accept any ‘actual’ consequences for their actions. From cradle to grave, however stupid, criminal or down right evil you are, the State will sustain the necessities of life for you. While this initially modifies people’s behaviour at the bottom of society, in the welfare classes, slowly it creeps up the food chain further and further, until it starts affecting the middle classes, on whom the weight of responsibility lies hardest for actually getting stuff done safely. Once it reaches there the society is done.

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