How do forensic engineers investigate bridge collapses, like the one in Miami?

The collapsed pedestrian bridge in Miami. Image: Getty.

On 15 March, a 950-ton partially assembled pedestrian bridge at Florida International University in Miami suddenly collapsed onto the busy highway below, killing six people and seriously injuring nine. Forensic engineers are taking centre stage in the ongoing investigation to find out what happened and why – and, crucially, to learn how to prevent similar tragedies in the future.

I’m not actively involved in this investigation, but I’ve been a forensic engineer for nearly 20 years and am the 2018 president of the National Academy of Forensic Engineers. Similar to forensic scientists, we visit scenes of disasters and crimes to determine what role engineering practices played in what happened.

The first step in any forensic investigation, collecting evidence, often can’t begin until survivors are rescued and victims are recovered. Those operations displace material and can damage evidence, which means forensic engineers must study the emergency response as well, to be able to tell whether, for instance, a support column collapsed during the event or was destroyed to reach a victim in need of help. During the FIU recovery efforts rescuers used large equipment to break up massive blocks of concrete so that victims’ bodies could be recovered.


In Miami at the moment, forensic engineers and technicians from the National Transportation Safety Board are on the scene. Right now they’re collecting samples of materials from the bridge to test for their physical properties. They’re reviewing drawings and plans, and examining both industry standards and site engineers’ calculations to understand what was supposed to be built – to compare with what was actually constructed. They’ll look at photographs and videos of the collapse to identify the sequence of events and locations of key problems. Of course, they’ll also talk to witnesses to find out what workers and passersby saw and heard around the time of its collapse.

Then they’ll combine and analyse all that data and information to identify as clearly as possible what went wrong, in what order. Often there are many factors, each leading to or amplifying the next, that ultimately caused the disaster. Putting that puzzle together is a key part of the forensic engineer’s role.

Weakness in partial structure

The FIU bridge was being built using a method called “accelerated bridge construction,” with separate sections that needed to be put together: the footings were installed beside the road and the span was built nearby and lifted into place just days before the collapse. In a plan like that, each piece must be able to withstand the forces acting on it as they’re all being put together. A weakness in one place can cause problems elsewhere, ultimately leading to catastrophe.

Two key elements of the bridge design, the tall centre pylon and pipe supports, were not yet in place when the structure collapsed. They hadn’t been scheduled to be added until later in the process – and the bridge wasn’t slated to open until next year, so it’s likely that the project’s designers and engineers expected the bridge segment to hold while construction continued.

An artist’s rendering of what the final bridge was supposed to look like. Image: City of Sweetwater.

Part of a forensic engineering evaluation will investigate whether that was a reasonable expectation, and whether those missing elements reduced the strength of what was there enough for it to collapse.

Searching for clues

There are some other publicly available clues, too, that shed light on avenues likely under investigation already. Dashcam video of the bridge collapse seems to indicate that the initial failure was very close to the north end of the structure. It has been reported that a couple of days before the collapse, a crack had been discovered near the bridge’s north end.

Additionally, the bridge span might have been either undergoing stress testing or other adjustments when it collapsed. It’s too early to say now – but the inquiry will certainly reveal – whether the crack and the stress testing put too much load at the north end of the bridge.

There will be other questions too, like “Why didn’t they use temporary supports to shore up the bridge?” There may be a perfectly sensible explanation: Perhaps the bridge was supposed to be strong enough to support itself, for example. Or maybe temporary supports would have created a traffic hazard on the road below.

Some of those questions will not be entirely engineering-related. For example, many are asking “Why wasn’t the road closed?” The Tamiami Trail was shut down for a few hours while the bridge span was put in place. But then it was reopened to cars – a decision that would have been informed by engineering, of course, but could also have been influenced by concerns about public safety or traffic congestion.

The ConversationAt the moment, many of the questions the public has are also being investigated by forensic engineers. Their goal is to ensure that eventually those questions are all answered, and many more as well, about designs, materials, processes, procedures and safety precautions. Those lessons will inform not just any replacement for this particular bridge in Miami but future bridge construction projects elsewhere in the country and around the world, as the rest of the engineering community takes lessons from whatever the investigation uncovers, so builders can avoid similar mistakes – and tragedies. In a sense, it is fortunate that one of the leading centres for accelerated bridge construction is right on the FIU campus.

Martin Gordon, Professor of Manufacturing and Mechanical Engineering Technology, Rochester Institute of Technology.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

There isn’t a war on the motorist. We should start one

These bloody people. Image: Getty.

When should you use the horn on a car? It’s not, and anyone who has been on a road in the UK in living memory will be surprised to hear this, when you are inconvenienced by traffic flow. Nor is it when you are annoyed that you have been very slightly inconvenienced by another driver refusing to break the law in a manner that is objectively dangerous, but which you perceive to be to your advantage.

According to the Highway Code:

“A horn should only be used when warning someone of any danger due to another vehicle or any other kind of danger.”

Let’s be frank: neither you nor I nor anyone we have ever met has ever heard a horn used in such a manner. Even those of us who live in or near places where horns perpetually ring out due to the entitled sociopathy of most drivers. Especially those of us who live in or near such places.

Several roads I frequently find myself pushing a pram up and down in north London are two way traffic, but allow parking on both sides. This being London that means that, in practice, they’re single track road which cars can enter from both ends.

And this being London that means, in practice, that on multiple occasions every day, men – it is literally always men – glower at each other from behind the steering wheels of needlessly big cars, banging their horns in fury that circumstances have, usually through the fault of neither of them, meant they are facing each other on a de facto single track road and now one of them is going to have to reverse for a metre or so.

This, of course, is an unacceptable surrender as far as the drivers’ ego is concerned, and a stalemate seemingly as protracted as the cold war and certainly nosier usually emerges. Occasionally someone will climb out of their beloved vehicle and shout and their opponent in person, which at least has the advantages of being quieter.

I mentioned all this to a friend recently, who suggested that maybe use of car horns should be formally restricted in certain circumstances.

Ha ha ha. Hah.

The Highway Code goes on to say -

“It is illegal to use a horn on a moving vehicle on a restricted road, a road that has street lights and a 30 mph limit, between the times of 11:30 p.m. and 07:00 a.m.”

Is there any UK legal provision more absolutely and comprehensively ignored by those to whom it applies? It might as well not be there. And you can bet that every single person who flouts it considers themselves law abiding. Rather than the perpetual criminal that they in point of fact are.


In the 25 years since I learned to drive I have used a car horn exactly no times, despite having lived in London for more than 20 of them. This is because I have never had occasion to use it appropriately. Neither has anyone else, of course, they’ve just used it inappropriately. Repeatedly.

So here’s my proposal for massively improving all UK  suburban and urban environments at a stroke: ban horns in all new cars and introduce massive, punitive, crippling, life-destroying fines for people caught using them on their old one.

There has never been a war on motorists, despite the persecution fantasies of the kind of middle aged man who thinks owning a book by Jeremy Clarkson is a substitute for a personality. There should be. Let’s start one. Now.

Phase 2 will be mandatory life sentences for people who don’t understand that a green traffic light doesn’t automatically mean you have right of way just because you’re in a car.

Do write in with your suggestions for Phase 3.