On the afternoon of Thursday, March 15, 2018, the concrete bridge that would have connected the Miami campus of Florida International University (FIU) with the student residential neighborhood of Sweetwater collapsed onto eight lanes of traffic on Southwest 8th Street. Consisting of a 174-foot-long concrete I-beam truss, the failing bridge rained 950 tons of concrete down on the cars underneath, killing six people. At the time of the collapse, construction workers were tightening the steel tension rods in the concrete, and engineers are concerned that this procedure may have contributed to the collapse.
Over the past month, investigations have been launched by both the National Transportation Safety Board as well as the Munilla Construction Management (MCM), the firm which built the bridge. In all likelihood, the experts will conclude that the collapse can’t be explained by one single cause but rather was the result of a “perfect storm” of factors which tragically came together that Thursday afternoon. As a former president of the American Society of Civil Engineers (ASCE), Andy Hermann, told ABC News, “It could be materials, it could be construction technique, it could be the engineering design itself.”
As an engineering educator, I have been wrestling with what my students should learn from this accident. As the engineer and historian Henry Petroski has argued, engineering has a long tradition of learning from failure; only by pushing the limits of materials, structural design and mathematical analysis do engineers discover the boundary between what is feasible and unfeasible. As a result, nearly every engineer watches the “Galloping Gertie” video—showing the spectacular failure of the Tacoma Narrows Bridge in 1940 due to strong winds and flutter—multiple times during his or her undergraduate career.
But rather than having them watch Galloping Gertie one more time, I want to challenge my students to think about whether we need a new engineering design philosophy. Perhaps what we need is a philosophy of Slow Engineering, inspired by the Slow Food Movement.
The Slow Food Movement started in 1986 to protest the fast-food restaurants then springing up across Italy. Founded by Carlo Petrini, the movement emphasizes the importance of providing all of humanity with food that is good (nutritious), clean )not treated with chemicals) and fair (not grown or harvested by underpaid workers). The Slow Food Movement encourages people to savor the taste of local ingredients and the ways in which food inspires conviviality and community.
In 2015, Ed Quesenberry suggested that Slow Engineering might focus on overcoming our relentless fetish for speed and consider how the assumption that “time is money” undergirds much of engineering practice. But I think that Slow Engineering might dig deeper into what makes for good and just design.
While the Slow Food Movement invites us to celebrate taste and conviviality, the movement’s pronouncements do not say much about how you achieve these virtues. As a dedicated home cook, I have found that you attain these virtues by paying attention to three elements: ingredients, cooking techniques and context. For Slow Engineering, we need to do the same, and I would suggest that these elements allow us to think through the “perfect storm” that brought about the tragic collapse of the FIU bridge.
Let’s start with ingredients. A central tenet of the Slow Food movement is to cook with the best ingredients, drawing particularly on the local fresh ingredients of a region. For the FIU bridge, the essential ingredient was concrete to which the designers added titanium oxide, hoping that the bridge would be self-cleaning and stay a bright white. Thinking like Slow Engineers, I would encourage my students to ask “Did the builders use the best available concrete, mixed to the designer’s specifications? What impact [if any] does titanium oxide have on the strength of the concrete?”
In cooking, it’s important not to forget to add key ingredients. The central load-bearing element of the FIU Bridge was the concrete I-beam truss which was built at the site and then lifted into place. The complete design was to have included a 109-foot high pylon from which pipes—looking rather like the cables on a suspension bridge—would have extended down to the top of the truss in order to add stability to the structure. Engineering students might ask why the construction crew were adjusting the steel tension rods before the pylon and pipes were in place.
Next, let’s consider cooking techniques. If we were preparing, say, a beef dish, we would consider whether to braise, broil, or roast the meat. In the case of concrete, the key technique is curing. We’re all familiar with watching the cement truck pull up to a construction site and pour concrete into a building’s foundation, but the process is actually much more complex. At the concrete plant, water, cement and aggregate [such as sand or gravel] are carefully mixed together and then transported to the construction site while being continuously agitated [hence the rolling drum of the cement truck]. At the site, the concrete must be poured continuously into the forms, as any delay may mean that one layer of the concrete starts to set ahead of the next, creating a cold joint and weakening the overall structure. Once the concrete is poured, it doesn’t simply dry out, but needs to be carefully hydrated for days or even weeks, during which it cures and acquires strength. Attempts to speed up the curing process can result in a concrete structure not having the strength necessary to carry the load of the bridge or building. Hence, from a Slow Engineering standpoint, engineering students should inquire about all the steps related to curing the concrete.
It will also be important to look at the process by which the FIU bridge was built. Rather than block traffic on Southwest 8th Street for weeks on end, MCM employed Accelerated Bridge Construction (ABC) whereby they assembled the concrete I-beam truss alongside 8th Street and then moved it into place. This innovative technique can save time and money, but it requires engineers to consider whether the material in the structure can handle the stresses which come from being moved. As former ASCE President Hermann explained, “ABC construction essentially builds a bridge off-site and then moves it into place for its final position. And when you do that you have different load points, different supports for the bridge that are different than the final supports . . . . Did they put enough material into the bridge to withstand the moving loads?”
Finally, the slow cook considers the context of the meal. Will the dish be eaten immediately? Will it need to be kept warm while other dishes are being prepared? Will the dish be plated and taken to guests by servers or will it be part of a buffet? To achieve optimal taste and conviviality, the cook needs to consider the role of the servers [if any] as well as the needs of the guests
Likewise, the Slow Engineer should take into account the role of the construction workers and the public at large. When is it safe for workers to be up on a recently poured concrete structure? What tasks should they perform and when? Were the cracks in the concrete detected two days before the collapse a sign of trouble or not? In the course of adjusting the steel tension rods, should the road below the bridge have been closed to ensure public safety? Like any technological artifact, the FIU Bridge did not exist in a vacuum but rather in a social context with all sorts of people moving around it and interacting with it—and that included the occupants of cars driving underneath the bridge
In drawing this analogy between Slow Food and Slow Engineering, I am not suggesting that engineering should merely slow down, that speed is simply the enemy. Just as some dishes—such as grilled fish—require speed and judgment in order to get a crispy surface while not overcooking the inside of the fish, so certain engineering tasks can—and should–be done quickly and efficiently. In certain contexts, Accelerated Bridge Construction is the appropriate technique. Instead, Slow Engineering is a holistic approach, challenging us to pay attention to the interplay of materials, techniques and context in order to create safe, sustainable and aesthetically pleasing designs.
To help students appreciate this holistic approach, I would tell them the mythic story associated with the great dining hall at New College, Oxford. The ceiling of the dining hall is supported by huge oak beams, some 2 square feet and 45 feet long. Legend has it that when New College was created in 1379, it was given forested land as part of its endowment, and over the centuries, the college’s foresters made sure to preserve very large oak trees. The foresters did so because they knew that, sooner or later, the beams in the dining hall would become infested with beetles, causing them to rot and would need to be replaced. While it is not clear there was ever a specific grove of oaks earmarked for the great hall, the myth conveys the importance of understanding how materials and natural processes underlie all of what we do as engineers. You can’t have a great hall with massive oak beams unless you understand where the oak beams come from and how long it takes for the oak trees to grow.
The lesson of the FIU bridge is that engineers need to continue to take into account the interplay of the limits of materials, natural processes and context. At its best, Slow Engineering reminds us that human activities must align with nature rather than forcing nature to conform to our expectations.