Last week’s deadly collapse of a 12-story oceanfront condominium in a small town on the same barrier island as Miami Beach, Fla., is raising concerns among structural engineers and designers about how to prevent future building failures.
Such unplanned collapses are rare in the modern history of structural design, experts say. But engineers and planners are keen to learn what caused the June 24 failure of Champlain Towers South in Surfside, Fla. To date, 16 deaths have been confirmed, and more than 140 people are missing. No immediate explanation for the disaster has emerged. Experts have speculated about structural damage and the possible corrosion of the reinforced concrete building’s foundation or stabilizing rebar.
Structural engineers aim to design buildings that can withstand the loads from forces and hazards such as gravity and weather. Engineers routinely update design practices, often in response to advances in technology or hard-won insights from failures. Nearly all the building stock in the U.S. is not newly designed. Champlain Towers South, for example, was erected in 1981. These buildings may face loads and other threats that designers did not anticipate, including those linked to climate change.
Until the conclusion of rescue operations and likely multiple investigations into what caused the Surfside collapse, structural engineers, leaders and policy makers may have to wait for useful insights into how to modify designs and building codes to prevent similar future tragedies.
To learn more about the long-term significance of the Champlain Towers South disaster for building designers, Scientific American spoke with structural engineer Benjamin W. Schafer, a professor of civil and systems engineering and director of the Ralph S. O’Connor Sustainable Energy Institute at Johns Hopkins University.[An edited transcript of the interview follows.]
How are structural engineers reacting to the collapse of Champlain Towers South?
Buildings don’t fail frequently, and the field takes very seriously the need to learn when failures do happen, particularly failures for which there isn’t just some obvious, large, external precipitating event that we didn’t account for. Collapses in the late 1970s and early 1980s, including the Kemper Arena roof collapse and walkway collapses at the Hyatt Regency Hotel, both in Kansas City, Mo., made the field question its design processes and led to improvements in construction and how we utilize computerized structural analysis. When earthquakes occur, we have a history of trying to get to the bottom of what happened and then changing our field in response. What’s disturbing about this latest failure in Florida is that even early conjectures about what went wrong don’t give us a lot of clues yet as to what we need to be doing differently. If this is just a corrosion issue, then, my goodness, the number of buildings that have corrosion issues in the U.S. is high. If this is a foundation issue, then perhaps we can figure out the more detailed cause and then go from there. There are lots of uncertainties that may have not been considered in 1981, when the design of Champlain Towers South was completed.
Is potential corrosion of the building’s columns, rebar or reinforced concrete likely to be closely examined?
One hundred percent. This is an older concrete building with sea-salt exposure and what sounds like a lot of flooding. Too much resulting corrosion eventually will bring a building down. But you still wonder, “Why right now? Why today?” Corrosion is a long, slow-moving process. Of course, there comes a day when it has gone too far. But one wonders, “Is there another precipitating factor?”
How significant will the rescue, recovery and other follow-up activities probably be at this site?
This level of debris itself would be a major, multimonth problem if it didn’t have the human tragedy involved in it as well. So this is a significantly complex project even without trying to understand the failure—just trying to get back to square one.
As the U.S. building stock continues to age, might we see a rise in the number and severity of events like the Surfside building collapse?
We can’t ignore our infrastructure, and we need to invest in it. Experts have been telling us that for 40 years. A major bridge between Memphis, Tenn., and Arkansas on Interstate 40 had to be shut down last month after a huge fracture was found in a beam. These examples are going to keep coming more frequently. They won’t all be a result of us ignoring our infrastructure, but many will be. And climate change isn’t helping. Our infrastructure is mostly in place and developed already, and we need to continue to invest in that development.
We’re also in unknown territory to a certain extent in terms of seeing demands on buildings that we didn’t expect, whether it is a climate-change-induced demand with flooding once a year where we would have expected no floods or more frequent higher-speed windstorms occurring. Buildings “live” in the environment that we live in. We design them for that environment.
But what are you going to do with an area that never had high snow loads before, and suddenly, one winter, there’s a storm in the South like one you’d normally get in Boston? We design roofs based on historical records for snow, but those rare events aren’t so rare anymore. We have bigger hurricanes. We have longer heat waves. It’s a challenge for us, as structural engineers, to keep up with those changing demands.
At the end of the day, gravity is still gravity. We can get much more precise these days in understanding the basic forces on a building. And we can trace what happens after something starts to fail much more precisely now than we could in past decades. But we need to have good estimates of the demands.
What sorts of past events and failures have led to changes in the designs of buildings in the modern era?
A lot of them have been earthquakes. The 1994 Northridge earthquake [in California] changed a lot of thinking around how we design buildings in earthquake-prone areas in the U.S. and around the world. In 1968 in [England], a resident’s gas stove explosion took out 22 stories of a building called Ronan Point, killing four people. That event marked the beginning of a growing focus on concerns about building collapses. In 2017 the Grenfell Tower fire in London spread to the building’s facade and then around the whole building. That is having a big impact on what should be allowed in the design of facades. And that’s why there’s such an interest, I think, in this particular failure in Surfside, Fla., because we don’t yet understand it.
How are investigations into a large building collapse such as this one conducted?
Investigators will gather all the the calculations and drawings for the original design. They then can try to compare those with records of the final construction, as well as changes that may have happened along the way. Then they will assess the actual condition of the building at the time of collapse. That might involve taking samples of the building debris and performing tests to determine the precollapse strength of the concrete and rebar. There has been a lot of speculation about the state of the columns at the base of the Champlain Towers South building, so in this case, they’ll do everything they can to try to understand that initial state, as well as the amount of corrosion and degradation. Investigators will then probably run a modern computer simulation on the building to see how well it withstands demands put on it against the codes in place at the time of design. But more importantly, they will check the building against current codes so that they know what performance we would expect today. That will yield an initial sense of whether the building, when viewed in a modern lens, had some unanticipated or critical design flaw that contributed to putting it close to failure. After that, they will work on scenarios based on all the information they collect to come up with plausible scenarios that they think are consistent with the failure. They will simulate, test and understand whether those scenarios are likely.
Are some cities headed for a built environment like that depicted in Kim Stanley Robinson’s New York 2140? That science-fiction novel describes a post-climate-disaster Manhattan, N.Y., where residents live in skyscrapers with heavily waterproofed foundations and commute by watercraft in a constantly flooded street grid.
The level of adaptation that he suggests is essentially that we can keep all our building infrastructure and just magically protect the bottom of it with some extension of current technologies for repairing concrete that suddenly becomes exposed to persistent salt water. That’s probably unrealistic. Much of our infrastructure is underground. Underground infrastructure that becomes underwater infrastructure is unusable. People won’t live in a building that doesn’t have power, water and sewer service.
A huge amount of adaptation of buildings and infrastructure is going to happen in the lifetime of today’s structural engineers. At least some high-wealth areas are going to be inundated and then moved because they have the capital to do so. The issue is how we will handle the inequity of mass movement from our population centers, which already have huge inequity in them.