Last week’s deadly collapse of a 12-story oceanfront condominium in a small town on the same barrier island as Miami Beach, Florida 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 designers are eager to find out what caused Champlain Towers South to fail on June 24 in Surfside, Florida. To date, 16 dead have been confirmed and more than 140 people are missing. No immediate explanation for the disaster has emerged. Experts hypothesized structural damage and possible corrosion of the foundation of the reinforced concrete building or stabilizing reinforcement.
Structural engineers aim to design buildings that can withstand the loads of forces and hazards such as gravity and weathering. Engineers regularly update design practices, often in response to technological advances or hard-earned insights from failures. However, nearly all of the building stock in the United States was not newly designed. Champlain Towers South, for example, was erected in 1981. These buildings may face loads and other threats that the designers had not anticipated, including those related to climate change.
Until the rescue operations are completed and the probable multiple investigations into what caused the Surfside collapse, structural engineers, leaders and policymakers may have to wait for useful insights into how to modify plans 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, American scientist spoke to structural engineer Benjamin W. Schafer, 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 do not fail frequently and the field takes very seriously the need to know when failures occur, especially failures for which there is not just an obvious, large external precipitating event that we have not taken into account. . Collapses in the late 1970s and early 1980s, including the Kemper Arena roof collapse and the Hyatt Regency Hotel boardwalk collapse, both in Kansas City, Missouri, brought the field into question. of its design processes and have led to improvements in construction and in the way we use computer structural analysis. When earthquakes do occur, we have a history of trying to get to the bottom of what happened and then change our field in response. The disturbing thing about this latest Florida bankruptcy is that even the first guesses as to what went wrong still don’t give us many clues as to what we need to do differently. If this is just a corrosion problem, then my God, the number of buildings that have corrosion problems in the United States is high. If this is a basic problem, then maybe we can figure out the more detailed cause and then go from there. There are many uncertainties that may not have been addressed in 1981 when the Champlain Towers South project was completed.
Is the potential corrosion of building columns, reinforcement or reinforced concrete likely to be closely examined?
Hundred percent. This is an old concrete building with exposure to sea salt and what sounds like a lot of flooding. Too much corrosion will eventually collapse a building. But you still ask yourself, “Why right now? Why today?” Corrosion is a long and slow process. Of course, there comes a day when he has gone too far. But one wonders: “Is there another precipitating factor?”
How significant are the rescue, retrieval and other follow-up activities on this site likely to be?
This same level of debris would be a major problem for many months if human tragedy wasn’t involved as well. So this is a significantly complex project even without trying to understand failure, just trying to get back to square one.
As the US housing stock continues to age, could we see an increase in the number and severity of events such as the Surfside building collapse?
We cannot ignore our infrastructure and must invest in it. Experts have been telling us this for 40 years. A major bridge between Memphis, Tennessee and Arkansas on Interstate 40 had to be closed last month after a huge fracture was found in a beam. These examples will continue to come more frequently. Not all of them will be the result of ignoring our infrastructure, but many will be. And climate change doesn’t help. Our infrastructure is mostly in place and already developed, and we must continue to invest in that development.
We are also in unknown territory to some extent in terms of building demands that we did not expect, whether it is climate change induced demand with flooding once a year where we would not have expected flooding or more frequent yes experience high-speed wind storms. Buildings “live” in the environment in which we live. We design them for that environment.
But what are you going to do with an area that has never had high snow loads before, and suddenly, one winter, there is a storm in the south like you would normally have in Boston? We design roofs based on historical documents for snow, but those rare events aren’t that rare anymore. We have bigger hurricanes. We have longer heat waves. It is a challenge for us, as structural engineers, to keep up with these changing needs.
At the end of the day, gravity is still gravity. Today we can be much more accurate in understanding the basic forces on a building. And we can track what happens after something starts to fail much more accurately now than we could have done in past decades. But we need to have good demand estimates.
What kinds of past events and failures have led to changes in building design in the modern era?
Many of them have been earthquakes. The 1994 Northridge earthquake [in California] has changed a lot in the way buildings are designed in earthquake-prone areas in the United States and around the world. In 1968 a [England], a resident’s gas stove explosion destroyed 22 floors of a building called Ronan Point, killing four people. That event marked the beginning of growing attention to concerns about building collapses. In 2017, the Grenfell Tower fire in London spread to the facade of the building and then around the entire building. This is having a big impact on what should be allowed in facade design. And that’s why there is such interest, I think, in this particular failure in Surfside, Florida, because we still don’t understand it.
How is the investigation of the collapse of a large building like this conducted?
Investigators will collect all calculations and drawings for the original project. They can then try to compare those to the records of the final construction, as well as the changes that may have occurred along the way. Then they will assess the real condition of the building at the time of the collapse. This could involve taking samples of building debris and conducting tests to determine the pre-collapse resistance of the concrete and reinforcement. 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 will do everything they can to try to understand that initial state, as well as the amount of corrosion and decay. Investigators will likely run a modern computer simulation on the building to see how well it stands up to demands placed against the codes in place at the time of design. Most importantly, they will check the building against current codes so they know what performance we would expect today. This will give an initial idea that the building, when viewed through a modern lens, had some unexpected or critical design flaw that helped put it close to failure. Next, they will work on scenarios based on all the information they gather to find plausible ones they deem consistent with failure. Then they will try to simulate and understand, including potentially running some tests, whether such scenarios are likely or not.
Are some cities headed for a built environment like the one pictured? by Kim Stanley Robinson New York 2140? That science fiction novel describes a Manhattan, New York, after a climate disaster, where residents live in skyscrapers with highly waterproof foundations and commute by jet skis on a constantly flooded road network.
The level of adaptation it suggests is essentially that we can maintain all of our building infrastructure and simply magically protect its bottom with some extension of current technologies to repair concrete that is suddenly exposed to persistent salt water. It is probably not realistic. Much of our infrastructure is underground. The underground infrastructure that becomes subsea infrastructure is unusable. People will not live in a building that does not have electricity, water and sewage services.
A tremendous amount of adaptation of buildings and infrastructure will occur in the lifetime of today’s structural engineers. At least some high-wealth areas will be flooded and then moved because they have the capital to do so. The problem is how we will manage the inequality of the mass movement from our population centers, which already have enormous inequality within them.