A Florida high-rise that collapsed early Thursday was determined to be sinking a year ago, according to a researcher at Florida International University.
The building, which was constructed in 1981, has been sinking at an alarming rate since the 1990s, according to a study in 2020 by Shimon Wdowinski, a professor in the Department of Earth and Environment.
When Wdowinski saw the news that the Champlain Towers South condominium in Surfside collapsed, he instantly remembered it from the study, he said.
“I looked at it this morning and said, ‘Oh my god.’ We did detect that,” he said.
Wdowinski said his research is not meant to suggest certainty about what caused the collapse. The building was sinking at a rate of about 2 millimeters a year in the 1990s and could have slowed or accelerated in the time since, he said.
In his experience, even the level of sinking observed in the 1990s typically results in impacts to buildings and their structures, Wdowinski said. He said that very well could have been the case for the Champlain building in the 1990s, based on his findings.
“It was a byproduct of analyzing the data. We saw this building had some kind of unusual movement,” Wdowinski said.
Daniel Dietch, who served as Surfside’s mayor from 2010 to 2020, warned against drawing conclusions too soon.
“This is an extraordinarily unusual event, and it is dangerous and counterproductive to speculate on its cause,” he said.
Workers sorted through the rubble Thursday afternoon. Officials said 35 people were rescued and confirmed at least one death, saying they expect the death toll to rise. At least 99 people remained unaccounted for.
According to Surfside Town Commissioner Eliana Salzhauer, “This was not an act of God. This was not a natural disaster. Buildings don't just fall.”
Water damage and cracks
The county requires commercial and multifamily buildings to be recertified every 40 years. The process involves electrical and structural inspections for a report to be filed with the town. It was underway for the condominium building but had not been completed, town officials said Thursday.
Salzhauer said no serious complaints about the building had been brought to the town’s attention.
"If a building had serious problems, we would certainly know about it," she said.
In 2015, a lawsuit alleged building management failed to maintain an outside wall, resulting in water damage and cracks. The owner who filed that suit had previously sued over the same issue, according to a court filing. The management company paid for damages in the earlier case, according to records.
Cracked walls or shifting foundations can be clues that sinking has affected the stability of a structure, according to Matthys Levy, a consulting engineer, professor at Columbia University and author of “Why Buildings Fall Down: How Structures Fail.”
Residents of the building might have noticed changes, he said.
“Had there been changes in the building? Cracks in the walls, in the floor? Floors not being level, things rolling off tables?” he said. That would indicate the building was shifting.
The city needs to invest in technology that can determine which buildings are at risk of collapse due to geologic processes, said Keren Bolter, a Florida-based geoscientist at the engineering firm Arcadis who has advised the Federal Emergency Management Agency on hazard mitigation.
“It's very sad that people are forced to be reactive. We're constantly putting out fires. I think there's a systemic problem we have,” she said. "Investing in preventative measures instead of reactive responses saves lives, money and time.”
Satellites, drones and other means are used to monitor where Florida is sinking and understand which buildings might be at risk, according to Ryan Shamet, a professor of engineering at the University of North Florida. Those efforts vary by jurisdiction and depend on whether structures are privately or publicly owned, he said. Aside from the analysis at the time of construction, monitoring is generally not done proactively, he said.
”Structural health monitoring is already there,” Shamet said. “But it's hard because we don't have the resources yet to monitor every single structure. You kind of have to know if there's an issue first before you start monitoring it.”
There is always concern for structures built on reclaimed land, according to Levy.
Reclaimed land, whether landfill or wetlands, can compact over time, leading to shifts in the ground under the building and potentially to the foundation.
“A millimeter may seem like a small number, but when you add them up over many years, it becomes a big number,” Levy said.
The building could have been especially vulnerable if the ground it was situated on was sinking at different rates, causing differential settlement.
“The fact that one part of it is still standing is important. The portion that collapsed might have been tipping compared to the other portion, which may not have been sinking as fast. So you have an unequal situation, and in between, things begin to crack and tilt,” Levy said.
“There has to be some trigger that occurs. If you have two parts of a building and one part is well-founded and doesn’t move that much and the other is not, then between the two, you get movement. That can cause distortion in the floor slabs. They can begin to crack; suddenly, you get cracking, breaking and fracturing,” he said.
That leads to what’s known as progressive collapse, when one part fails, then another and another until the entire structure fails. That is what happened to the World Trade Center after the 9/11 attacks, he said.
“Buildings are not super strong; they’re not built to sustain an unusual event like this,” he said.
“If one part of the building fails, it drags the rest with it,” he said. “It just continues, you can’t stop. There’s nothing there to stop it, there’s no strong elements to hold it back. It’s a cascade.”
Impact of sea level rise and flooding
Over the past several years, Wdowinski and his team have researched which parts of the Miami area are sinking, primarily to identify where sea level rise and flooding could have the most impact. They obtained historical data from European satellites, which mapped the area by bouncing signals down to the ground and back to identify shifting elevations.
They published the results in April 2020.
The data, collected from 1993 to 1999, showed that most of the Miami area was not sinking appreciably, save for a few hot spots. Wdowinski said most of those occurred in the western part of Miami, where the elevation is lower. The level of sinking at the Champlain condo was unusual, he said.
Wdownski said he doesn’t believe anybody in the city or state government would have had a reason to be aware of the findings of the study. The bulk of it focused on potential flooding hazards, not engineering concerns. The study’s mention of the “12-story condominium” was relegated to a single line.
“We didn’t give it too much importance,” Wdowinski said.
The incident has made him think about the possibility of using such data to identify areas of potential structural risk, he said.
This article originally appeared on USA TODAY: Building collapse in Miami: Structure had been sinking into the earth