Multiple factors could contribute, experts say
SURFSIDE, Fla. — For four decades, the Champlain Tower South condominium sat about 100 yards from the sea, much of that distance covered by sand. During that time, the tide ebbed and flowed toward the building nearly 60,000 times. A full moon rose in the sky 500 times. The condo witnessed it all.
Then, on Thursday, it was gone.
Now researchers and engineers across the nation are trying to figure out what caused the building’s early morning collapse that left at least four dead and 159 others unaccounted for, and what that might mean for other aging high-rises along the Florida coast and the rest of the country.
For now, there are no clear answers. USA TODAY spoke Friday with more than a dozen experts without finding a consensus. Some pointed to sea level rise and the corrosive effect of saltwater brought with encroaching tides. Others wondered about the stability of the ground beneath or more mundane matters like shoddy construction or lax oversight.
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Two engineers who reviewed a surveillance video of the collapse in slow motion said it appears the upper part of the building’s middle section collapsed before the lower part.
If the collapse had begun with the foundation, geotechnical engineering professor Steven Kramer of the University of Washington in Seattle would have expected to see everything going together. Instead, he said, the top several stories appear to fall first.
A clue was when dust first appeared in the image.
“The view [in the surveillance video] of the base of the building is obscured by the trees, but I think that dust would have appeared above the trees earlier if the failure had started [at the base],” he said.
Michael Chajes, a professor of civil and environmental engineering at the University of Delaware who does structural forensics, agreed.
“If a lot of things were breaking lower down you would have seen the dust below,” he said.
Another clue came in how the building fell almost straight down.
“When the bottom gives out, unless it gave out uniformly, you would have a lot of twisting and leaning,” Kramer said. “If one of four columns goes at the base, the thing would tend to list to the side.”
The video shows that as the central section began to fall, the eastern section twisted toward it a little before the center collapsed. The eastern part remained standing for another 20 seconds or so before it too began to collapse. In that instance, Kramer believes debris from the center smashed into support beams for the eastern section, rendering it structurally unstable.
On this point experts did all agree: It will take a long time to discern exactly how and why Champlain Tower South collapsed and that, once the answers are known, they’re likely to prompt changes to the building industry.
“The whole regulatory apparatus is behind the times, relative to current risks,” said Clinton Andrews, a professor of urban planning and director of the Center for Green Building at Rutgers University. “I think the case in Florida illustrates that problem.”
Changes to inspection process?
Records about the tower’s development, construction and any major renovations could provide clues about why it collapsed. The town posted a dozen documents to its website late Friday night, including a required 40-year inspection report that was posted as “unverified” and received 16 hours after the Florida condo building’s catastrophic failure.
None of the documents, dating to 2018, appeared to contain details that would explain the building’s collapse. The Champlain Tower South had begun this year a recertification process mandated by Miami-Dade County for commercial and multifamily buildings when they turn 40. Many of the experts interviewed by USA TODAY said that’s too long to wait for electrical and structural inspections of an oceanfront high-rise.
Atorod Azizinamini, a professor at Florida International University who specializes in structural and bridge engineering, noted that federal law requires bridges be inspected every two years.
“From a structural engineering standpoint, some of these buildings located in certain locations, they probably need to be inspected structurally maybe every five, 10 years. Certainly not 40,” Azizinamini said. “My feeling is [the Champlain Towers South collapse] is going to result in some changes in how we design, construct, and inspect our high-rise buildings.”
Jorge Kuperman, principal architect of Coral Gables-based JSK Architectural Group, predicted the county would revamp its codes, shortening the time to 30 years while mandating stricter requirements for recertification.
“They’re not requiring any X-ray of the structure or any excavations” to test the concrete, Kuperman said. “It’s strictly based on visual inspection, and it’s up to the professional whether he or she wants to go above and beyond the requirements.
Syed Ashraf, a structural engineer who has experience retrofitting older high-rises in Miami, also cited a need for concrete testing.
“There’s no requirement to test the concrete in the 40-year certification,” he said. “Especially on older buildings, invariably there is considerable deterioration in the strength of the concrete.”
Location a factor?
The investigation into Champlain Tower South’s destruction will look closely at its location, experts told USA TODAY, noting that the site itself could have been a contributing factor for many reasons.
The condo sat close to the Atlantic coast, where ocean salt can seep into the concrete and corrode the reinforced steel rods known as rebar with such severity that they disintegrate, Ashraf said. He also pointed out that beach sand, high in chloride ions from sea salt, was commonly used decades ago to make concrete, which can corrode the steel from within.
That was a factor in the 1974 collapse of the four-story federal Drug Enforcement Agency building in downtown Miami. The tragedy, which killed seven people, prompted the county to develop its recertification program.
“At that time, engineers and building officials for the county decided to be sure that it didn’t happen again, so they decided to look at buildings every 40 years,” recalled Paul Novack, who served as Surfside mayor from 1992 to 2005.
Balcony repairs are a sure-fire way to tell when a building has started the recertification process, Novak said.
“If you drive by a building and all the balconies are closed off and being renovated, you know it’s undergone its inspection recently,” he said.
Too little attention has been paid to rising waters and their potential to impact structures, said Harold Wanless, a geologist and sea level expert at the University of Miami. Research shows Miami has experienced about a foot of sea level rise since 1940, he said, but less is known about how and where the corrosive saltwater is impacting structures.
“Is that enough to dramatically change the salt in the groundwater? I don’t know,” Wanless said.
Several experts questioned the wisdom of building massive structures like a high-rise condo in a coastal area.
Andrews, the professor from New Jersey, said that he noticed a few significant differences between buildings in his state and Florida. The first was the prevalence of such high-rises, which proliferated as Miami-Dade County’s population began rising in the 1980s.
The second was how close to the ocean they sit. Andrews says a major vulnerability of building along the coast is the corrosiveness of the air, which can impact important components such as metal clips that hold concrete paneling together.
“Salt air reveals the weaknesses in buildings,” Andrews said. “And it’s a little bit worse in a context like the building in Florida where they are literally on the beach.”
The area’s geology comes with weaknesses, warned James Englehardt, an environmental engineering professor at the University of Miami. Surfside sits on top of a barrier island; beneath it lies highly porous limestone made from old coral beds.
“My understanding is they sink pilings down into the rock, but lime rock is, well that’s the rock we sit on, and it is not a strong rock,” Englehardt said. “It’s friable, even in your hand.”
Experts say large buildings built on coastal areas typically rest on pilings that are drilled down dozens of feet into underlying bedrock.
It’s not known whether the Champlain Tower South was built on pilings or how far down into the earth they extended. But Hugo Soto, an engineer and manager of the Miami offices of the engineering firm Terracon, said the first layer of limestone in that area starts about 20 feet below the surface. Pilings, then, are typically drilled at least 40 feet deep to hit a layer firm enough to secure a building.
“A 12-story building is pretty heavy,” said Soto, who specializes in pilings and has installed them in Surfside near the Champlain. “You have to consider where you need to put your piles so it’s not going to move.”
As reported Thursday by USA TODAY, research by FIU scientist Shimon Wdowinski found that satellite data from the 1990s indicated the building was sinking at a rate of about 1.9 millimeters a year. That raises questions about whether the earth beneath the building was moving, or whether the building was not properly secured.
Some experts wondered if the soil under the building had changed in any way, either compacting or shifting and undermining its support.
“Did it move or loosen?” wondered Dawn Lehman, a structural engineer at the University of Washington in Seattle. “You would look at the soil, the soil structure interaction and the condition of the foundation. What was happening to the other buildings nearby?”
Such movement could have put stress on the building, especially its foundation. If the foundation was under stress and moving, it would almost certainly have been apparent for weeks if not longer, said Mehrdad Sasani, a professor of environmental engineering at Northeastern University in Boston.
“Usually, such failures are not sudden,” he said. “People should have seen [substantial] cracks, they should have heard noises for a long time. Unless this is an exceptional case, usually foundation failure is more gradual and there are lots of signs.”
Potential for human error?
It’s also possible the collapse stemmed from negligence and human error more so than any environmental cause, several experts said.
The condo’s recent inspection and ongoing work raised red flags for Chajes, the Delaware engineering professor.
“I’m always suspicious any time work has gone on at a structure in the weeks and days leading up to a failure,” he said.
Of special concern are some reports that work was being done on the roof of the building.
“I’m thinking they were putting supplies up there. Did they overload it in some way?” he said.
Ashraf, the structural engineering consultant and author of “Practical Design of Reinforced Concrete Buildings,” took note of residents’ complaints that their building was shaking because of nearby construction. He was recently called in to fortify an ocean-facing residential building on Miami’s Brickell Avenue. Like Champlain Towers South, there is construction near the Brickell building.
“Those vibrations are a lot of forces on the building, for which it is not designed,” said Ashraf, who decided to lay out a temporary reinforcement plan. “We tested the concrete and we shored it up. We took steel rods and braced the building. Once construction is over, we’re going to retrofit the building with carbon fiber wrapper or steel plates.”
Ashraf says a similar plan should have been devised for Champlain Towers South.
“This is not a design failure. This is a maintenance issue,” he said. “If those things are not addressed, these kinds of tragic things can happen.”
In the end, most of the experts agreed, it’s rarely a single thing that causes a building to collapse.
“It’s almost always a series of things that build up,” said John Wallace, a professor of structural engineering at the University of California, Los Angeles who has participated in multiple forensic analyses of building failures. “Each item adds additional demands upon the building. These things cascade and then it reaches a tipping point where there is this type of collapse.”
Englehardt, the University of Miami professor, agreed.
“When incidents do occur it’s because of a series of preceding failures, so there had to be more than one cause for this,” he said. “It had to be a series of sequential failures that would result in anything like this.”
Contributing: USA TODAY reporters Katie Wedell, John Panceti, Pat Beall and Hannah Winston of the Palm Beach Post.
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