New findings reveal corrosion and design flaws behind Surfside collapse

• Investigators with the National Construction Safety Team released their technical findings on what contributed to the collapse of Champlain Towers South in Surfside.
• Investigators found "no evidence of any specific initiating event" in the 2021 collapse.
• "The final factor that brought the critically low margins of safety to the point of failure was most likely long-term degradation from corrosion," said Glenn Bell, co-lead of the investigation.

Investigators with the National Construction Safety Team released new technical findings on what contributed to the collapse of Champlain Towers South in Surfside, Florida, which occurred five years ago on June 24.

"The building had stood on this stretch of the Atlantic coast since 1981," said Judith Mitrani-Reiser, colead of the investigation, in a video presentation published on June 8. "There was no obvious cause of the collapse, such as an explosion or a storm."

The collapse occurred nearly half a decade ago, on June 24, 2021. Ninety-eight people were killed. A massive rescue response of over 80 Miami-Dade Fire Rescue units, among other agencies, saved 35 people trapped in the building.

Mitrani-Reiser, who led the investigation along with Glenn Bell, said their team has "completed the technical portion of its investigation," which included analyzing physical evidence and historical records, along with "extensive" interviews.

"We examined two dozen possible scenarios for where and how the failure started," she said. "Based on this extensive work, we have concluded that the failure most likely began in early June, about three weeks before the collapse, when two connections between garage columns and the pool deck slab failed."

What contributed to the Surfside condo collapse?

When those initial connections failed, Mitrani-Reiser said, "other elements of the pool deck were left to carry their loads," but they "were not strong enough" to bear them, due to issues that "stemmed from the original design and construction of the building."

"When building structures are designed and built to required codes and standards, they have margins against failure, meaning they should be able to support much more load than they are expected to bear," she said. "In the case of Champlain Towers South, these margins against failure were too narrow from the start."

The investigation revealed that the collapse started with "punching shear failures," which occur when the slab breaks around the column, "giving the appearance that the column punched through it," according to Mitrani-Reiser. This occurs when the load the slab is bearing grows too great, which causes it to bend and crack around the column, "weakening the connection that is holding the slab in place."

The first two slab-column connections failed in early June and mid-June, but the slab they were helping hold up didn't fall right away, as it was supported by the pool deck and the street-level parking deck slabs around it.

"When the connections between the pool deck slab and these two columns in the garage below failed, it increased the loads on neighboring connections, eventually causing them to fail as well," Mitrani-Reiser. "The failures spread to other elements of the pool deck and street-level parking structure, eventually unseating the southern edge of the pool deck slab from a supporting wall."

That only made the slab sag further, eventually breaking away and resting "completely on crushed cars and the garage floor below it."

"Most importantly, when the pool deck broke away from the middle part of the tower on June 24, 2021, it damaged two connections," Mitrani-Reiser said. "The damage weakened these joints, causing the failure to enter and to spread through the middle part of the tower. Once the failure began in the middle part of the tower, it caused what's called a progressive collapse in the tower."

What happened during the Surfside condominium collapse?

The collapse occurred at around 1 a.m., and the death toll rose to 98 after multiple days of rescue efforts.

More than 80 Miami-Dade Fire Rescue units initially responded, and rescue operations saved 35 people, according to MDFR ‒ 10 were "assessed and treated," and two were sent to nearby hospitals.

What was discovered regarding the building's initial structural failures?

From the time Champlain Towers South was originally built, "low margins against failure existed," largely due to two factors, said Bell, colead of the investigation.

"First, severe and widespread deviations in the building's original structural design from the codes and standards of the day, but also some limitations in those codes and standards," Bell said. "And second, deviation in the building's construction from the design drawings. Loads added to the structure over its life further diminished the margins against failure."

As for what actually caused the collapse in 2021, the team found "no evidence of any specific initiating event."

"The final factor that brought the critically low margins of safety to the point of failure was most likely long-term degradation from corrosion," Bell said.

The corrosion of steel reinforcement to the pool deck slabs is the "most likely scenario" for long-term degradation of the pool deck structure, according to Bell.

"We know that corrosion of reinforcing steel was evident more than 25 years before the collapse and had progressed to the point that structural repairs and waterproofing were conducted in 1996 and '97," Bell said. "Problems persisted after those repairs. There was continued leakage and rust staining."

What likely did not cause the Surfside condominium collapse?

Things that "most probably did not contribute significantly to the collapse" include vibrations from the construction of a luxury condominium building called 87 Park, which was completed south of Champlain Towers South in 2019.

"Vibrations at the critical slab-column connections were too small to have caused structural damage," Bell said.

According to Bell, other factors that "did not contribute significantly" to the collapse include sinkholes or differential settlement, foundation failure, hurricanes and storm surge effects, "impulsive loads" like explosions or vehicle impacts, and accidental "loads or overloads" due to the roof repair and roof anchor projects that were ongoing when the collapse occurred.

"While this summary has been highly technical, what has driven the demanding and meticulous work of our investigative team is the human element, the loss of 98 lives," said Mitrani-Reiser. "No one in the U.S. should ever have to go to bed wondering if their building will collapse during the night."

"We are confident the recommendations from this investigation will move us closer to fulfilling that expectation," she added."

Sarah Perkel is a South Florida Connect Reporter for the USA TODAY Network's Florida Connect team.

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