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The building Champlain Towers South began to silently collapse weeks before its 12 floors fell during the early morning of June 24, 2021, according to the final technical report by the National Institute of Standards and Technology (NIST), published this Monday.
The tragedy claimed the lives of 98 people in Surfside, Florida, but its true origin dates back three weeks before the world witnessed the building collapse.
The building began to collapse three weeks earlier
What federal investigators describe is chilling: in early June 2021, two connections between the columns of the underground garage and the pool deck failed.
Engineers refer to this phenomenon as "punching shear," a process in which the forces on the reinforced concrete slab bend and crack it around a supporting column until the connection fails completely.
During those three weeks, the cracks progressively widened, and the weight of the structure was redistributed to adjacent columns that lacked the capacity to bear the additional load, resulting in a gradual and irreversible collapse that culminated at 1:22 a.m. on June 24, 2021, while most residents were asleep.
"When building structures are designed and constructed according to the required codes and standards, they have safety margins that allow them to withstand loads much greater than those anticipated," stated Judith Mitrani-Reiser, co-leader of the research.
"In the case of Champlain Towers South, these safety margins were too narrow from the outset," he added.
Signs that nobody interpreted as an alarm
Perhaps the most disturbing aspect of the report is the confirmation that there were visible physical signs weeks before the disaster.
Photos taken by residents showed a long crack in a retaining wall on the pool terrace, as well as cracks in the corner where that wall met a planter.
A witness testified to investigators that, three weeks before the collapse, part of a door located just beneath the garden wall had sunk slightly and was getting stuck when opened.
These signs, now confirmed as manifestations of the collapse that was already in progress, were not interpreted at the time as signals of imminent danger.
A defective building since its construction
Glenn Bell, the other co-leader of the research, explained that the low safety margins had two main causes:
"First, serious and widespread deviations in the original structural design of the building concerning the codes and standards of the time. And second, deviations in the construction of the building compared to the design plans."
In some areas of the pool deck, the design provided less than half of the strength required by current codes.
To these original defects were added decades of modifications: subsequent work around the pool—heavy planters, sand, and paving stones—"further reduced the safety margins against failures, as did long-term degradation from corrosion," the report states.
The building, constructed in 1981 on the Atlantic coast of Surfside, had been receiving warnings since 2018, when the firm Morabito Consultants identified "serious structural damage" and warned that the deterioration would "exponentially increase" if not addressed.
Despite this, a municipal inspector assured the residents that the building was in "very good condition."
Legal and legislative consequences
After the collapse, a judge in Miami-Dade approved a settlement of over 1 billion dollars to compensate victims and their families.
Among the 98 deceased are at least 15 Cubans or Cuban Americans.
Florida enacted a law in 2022 that requires condominium associations to conduct periodic structural inspections and maintain reserves for major repairs, although in 2025 a new regulation was approved allowing greater financial flexibility for associations.
The report published on Monday precedes the full final document, which will include all the analyzed evidence and recommendations to prevent similar tragedies, and is expected by the end of 2026.
"With its invaluable contribution, this effort will help make other buildings safer, prevent tragedies like this one, and honor the lives of the victims of Champlain Towers South," Bell stated.
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