MIAMI — More than two years after 98 people died in the collapse of a Florida condominium tower, federal investigators have released new details about the cause of the collapse. They're focusing on construction flaws on the building's pool deck.

Structural engineers with the National Institute of Standards and Technology say it's one of the most complex investigations ever undertaken. It began days after the 2021 collapse of the Champlain Towers South building in Surfside.

In a progress report, one of the team's leaders, Glenn Bell said the investigation continues to focus on the condo tower's pool deck. Investigators have previously said they found significant design and construction problems that left the deck weaker than required by building codes.

The team now has also found problems in how the concrete columns that supported the building were constructed. At a meeting at NIST headquarters in Maryland, Bell said, "These additional construction deviations further reduce the strength of the pool deck slab-to-column connections from the already compromised conditions that I reported in June."

Investigators continue to point to problems with the pool deck as their "leading failure hypothesis," the reason why the 40-year old 12-story building collapsed with little warning in a matter of seconds. The NIST team says it's still investigating 24 other possible failure hypotheses, though it plans to begin narrowing down the field soon.

NIST has already spent more than $20 million on the investigation. The team has moved tons of concrete columns, flooring and other rubble to a warehouse where its undergone extensive testing. It's a painstaking, labor intensive operation.

Investigators made a plea to former residents and members of the public to come forward with any photos or video they may have of the building's collapse. At the meeting, Bell showed stills of a video recovered from a motion activated camera that has provided investigators with intriguing information in the final moments as the building collapsed.

Investigation head Judith Mitrani-Reiser says the team has recovered 24 computer hard drives that may hold videos and is actively working to rebuild seven of them. She said, "if even one of those seven has a short amount of footage, that would be a huge impact to our investigation."

Meanwhile family members of those who died in Surfside are impatient with the investigation and unhappy about plans for a new building on the site. One of those attending the NIST meeting in Maryland Thursday was Martin Langesfeld. His sister Nicole and his brother-in-law Luis Sadovnic died in the collapse. At the meeting, he asked, "How can we even contemplate having a new developer build on this land when we have not come close to understanding why it collapsed in the first place, taking 98 lives with it?"

In Surfside, city officials recently approved a developer's plans for a new 12-story condominium to be built on the site of the collapse. Family members of those who died have objected, in part because it would place a memorial to their loved ones next to a loading dock. Langesfeld also believes the federal government should intervene and prevent any work from beginning on the site until the NIST investigation is complete, which is not expected until 2025.

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